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INTERNATIONAL ATOMIC ENERGY AGENCYVIENNA

ISBN 92–0–114705–8ISSN 1020–6566

The explosion on 26 April 1986 at the Chernobyl nuclear power plant and the consequent reactor fire resulted in an unprecedented release of radioactive material from a nuclear reactor and adverse consequences for the public and the environment. Although the accident occurred nearly two decades ago, controversy still surrounds the real impact of the disaster. Therefore the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations, the United Nations Development Programme, the United Nations Environment Programme, the United Nations Office for the Coordination of Humanitarian Affairs, the United Nations Scientific Committee on the Effects of Atomic Radiation, the World Health Organization and the World Bank, as well as the competent authorities of Belarus, the Russian Federation and Ukraine, established the Chernobyl Forum in 2003. The mission of the Forum was to generate “authoritative consensual statements” on the environmental consequences and health effects attributable to radiation exposure arising from the accident as well as to provide advice on environmental remediation and special health care programmes, and to suggest areas in which further research is required. This report presents the findings and recommendations of the Chernobyl Forum concerning the environmental effects of the Chernobyl accident.

Report of the Chernobyl Forum Expert Group ‘Environment’

Environmental Consequences of the Chernobyl Accident and their Remediation: Twenty Years of Experience

RADIOLOGICALASSESSMENTR E P O R T SS E R I E S

Environmental C

onsequences of the Chernobyl A

ccident and their Rem

ediation: Twenty Years of Experience

9.9 mm 180 pages

P1239_covI+IV.indd 1 2006-03-30 14:41:37

ENVIRONMENTAL CONSEQUENCES OF THE CHERNOBYL ACCIDENT

AND THEIR REMEDIATION: TWENTY YEARS OF EXPERIENCE


The following States are Members of the International Atomic Energy Agency:

AFGHANISTANALBANIAALGERIAANGOLAARGENTINAARMENIAAUSTRALIAAUSTRIAAZERBAIJANBANGLADESHBELARUSBELGIUMBENINBOLIVIABOSNIA AND HERZEGOVINABOTSWANABRAZILBULGARIABURKINA FASOCAMEROONCANADACENTRAL AFRICAN REPUBLICCHADCHILECHINACOLOMBIACOSTA RICACÔTE D’IVOIRECROATIACUBACYPRUSCZECH REPUBLICDEMOCRATIC REPUBLIC OF THE CONGODENMARKDOMINICAN REPUBLICECUADOREGYPTEL SALVADORERITREAESTONIAETHIOPIAFINLANDFRANCEGABONGEORGIAGERMANYGHANA

GREECEGUATEMALAHAITIHOLY SEEHONDURASHUNGARYICELANDINDIAINDONESIAIRAN, ISLAMIC REPUBLIC OF IRAQIRELANDISRAELITALYJAMAICAJAPANJORDANKAZAKHSTANKENYAKOREA, REPUBLIC OFKUWAITKYRGYZSTANLATVIALEBANONLIBERIALIBYAN ARAB JAMAHIRIYALIECHTENSTEINLITHUANIALUXEMBOURGMADAGASCARMALAYSIAMALIMALTAMARSHALL ISLANDSMAURITANIAMAURITIUSMEXICOMONACOMONGOLIAMOROCCOMYANMARNAMIBIANETHERLANDSNEW ZEALANDNICARAGUANIGERNIGERIANORWAYPAKISTANPANAMA

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SOUTH AFRICA

SPAIN

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SUDAN

SWEDEN

SWITZERLAND

SYRIAN ARAB REPUBLIC

TAJIKISTAN

THAILAND

THE FORMER YUGOSLAV

REPUBLIC OF MACEDONIA

TUNISIA

TURKEY

UGANDA

UKRAINE

UNITED ARAB EMIRATES

UNITED KINGDOM OF

GREAT BRITAIN AND

NORTHERN IRELAND

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OF TANZANIA

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The Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEAheld at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of theAgency are situated in Vienna. Its principal objective is “to accelerate and enlarge the contribution of atomicenergy to peace, health and prosperity throughout the world’’.

ENVIRONMENTAL CONSEQUENCES OF THE CHERNOBYL ACCIDENT

AND THEIR REMEDIATION: TWENTY YEARS OF EXPERIENCE


RADIOLOGICAL ASSESSMENT REPORTS SERIES

INTERNATIONAL ATOMIC ENERGY AGENCYVIENNA, 2006

IAEA Library Cataloguing in Publication Data

Environmental consequences of the Chernobyl accident and theirremediation : twenty years of experience / report of the ChernobylForum Expert Group ‘Environment’. — Vienna : InternationalAtomic Energy Agency, 2006.

p. ; 29 cm. — (Radiological assessment reports series, ISSN1020-6566)

STI/PUB/1239ISBN 92–0–114705–8Includes bibliographical references.

1. Chernobyl Nuclear Accident, Chornobyl, Ukraine, 1986 —Environmental aspects. 2. Radioactive waste sites — Cleanup.I. International Atomic Energy Agency. II. Series.

IAEAL 06–00424

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© IAEA, 2006

Printed by the IAEA in AustriaApril 2006

STI/PUB/1239

FOREWORD

The explosion on 26 April 1986 at the Chernobyl nuclear power plant, which is located 100 km from Kievin Ukraine (at that time part of the USSR), and the consequent reactor fire, which lasted for 10 days, resulted inan unprecedented release of radioactive material from a nuclear reactor and adverse consequences for the publicand the environment.

The resulting contamination of the environment with radioactive material caused the evacuation of morethan 100 000 people from the affected region during 1986 and the relocation, after 1986, of another 200 000people from Belarus, the Russian Federation and Ukraine. Some five million people continue to live in areascontaminated by the accident. The national governments of the three affected countries, supported byinternational organizations, have undertaken costly efforts to remediate the areas affected by the contamination,provide medical services and restore the region’s social and economic well-being.

The accident’s consequences were not limited to the territories of Belarus, the Russian Federation andUkraine, since other European countries were also affected as a result of the atmospheric transfer of radioactivematerial. These countries also encountered problems in the radiation protection of their populations, but to alesser extent than the three most affected countries.

Although the accident occurred nearly two decades ago, controversy still surrounds the real impact of thedisaster. Therefore the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations(FAO), the United Nations Development Programme (UNDP), the United Nations Environment Programme(UNEP), the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), the United NationsScientific Committee on the Effects of Atomic Radiation (UNSCEAR), the World Health Organization (WHO)and the World Bank, as well as the competent authorities of Belarus, the Russian Federation and Ukraine,established the Chernobyl Forum in 2003. The mission of the Forum was — through a series of managerial andexpert meetings — to generate “authoritative consensual statements” on the environmental consequences andhealth effects attributable to radiation exposure arising from the accident, as well as to provide advice onenvironmental remediation and special health care programmes, and to suggest areas in which further researchis required. The Forum was created as a contribution to the United Nations’ ten year strategy for Chernobyl,launched in 2002 with the publication of Human Consequences of the Chernobyl Nuclear Accident — A Strategyfor Recovery.

Over a two year period, two groups of experts from 12 countries, including Belarus, the Russian Federationand Ukraine, and from relevant international organizations, assessed the accident’s environmental and healthconsequences. In early 2005 the Expert Group ‘Environment’, coordinated by the IAEA, and the Expert Group‘Health’, coordinated by the WHO, presented their reports for the consideration of the Chernobyl Forum. Bothreports were considered and approved by the Forum at its meeting on 18–20 April 2005. This meeting alsodecided, inter alia, “to consider the approved reports… as a common position of the Forum members, i.e., of theeight United Nations organizations and the three most affected countries, regarding the environmental andhealth consequences of the Chernobyl accident, as well as recommended future actions, i.e., as a consensus withinthe United Nations system.”

This report presents the findings and recommendations of the Chernobyl Forum concerning theenvironmental effects of the Chernobyl accident. The Forum’s report considering the health effects of theChernobyl accident is being published by the WHO. The Expert Group ‘Environment’ was chaired by L. Anspaughof the United States of America. The IAEA technical officer responsible for this report was M. Balonov of theIAEA Division of Radiation, Transport and Waste Safety.

EDITORIAL NOTE

Although great care has been taken to maintain the accuracy of information contained in this publication, neither theIAEA nor its Member States assume any responsibility for consequences which may arise from its use.

The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, asto the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries.

The mention of names of specific companies or products (whether or not indicated as registered) does not imply anyintention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of theIAEA.

CONTENTS

1. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2. Radioactive contamination of the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.1.1. Radionuclide release and deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.1.2. Urban environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.1.3. Agricultural environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.1.4. Forest environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.1.5. Aquatic environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.2. Recommendations for future research and monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.2.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.2.2. Practical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2.2.3. Scientific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2.2.4. Specific recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3. Environmental countermeasures and remediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.1.1. Radiological criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.1.2. Urban countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3.1.3. Agricultural countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3.1.4. Forest countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.3.1.5. Aquatic countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.3.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.3.2.1. Countries affected by the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.3.2.2. Worldwide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.3.2.3. Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.4. Human exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.4.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.4.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.5. Radiation induced effects on plants and animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.5.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.5.2. Recommendations for future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.5.3. Recommendations for countermeasures and remediation . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.6. Environmental and radioactive waste management aspects of the dismantling of the Chernobyl shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.6.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.6.2. Recommendations for future actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Reference to Section 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.2. Objectives of the Chernobyl Forum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.3. Method of operation and output of the Chernobyl Forum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4. Structure of the report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17References to Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3. RADIOACTIVE CONTAMINATION OF THE ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1. Radionuclide release and deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1.1. Radionuclide source term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1.2. Physical and chemical forms of released material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.1.3. Meteorological conditions during the course of the accident. . . . . . . . . . . . . . . . . . . . . . . . 213.1.4. Concentration of radionuclides in air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.1.5. Deposition of radionuclides on soil surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.1.6. Isotopic composition of the deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2. Urban environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.2.1. Deposition patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.2.2. Migration of radionuclides in the urban environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.2.3. Dynamics of the exposure rate in urban environments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3. Agricultural environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.3.1. Radionuclide transfer in the terrestrial environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.3.2. Food production systems affected by the accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.3.3. Effects on agriculture in the early phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.3.4. Effects on agriculture in the long term phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.3.4.1. Physicochemistry of radionuclides in the soil–plant system . . . . . . . . . . . . . . . . . 323.3.4.2. Migration of radionuclides in soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.3.4.3. Radionuclide transfer from soil to crops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343.3.4.4. Dynamics of radionuclide transfer to crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.3.4.5. Radionuclide transfer to animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.3.5. Current contamination of foodstuffs and expected future trends . . . . . . . . . . . . . . . . . . . . 403.4. Forest environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.4.1. Radionuclides in European forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.4.2. Dynamics of contamination during the early phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423.4.3. Long term dynamics of radiocaesium in forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.4.4. Uptake into edible products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.4.5. Contamination of wood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.4.6. Expected future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.4.7. Radiation exposure pathways associated with forests and forest products . . . . . . . . . . . . 46

3.5. Radionuclides in aquatic systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.5.2. Radionuclides in surface waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.5.2.1. Distribution of radionuclides between dissolved and particulate phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.5.2.2. Radioactivity in rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.5.2.3. Radioactivity in lakes and reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.5.2.4. Radionuclides in freshwater sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

3.5.3. Uptake of radionuclides to freshwater fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.5.3.1. Iodine-131 in freshwater fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.5.3.2. Caesium-137 in freshwater fish and other aquatic biota . . . . . . . . . . . . . . . . . . . . 533.5.3.3. Strontium-90 in freshwater fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.5.4. Radioactivity in marine ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553.5.4.1. Distribution of radionuclides in the sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553.5.4.2. Transfers of radionuclides to marine biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

3.5.5. Radionuclides in groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.5.5.1. Radionuclides in groundwater: Chernobyl exclusion zone. . . . . . . . . . . . . . . . . . 563.5.5.2. Radionuclides in groundwater: outside the Chernobyl exclusion zone. . . . . . . . 583.5.5.3. Irrigation water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3.5.6. Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.5.6.1. Freshwater ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.5.6.2. Marine ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

3.6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603.7. Further monitoring and research needed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61References to Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

4. ENVIRONMENTAL COUNTERMEASURES AND REMEDIATION. . . . . . . . . . . . . . . . . . . . . . . 69

4.1. Radiological criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694.1.1. International radiological criteria and standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694.1.2. National radiological criteria and standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

4.2. Urban decontamination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.2.1. Decontamination research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734.2.2. Chernobyl experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734.2.3. Recommended decontamination technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

4.3. Agricultural countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754.3.1. Early phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754.3.2. Late phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774.3.3. Countermeasures in intensive agricultural production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

4.3.3.1. Soil treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794.3.3.2. Change in fodder crops grown on contaminated land. . . . . . . . . . . . . . . . . . . . . . 804.3.3.3. Clean feeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804.3.3.4. Administration of caesium binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

4.3.4. Summary of countermeasure effectiveness in intensive production . . . . . . . . . . . . . . . . . . 814.3.5. Countermeasures in extensive production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814.3.6. Current status of agricultural countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834.3.7. A wider perspective on remediation, including socioeconomic issues . . . . . . . . . . . . . . . . 834.3.8. Current status and future of abandoned land. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

4.3.8.1. Exclusion and resettlement zones in Belarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844.3.8.2. Rehabilitation of contaminated lands in Ukraine . . . . . . . . . . . . . . . . . . . . . . . . . 854.3.8.3. Abandoned zones in the Russian Federation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

4.4. Forest countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864.4.1. Studies on forest countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874.4.2. Countermeasures for forests contaminated with radiocaesium . . . . . . . . . . . . . . . . . . . . . . 87

4.4.2.1. Management based countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874.4.2.2. Technology based countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.4.3. Examples of forest countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894.5. Aquatic countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

4.5.1. Measures to reduce doses at the water supply and treatment stage . . . . . . . . . . . . . . . . . . 904.5.2. Measures to reduce direct and secondary contamination of surface waters. . . . . . . . . . . . 914.5.3. Measures to reduce uptake by fish and aquatic foodstuffs . . . . . . . . . . . . . . . . . . . . . . . . . . 924.5.4. Countermeasures for groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.5.5. Countermeasures for irrigation water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4.6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.6.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.6.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

4.6.2.1. Countries affected by the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944.6.2.2. Worldwide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 954.6.2.3. Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

References to Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

5. HUMAN EXPOSURE LEVELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

5.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.1.1. Populations and areas of concern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.1.2. Exposure pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.1.3. Concepts of dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1015.1.4. Background radiation levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1015.1.5. Decrease of dose rate with time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1025.1.6. Critical groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

5.2. External exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035.2.1. Formulation of the model of external exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035.2.2. Input data for the estimation of effective external dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

5.2.2.1. Dynamics of external gamma dose rate over open undisturbed soil . . . . . . . . . . 1035.2.2.2. Dynamics of external gamma dose rate in anthropogenic areas . . . . . . . . . . . . . 1055.2.2.3. Behaviour of people in the radiation field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1055.2.2.4. Effective dose per unit gamma dose in air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

5.2.3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065.2.3.1. Dynamics of external effective dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065.2.3.2. Measurement of individual external dose with

thermoluminescent dosimeters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065.2.3.3. Levels of external exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

5.3. Internal dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095.3.1. Model for internal dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095.3.2. Monitoring data as input for the assessment of internal dose . . . . . . . . . . . . . . . . . . . . . . . 1095.3.3. Avoidance of dose by human behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.3.4. Results for doses to individuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

5.3.4.1. Thyroid doses due to radioiodines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.3.4.2. Long term internal doses from terrestrial pathways . . . . . . . . . . . . . . . . . . . . . . . 1125.3.4.3. Long term doses from aquatic pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

5.4. Total (external and internal) exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165.5. Collective doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

5.5.1. Thyroid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185.5.2. Total (external and internal) dose from terrestrial pathways . . . . . . . . . . . . . . . . . . . . . . . . 1185.5.3. Internal dose from aquatic pathways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

5.6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1195.6.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1195.6.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121


6. RADIATION INDUCED EFFECTS ON PLANTS AND ANIMALS . . . . . . . . . . . . . . . . . . . . . . . . . 125

6.1. Prior knowledge of radiation effects on biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256.2. Temporal dynamics of radiation exposure following the Chernobyl accident . . . . . . . . . . . . . . . . 1276.3. Radiation effects on plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1286.4. Radiation effects on soil invertebrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1306.5. Radiation effects on farm animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1316.6. Radiation effects on other terrestrial animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.7. Radiation effects on aquatic organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.8. Genetic effects in animals and plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1336.9. Secondary impacts and current conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1356.10. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

6.10.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1376.10.2. Recommendations for future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1376.10.3. Recommendations for countermeasures and remediation . . . . . . . . . . . . . . . . . . . . . . . . . . 138


7. ENVIRONMENTAL AND RADIOACTIVE WASTE MANAGEMENT ASPECTS OF THE DISMANTLING OF THE CHERNOBYL SHELTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

7.1. Current status and the future of unit 4 and the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1417.1.1. Unit 4 of the Chernobyl nuclear power plant after the accident . . . . . . . . . . . . . . . . . . . . . 1417.1.2. Current status of the damaged unit 4 and the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1427.1.3. Long term strategy for the shelter and the new safe confinement. . . . . . . . . . . . . . . . . . . . 144

7.1.4. Environmental aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457.1.4.1. Current status of the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457.1.4.2. Impact on air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457.1.4.3. Impact on surface water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457.1.4.4. Impact on groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1487.1.4.5. Impacts of shelter collapse without the new safe confinement . . . . . . . . . . . . . . 1487.1.4.6. Impacts of shelter collapse within the new safe confinement. . . . . . . . . . . . . . . . 150

7.1.5. Issues and areas for improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.1.5.1. Influence of the source term uncertainty on environmental decisions . . . . . . . . 1517.1.5.2. Characterization of fuel-containing material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.1.5.3. Removal of fuel-containing material concurrent with development

of a geological disposal facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.2. Management of radioactive waste from the accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

7.2.1. Current status of radioactive waste from the accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1537.2.1.1. Radioactive waste associated with the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1537.2.1.2. Mixing of accident related waste with operational radioactive waste . . . . . . . . . 1547.2.1.3. Temporary radioactive waste storage facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . 1547.2.1.4. Radioactive waste disposal facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

7.2.2. Radioactive waste management strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1567.2.3. Environmental aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1577.2.4. Issues and areas of improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

7.2.4.1. Radioactive waste management programme for the exclusion zone and the Chernobyl nuclear power plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

7.2.4.2. Decommissioning of unit 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1597.2.4.3. Waste acceptance criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1597.2.4.4. Long term safety assessment of existing radioactive waste storage sites . . . . . . 1607.2.4.5. Potential recovery of temporary waste storage facilities located in the

Chernobyl exclusion zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1607.3. Future of the Chernobyl exclusion zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1607.4. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

7.4.1. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1617.4.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162


CONTRIBUTORS TO DRAFTING AND REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

1. SUMMARY

1.1. INTRODUCTION

This report provides an up to date evaluationof the environmental effects of the accident thatoccurred on 26 April 1986 at the Chernobyl nuclearpower plant. Even though it is now nearly 20 yearsafter the accident, there are still many conflictingreports and rumours concerning its consequences.For this reason the Chernobyl Forum was initiatedby the IAEA in cooperation with the Food andAgriculture Organization of the United Nations(FAO), the United Nations DevelopmentProgramme (UNDP), the United NationsEnvironment Programme (UNEP), the UnitedNations Office for the Coordination of Humani-tarian Affairs (OCHA), the United NationsScientific Committee on the Effects of AtomicRadiation (UNSCEAR), the World Health Organi-zation (WHO) and the World Bank, as well as thecompetent authorities of Belarus, the RussianFederation and Ukraine. The first organizationalmeeting of the Chernobyl Forum was held on3-5 February 2003, at which time the decision wastaken to establish the Forum as an ongoing entity ofthe above named organizations.

The Chernobyl Forum was established as aseries of managerial, expert and public meetingswith the purpose of generating authoritativeconsensual statements on the health effects attrib-utable to radiation exposure arising from theaccident and the environmental consequencesinduced by the released radioactive material,providing advice on remediation and special healthcare programmes and suggesting areas in whichfurther research is required. The terms ofreference of the Forum as approved at the meetingwere:

(a) To explore and refine the current scientificassessments on the long term health andenvironmental consequences of theChernobyl accident, with a view to producingauthoritative consensus statements focusingon:

(i) The health effects attributable toradiation exposure caused by theaccident;

(ii) The environmental consequencesinduced by the radioactive material

released due to the accident (e.g. contam-ination of foodstuffs);

(iii) The consequences attributable to theaccident but not directly related to theradiation exposure or radioactivecontamination.

(b) To identify gaps in scientific research relevantto the radiation induced or radioactivecontamination induced health and environ-mental impacts of the accident, and to suggestareas in which further work is required basedon an assessment of the work done in the pastand bearing in mind ongoing work andprojects.

(c) To provide advice on, and to facilitate imple-mentation of, scientifically sound programmeson mitigation of the accident consequences,including possible joint actions of the organi-zations participating in the Forum, such as:

(i) Remediation of contaminated land, withthe aim of making it suitable for normalagricultural, economic and social lifeunder safe conditions;

(ii) Special health care of the affectedpopulation;

(iii) Monitoring of long term human exposureto radiation;

(iv) Addressing the environmental issuespertaining to the decommissioning of theChernobyl shelter and the managementof radioactive waste originating from theChernobyl accident.

The Chernobyl Forum is a high level organi-zation of senior officials of United Nations agenciesand the three most affected countries. The technicalreports of the Forum were produced by two expertgroups: Expert Group ‘Environment’ (EGE) andExpert Group ‘Health’ (EGH). The membership ofthe two groups comprised recognized internationalscientists and experts from the three most affectedcountries. Through the work of these two groupsand their subworking groups, the technicaldocuments were prepared. The EGE wascoordinated by the IAEA and the EGH wascoordinated by the WHO.

In all cases, the scientists of the EGE andEGH were able to reach consensus on the contentsof their respective technical documents. The

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technical reports were finally approved by theChernobyl Forum itself. This report, on the environ-mental consequences, is published by the IAEA; thereport on the health consequences will be publishedby the WHO.

1.2. RADIOACTIVE CONTAMINATION OF THE ENVIRONMENT

The Chernobyl accident caused a largeregional release of radionuclides into theatmosphere and subsequent radioactive contami-nation of the environment. Many Europeancountries were affected by the radioactive contami-nation; among the most affected were three formerrepublics of the Soviet Union, now Belarus, theRussian Federation and Ukraine. The depositedradionuclides gradually decayed and moved withinand among the environments — atmospheric,aquatic, terrestrial and urban.

1.2.1. Conclusions

1.2.1.1. Radionuclide release and deposition

Major releases from unit 4 of the Chernobylnuclear power plant continued for ten days, andincluded radioactive gases, condensed aerosols anda large amount of fuel particles. The total release ofradioactive substances was about 14 EBq1 (as of26 April 1986), which included 1.8 EBq of 131I,0.085 EBq of 137Cs and other caesium radioisotopes,0.01 EBq of 90Sr and 0.003 EBq of plutoniumradioisotopes. The noble gases contributed about50% of the total release of radioactivity.

Large areas of Europe were affected to somedegree by the Chernobyl releases. An area of morethan 200 000 km2 in Europe was contaminated withradiocaesium (above 0.04 MBq of 137Cs/m2), ofwhich 71% was in the three most affected countries(Belarus, the Russian Federation and Ukraine). Thedeposition was highly heterogeneous; it wasstrongly influenced by rain when the contaminatedair masses passed. In the mapping of the deposition,137Cs was chosen because it is easy to measure and isof radiological significance. Most of the strontiumand plutonium radioisotopes were deposited close(less than 100 km) to the reactor, due to their beingcontained within larger particles.

Much of the release comprised radionuclideswith short physical half-lives; long lived radio-nuclides were released in smaller amounts. Thusmany of the radionuclides released by the accidenthave already decayed. The releases of radioactiveiodines caused concern immediately after theaccident. Owing to the emergency situation and theshort half-life of 131I, few reliable measurementswere made of the spatial distribution of depositedradioiodine (which is important in determiningdoses to the thyroid). Current measurements of 129Imay assist in estimating 131I deposition better andthereby improve thyroid dose reconstruction.

After the initial period, 137Cs became thenuclide of greatest radiological importance, with90Sr being of less importance. For the first years134Cs was also important. Over the longer term(hundreds to thousands of years), the only radio-nuclides anticipated to be of interest are theplutonium isotopes and 241Am.

1.2.1.2. Urban environment

In urban areas, open surfaces such as lawns,parks, streets, roads, squares, roofs and wallsbecame contaminated with radionuclides. Underdry conditions, trees, bushes, lawns and roofsbecame more contaminated; under wet conditions,horizontal surfaces such as soil plots, lawns, etc.,received the highest contamination. Particularlyhigh 137Cs activity concentrations were foundaround houses where rain had transported theradioactive material from the roofs to the ground.The deposition in urban areas in the nearest city ofPripyat and surrounding settlements could haveinitially given rise to substantial external radiationdoses, but this was partially averted by theevacuation of the people. The deposited radioactivematerial in other urban areas has given rise toexposure of the public in the subsequent years andcontinues to do so.

Due to wind and rain and human activities,including traffic, street washing and cleanup, surfacecontamination by radioactive material was reducedsignificantly in inhabited and recreational areasduring 1986 and afterwards. One of the conse-quences of these processes has been the secondarycontamination of sewage systems and sludgestorage areas.

At present, in most of the settlementssubjected to radioactive contamination, the air doserate above solid surfaces has returned to the pre-accident background level. The elevated air dose1 1 EBq = 1018 Bq (becquerel).

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rate remains mainly over undisturbed soil ingardens, kitchen gardens and parks.

1.2.1.3. Agricultural environment

In the early phase, direct surface deposition ofmany different radionuclides dominated thecontamination of agricultural plants and the animalsconsuming them. The release and deposition ofradioiodine isotopes caused the most immediateconcern, but the problem was confined to the firsttwo months, because of the short physical half-life(eight days) of the most important iodine isotope,131I. The radioiodine was rapidly transferred to milkat a high rate in Belarus, the Russian Federationand Ukraine, leading to significant thyroid doses tothose consuming milk, especially children. In therest of Europe the consequences of the accidentvaried; increased levels of radioiodine in milk wereobserved in some contaminated southern areaswhere dairy animals were already outdoors.

Different crop types, in particular green leafyvegetables, were also contaminated with radio-nuclides to varying degrees, depending on thedeposition levels and the stage of the growingseason. Direct deposition on to plant surfaces was ofconcern for about two months.

After the early phase of direct contamination,uptake of radionuclides through plant roots fromsoil became increasingly important and showedstrong time dependence. Radioisotopes of caesium(137Cs and 134Cs) were the nuclides that led to thegreatest problems, and after the decay of 134Cs, 137Csremains to cause problems in some Belarusian,Russian and Ukrainian areas. In addition, 90Srcauses problems in the near field of the reactor, butat longer distances the deposition levels were toolow to be of radiological significance. Other radio-nuclides, such as plutonium isotopes and 241Am,either were present at very low deposition levels orwere not very available for root uptake, andtherefore did not cause real problems inagriculture.

In general, there was an initial substantialreduction in the transfer of radionuclides tovegetation and animals, as would be expected, dueto weathering, physical decay, migration of radio-nuclides down the soil column and reduction inradionuclide bioavailability in soil. Particularly incontaminated intensive agricultural systems, mostlyin the former USSR, there was substantialreduction in the transfer of 137Cs to plants andanimals, especially in the first few years. However,

in the past decade there has been little furtherobvious decline, and long term effective half-liveshave been difficult to quantify with precision.

The radiocaesium activity concentrations infoodstuffs after the early phase were influenced notonly by deposition levels but also by soil types,management practices and types of ecosystem. Themajor and persistent problems in the affected areasoccur in extensive agricultural systems with soilswith a high organic content and where animals grazeon unimproved pastures that are not ploughed orfertilized. In particular, this affects rural residents inthe former USSR, who are commonly subsistencefarmers with privately owned dairy cattle.

In the long term, 137Cs in meat and milk, andto a lesser extent 137Cs in vegetables, remains themost important contributor to human internal dose.As its activity concentration, in both vegetable andanimal foods, has been decreasing during the pastdecade very slowly, at 3–7%/a, the contribution of137Cs to dose will continue to dominate for decadesto come. The contribution of other long lived radio-nuclides, 90Sr, plutonium isotopes and 241Am, tohuman dose will remain insignificant.

1.2.1.4. Forest environment

Following the Chernobyl accident, vegetationand animals in forests and mountain areas showed aparticularly high uptake of radiocaesium, with thehighest recorded 137Cs activity concentrations beingfound in forest products, due to the persistentrecycling of radiocaesium in forest ecosystems.Particularly high 137Cs activity concentrations havebeen found in mushrooms, berries and game, andthese high levels have persisted since the accident.Thus, while there has been a general decline in themagnitude of exposures due to the consumption ofagricultural products, there have been continuedhigh levels of contamination in forest food products,which still exceed intervention limits in manycountries. This can be expected to continue forseveral decades to come. Therefore, the relativeimportance of forests in contributing to theradiation exposures of the populations of severalaffected countries has increased with time. It will be,primarily, the combination of downward migrationin the soil and the physical decay of 137Cs thatcontribute to any further reduction in the contami-nation of forest food products.

The high transfer of radiocaesium in thelichen–reindeer meat–humans pathway was demon-strated after the Chernobyl accident in the Arctic

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and sub-Arctic areas of Europe. The Chernobylaccident led to considerable contamination ofreindeer meat in Finland, Norway, the RussianFederation and Sweden, and caused significantproblems for the Sami people.

The use of timber and associated productsmakes only a small contribution to the exposure ofthe general public, although wood ash can containhigh amounts of 137Cs and could potentially give riseto higher doses than other uses of wood. Caesium-137 in timber is of minor importance, althoughdoses in the wood pulp industry have to beconsidered.

Forest fires increased air activity concentra-tions in 1992, but not to a high extent. The possibleradiological consequences of forest fires have beenmuch discussed, but these are not expected to causeany problems of radionuclide transfer from contam-inated forests, except, possibly, in the nearestsurroundings of the fire.

1.2.1.5. Aquatic environment

Radionuclides from Chernobyl contaminatedsurface water systems not only in areas close to thesite but also in many other parts of Europe. Theinitial contamination of water was due primarily todirect deposition of radionuclides on to the surfacesof rivers and lakes and was dominated by short livedradionuclides (most importantly 131I). In the firstfew weeks after the accident, activity concentrationsin drinking water from the Kiev reservoir were aparticular concern.

The contamination of water bodies decreasedrapidly during the weeks after fallout throughdilution, physical decay and absorption of radio-nuclides by catchment soils. For lakes andreservoirs, the settling of suspended particles to thebed sediments also played an important role inreducing radionuclide levels in water. Bedsediments are an important long term sink forradionuclides.

The initial uptake of radioiodine by fish wasrapid, but activity concentrations declined quickly,due primarily to physical decay. Bioaccumulation ofradiocaesium in the aquatic food chain led tosignificant concentrations in fish in the mostaffected areas, and in some lakes as far away asScandinavia and Germany. Owing to generallylower fallout and lower bioaccumulation, 90Sractivity concentrations in fish were not a significantcontributor to human dose in comparison with

radiocaesium, particularly since 90Sr is accumulatedin bone rather than in edible muscle.

In the long term, secondary contamination bywash-off of long lived 137Cs and 90Sr from contami-nated soils and remobilization from bed sedimentscontinues (at a much lower level) to the present day.Catchments with a high organic content (peat soils)release much more radiocaesium to surface watersthan those with mostly mineral soils. At present,surface water activity concentrations are low;irrigation with surface water is therefore notconsidered to be a problem.

Fuel particles deposited in the sediments ofrivers and lakes close to the Chernobyl nuclearpower plant show significantly lower weatheringrates than the same particles in terrestrial soils. Thehalf-life of these particles is roughly the same as thephysical half-life of the radionuclides 90Sr and 137Cs.

While 137Cs and 90Sr activity concentrations inthe water and fish of rivers, open lakes andreservoirs are currently low, the most contaminatedlakes are those few lakes with limited inflowing andoutflowing streams (‘closed’ lakes) in Belarus, theRussian Federation and Ukraine that have a poormineral nutrient status. Activity concentrations of137Cs in fish in some of these lakes will remain for asignificant time into the future. In a populationliving next to a closed lake system (e.g. LakeKozhanovskoe in the Russian Federation),consumption of fish has dominated the total 137Csingestion for some people.

Owing to the large distance of the Black andBaltic Seas from Chernobyl, and the dilution inthese systems, activity concentrations in sea waterhave been much lower than in fresh water. The lowradionuclide concentrations in the water combinedwith the low bioaccumulation of radiocaesium inmarine biota has led to activity concentrations inmarine fish that are not of concern.

1.2.2. Recommendations for future research and monitoring

1.2.2.1. General

Various ecosystems considered in this reporthave been intensively monitored and studied duringthe years after the Chernobyl accident, and thetransfer and bioaccumulation of the most importantlong term contaminants, 137Cs and 90Sr, are nowgenerally well understood. There is, therefore, littleurgent need for major new research programmes onradionuclides in ecosystems; there is, however, a

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requirement for continued, but more limited,targeted monitoring of the environments, and forfurther research in some specific areas, as detailedbelow.

Long term monitoring of radionuclides(especially 137Cs and 90Sr) in various environmentalcompartments is required to meet the generalpractical and scientific needs described below.

1.2.2.2. Practical

The practical needs are to:

(a) Assess current and predict future levels ofhuman exposure and contamination of foodsin order to justify remedial actions and longterm countermeasures.

(b) Inform the general public in affected areasabout the persistence of radioactive contami-nation in food products and its seasonal andannual variability in natural food productsgathered by themselves (such as mushrooms,game, freshwater fish from closed lakes,berries, etc.) and give advice on dietary andfood preparation methods to reduce radionu-clide intake by humans.

(c) Inform the general public in affected areasabout changing radiological conditions inorder to relieve public concerns.

1.2.2.3. Scientific

The scientific needs are to:

(a) Determine the parameters of the long termtransfer of radionuclides in variousecosystems and different natural conditions inorder to improve predictive models both foruse in Chernobyl affected areas and forapplication to potential future radioactivereleases.

(b) Determine mechanisms of radionuclidebehaviour in less studied ecosystems (e.g. therole of fungi in forests) in order tounderstand the mechanisms determining thepersistence of radionuclides in theseecosystems and to explore possibilities forremediation, with special attention to be paidto processes of importance for contributionto human and biota doses.

As activity concentrations in environmentalcompartments are now in quasi-equilibrium and

changing slowly, the number and frequency ofsampling and measurements performed inmonitoring and research programmes can besubstantially reduced compared with the early yearsafter the Chernobyl accident.

The deposits of 137Cs and a number of otherlong lived radionuclides in the 30 km zone should beused for radioecological studies of the variousecosystems located in this highly contaminatedarea. Such studies are, except for very small scaleexperiments, not possible or difficult to performelsewhere.

1.2.2.4. Specific recommendations

Updated mapping of 137Cs deposition inAlbania, Bulgaria and Georgia should beperformed in order to complete the study of thepost-Chernobyl contamination of Europe.

Improved mapping of 131I deposition, basedboth on historical environmental measurementscarried out in 1986 and on recent measurements of129I in soil samples in areas where elevated thyroidcancer incidence has been detected after theChernobyl accident, would reduce the uncertaintyin thyroid dose reconstruction needed for the deter-mination of radiation risks.

Long term monitoring of 137Cs and 90Sractivity concentrations in agricultural plant andanimal products produced in areas with various soiland climate conditions and different agriculturalpractices should be performed in the next decades,in the form of limited target research programmeson selected sites, to determine parameters for themodelling of long term transfer.

Studies of the distribution of 137Cs andplutonium radionuclides in the urban environment(Pripyat, Chernobyl and some other contaminatedtowns) at long times after the accident wouldimprove modelling of human external exposure andinhalation of radionuclides in the event of a nuclearor radiological accident or malicious action.

Continued long term monitoring of specificforest products, such as mushrooms, berries andgame, should be carried out in those areas in whichforests were significantly contaminated and wherethe public consumes wild foods. The results fromsuch monitoring are being used by the relevantauthorities in the affected countries to provideadvice to the general public on the continued use offorests for recreation and the gathering of wildfoods.

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In addition to the general monitoring of forestproducts, required for radiation protection, moredetailed, scientifically based, long term monitoringof specific forest sites is required to provide anongoing and improved understanding of themechanisms, long term dynamics and persistence ofradiocaesium contamination and its variability. It isdesirable to explore further the key organisms, forexample fungi, and their role in radiocaesiummobility and long term behaviour in forestecosystems. Such monitoring programmes are beingcarried out in the more severely affected countries,such as Belarus and the Russian Federation, and itis important that these continue into the foreseeablefuture if the current uncertainties on long termforecasts are to be reduced.

Aquatic systems have been intensivelymonitored and studied during the years after theChernobyl accident, and transfers andbioaccumulation of the most important long termcontaminants, 90Sr and 137Cs, are now wellunderstood. There is, however, a requirement forcontinued (but perhaps more limited) monitoring ofthe aquatic environment, and for further research insome specific areas, as detailed below.

Although there is currently no need for majornew research programmes on radioactivity inaquatic systems, predictions of future contami-nation of aquatic systems by 90Sr and 137Cs would beimproved by continued monitoring of radioactivityin key systems (the Pripyat–Dnieper system, theseas, and selected rivers and lakes in the mostaffected areas and western Europe). This wouldcontinue the excellent existing time series measure-ments of activity concentrations in water, sedimentsand fish, and enable the refinement of predictivemodels for these radionuclides.

Although they are currently of minor radio-logical importance in comparison with 90Sr and137Cs, further studies of transuranic elements in theChernobyl zone would help to improve predictionsof environmental contamination in the very longterm (hundreds to thousands of years). Furtherempirical studies of transuranic radionuclides and99Tc are unlikely to have direct implications forradiological protection in the Chernobyl affectedareas, but would add to knowledge of the environ-mental behaviour of these very long lived radio-nuclides.

Future plans to reduce the water level of theChernobyl cooling pond will have significantimplications for its ecology and the behaviour ofradionuclides/fuel particles in newly exposed

sediments. Specific studies on the cooling pondshould therefore continue. In particular, furtherstudy of fuel particle dissolution rates in aquaticsystems such as the cooling pond would improveknowledge of these processes.

1.3. ENVIRONMENTAL COUNTERMEASURES AND REMEDIATION

After the Chernobyl accident, the authoritiesin the USSR introduced a range of short term andlong term countermeasures to reduce the effects ofthe environmental contamination. The counter-measures consumed a great amount of human,economic and scientific resources. Unfortunately,there was not always openness and transparency inthe actions of the authorities, and information waswithheld from the public. This can, in part, explainsome of the problems experienced later in commu-nication with the public, and the public’s mistrust ofthe authorities. Similar behaviour in many othercountries outside the Russian Federation, Belarusand Ukraine led to a distrust in authority that, inmany countries, prompted investigations on how todeal with such major accidents in an open andtransparent way and on how the affected people canbe involved in decision making processes.

The unique experience of countermeasureapplication after the Chernobyl accident hasalready been widely used both at the national andinternational levels in order to improve prepar-edness against future nuclear and radiologicalemergencies.

1.3.1. Conclusions

1.3.1.1. Radiological criteria

At the time of the Chernobyl accident, welldeveloped international and national guidance ongeneral radiation protection of the public andspecific guidance applicable to major nuclearemergencies was in place. The basic methodology ofthe guidance used in the former USSR was differentfrom that of the international system, but the doselimits of the radiation safety standards were similar.The then available international and nationalstandards were widely applied for the protection ofthe populations of the European countries affectedby the accident.

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The scale and long term consequences of theChernobyl accident required the development ofsome additional national and internationalradiation safety standards as a result of changingradiological conditions.

1.3.1.2. Urban countermeasures

Decontamination of settlements was widelyapplied as a countermeasure in the contaminatedregions of the USSR during the first years after theChernobyl accident as a means of reducing theexternal exposure of the public and the inhalationof resuspended radioactive substances.

Decontamination was cost effective withregard to reduction of external dose when itsplanning and implementation were preceded by aremediation assessment based on cost–benefittechniques and external dosimetry data. Since theareas have been cleaned up, no secondarycontamination of cleaned up plots has beenobserved.

The decontamination of urban environmentshas produced a considerable amount of low levelradioactive waste, which, in turn, has created aproblem of disposal.

Numerous experimental studies andassociated modelling have been used as thescientific basis for developing improved recommen-dations for decontamination of the urbanenvironment. Such recommendations could be usedin the event of any future large scale radioactivecontamination of urban areas.

1.3.1.3. Agricultural countermeasures

Countermeasures applied in the early phase ofthe Chernobyl accident were only partially effectivein reducing radioiodine intake via milk, because ofthe lack of timely information about the accidentand guidance on recommended actions, particularlyfor private farmers. This led to significantradioiodine exposure of some people in the affectedcountries.

The most effective countermeasures in theearly phase were exclusion of contaminated pasturegrasses from animals’ diets and the rejection ofmilk. Feeding animals with clean fodder waseffectively implemented in some countries;however, this countermeasure was not widelyapplied in the USSR, due to a lack of uncontami-nated feeds. Slaughtering of cattle was often carriedout, but it was unjustified from a radiological point

of view and caused significant hygienic, practicaland economic problems.

Several months after the accident, long termagricultural countermeasures against radiocaesiumand radiostrontium were effectively implemented inall contaminated regions; these countermeasuresincluded feeding animals with clean fodder andobligatory milk processing. This enabled mostfarming practices to continue in affected areas andresulted in a large reduction in dose. The mostimportant precondition was the radiationmonitoring of agricultural lands, feeds andfoodstuffs, including in vivo monitoring of caesiumactivity concentrations in the muscle of cattle.

The greatest long term problem has beenradiocaesium contamination of milk and meat. Inthe USSR, and later in the three independentcountries, this was addressed by the treatment ofland used for fodder crops, clean feeding and theapplication of caesium binders to animals. Cleanfeeding is one of the most important and effectivemeasures used in countries where animal productshave 137Cs activity concentrations exceeding theaction levels. In the long term, environmentalradiation conditions are changing only slowly;however, the efficiency of environmental counter-measures remains at a constant level.

The application of agricultural counter-measures in the three most affected countries hassubstantially decreased since the mid-1990s,because of economic problems. Within a short timethis resulted in an increase of radionuclide contentin plant and animal agricultural products.

There are still agricultural areas in the threecountries that remain out of use. This land could beused after appropriate remediation, but at presentlegal, economic and social constraints make thisdifficult.

Where social and economic factors, along withradiological factors, have been taken into accountduring the planning and application of counter-measures, better acceptability of the counter-measures by the public has been achieved.

In western Europe, because of the high andprolonged uptake of radiocaesium in the affectedextensive systems, a range of countermeasures isstill being used for animal products from uplandsand forests.

For the first time, practical, long term agricul-tural countermeasures have been developed, testedand implemented on a large scale; these includeradical improvement of meadows, pre-slaughterclean feeding, the application of caesium binders,

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and soil treatment and cultivation. Their implemen-tation on more than three billion hectares ofagricultural land has made it possible to minimizethe amount of products with radionuclide activityconcentrations above the action levels in all threecountries.

1.3.1.4. Forest countermeasures

The principal forest related countermeasuresapplied after the Chernobyl accident weremanagement based countermeasures (restrictionsof various activities normally carried out in forests)and technology based countermeasures.

Restrictions widely applied in the three mostaffected countries, and partially in Scandinavia,included the following actions that have reducedhuman exposure due to residence in radioactivelycontaminated forests and the use of forest products:

(a) Restrictions on public and forest workeraccess, as a countermeasure against externalexposure.

(a) Restrictions on the harvesting of foodproducts such as game, berries andmushrooms. In the three most affectedcountries mushrooms are widely consumed,and therefore this restriction has beenparticularly important.

(b) Restrictions on the collection of firewood bythe public, in order to prevent externalexposures in the home and garden when thewood is burned and the ash is disposed of orused as a fertilizer.

(c) Alteration of hunting practices, aimed atavoiding the consumption of meat with highseasonal levels of radiocaesium.

(d) Fire prevention, especially in areas with largescale radionuclide deposition, aimed at theavoidance of secondary contamination of theenvironment.

However, experience in the three mostaffected countries has shown that such restrictionscan also result in significant negative social conse-quences, and advice from the authorities to thegeneral public may be ignored as a result. Thissituation can be offset by the provision of suitableeducational programmes targeted at the local scaleto emphasize the relevance of suggested changes inthe use of some forest areas.

It is unlikely that any technology based forestcountermeasures (i.e. the use of machinery and/or

chemical treatments to alter the distribution ortransfer of radiocaesium in the forest) will bepracticable on a large scale.

1.3.1.5. Aquatic countermeasures

Numerous countermeasures were put in placein the months and years after the accident to protectwater systems from the transfer of radionuclidesfrom contaminated soils. In general, these measureswere ineffective and expensive and led to relativelyhigh exposures of the workers implementing thecountermeasures.

The most effective countermeasure was theearly restriction of drinking water abstraction andthe change to alternative supplies. Restrictions onthe consumption of freshwater fish have provedeffective in Scandinavia and Germany; however, inBelarus, the Russian Federation and Ukraine suchrestrictions may not always have been adhered to.

It is unlikely that any future countermeasuresto protect surface waters would be justifiable interms of economic cost per unit of dose reduction. Itis expected that restrictions on the consumption offish will remain in a few cases (in closed lakes) forseveral more decades.

Future efforts in this area should be focusedon public information, because there are still publicmisconceptions concerning the perceived healthrisks due to radioactively contaminated waters andfish.

1.3.2. Recommendations

1.3.2.1. Countries affected by the Chernobyl accident

Long term remediation measures andcountermeasures should be applied in the areascontaminated with radionuclides if they are radio-logically justified and optimized.

Members of the general public should beinformed, along with the authorities, about theexisting radiation risk factors and the technologicalpossibilities to reduce them in the long term viaremediation and countermeasures, and be involvedin discussions and decision making.

In the long term, remediation measures andcountermeasures remain efficient and justified —mainly in the agricultural areas with poor (sandyand peaty) soils, where high radionuclide transferfrom soil to plants can occur.

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Particular attention must be given to privatefarms in several hundred settlements and to about50 intensive farms in Belarus, the RussianFederation and Ukraine, where radionuclideconcentrations in milk still exceed the nationalaction levels.

Among long term remediation measures,radical improvement of pastures and grasslands, aswell as the draining of wet peaty areas, is highlyefficient. The most efficient agricultural counter-measures are pre-slaughter clean feeding of animalsaccompanied by in vivo monitoring, application ofPrussian blue to cattle and enhanced application ofmineral fertilizers in plant cultivation.

Restricting harvesting by the public of wildfood products such as game, berries, mushroomsand fish from closed lakes may still be needed inareas where radionuclide activity concentrationsexceed the national action levels.

Advice should continue to be given onindividual diets, as a way of reducing consumptionof highly contaminated wild food products, and onsimple cooking procedures to remove radioactivecaesium.

It is necessary to identify sustainable ways ofmaking use of the most affected areas, but also torevive the economic potential of such areas forthe benefit of the community. Such strategiesshould take into account the associated radiationhazard.

1.3.2.2. Worldwide

The unique experience of countermeasureapplication after the Chernobyl accident should becarefully documented and used for the preparationof international and national guidance forauthorities and experts responsible for radiationprotection of the public and the environment.

Practically all the long term agriculturalcountermeasures implemented on a large scale incontaminated lands of the three most affectedcountries can be recommended for use in the eventof future accidents. However, the effectiveness ofsoil based countermeasures varies at each site.Analysis of soil properties and agricultural practicebefore the application of countermeasures istherefore of great importance.

Recommendations on the decontamination ofthe urban environment in the event of large scaleradioactive contamination should be distributed tothe management of nuclear facilities that have the

potential for substantial accidental radioactiverelease (nuclear power plants and reprocessingplants) and to authorities in adjacent regions.

1.3.2.3. Research

Generally, the physical and chemicalprocesses involved in environmental counter-measures and remediation technologies, both of amechanical nature (radionuclide removal, mixingwith soil, etc.) or of a chemical nature (soil liming,fertilization, etc.), or their combinations, areunderstood well enough to be modelled and appliedin similar circumstances worldwide. Much less wellunderstood are the biological processes that couldbe used in environmental remediation (e.g.reprofiling of agricultural production, bioremedi-ation, etc.). These processes require more research.

An important issue that requires more socio-logical research is the perception by the public ofthe introduction, performance and withdrawal ofcountermeasures in the event of an emergency, aswell as the development of social measures aimed atinvolving the public in these processes at all stages,beginning with the decision making process.

There is still substantial diversity in the inter-national and national radiological criteria and safetystandards applicable to the remediation of areasaffected by environmental contamination withradionuclides. The experience of radiologicalprotection of the public after the Chernobylaccident has clearly shown the need for furtherinternational harmonization of appropriate radio-logical criteria and safety standards.

1.4. HUMAN EXPOSURE

Following the Chernobyl accident, bothworkers and the general public were affected byradiation that resulted, or can result, in adversehealth effects. In this report consideration is givenprimarily to the exposure patterns of members ofthe general public exposed to radionuclidesreleased to the environment. Information on dosesreceived by members of the general public, boththose evacuated from the accident area and thosewho live permanently in contaminated areas, isrequired for the following health related purposes:

(a) Substantiation of countermeasures andremediation programmes;

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(b) Forecast of expected adverse health effectsand justification of corresponding healthprotection measures;

(c) Information for the public and the authorities; (d) Epidemiological and other medical studies of

radiation induced adverse health effects.

The results of post-accident environmentalmonitoring indicate that the most affected countrieswere Belarus, the Russian Federation and Ukraine.Much of the information on doses from theChernobyl accident relates to these countries.

There were four main mechanisms fordelivering radiation dose to the public: externaldose from cloud passage, internal dose frominhalation of the cloud and resuspended material,external dose from radioactive material depositedon soil and other surfaces, and internal dose fromthe ingestion of food products and water. Except forunusual circumstances, the latter two pathwayswere the more important. External dose andinternal dose tended to be approximately equallyimportant, although this general conclusion issubject to large variation, due to the shieldingafforded by buildings and the soil from which cropswere grown.

Estimates of doses to individual members ofpopulation groups were based on millions ofmeasurements of concentrations of radioactivematerial in air, soil, foods, water, human thyroidsand the whole body contents of humans. Inaddition, many measurements were made of theexternal gamma exposure rate over undisturbedand disturbed fields, and external doses to humanswere measured with individual thermoluminescentdosimeters. Thus the results of estimated doses arefirmly based upon measurements and tend to berealistic rather than conservative.

As the major health effect of the Chernobylaccident for the general public was an elevatedthyroid cancer incidence in children and adoles-cents, much attention has been paid to thedosimetry of the thyroid gland. The assessment ofthyroid doses resulting from the intake of 131I isbased on the results of 350 000 human measure-ments and a few thousand measurements of 131I inmilk performed in Belarus, the Russian Federationand Ukraine within a few weeks of the accident.

Doses to humans were reduced significantlyby a number of countermeasures. Official counter-measures included evacuation and relocation ofpersons, the blockage of contaminated foodsupplies, the removal of contaminated soil, the

treatment of agricultural fields to reduce the uptakeof radionuclides, the substitution of foods and theprohibition of the use of wild foods. Unofficialcountermeasures included the self-initiatedavoidance of foods judged to be contaminated.

1.4.1. Conclusions

The collective effective dose (not includingdose to the thyroid) received by about five millionresidents living in the areas of Belarus, the RussianFederation and Ukraine contaminated by theChernobyl accident (137Cs deposition on soil>37 kBq/m2) was approximately 40 000 man Svduring the period 1986–1995. The groups of exposedpersons within each country received an approxi-mately equal collective dose. The additional amountof collective effective dose projected to be receivedbetween 1996 and 2006 is about 9000 man Sv.

The collective dose to the thyroid was nearly2 × 106 man Gy, with nearly half received by personsexposed in Ukraine.

The main pathways leading to humanexposure were external exposure from radio-nuclides deposited on the ground and the ingestionof contaminated terrestrial food products.Inhalation and ingestion of drinking water, fish andproducts contaminated with irrigation water weregenerally minor pathways.

The range in thyroid dose in differentsettlements and in all age–gender groups is large,between less than 0.1 Gy and more than 10 Gy. Insome groups, and especially in younger children,doses were high enough to cause both short termfunctional thyroid changes and thyroid cancer insome individuals.

The internal thyroid dose from the intake of131I was mainly due to the consumption of freshcow’s milk and, to a lesser extent, of greenvegetables; children, on average, received a dosethat was much higher than that received by adults,because of their small thyroid masses andconsumption rates of fresh cow’s milk that weresimilar to those of adults.

For populations permanently residing incontaminated areas and exposed predominantly viaingestion, the contribution of short lived radio-iodines (i.e. 132I, 133I and 135I) to thyroid dose wasminor (i.e. about 1% of the 131I thyroid dose), sinceshort lived radioiodines decayed during transport ofthe radioiodines along the food chains. The highestrelative contribution (20–50%) to the thyroid dosesto the public from short lived radionuclides was

10

received by the residents of Pripyat throughinhalation; these residents were evacuated beforethey could consume contaminated food.

Both measurement and modelling data showthat the urban population was exposed to a lowerexternal dose by a factor of 1.5–2 compared withthe rural population living in areas with similarlevels of radioactive contamination. This arisesbecause of the better shielding features of urbanbuildings and different occupational habits. Also,as the urban population depends less on localagricultural products and wild foods than the ruralpopulation, both effective and thyroid internaldoses caused predominantly by ingestion werelower by a factor of two to three in the urban thanin the rural population.

The initial high rates of exposure declinedrapidly due to the decay of short lived radionuclidesand to the movement of radiocaesium into the soilprofile. The latter caused a decrease in the rate ofexternal dose due to increased shielding. Inaddition, as caesium moves into the soil column itbinds to soil particles, which reduces the availabilityof caesium to plants and thus to the human foodchain.

The great majority of dose from the accidenthas already been accumulated.

Persons who received effective doses (notincluding dose to the thyroid) higher than theaverage by a factor of two to three were those wholived in rural areas in single storey homes and whoate large amounts of wild foods such as game meats,mushrooms and berries.

The long term internal doses to residents ofrural settlements strongly depend on soil properties.Contributions due to internal and external exposureare comparable in areas with light sandy soil, andthe contribution of internal exposure to the total(external and internal) dose does not exceed 10% inareas with predominantly black soil. The contri-bution of 90Sr to the internal dose, regardless ofnatural conditions, is usually less than 5%.

The long term internal doses to childrencaused by ingestion of food containing caesiumradionuclides are usually lower by a factor of about1.1–1.5 than those to adults and adolescents.

Both accumulated and predicted mean dosesin settlement residents vary in the range of twoorders of magnitude, depending on the radioactivecontamination of the area, predominant soil typeand settlement type. In the period 1986–2000 theaccumulated dose ranged from 2 mSv in townslocated in black soil areas up to 300 mSv in villages

located in areas with podzol sandy soil. The dosesexpected in the period 2001–2056 are substantiallylower than the doses already received (i.e. in therange of 1–100 mSv).

If countermeasures had not been applied, thepopulations of some of the more contaminatedvillages could have received lifetime (70 years)effective doses of up to 400 mSv. Intensiveapplication of countermeasures such as settlementdecontamination and agricultural countermeasureshas substantially reduced the doses. Forcomparison, a worldwide average lifetime dosefrom natural background radiation is about170 mSv, with a typical range of 70–700 mSv invarious regions of the world.

The vast majority of the approximately fivemillion people residing in the contaminated areas ofBelarus, the Russian Federation and Ukrainecurrently receive annual effective doses of less than1 mSv (equal to the national action levels in thethree countries). For comparison, a worldwideaverage annual dose from natural backgroundradiation is about 2.4 mSv, with a typical range of 1–10 mSv in various regions of the world.

The number of residents of the contaminatedareas in the three most affected countries thatcurrently receive more than 1 mSv annually can beestimated to be about 100 000 persons. As the futurereduction of both the external dose rate and theradionuclide (mainly 137Cs) activity concentrationsin food is predicted to be rather slow, the reductionin the human exposure levels is also expected to beslow (i.e. about 3–5%/a with current counter-measures).

Based upon available information, it does notappear that the doses associated with hot particleswere significant.

The assessment of the Chernobyl Forumagrees with that of UNSCEAR [1.1] in terms of thedose received by the populations of the three mostaffected countries: Belarus, the Russian Federationand Ukraine.


Large scale monitoring of foodstuffs, wholebody counting of individuals and provision ofthermoluminescent dosimeters to members of thegeneral public are no longer necessary. The criticalgroups in areas of high contamination and/or hightransfer of radiocaesium to foods are known.Representative members of these critical groupsshould be monitored with dosimeters for external

11

dose and with whole body counting for internaldose.

Sentinel or marker individuals in more highlycontaminated areas not scheduled for furtherremediation might be identified for continuedperiodic whole body counting and monitoring forexternal dose. The goal would be to follow theexpected continued decrease in external andinternal dose rate and to determine whether suchdecreases are due to radioactive decay alone or tofurther ecological elimination.

1.5. RADIATION INDUCED EFFECTS ON PLANTS AND ANIMALS

The biological effects of radiation on plantsand animals have long been of interest to scientists;in fact, much of the information on the effects onhumans has evolved from experimental studies onplants and animals. Additional research followedthe development of nuclear energy and concernsabout the possible impacts of radioactive releasesinto the terrestrial and aquatic environments. Bythe mid-1970s, a large amount of information hadbeen accrued on the effects of ionizing radiation onplants and animals.

The Chernobyl nuclear accident in April 1986occurred not in a desert or ocean but in a territorywith a temperate climate and flourishing flora andfauna. Both acute radiation effects (radiation deathof plants and animals, loss of reproduction, etc.) andlong term effects (change of biodiversity,cytogenetic anomalies, etc.) have been observed inthe affected areas. Biota located in the area nearestto the source of the radioactive release, the 30 kmzone or Chernobyl exclusion zone (CEZ), weremost affected. As a result, in this area populationand ecosystem effects on biota, caused, on the onehand, by high radiation levels, and, on the otherhand, by plant succession and animal migration dueto intraspecific and interspecific competition, haveoccurred.

The plant and animal conditions in the CEZchanged rapidly during the first months and yearsafter the accident and later arrived at a quasi-stationary equilibrium. At present, traces of adverseradiation effects on biota can hardly be found in thenear vicinity of the radiation source (a fewkilometres from the damaged reactor), and on therest of the territory both wild plants and animals areflourishing because of the removal of the majornatural stressor: humans.

1.5.1. Conclusions

Radiation from radionuclides released by theChernobyl accident caused numerous acute adverseeffects in the biota located in the areas of highestexposure (i.e. up to a distance of a few tens ofkilometres from the release point). Beyond theCEZ, no acute radiation induced effects on biotahave been reported.

The environmental response to the Chernobylaccident was a complex interaction among radiationdose, dose rate and its temporal and spatialvariations, and the radiosensitivities of the differenttaxons. Both individual and population effectscaused by radiation induced cell death have beenobserved in plants and animals as follows:

(a) Increased mortality of coniferous plants, soilinvertebrates and mammals;

(b) Reproductive losses in plants and animals;(c) Chronic radiation syndrome in animals

(mammals, birds, etc.).

No adverse radiation induced effects havebeen reported in plants and animals exposed to acumulative dose of less than 0.3 Gy during the firstmonth after the radionuclide fallout.

Following the natural reduction of exposurelevels due to radionuclide decay and migration,populations have been recovering from the acuteradiation effects. By the next growing season afterthe accident, the population viability of plants andanimals substantially recovered as a result of thecombined effects of reproduction and immigration.A few years were needed for recovery from themajor radiation induced adverse effects in plantsand animals.

The acute radiobiological effects observed inthe Chernobyl accident area are consistent withradiobiological data obtained in experimentalstudies or observed in natural conditions in otherareas affected by ionizing radiation. Thus rapidlydeveloping cell systems, such as meristems of plantsand insect larvae, were predominantly affected byradiation. At the organism level, young plants andanimals were found to be the most sensitive to theacute effects of radiation.

Genetic effects of radiation, in both somaticand germ cells, were observed in plants and animalsin the CEZ during the first few years after theaccident. Both in the CEZ and beyond, differentcytogenetic anomalies attributable to radiationcontinue to be reported from experimental studies

12

performed on plants and animals. Whether theobserved cytogenetic anomalies have anydetrimental biological significance is not known.

The recovery of affected biota in the CEZ hasbeen confounded by the overriding response to theremoval of human activities (e.g. termination ofagricultural and industrial activities and theaccompanying environmental pollution in the mostaffected area). As a result, the populations of manyplants and animals have expanded, and the presentenvironmental conditions have had a positiveimpact on the biota in the CEZ.

1.5.2. Recommendations for future research

In order to develop a system of environmentalprotection against radiation, the long term impactof radiation on plant and animal populations shouldbe further investigated in the CEZ; this is a globallyunique area for radioecological and radiobiologicalresearch in an otherwise natural setting.

In particular, multigenerational studies ofradiation effects on the genetic structure of plantand animal populations might bring fundamentallynew scientific information.

There is a need to develop standardizedmethods for biota–dose reconstruction, for examplein the form of a unified dosimetric protocol.

1.5.3. Recommendations for countermeasures and remediation

Protective actions for farm animals in theevent of a nuclear or radiological emergency shouldbe developed and internationally harmonized basedon modern radiobiological data, including theexperience gained in the CEZ.

It is likely that any technology basedremediation actions aimed at improving the radio-logical conditions for plants and animals in the CEZwould have adverse impacts on biota.

1.6. ENVIRONMENTAL AND RADIOACTIVE WASTE MANAGEMENT ASPECTS OF THE DISMANTLING OF THE CHERNOBYL SHELTER

1.6.1. Conclusions

The accidental destruction of unit 4 of theChernobyl nuclear power plant resulted inextensive radioactive contamination and the

generation of large amounts of radioactive waste inthe unit, the Chernobyl nuclear power plant site andthe surrounding area (CEZ). Construction of theshelter between May and November 1986 wasaimed at environmental containment of thedamaged reactor, reduction of radiation levels onthe site and the prevention of further release ofradionuclides off the site.

The shelter was erected in an extremely shortperiod of time under conditions of severe radiationexposure of personnel. As a result, the measurestaken to save time and reduce dose during theconstruction led to imperfection in the newlyconstructed shelter as well as to a lack of compre-hensive data on the stability of the damaged unit 4structures. In addition to uncertainties on stabilityat the time of its construction, structural elements ofthe shelter have degraded as a result of moistureinduced corrosion during the two decades that havepassed since the shelter was erected. The mainpotential hazard associated with the shelter is apossible collapse of its top structures and release ofradioactive dust into the environment.

In order to avoid the potential collapse of theshelter in the future, measures are planned tostrengthen the unstable structures of the shelter. Inaddition, a new safe confinement (NSC) with morethan 100 years of service life is planned to be built asa cover over the existing shelter as a longer termsolution. The construction of the NSC is expected toallow for the dismantlement of the current shelter,removal of highly radioactive fuel-containingmaterial (FCM) from unit 4 and eventualdecommissioning of the damaged reactor.

In the course of remediation activities, both atthe Chernobyl nuclear power plant site and in itsvicinity, large volumes of radioactive waste weregenerated as a result of the cleanup of contaminatedareas and placed in temporary near surface wastestorage and disposal facilities. Facilities of thetrench and landfill type were created from 1986 to1987 in the CEZ at distances of 0.5–15 km from thenuclear power plant site with the intention ofavoiding dust spread, reducing the radiation levelsand enabling better working conditions at unit 4 andin its surroundings. These facilities were establishedwithout proper design documentation, engineeredbarriers or hydrogeological investigations and donot meet current waste safety requirements.

During the years following the accident, largeresources were expanded to provide a systematicanalysis and an acceptable strategy for themanagement of the existing radioactive waste.

13

However, to date, a broadly accepted strategy forradioactive waste management at the Chernobylnuclear power plant site and the CEZ, andespecially for high level and long lived waste, hasnot been developed. The main reason for this is thelarge number of radioactive waste storage anddisposal facilities, of which only half are well studiedand inventoried. This results in large uncertaintieson the radioactive waste inventories.

More radioactive waste is expected in theyears to come, generated during the construction ofthe NSC, the possible shelter dismantling, FCMremoval and the decommissioning of unit 4. Thiswaste, belonging to different categories, must beproperly managed.

According to the Ukrainian nationalprogramme on radioactive waste management,there are different options for the different wastecategories. The planned options for low levelradioactive waste are to sort the waste according toits physical characteristics (e.g. soil, concrete, metal)and possibly decontaminate and/or condition it forbeneficial reuse (reuse of soil for NSC foundations,melting of metal pieces, etc.), or send it for disposal.

The long lived waste is planned to be placed ininterim storage. Different storage options are beingconsidered, and a decision has not yet been made.After construction of the NSC and decommis-sioning of the shelter facilities, it is envisaged thatshelter dismantling and further removal of FCMwill occur. High level radioactive waste is plannedto be partially processed in place and then stored ata temporary storage site until a deep geologicdisposal site is ready.

Such a strategic approach is foreseen by theComprehensive Programme on Radioactive WasteManagement, which was approved by theUkrainian Government in 1996 and confirmed in2004. According to this concept, it is consideredreasonable to begin a specific investigation forexploring the most appropriate geological site inthis area in 2006. Following such planning, theconstruction of a deep geologic disposal facilitymight be completed before 2035–2040.

The future development of the CEZ as anindustrial site or nature reserve depends on thefuture strategy for the conversion of unit 4 into anecologically safe system (i.e. the development of theNSC, the dismantlement of the current shelter, theremoval of FCM and the eventual decommissioningof the unit 4 reactor site). Currently units 1, 2 and 3(1000 MW RBMK (high power channel type)reactors) are shut down with a view to being decom-

missioned, and two additional reactors (units 5 and6) that had been near completion were abandonedin 1986 following the accident.

There are uncertainties related to the currentradioactive material inventory at the shelter andalso at the waste storage and disposal sites withinthe CEZ. This situation affects not only safetyassessments and environmental analyses but alsothe design of remediation actions and the criteriafor new facilities.

1.6.2. Recommendations for future actions

Recognizing the ongoing effort on improvingsafety and addressing the aforementioned uncer-tainties in the existing input data, the followingmain recommendations are made regarding thedismantling of the shelter and the management ofthe radioactive waste generated as a result of theaccident.

Since individual safety and environmentalassessments have been performed only forindividual facilities at and around the Chernobylnuclear power plant, a comprehensive safety andenvironmental impact assessment, in accordancewith international standards and recommendations,that encompasses all activities inside the entireCEZ, should be performed.

During the preparation and construction ofthe NSC and soil removal, special monitoring wellsare expected to be destroyed. Therefore, it isimportant to maintain and improve the environ-mental monitoring strategies, methods, equipmentand staff qualification needed for the adequateperformance of monitoring of the conditions at theChernobyl nuclear power plant site and the CEZ.

Development of an integrated radioactivewaste management programme for the shelter, theChernobyl nuclear power plant site and the CEZ isneeded to ensure application of consistentmanagement approaches and sufficient facilitycapacity for all waste types. Specific emphasis needsto be given to the characterization and classificationof waste (in particular waste with transuranicelements) from all remediation and decommis-sioning activities, as well as to the establishment ofsufficient infrastructure for the safe long termmanagement of long lived and high level waste.Therefore, development of an appropriate wastemanagement infrastructure is needed in order toensure sufficient waste storage capacity; at present,the rate and continuity of remediation activities at

14

the Chernobyl nuclear power plant site and in theCEZ are being limited.

A coherent and comprehensive strategy forthe rehabilitation of the CEZ is needed, withparticular focus on improving the safety of theexisting waste storage and disposal facilities. Thiswill require development of a prioritizationapproach for remediation of the sites, based onsafety assessment results, aimed at making decisionsabout those sites at which waste will be retrieved

and disposed of and those sites at which the wastewill be allowed to decay in situ.

REFERENCE TO SECTION 1

[1.1] UNITED NATIONS, Sources and Effects ofIonizing Radiation (Report to the GeneralAssembly, with Scientific Annexes), Vol. II, Scien-tific Committee on the Effects of AtomicRadiation (UNSCEAR), UN, New York (2000).

15

2. INTRODUCTION

2.1. BACKGROUND

The Chernobyl Forum was initiated by theIAEA in cooperation with the Food andAgriculture Organization of the United Nations(FAO), the United Nations DevelopmentProgramme (UNDP), the United NationsEnvironment Programme (UNEP), the UnitedNations Office for the Coordination of Humani-tarian Affairs (OCHA), the United NationsScientific Committee on the Effects of AtomicRadiation (UNSCEAR), the World Health Organi-zation (WHO) and the World Bank, as well as thecompetent authorities of Belarus, the RussianFederation and Ukraine. The organizationalmeeting for the Chernobyl Forum was held on 3–5 February 2003, at which time the decision wastaken to establish the Forum as an ongoing entity ofthe above named organizations.

The background for the establishment of theForum dates back to 2000, when UNSCEARpublished its 2000 report to the United NationsGeneral Assembly [2.1]. In this report it was statedthat, apart from the very early deaths due toextreme overexposure, the only clearly indicatedhealth effect on the population that could beattributed to radiation exposure was an increasedrate in the diagnosis of thyroid cancer amongpersons who were young children at the time ofexposure. The political representatives of Belarus,the Russian Federation and Ukraine had strongreservations regarding the report. These reserva-tions seem to have had two bases:

(a) The statement on health effects was widelydivergent from what was being reported in thepopular press and even by some othermembers of the United Nations family;

(b) The political representatives felt that theviews of scientists from the three affectedcountries had not been considered byUNSCEAR.

Subsequently, during his visit to Belarus and inmeetings with the Belarusian authorities and itsscientific community, the Director General of theIAEA, M. ElBaradei, noted that “a lack of trust stillprevails among the people of the region…, due inpart to the contradictory data and reports — on the

precise environmental and health impacts of theaccident — among national authorities, as well asamong the relevant international organizations.”This was in general agreement with the stated viewsof the political authorities of the three countries. Itwas evident that the authorities desired a newopportunity for an exchange of views and for thediscussion of issues such as optimization of activitiesrelated to the remediation of contaminated landand the provision of health care to those affected bythe accident. During meetings with these represent-atives, the Director General of the IAEA indicatedhis support for the concept of a Chernobyl Forum asa joint activity of the United Nations family and thethree affected countries.

2.2. OBJECTIVES OF THE CHERNOBYL FORUM

At the organizational meeting of the Forum itwas decided to establish the Chernobyl Forum as aseries of managerial, expert and public meetings forthe purpose of generating authoritative consensualstatements on the health effects attributable toradiation exposure arising from the accident and onthe environmental consequences induced by thereleased radioactive material, to provide advice onremediation and special health care programmes,and to suggest areas in which further research isrequired.

Participants at the organization meetingaccepted the terms of reference of the Forum asbeing:

(a) To explore and refine the current scientificassessments on the long term health andenvironmental consequences of theChernobyl accident, with a view to producingauthoritative consensus statements focusingon:

(i) The health effects attributable toradiation exposure caused by theaccident;

(ii) The environmental consequencesinduced by the radioactive materialreleased due to the accident (e.g. contam-ination of foodstuffs);

16

(iii) The consequences attributable to theaccident but not directly related to theradiation exposure or radioactivecontamination.

(b) To identify gaps in scientific research relevantto the radiation induced or radioactivecontamination induced health and environ-mental impacts of the accident, and to suggestareas in which further work is required basedon an assessment of the work done in the pastand bearing in mind the ongoing work andprojects.

(c) To provide advice on, and to facilitate imple-mentation of, scientifically sound programmeson mitigation of the accident consequences,including possible joint actions of the organi-zations participating in the Forum, such as:

(i) Remediation of contaminated land, withthe aim of making it suitable for normalagricultural, economic and social lifeunder safe conditions;

(ii) Special health care of the affectedpopulation;

(iii) Monitoring of long term human exposureto radiation;

(iv) Addressing the environmental issuespertaining to the decommissioning of theChernobyl shelter and the managementof radioactive waste originating from theChernobyl accident.

2.3. METHOD OF OPERATION AND OUTPUT OF THE CHERNOBYL FORUM

The Chernobyl Forum is a high level organi-zation of senior officials of United Nations agenciesand the three affected countries. The technicalreports of the Forum were produced by two expertgroups: Expert Group ‘Environment’ (EGE) andExpert Group ‘Health’ (EGH). The membership ofthe two groups comprised recognized internationalscientists and experts from the three affectedcountries. Through the work of these two groupsand their subworking groups, the technicaldocuments were prepared. The EGE wascoordinated by the IAEA and the EGH wascoordinated by the WHO.

The documents were produced throughmeetings of groups of experts on specific topics. Thegroups considered in detail the data available fromthe literature as well as unpublished data from thethree most affected countries. The documents were

used as the basis for the final reports of theChernobyl Forum, which were approved by theForum itself.

This report is the Chernobyl Forum’s reporton the environmental consequences of theChernobyl accident. The Chernobyl Forum’s reporton the health effects of the Chernobyl accident willbe published by the WHO [2.2].

2.4. STRUCTURE OF THE REPORT

This report consists of seven sections.Following the Introduction, Section 3 describes theprocesses and patterns of radioactive contaminationof the urban, agricultural, forest and aquaticenvironments as a result of the deposition of theChernobyl release. Section 4 identifies the majorenvironmental countermeasures and remediationmeasures applied to the aforementioned fourenvironments in order to mitigate the accident’sconsequences and, specifically, to reduce humanexposure. Section 5 deals with an assessment ofhuman exposure to radiation within the affectedareas, based on data on environmental radioactivecontamination and the countermeasures presentedin Sections 3 and 4. Section 6 presents an overviewof experimental data on the radiation inducedeffects in plants and animals observed predomi-nantly in the near zone of radioactive contami-nation. Finally, Section 7 discusses theenvironmental aspects of the dismantling of theshelter facility at the Chernobyl site and radioactivewaste management in the CEZ.

Each section is completed with relevantconclusions and recommendations for futureenvironmental remediation actions, monitoring andresearch. The entire report is preceded by Section 1,the Summary.

REFERENCES TO SECTION 2

[2.1] UNITED NATIONS, Sources and Effects ofIonizing Radiation (Report to the GeneralAssembly, with Scientific Annexes), Vol. II, Scien-tific Committee on the Effects of AtomicRadiation (UNSCEAR), UN, New York (2000)451–566.

[2.2] WORLD HEALTH ORGANIZATION, HealthEffects of the Chernobyl Accident and SpecialHealth Care Programmes, Report of theChernobyl Forum Expert Group “Health”(EGH), WHO, Geneva (in press).

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3. RADIOACTIVE CONTAMINATION OF THE ENVIRONMENT

The accident at the Chernobyl nuclear powerplant resulted in a substantial release of radionu-clides to the atmosphere and caused extensivecontamination of the environment. A number ofEuropean countries were subjected to radioactivecontamination; among the most affected were threeformer republics of the USSR, now Belarus, theRussian Federation and Ukraine. The activity levelsof the radionuclides in the environment graduallydeclined due to radioactive decay. At the same time,there was movement of the radionuclides within theenvironments — atmospheric, aquatic, terrestrialand urban — and among the environments. Theprocesses that determined the patterns ofradioactive contamination in those environmentsare presented in this section.

The focus of this section is mainly onradioactive contamination of the off-siteenvironment. Significant attention is given inSection 7 to the Chernobyl nuclear power plant site,the CEZ and the Chernobyl shelter.

3.1. RADIONUCLIDE RELEASE AND DEPOSITION

3.1.1. Radionuclide source term

The accident at unit 4 of the Chernobylnuclear power plant took place shortly aftermidnight on 26 April 1986. Prior to the accident, thereactor had been operated for many hours in non-design configurations in preparation for anexperiment on recovery of the energy in the turbinein the event of an unplanned shutdown. The causeof the accident is rather complicated, but can beconsidered as a runaway surge in the power levelthat caused the water coolant to vaporize inside thereactor. This in turn caused a further increase in thepower level, with a resulting steam explosion thatdestroyed the reactor. After the initial explosion,the graphite in the reactor caught fire. Despite theheroic efforts of the staff to control the fire, thegraphite burned for many days, and releases ofradioactive material continued until 6 May 1986.The reconstructed time course of the release ofradioactive material is shown in Fig. 3.1 [3.1–3.3].

The occurrence of the accident was notimmediately announced by the authorities of thethen USSR. However, the releases were so largethat the presence of fresh fission products was soondetected in Scandinavian countries, and retro-spective calculations of possible trajectoriesindicated that the accident had occurred in theformer USSR. Further details of the accident and itsimmediate consequences are available in reports bythe International Nuclear Safety Advisory Group[3.1], the International Advisory Committee [3.4]and UNSCEAR [3.5, 3.6].

An early estimate of the amount of 137Csreleased by the accident and deposited in theformer USSR was made based on an airborneradiometric measurement of the contaminated partsof the former USSR; this estimate indicated thatabout 40 PBq (1 × 106 Ci) was deposited. Estimatesof the releases have been refined over the years, andthe current estimate of the total amount of 137Csdeposited in the former USSR is about twice theearlier estimate (i.e. 80 PBq). Current estimates ofthe amounts of the more important radionuclidesreleased are shown in Table 3.1. Most of the radio-nuclides for which there were large releases haveshort physical half-lives, and the radionuclides withlong half-lives were mostly released in small

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

1 2 3 4 5 6 7 8 9 10 11

Days after initiation of the accident on 26 April 1986

Cooldown period

Heatup period

Sharp drop

Rel

ease

rat

e (E

Bq

/d)

0.00

2–0.

006

EB

q/d

FIG. 3.1. Daily release rate to the atmosphere of radioac-tive material, excluding noble gases, during the Chernobylaccident. The values are decay corrected to 6 May 1986 andare uncertain by ±50% [3.1].

18

amounts. In the early period after the accident, theradionuclide of most radiological concern was 131I;later, the emphasis shifted to 137Cs.

By 2005 most of the radionuclides released bythe accident had already decayed below levels ofconcern. Interest over the next few decades will

continue to be on 137Cs and, to a lesser extent, 90Sr;the latter remains more important in the near zoneof the Chernobyl nuclear power plant. Over thelonger term (hundreds to thousands of years), theonly radionuclides anticipated to be of interest arethe plutonium isotopes. The only radionuclide

TABLE 3.1. REVISED ESTIMATES OF THE PRINCIPAL RADIONUCLIDESRELEASED DURING THE COURSE OF THE CHERNOBYL ACCIDENTa

(decay corrected to 26 April 1986)

Half-life Activity released (PBq)

Inert gases

Krypton-85 10.72 a 33

Xenon-133 5.25 d 6500

Volatile elements

Tellurium-129m 33.6 d 240

Tellurium-132 3.26 d ~1150

Iodine-131 8.04 d ~1760

Iodine-133 20.8 h 2500

Caesium-134 2.06 a ~47.b

Caesium-136 13.1 d 36

Caesium-137 30.0 a ~85

Elements with intermediate volatility

Strontium-89 50.5 d ~115

Strontium-90 29.12 a ~10

Ruthenium-103 39.3 d >168

Ruthenium-106 368 d >73

Barium-140 12.7 d 240

Refractory elements (including fuel particles)c

Zirconium-95 64.0 d 84

Molybdenum-99 2.75 d >72

Cerium-141 32.5 d 84

Cerium-144 284 d ~50

Neptunium-239 2.35 d 400

Plutonium-238 87.74 a 0.015

Plutonium-239 24 065 a 0.013

Plutonium-240 6 537 a 0.018

Plutonium-241 14.4 a ~2.6

Plutonium-242 376 000 a 0.00004

Curium-242 18.1 a ~0.4

a Most of the data are from Refs [3.6, 3.7].b Based on 134Cs/137Cs ratio of 0.55 as of 26 April 1986 [3.8].c Based on fuel particle release of 1.5% [3.9].

19

expected to increase in its levels in the coming yearsis 241Am, which arises from the decay of 241Pu; ittakes about 100 years for the maximum amount of241Am to form from 241Pu.

3.1.2. Physical and chemical forms of released material

Radionuclides in the releases from thestricken reactor were in the form of gases,condensed particles and fuel particles. The presenceof the latter was an important characteristic of theaccident. The oxidation of nuclear fuel was the basicmechanism of fuel particle formation. Less oxidizedfuel particles were formed as a result of the initialexplosion and were released primarily towards thewestern direction. More oxidized and solubleparticles predominated in the remaining fallout,which was deposited in many other areas.

During oxidation and dispersal of the nuclearfuel, volatilization of some radionuclides took place.After the initial cloud cooled, the more volatile ofthe released radionuclides remained in the gasphase, whilst the less volatile radionuclidescondensed on particles of construction material,soot and dust. Thus the chemical and physical formsof the radionuclides in the Chernobyl release weredetermined by the volatility of their compounds andthe conditions inside the reactor. Radioactivecompounds with relatively high vapour pressure(primarily isotopes of inert gases and iodine indifferent chemical forms) were transported in theatmosphere in the gas phase. Isotopes of refractoryelements (e.g. cerium, zirconium, niobium andplutonium) were released into the atmosphereprimarily in the form of fuel particles. Other radio-nuclides (isotopes of caesium, tellurium, antimony,etc.) were found in both fuel and condensedparticles. The relative contributions of condensedand fuel components in the deposition at a givensite can be estimated from the activity ratios ofradionuclides of different volatility classes.

Fuel particles made up the most importantpart of the fallout in the vicinity of the releasesource. Radionuclides such as 95Zr, 95Nb, 99Mo,141,144Ce, 154,155Eu, 237,239Np, 238–242Pu, 241,243Am and242,244Cm were released in a matrix of fuel particlesonly. More than 90% of 89,90Sr and 103,106Ru activitieswas also released in fuel particles. The releasefraction of 90Sr, 154Eu, 238Pu, 239,240Pu and 241Am,and, therefore, of the nuclear fuel itself, depositedoutside the Chernobyl nuclear power plantindustrial site has been recently estimated to be

only 1.5% ± 0.5% [3.9], which is half that of earlierestimates [3.1].

The chemical and radionuclide composition offuel particles was close to that of irradiated nuclearfuel, but with a lower fraction of volatile radionu-clides, a higher oxidation state of uranium and thepresence of various admixtures, especially in thesurface layer. In contrast, the chemical and radionu-clide composition of condensed particles variedwidely. The specific activity of the radionuclides inthese particles was determined by the duration ofthe condensation process and the process temper-ature, as well as by the particle characteristics. Theradionuclide content of some of the particles wasdominated by just one or two nuclides, for example103,106Ru or 140Ba/140La [3.10].

The form of a radionuclide in the releasedetermined the distance of its atmospherictransport. Even the smallest fuel particles consistingof a single grain of nuclear fuel crystallite had arelatively large size (up to 10 µm) and high density(8–10 g/cm3). Owing to their size, they weretransported only a few tens of kilometres. Largeraggregates of particles were found only withindistances of several kilometres from the powerplant. For this reason, the deposition of refractoryradionuclides strongly decreased with distance fromthe damaged reactor, and only traces of refractoryelements could be found outside the industrial siteof the power plant. In contrast, significantdeposition of gaseous radionuclides and sub-micrometre condensed particles took placethousands of kilometres from Chernobyl.Ruthenium particles, for example, were foundthroughout Europe [3.11]. At distances of hundredsof kilometres from Chernobyl the deposition of137Cs was as high as 1 MBq/m2 [3.12, 3.13].

Another important characteristic of fallout isrelated to its solubility in aqueous solutions. Thisdetermines the mobility and bioavailability ofdeposited radionuclides in soils and surface watersduring the initial period after deposition. In falloutsampled at the Chernobyl meteorological stationfrom 26 April to 5 May 1986 with a 24 h samplingperiod, the water soluble and exchangeable(extractable with 1M CH3COONH4) forms of 137Csvaried from 5% to more than 30% [3.14]. The watersoluble and exchangeable forms of 90Sr in deposits on26 April accounted for only about 1% of the total;this value increased to 5–10% in subsequent days.

The low solubility of deposited 137Cs and 90Srnear the nuclear power plant indicates that fuelparticles were the major part of the fallout, even at

20

20 km from the source. At shorter distances theportion of water soluble and exchangeable forms of137Cs and 90Sr was, obviously, lower, due to thepresence of larger particles; at longer distances thefraction of soluble condensed particles increased.As one example, almost all the 137Cs deposited in1986 in the United Kingdom was water soluble andexchangeable [3.15].

3.1.3. Meteorological conditions during the course of the accident

At the time of the accident the weather inmost of Europe was dominated by a vast anti-cyclone. At the 700–800 m and 1500 m altitudes, thearea of the Chernobyl nuclear power plant was atthe south-west periphery of a high atmosphericpressure zone with air masses moving north-westwith a velocity of 5–10 m/s [3.12].

At daybreak, the altitude of the air mixinglayer was about 2500 m. This resulted in rapidmixing of the airborne debris throughout the mixinglayer and dispersion of the cloud at different layersof the mixing height. Further dissemination of theparticles originating from the time of the accidentwithin the 700–1500 m layer occurred as the airmass moved towards the north-east, with asubsequent turn to the north; this plume wasdetected in Scandinavian countries.

Ground level air on 26 April was transportedto the west and north-west and reached Poland andthe Scandinavian countries by 27–29 April. Insouthern and western Ukraine, the Republic ofMoldova, Romania, Slovakia and Poland theweather was influenced by a low gradient pressurefield. In the following days the cyclone movedslowly south-east and the low gradient pressurefield with several poorly defined pressure areasdispersed over the major part of the Europeansector of the former USSR. One of the pressureareas was a small near surface cyclone located onthe morning of 27 April south of Gomel.

Later, the releases from the reactor werecarried predominantly in the south-western andsouthern directions until 7–8 May. During the firstfive days after the accident commenced, the windpattern had changed through all directions of thecompass [3.12].

Within a few days after the accident,measurements of radiation levels in air over Europe,Japan and the USA showed the presence ofradionuclides at altitudes of up to 7000 m. The forceof the explosion, rapid mixing of air layers due to

thunderstorms near the Chernobyl nuclear powerplant and the presence of warm frontal air massesbetween the Chernobyl nuclear power plant and theBaltic Sea all contributed to the transport ofradionuclides to such heights.

To understand the complex meteorologicalsituation better, Borzilov and Klepikova [3.16]carried out calculations with assumed input pulsesof unit activity at various times of the accident. Theheight of the source was selected to be 1000 m until14:00 (GMT) on 28 April, and later 500 m. Theresults of calculations are presented in Fig. 3.2 forsix time periods (GMT time) with differing longrange transport conditions as follows:

(1) From the start of the accident to 12:00 (GMT)on 26 April: towards Belarus, Lithuania, theKaliningrad region (of the Russian Feder-ation), Sweden and Finland.

(2) From 12:00 on 26 April to 12:00 on 27 April: toPolessye, then Poland and then south-west.

(3) From 12:00 on 27 April to 29 April: to theGomel (Belarus) region, the Bryansk(Russian Federation) region and then the east.

(4) 29 April to 30 April: to the Sumy and Poltavaregions (Ukraine) and towards Romania.

(5) 1–3 May: to southern Ukraine and across theBlack Sea to Turkey.

(6) 4–5 May: to western Ukraine and Romania,and then to Belarus.

Atmospheric precipitation plays an importantrole in determining whether an area might receiveheavy contamination, as the processes of rainout(entrainment in a storm system) and washout (rainfalling through a contaminated air mass) areimportant mechanisms in bringing released materialto the ground. In particular, significant heteroge-neity in the deposition of radioactive material isrelated to the presence or absence of precipitationduring passage of the cloud. Also, there aredifferences in behaviour regarding how effectivelydifferent radionuclides, or chemical forms of thesame radionuclide, are rained or washed out.

There were many precipitation events duringthe course of the accident, and these eventsproduced some areas of high ground deposition atdistances far from the reactor. An example of thecomplex precipitation situation during the accidentis shown in Fig. 3.3, which is a map of average dailyprecipitation intensity on 29 April for the parts ofBelarus, the Russian Federation and Ukraine mostheavily affected by the accident.

21

In the case of dry deposition, the contami-nation levels were lower, but the radionuclidemixture intercepted by vegetation was substantiallyenriched with radioiodine isotopes; in the case ofwet deposition, the radionuclide content in thefallout was similar to that in the radioactive cloud.

As a result, both the levels and ratios of radio-nuclides in areas with different deposition typesvaried.

3.1.4. Concentration of radionuclides in air

The activity concentrations of radioactivematerial in air were measured at many locations inthe former USSR and throughout the world.Examples of such activity concentrations in air areshown in Fig. 3.4 for two locations: Chernobyl andBaryshevka, Ukraine. The location of theChernobyl sampler was the meteorological stationin the city of Chernobyl, which is more than 15 kmsouth-east of the Chernobyl nuclear power plant.The initial concentrations of airborne material werevery high, but dropped in two phases. There was arapid fall over a few months, and a more gradualdecrease over several years. Over the long term, thesampler at Chernobyl records consistently higheractivity concentrations than the sampler atBaryshevka (about 150 km south-east of theChernobyl nuclear power plant), presumably due toresuspension [3.17].

Even with the data smoothed by a rollingaverage, there are some notable features in the data

32

4

6

WARSAW

VILNIUS

MINSK

Smolensk

Bryansk

Orel

Tula

Kaluga

Mogilev

Gomel

Cherkassy

Vinnitsa

Rovno

Lvov

Sumy

Brest

Chernovtsy

Kirovograd

Kharkov

300 km250200100 1500 50

Lublin

KIEV

Chernobyl Chernigov

Zhitomir

1

5

FIG. 3.2. Calculated plume formation according to the meteorological conditions for instantaneous releases on the followingdates and times (GMT): (1) 26 April 1986, 00:00; (2) 27 April, 00:00; (3) 27 April, 12:00; (4) 29 April, 00:00; (5) 2 May, 00:00;and (6) 4 May, 12:00 [3.16].

FIG. 3.3. Map of average precipitation intensity (mm/h) on29 April 1986 in the area near the Chernobyl nuclear powerplant [3.12].

22

collected over the long term. The clearly discerniblepeak that occurred during the summer of 1992(month 78) was due to widespread forest fires inBelarus and Ukraine.

3.1.5. Deposition of radionuclides on soil surfaces

As already mentioned, surveys with airbornespectrometers over large areas were undertakensoon after the accident to measure the deposition of137Cs (and other radionuclides) on the soil surface in

several countries. In the mapping of the deposition,137Cs was chosen because it is easy to measure and isof radiological significance. Soil deposition of 137Csequal to 37 kBq/m2 (1 Ci/km2) was chosen as aprovisional minimum contamination level, because:(a) this level was about ten times higher than the137Cs deposition in Europe from global fallout; and(b) at this level the human dose during the first yearafter the accident was about 1 mSv and wasconsidered to be radiologically important.Knowledge of the extent and spatial variation ofdeposition is critical in defining the magnitude ofthe accident, predicting future levels of external andinternal dose, and determining what radiationprotection measures are necessary. In addition,many soil samples were collected and analysed atradiological laboratories.

Thus massive amounts of data were collectedand subsequently published in the form of an atlasthat covers essentially all of Europe [3.13]. Anotheratlas produced in the Russian Federation [3.12]covers the European part of the former USSR. Anexample is shown in Fig. 3.5.

It is clear from Fig. 3.5 and Table 3.2 that thethree countries most heavily affected by theaccident were Belarus, the Russian Federation andUkraine. From the total 137Cs activity of about64 TBq (1.7 MCi) deposited on European territoryin 1986, Belarus received 23%, the RussianFederation 30% and Ukraine 18%. However, due

/

FIG. 3.4. Rolling seven month mean atmospheric concen-tration of 137Cs at Baryshevka and Chernobyl (June 1986–August 1994) [3.17].

TABLE 3.2. AREAS IN EUROPE CONTAMINATED BY CHERNOBYL FALLOUT IN 1986[3.6, 3.13]

Area with 137Cs deposition density range (km2)

37–185 kBq/m2 185–555 kBq/m2 555–1480 kBq/m2 >1480 kBq/m2

Russian Federation 49 800 5 700 2100 300

Belarus 29 900 10 200 4200 2200

Ukraine 37 200 3 200 900 600

Sweden 12 000 — — —

Finland 11 500 — — —

Austria 8 600 — — —

Norway 5 200 — — —

Bulgaria 4 800 — — —

Switzerland 1 300 — — —

Greece 1 200 — — —

Slovenia 300 — — —

Italy 300 — — —

Republic of Moldova 60 — — —

23

to the wet deposition processes discussed above,there were also major contaminated areas inAustria, Finland, Germany, Norway, Romania andSweden. A more detailed view of the nearby heavilycontaminated areas is shown in Fig. 3.6 [3.4].

Water and wind erosion of soil may lead to137Cs transfer and redistribution on a local scale atrelatively short distances. Wind erosion may alsolead to 137Cs transfer with soil particles on a regionalscale.

Soon after the accident, a 30 km radiusexclusion zone (the CEZ) was established aroundthe reactor. Further relocations of populations tookplace in subsequent months and years in Belarus,the Russian Federation and Ukraine; eventually,116 000 persons were evacuated or relocated.

The total area with 137Cs soil deposition of0.6 MBq/m2 (15 Ci/km2) and above in 1986 was10 300 km2, including 6400 km2 in Belarus, 2400 km2

in the Russian Federation and 1500 km2 in Ukraine.In total, 640 settlements with about 230 000inhabitants were located on these contaminatedterritories. Areas with 137Cs depositions of morethan 1 Ci/km2 (37 kBq/m2) are classified as radioac-tively contaminated according to the laws on socialprotection in the three most affected countries. The

number of people who were living in such contami-nated areas in 1995 is shown in Table 3.3.

Immediately after the accident, most concernwas focused on contamination of food with 131I. Thebroad pattern of the deposition of 131I is shown inFig. 3.7. Unfortunately, due to the rapid decay of 131Iafter its deposition, there was not enough time tocollect a large number of samples for detailedanalysis. At first, it was assumed that a strongcorrelation could be assumed between depositionsof 131I and 137Cs. However, this has not been foundto be consistently valid. More recently, soil sampleshave been collected and analysed for 129I, which hasa physical half-life of 16 × 106 years and can only bemeasured at very low levels by means of acceleratormass spectrometry. Straume et al. [3.19] havereported the successful analysis of samples taken inBelarus, from which they have established that, atthe time of the accident, there were 15 ± 3 atoms of129I for each atom of 131I. This estimated ratioenables better estimates of the deposition of 131I forthe purpose of reconstructing radiation dosesreceived by people.

Similar maps can be drawn for the other radio-nuclides of interest shown in Table 3.1. Thedeposition of 90Sr is shown in Fig. 3.8. In comparison

40

5

1.08

0.27

0.054

1480

185

40

10

2

kBq/m2 Ci/km2

Total caesium-137(nuclear weapons test,

Chernobyl, ...) deposition

Data not available

National capital

Scale 1:11 250 000Projection: Lambert Azimuthal

800

600

400

200

kilometres 0

100

200

500

400

300

200

100

0 miles

100

200

© EC/IGCE,Roshydromet

(Russia)/Minchernobyl(Ukraine)/Belhydromet (Belarus),

1998

FIG. 3.5. Surface ground deposition of 137Cs throughout Europe as a result of the Chernobyl accident [3.13].

24

with 137Cs, (a) there was less 90Sr released from thereactor and (b) strontium is less volatile thancaesium. Thus the spatial extent of 90Sr depositionwas much more confined to areas close to theChernobyl nuclear power plant than that of 137Cs.The amounts of plutonium deposited on soil havealso been measured (see Fig. 3.9). Nearly all areaswith plutonium deposits above 3.7 kBq/m2 (0.1Ci/km2) are within the CEZ.

3.1.6. Isotopic composition of the deposition

The most extensive measurements of surfaceactivity concentrations have been performed for137Cs. Values for other radionuclides, especially134Cs, 136Cs, 131I, 133I, 140Ba/140La, 95Zr/95Nb, 103Ru,106Ru, 132Te, 125Sb and 144Ce, have been expressed asratios to the reference radionuclide, 137Cs. Theseratios depend on the location, because of (a) the

Stdohko

Styr

’nyr

oG

anse

D

Trete

ve

anse

D

rpenD

rpenD

aksoR

FIG. 3.6. Surface ground deposition of 137Cs in areas of Belarus, the Russian Federation and Ukraine near the accident site[3.4].

TABLE 3.3. DISTRIBUTION OF INHABITANTS LIVING IN AREAS CONSIDERED TO BE RADIO-ACTIVELY CONTAMINATED IN BELARUS, THE RUSSIAN FEDERATION AND UKRAINE IN 1995[3.6]

Caesium-137 deposition density (kBq/m2)

Thousands of inhabitantsa

Belarus Russian Federation Ukraine Total

37–185 1543 1654 1189 4386

185–555 239 234 107 580

555–1480 98 95 0.3 193

Total 1880 1983 1296 5159

a For social and economic reasons, some people living in areas of contamination of less than 37 kBq/m2 are also included.

25

different deposition behaviour of fuel particles,aerosols and gaseous radionuclides and (b) thevariation in radionuclide composition with time ofrelease. In fact, these ratios are not necessarily

constant with time. Depending on the time ofrelease and the corresponding release character-istics (e.g. temperature of the core), significantvariations in the release ratios were observed afterthe Chernobyl accident [3.2, 3.20].

The first plume, which moved to the west,carried the release that occurred during theexplosive phase, when the exposed core was not ashot as in the later phases. The second plume, whichmoved north to north-east, carried releases from acore that was becoming increasingly hot, while thethird plume, moving mainly south, was charac-terized by releases from a core heated to tempera-tures above 2000°C; at such temperatures the lessvolatile radionuclides, such as molybdenum,strontium, zirconium, ruthenium and barium, arereadily released. During this phase, releases ofiodine radioisotopes also increased.

Caesium hot spots occurred in the far zone ofBelarus and in the Kaluga, Tula and Orel regions of

FIG. 3.7. Surface ground deposition of 131I [3.18] (Ci/km2

on 15 May 1986).

Pripyat

Dnepr

Sozh

Berezina

Des

na

Tetere

v

Zhlobin

Rogachev

Chernin Svetilovichi

Vetka

Dobrush

Terekhovka

Lyubech

Chernobyl

Kraslikovka

Termakhovka

Varovsk

Bazar

Bogdany

Morovsk

Oster

Dovlyady

Kirovo

Dernovichi

Polesskoye

Dronyki

Mikulichi

Narovlya

Dobryny

Nov. Radcha

Ilyincy

Zimovisce

Pirki

Slavutich

Komarin

Gdeny Kovpyta

Krasnoje

IvanovkaPripyat

Repki

Loev

Bragin

Malozhin

Chemerisy

Savichi

Zabolotje

Chechersk

Sidorovichi

Svetlogorsk

Rechitsa

Mozyr

Khoyniki

Kalinkovichi

Vasilevichi

GOMEL

CHERNIGOV

Novo ShepelichiDenisovichi

Stracholese -2

74-111 kBq m-2

37-74 kBq m-2

>111 kBq m

FIG. 3.8. Surface ground deposition of 90Sr [3.4].

Teterev

Des

na

Dne

pr

Slovecna

Pripyat

K iev

PripyatSepelichi

Dovlyady

Savici

Pirki

Slavutich

Dronyki

Kovpyta

Komarin

Gdeny

Morovsk

Chernobyl

Polesskoye

Nov. Radcha

Kirovo

Dernovichi

Dobryny

Narovlya

Bragin

Mikulichi

MalozhinChemerisy

BorscevkaMikhalkiYurovichi

Khoyniki

Volchkov

Termakhovka

Gornostojpol

Krasilovka

Ilyincy

Novo-

IvankovVarovsk

Kuchari

Zarudje

BujanVorzely

Motyzhin

Dymer Chernin

Bazar

Bojarka

Brovary

Irpeny

KIEV

DenisovichiZimovishche

FIG. 3.9. Areas (orange) where the surface ground deposi-tion of 239,240Pu exceeds 3.7 kBq/m2 [3.4].

26

the Russian Federation. The composition of thedeposited radionuclides in each of these highlycontaminated areas was similar. The ratios ofdifferent radionuclides to 137Cs as observed inground deposits in the different release vectors areshown in Table 3.4.

The activity ratios for the western andnorthern plumes were similar and in many casesidentical, in contrast to the ratios for the southernplume. All activity ratios show, with the exceptionof 132Te/137Cs, a decrease with increasing distancefrom the nuclear power plant. The decrease is lessprofound for 95Zr and 144Ce (about a factor of three)than with 99Mo and 140Ba (two orders of magnitude)or 90Sr and 103Ru (one order of magnitude). For theratio 131I/137Cs only a slight decrease, by about afactor of four, was observed over a 1000 kmdistance. Within the first 200 km virtually novariation in the ratio was observed.

3.2. URBAN ENVIRONMENT

3.2.1. Deposition patterns

Radioactive fallout resulted in long termcontamination of thousands of settlements in theUSSR and some other European countries and in

the irradiation of their inhabitants due to bothexternal gamma radiation and internal exposure dueto consumption of contaminated food. Near to theChernobyl nuclear power plant, the towns ofPripyat and Chernobyl and some other smallersettlements were subjected to substantial contami-nation from an ‘undiluted’ radioactive cloud underdry meteorological conditions, whereas more distantsettlements were significantly affected because ofprecipitation at the time of cloud passage.

When the radioactive fallout was deposited onsettlements, exposed surfaces such as lawns, parks,streets, roofs and walls became contaminated withradionuclides. Both the activity level and elementalcomposition of the radioactive fallout was signifi-cantly influenced by the type of depositionmechanism, namely wet deposition with precipi-tation or dry deposition influenced by atmosphericmixing, diffusion and chemical adsorption. Surfacessuch as trees, bushes, lawns and roofs becomerelatively more contaminated under dry conditionsthan when there is precipitation. Under wetconditions, horizontal surfaces, including soil plotsand lawns (see Fig. 3.10), receive the highest levelsof contamination. Particularly high 137Cs activityconcentrations have been found around houseswhere rain has transported radioactive materialfrom roofs to the ground.

TABLE 3.4. ESTIMATED RELATIVE SURFACE ACTIVITY CONCENTRATION OF DIFFERENTRADIONUCLIDES AFTER RELEASE FROM THE CHERNOBYL NUCLEAR POWER PLANT(26 APRIL 1986) [3.2]

Half-life

Activity per unit area relative to 137Cs

Western plume (near zone)

Northern plume (near zone)

Southern plume (near zone)

At caesium hot spots (far zone)

Strontium-90 28.5 a 0.5 0.13 1.5 0.014

Zirconium-95 64.0 d 5 3 10 0.06

Molybdenum-99 66.0 h 8 3 25 0.11

Ruthenium-103 39.35 d 4 2.7 12 1.9

Tellurium-132 78.0 h 15 17 13 13

Iodine-131 8.02 d 18 17 30 10

Caesium-137 30.0 a 1.0 1.0 1.0 1.0

Barium-140 12.79 d 7 3 20 0.7

Cerium-144 284.8 d 3 2.3 6 0.07

Neptunium-239 2.355 d 25 7 140 0.6

Plutonium-239 24 400.a 0.0015 0.0015 — —

27

3.2.2. Migration of radionuclides in the urban environment

Due to natural weathering processes such asthe effects of rainfall and snow melting, and tohuman activities such as traffic movement andstreet washing and cleaning, radionuclides becamedetached from the surfaces on which they weredeposited and were transported within settlements.Contaminated leaves and needles from trees andbushes are removed from settlements after seasonaldefoliation and radionuclides deposited on asphaltand concrete pavements are eroded or washed offand removed via sewage systems. These naturalprocesses and human activities significantly reduceddose rates in inhabited and recreational areasduring 1986 and in successive years [3.21].

In general, vertical surfaces of houses are notsubjected to the same degree of weathering throughrain as horizontal surfaces such as roofs. The loss ofcontamination from walls after 14 years has been

typically 50–70% of the initial deposit. Roofcontamination levels in Denmark decreased after14 years by 60–95% of those originally present, dueto natural processes (see Fig. 3.11) [3.22].

In contrast, the level of radiocaesium onasphalt surfaces has decreased substantially, suchthat, generally, less than 10% of the initiallyretained radiocaesium is now left. Only a smallfraction of the radiocaesium contamination isassociated with the bitumen fraction of the asphalt;most is associated with a thin layer of street dust,which will eventually be weathered off.

Measurements made in 1993 in the city ofPripyat near the Chernobyl nuclear power plantshowed high residual levels of radiocaesium on theroads. However, this town was evacuated in theearly accident phase, and therefore traffic there hasbeen limited. Some 5–10% of the initially depositedradiocaesium seems to be firmly fixed to concretepaved surfaces, and no significant decrease has beenrecorded over the past few years. The weathering onhorizontal hard surfaces was, as expected, generallyfaster in the areas with more traffic.

One of the consequences of these processeshas been secondary contamination of sewagesystems and sludge storage areas, which has necessi-tated special cleanup measures. Generally, radionu-clides in soil have not been transferred to otherurban areas but have migrated down into the soilcolumn due to natural processes or due to mixingduring the digging of gardens, kitchen gardens andparks.

0

1

2

3

4

1986 2000

Undisturbedsoil

Trees, bushes Roofs Walls Streets,pavements

Dis

trib

utio

n of

cae

sium

-137

(rel

ativ

e un

its)

(a)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1986 2000

Undisturbedsoil

Trees, bushes Roofs Walls Streets,pavements

Dis

trib

utio

n of

cae

sium

-137

(rel

ativ

e un

its)

(b)

FIG. 3.10. Typical distribution of 137Cs on differentsurfaces within settlements in 1986 and 14 years after depo-sition of the Chernobyl fallout. (a) Dry deposition; (b) wetdeposition [3.23].

Time after deposition (years)

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14

Corrugated Eternit – 45°

Red clay tile – 45°

Silicon treated Eternit – 30°

Aro

of(t)

/ A

soil(

0)

FIG. 3.11. Measured 137Cs contamination levels (relative tothe initial soil contamination) on three types of roof atRisø, Denmark [3.22].

28

3.2.3. Dynamics of the exposure rate in urban environments

Gamma radiation from radionuclidesdeposited in the urban environment has contributedto human external exposure. Compared with thedose rate in open fields (see Section 5.2.2), the doserate within a settlement is significantly lower,because of photon absorption in building structures,especially those made of brick and concrete. Thelowest dose rates have been observed insidebuildings, and especially on the upper floors ofmultistorey buildings. Due to radioactive decay ofthe initial radionuclide mixture, wash-off from solidsurfaces and soil migration, dose rates in air havebeen gradually decreasing with time in typical urbanareas.

Another relevant parameter is the timedependence of the ratio of the dose rate in air at anurban location to that in an open field (the ‘locationfactor’) due to radionuclide migration processes.The dependence of urban location factors on timeafter the Chernobyl accident, as derived frommeasurements performed in the town ofNovozybkov in the Russian Federation, is shown inFig. 3.12 [3.24]. While for virgin sites such as parksor grassy plots the location factors are relativelyconstant, values for hard surfaces such as asphaltdecrease considerably with time. Similar timedependences have been found in other countries[3.25, 3.26].

At present, in most of the settlementssubjected to radioactive contamination after theChernobyl accident, the air dose rate above solid

surfaces has returned to the pre-accidentbackground level. Some elevated air dose rates canbe measured, mainly in areas of undisturbed soil.The highest level of urban radioactive contami-nation is found in Pripyat, which is 3 km from theChernobyl nuclear power plant; its inhabitants wereresettled to non-contaminated areas within 1.5 daysof the accident.

3.3. AGRICULTURAL ENVIRONMENT

3.3.1. Radionuclide transfer in the terrestrial environment

Radioactive elements behave differently inthe environment; some, such as caesium, iodine andstrontium, are environmentally mobile and transferreadily, under certain environmental conditions, tofoodstuffs. In contrast, radionuclides with lowsolubility, such as the actinides, are relativelyimmobile and largely remain in the soil. The mainroutes for the cycling of radionuclides and thepossible pathways to humans are shown in Fig. 3.13.

Many factors influence the extent to whichradionuclides are transferred through terrestrialpathways. If transfer is high in a particularenvironment it is said to be radioecologicallysensitive, because such transfer can lead torelatively high radiological exposure [3.28].

0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 5 6 7 8 9 10

Time after the accident (years)

Loca

tion

fact

or

Virgin land (inside town)

Dirt surfaces

Asphalt

FIG. 3.12. Ratio of the radiation dose rate above differentsurfaces to that in open fields in the town of Novozybkov,Russian Federation, after the Chernobyl accident [3.24].

Groundwater and rocks of geological environment

Organic–mineral soil component

Soil solution

Surface washout

Sorbed radionuclides

Soil–vegetation litter

Initial radionuclide fallout: - Condensation component - Fuel particles

Dissolution offuel particles

Sorption–desorption

Mig

ratio

n

FIG. 3.13. Main transfer pathways of radionuclides in theterrestrial environment [3.27].

29

Of the radionuclides deposited after theChernobyl accident, during the short initial phase(zero to two months) those of iodine were the mostimportant with regard to human exposure viaagricultural food chains. In the longer term, radio-caesium has been the most important (and, to amuch lesser extent, radiostrontium).

Radioecological sensitivity to radiocaesium isgenerally higher in seminatural ecosystems than inagricultural ecosystems, sometimes by a few ordersof magnitude [3.29]. This difference is caused by anumber of factors, the more important being insome natural ecosystems the different physico-chemical behaviour in soils (lack of competitionbetween caesium and potassium, resulting in highertransfer rates of radiocaesium in nutrient-poorecosystems) and the presence of specific food chainpathways, leading to highly contaminated producefrom seminatural ecosystems. Also, forest soils arefundamentally different from agricultural soils; theyhave a clear multilayered vertical structure charac-terized mainly by a clay-poor mineral layer, whichsupports a layer rich in organic matter. In contrast,agricultural soils generally contain less organicmatter and higher amounts of clay.

3.3.2. Food production systems affected by the accident

The radioactive material released by theChernobyl accident contaminated large areas of theterrestrial environment and had a major impact onboth agricultural and natural ecosystems not onlywithin the former USSR but also in many othercountries in Europe.

In the former USSR countries, the foodproduction system that existed at the time of theaccident can be divided into two types: largecollective farms and small private farms. Collectivefarms routinely apply land rotation combined withploughing and fertilization to improve productivity.Traditional small private farms, in contrast, seldomapply artificial fertilizers and often use manure forimproving yield. Typically they have one or, at most,a few cows, and produce milk mainly for privateconsumption. The grazing regime of private farmswas initially limited to the utilization of marginalland not used by the collective farms, but nowadaysincludes some better quality pasture.

In western Europe, poor soils are usedextensively for agriculture, mainly for grazing ofruminants (e.g. sheep, goats, reindeer and cattle).Such areas include alpine meadows and upland

regions in western and northern Europe that haveorganic soils.

3.3.3. Effects on agriculture in the early phase

At the time of the Chernobyl nuclear powerplant accident, vegetation in the affected areas wasat different stages of growth, depending on latitudeand elevation. Initially, interception on plant leavesof dry deposition and atmospheric washout withprecipitation were the main mechanisms by whichvegetation became contaminated. In the mediumand long term, root uptake predominated. Thehighest activity concentrations of radionuclides inmost foodstuffs occurred in 1986.

In the initial phase, 131I was the radionuclide ofmost concern and milk was the main contributor tointernal dose. This is because radioiodine wasreleased in large amounts and intercepted by plantsurfaces that were then grazed by dairy cows. Theingested radioiodine was completely absorbed inthe gut of the cow [3.31] and then rapidlytransferred to the animal’s thyroid and milk (withinabout one day). Thus peak values occurred rapidlyafter deposition in late April or early May 1986,depending on when deposition occurred in differentcountries. During this period, in the former USSRand some other European countries, 131I activityconcentrations in milk exceeded the national andregional (European Union (EU)) action levels of afew hundred to a few thousand becquerels per litre(see Section 4.1).

There are no time trend data available for 131Iactivity concentrations in milk in the first few daysafter the accident in the heavily affected areas of theUSSR, for the obvious and understandable reasonthat the authorities were dealing with otherimmediate accident response priorities. Never-theless, data are available for the period starting twoweeks after the accident from the Tula region of theRussian Federation, and the data in Fig. 3.14(a)show an exponential decline in 131I activity concen-tration in milk normalized to 137Cs deposition,which can be extrapolated back to the first days toestimate the initial 131I activity concentration inmilk. Furthermore, a direct comparison of 131Iactivity in milk in early May with 137Cs depositionshows the contribution of dry deposition to 131I inmilk, because the linear relationship line showndoes not go through the zero deposition point(Fig. 3.14(b)). In the early spring in northernEurope, dairy cows and goats were not yet onpasture, therefore there was very little milk

30

contamination. In contrast, in the southern regionsof the USSR, as well as in Germany, France andsouthern Europe, dairy animals were alreadygrazing outdoors and some contamination of cow,goat and sheep milk occurred. The 131I activityconcentration in milk decreased with an effectivehalf-life of four to five days [3.32], due to its shortphysical half-life and the reduction in iodine activityconcentrations on plants due to atmosphericremoval processes from leaf surfaces (Fig. 3.15).This removal occurred with a mean weathering half-life on grass of nine days for radioiodine and 11 daysfor radiocaesium [3.33]. Leafy vegetables were alsocontaminated on their surfaces and also made acontribution to the radiation dose to humans via thefood chain (Fig. 3.15).

Both plants and animals were also contami-nated with radiocaesium and, to a lesser extent,radiostrontium. From June 1986 radiocaesium wasthe dominant radionuclide in most environmental

samples (except in the CEZ) and in food products.As shown in Fig. 3.16, the contamination of milkwith radiocaesium decreased during spring 1986with an effective half-life of about two weeks, due to

(b)

Caesium-137 in soil (kBq/m2)

45

40

35

30

25

20

15

10

5

00 50 100 150 200 250 300 350 400 450

Iod

ine-

131

in m

ilk o

n 8

May

198

6 (k

Bq

/kg)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

1000

100

10

1

Iod

ine-

131

in m

ilk n

orm

aliz

ed t

o 13

7 Cs

soil

dep

ositi

on

(Bq

131 l/

kg)/

(kB

q13

7 Cs/

m2 )

(a)

Days after fallout

FIG. 3.14. Variation in 131I activity concentration in milkin the Tula region of the Russian Federation (a) with timeafter deposition, standardized by 137Cs soil deposition, and(b) with 137Cs soil deposition (time corrected to8 May 1986) [3.30].

10 000

1000

100

10

0

ASTRAL assessment

60 000 Bq/m2

20 000 Bq/m2

Measurement resultsAlsaceHt RhinMoselleMeurthe et MBas RhinArdennes/Meuse

1 May 11 May 21 May 31 May 10 June 20 June 30 June

Iod

ine-

131

activ

ity in

leaf

y ve

geta

ble

s (B

q/k

g fr

esh)

(a)

Iod

ine-

131

activ

ity in

milk

(Bq

/L)

ArdennesHt Marne/AubeMeurthe et MMeuseMoselleHt Rhin/Ter. BelVosges

10 000 Bq/m2

40 000 Bq/m2

ASTRAL assessment:

1000

100

10

128 Apr. 8 May 18 May 28 May 8 Jun. 18 Jun.

Measurement results:

(b)

FIG. 3.15. Changes with time of 131I activity concentrationsin (a) leafy vegetables and (b) cow’s milk in differentregions of France, May–June 1986 [3.34].

Measurements from eastern France

Measurements from central France

Measurements from western France

ASTRAL assessments: 5000 Bq/m2

2000 Bq/m2

400 Bq/m2

May 1986 Jul. Sep. Nov. Jan. 1987 Mar. May Jul. 1987

100

10

1

Cae

sium

-137

act

ivity

in m

ilk (B

q/L

)

FIG. 3.16. Changes with time of 137Cs activity concentra-tions in cow’s milk in France in 1986–1987 as observed andsimulated by the ASTRAL model [3.34].

31

weathering, biomass growth and other naturalprocesses. However, radiocaesium activity concen-trations increased again during winter 1986/1987,due to the feeding of cows with contaminated hayharvested in spring/summer 1986. This phenomenonwas observed in the winter period in many countriesafter the accident.

The transfer to milk of many of the otherradionuclides present in the terrestrial environmentduring the early phase of the accident was low. Thiswas because of low inherent transfer in the gut ofthose elements, compounded by low bioavailabilitydue to their association within the matrix of fuelparticles [3.35]. Nevertheless, some high transfersoccurred, notably that of 110mAg to the liver ofruminants [3.36].

3.3.4. Effects on agriculture in the long term

Since 1987, the radionuclide content of bothplants and animals has been largely determined bythe interaction between radionuclides and differentsoil components, as soil is the main reservoir of longlived radionuclides deposited on terrestrialecosystems. This process controls radionuclideavailability [3.37, 3.38] for uptake into plants andanimals and also influences radionuclide migrationdown the soil column.

3.3.4.1. Physicochemistry of radionuclides in the soil–plant system

Plants take up nutrients and pollutants fromthe soil solution. The activity concentration ofradionuclides in the soil solution is the result ofphysicochemical interactions with the soil matrix, ofwhich competitive ion exchange is the dominantmechanism. The concentration and composition ofthe major and competitive elements present in thesoil are thus of prime importance for determiningthe radionuclide distribution between the soil andthe soil solution. Many data obtained after theChernobyl accident demonstrate that the amountand nature of clay minerals present in soil are keyfactors in determining radioecological sensitivitywith regard to radiocaesium. These features arecrucially important for understanding radiocaesiumbehaviour, especially in areas distant from theChernobyl nuclear power plant, where 137Cs wasinitially deposited mainly in condensed, watersoluble forms.

Close to the nuclear power plant, radio-nuclides were deposited in a matrix of fuel particles

that have slowly dissolved with time; this process isnot complete today. The more significant factorsinfluencing the fuel particle dissolution rate in soilare the acidity of the soil solution and the physico-chemical properties of the particles (notably thedegree of oxidization) (see Fig. 3.17). In a low pH ofpH4, the time taken for 50% dissolution of particleswas about one year, whereas for a higher pH of pH7up to 14 years were needed [3.39–3.41]. Thus in acidsoils most of the fuel particles have alreadydissolved. In neutral soils, the amount of mobile 90Srreleased from the fuel particles is now increasing,and this will continue over the next 10–20 years.

In addition to soil minerals, microorganismscan significantly influence the fate of radionuclidesin soils [3.42, 3.43]. They can interact with mineralsand organic matter and consequently affect thebioavailability of radionuclides. In the specific caseof mycorrhizal fungi, soil microorganisms may evenact as a carrier, transporting radionuclides from thesoil solution to the associated plant.

U3O8/U2O5Oxidation state +5 ± 0.5

UO2Oxidation state +4 ± 0.5

(a)

0

10

20

30

40

50

60

70

80

90

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

pH

South North West

FP (%

act

ivity

in fu

el p

artic

les)

(b)

FIG. 3.17. (a) Variation in the oxidation within aChernobyl fuel particle [3.40]; (b) fraction of 90Sr presentin fuel particles (FP) ten years after the Chernobyl accidentas a function of soil acidity [3.39].

32

A traditional approach of characterizing themobility and bioavailability of a radioactivecontaminant in soil is by applying sequentialextraction techniques. A number of experimentalprotocols have been developed that use a sequenceof progressively aggressive chemicals, each of whichis assumed to selectively leach a fraction of thecontaminant bound to a specific soil constituent. Anexample of the results available from this procedureis presented in Fig. 3.18, which shows that a muchhigher proportion of radiocaesium was fixed in thesoil than of radiostrontium. The selectivity andreproducibility of chemical extraction proceduresvaries and therefore often should be considered togive only qualitative estimates of bioavailability.

By use of sequential extraction techniques, thefraction of exchangeable 137Cs was found todecrease by a factor of three to five within a decadeafter 1986 [3.44, 3.45]. This time trend, whichresulted in a reduction of plant contamination, maybe due to progressive fixation of radiocaesium ininterlayer positions of clay minerals and to its slowdiffusion and binding to the frayed edge sites of clayminerals. This process reduces the exchangeability

of radiocaesium so that is not then available to enterthe soil solution from which plants take up most ofthe radiocaesium via the roots. For 90Sr an increasewith time of the exchangeable fraction has beenobserved, which is attributed to the leaching of thefuel particles [3.39].

3.3.4.2. Migration of radionuclides in soil

The vertical migration of radionuclides downthe soil column can be caused by various transportmechanisms, including convection, dispersion,diffusion and biological mixing. Root uptake ofradionuclides into plants is correlated with verticalmigration. Typically, the rate of movement of radio-nuclides varies with soil type and physicochemicalform. As an example, Fig. 3.19 shows the changewith time of the depth distributions of 90Sr and 137Csmeasured in the Gomel region of Belarus. Althoughthere has been a significant downward migration ofboth radionuclides, much of the radionuclideactivity has remained within the rooting zone ofplants. At such sites, where contamination occurredthrough atmospheric deposition, there is a low riskof radionuclide migration to groundwater.

The rate of downward migration in differenttypes of soil varies for radiocaesium and radio-strontium. Low rates of 90Sr vertical migration areobserved in peat soils, whereas 137Cs migrates at thehighest rate in these (highly organic) soils, butmoves much more slowly in soddy podzolic sandysoils. In dry meadows, the migration of 137Cs belowthe root-containing zone (0–10 cm) was hardlydetectable in the ten years after the falloutdeposition. Thus the contribution of verticalmigration to the decrease of 137Cs activity concen-trations in the root-containing zone of mineral soils

86%

12% 2% 12%

37%51%

Fixed Extractable Exchangeable

Caesium-137 Strontium-90

FIG. 3.18. Forms of radionuclides in soddy podzolic loamsand soil of the Gomel region of Belarus in 1998 [3.46].

0 20 40 60 80 100

0–5

6–10

11–15

16–20

21–25

26–30

31–35

1987

2000

0 20 40 60 80 100

0–5

6–10

11–15

16–20

21–25

26–30

31–35

Strontium-90 activity (%)

1987

2000

Dep

th (c

m)

Dep

th (c

m)

Caesium-137 activity (%)

FIG. 3.19. Depth distributions of 137Cs and 90Sr measured in 1987 and 2000 in a soddy gley sandy soil (in per cent of totalactivity) in the Gomel region of Belarus [3.46].

33

is negligible. In contrast, in wet meadows and inpeatland, downward migration can be an importantfactor in reducing the availability of 137Cs for plants[3.48].

The higher rates of 90Sr vertical migration areobserved in low humified sandy soil (Fig. 3.20),soddy podzolic sandy soil and sandy loam soil withan organic content of less than 1% [3.27]. Generally,the highest rate of 90Sr vertical migration occurswhere there are completely non-equilibrium soilconditions. This occurs in the floodplains of rivers,where the soil is not structurally formed (lighthumified sands), in arable lands in a non-equilibrium state and in soils in which the organiclayers have been removed, for example at sites offorest fires and sites with deposited sand with a lowcontent of organic matter (<1%). In such conditionsthere is a high rate of radiostrontium verticalmigration to groundwater with convective moistureflow, and high activity levels can occur in localizedsoil zones. Thus the spatial distribution of 90Sr canbe particularly heterogeneous in soils in which therehave been changes in sorption properties.

Agricultural practices have a major impact onradionuclide behaviour. Depending on the type of

soil tillage and on the tools used, a mechanical redis-tribution of radionuclides in the soil may occur. Inarable soils, radionuclides are distributed fairlyuniformly down the whole depth of the tilled layer.

The lateral redistribution of radionuclides incatchments, which can be caused by both water andwind erosion, is significantly less than their verticalmigration into the soil and the underlying geologicallayers [3.27]. The type and density of plant covermay significantly affect erosion rates. Depending onthe intensity of erosive processes, the content ofradionuclides in the arable layer on flat land withsmall slopes may vary by up to 75% [3.49].

3.3.4.3. Radionuclide transfer from soil to crops

The uptake of radionuclides, as well as ofother trace elements, by plant roots is a competitiveprocess [3.50]. For radiocaesium and radiostrontiumthe main competing elements are potassium andcalcium, respectively. The major processesinfluencing radionuclide transport processes withinthe rooting zone are schematically represented inFig. 3.21, although the relative importance of eachcomponent varies with the radionuclide and soiltype.

The fraction of deposited radionuclides takenup by plant roots differs by orders of magnitude,depending primarily on soil type. For radiocaesiumand radiostrontium, the radioecological sensitivityof soils can be broadly divided into the categorieslisted in Table 3.5. For all soils and plant species, theroot uptake of plutonium is negligible comparedwith the direct contamination of leaves via rainsplash or resuspension.

Transfer from soil to plants is commonlyquantified using either the transfer factor (TF,

0 20 40 60 80 100

0–2

2–4

4–6

6–8

8–10

10–14

14–18

18–22

22–26

26–30

30–34

34–38

38–42

42–46

46–50

50–54

54–60

60–65

65–100

Part of radionuclide activity (%)

Americium-241

Europium-154

Strontium-90

Caesium-137

Dep

th (c

m)

FIG. 3.20. Depth distributions of radionuclides in lowhumified sandy soil (in per cent of total activity) measuredin 1996 [3.47].

Soil organic matrix

PLANTS

Soil Solution [RN] p

[RN] d

ROOTS, Mycorhiza

[RN] min[RN] mic

Soil mineral matrix

Additionalnon-radioactive pollutants

[RN] org

Plants

Soil solution

Roots, mycorrhiza

Soil microorganismsSoil mineral matrix

Fertilizers

Soil organic matrix

FIG. 3.21. Radionuclide pathways from soil to plants withconsideration of biotic and abiotic processes [3.43].

34

dimensionless, equal to plant activity concentration,Bq/kg, divided by soil activity concentration, Bq/kg)or the aggregated transfer coefficient (Tag, m2/kg,equal to plant activity concentration, Bq/kg, dividedby activity deposition on soil, Bq/m2).

The highest 137Cs uptake by roots from soil toplants occurs in peaty, boggy soils, and is one to twoorders of magnitude higher than in sandy soils; thisuptake often exceeds that of plants grown on fertileagricultural soils by more than three orders ofmagnitude. The high radiocaesium uptake frompeaty soils became important after the Chernobylaccident because in many European countries suchsoils are vegetated by natural unmanaged grasslandused for the grazing of ruminants and theproduction of hay.

The amount of radiocaesium in agriculturalproducts in the medium to long term depends notonly on the density of contamination but also on thesoil type, moisture regime, texture, agrochemicalproperties and plant species. Agricultural activityoften reduces the transfer of radionuclides from soilto plants by physical dilution (e.g. ploughing) or byadding competitive elements (e.g. fertilizing). Thereare also differences in radionuclide uptake betweenplant species. Although among species variations inuptake may exceed one or more orders of

magnitude for radiocaesium, the impact of differingradioecological sensitivities of soils is often moreimportant in explaining the spatial variation intransfer in agricultural systems.

The influence of other factors that have beenreported to influence plant root uptake of radionu-clides (e.g. soil moisture) is less clear or may beexplained by the basic mechanisms discussed above;for example, the accumulation of radiocaesium incrops and pastures is related to soil texture. In sandysoils the uptake of radiocaesium by plants is approx-imately twice as high as in loam soils, but this effectis mainly due to the lower concentrations of its maincompeting element, potassium, in sand.

The main process controlling the root uptakeof radiocaesium into plants is the interactionbetween the soil matrix and solution, whichdepends primarily on the cation exchange capacityof the soil. For mineral soils this is influenced by theconcentrations and types of clay minerals and theconcentrations of competitive major cations,especially potassium and ammonium. Examples ofthese relationships are shown in Fig. 3.22 for bothradiocaesium and radiostrontium. The modelling ofsoil solution physicochemistry, which takes accountof these major factors, enables prediction of the rootuptake of both radionuclides [3.51, 3.52].

TABLE 3.5. CLASSIFICATION OF RADIOECOLOGICAL SENSITIVITY FOR SOIL–PLANTTRANSFER OF RADIOCAESIUM AND RADIOSTRONTIUM

Sensitivity Characteristic Mechanism Example

Radiocaesium

High Low nutrient contentAbsence of clay mineralsHigh organic content

Little competition with potassium and ammonium in root uptake

Peat soils

Medium Poor nutrient status, consisting of minerals, including some clays

Limited competition with potassium and ammonium in root uptake

Podzol, other sandy soils

Low High nutrient statusConsiderable fraction of clay minerals

Radiocaesium strongly held to soil matrix (clay minerals), strong competition with potassium and ammonium in root uptake

Chernozem, clay and loam soils (used for intensive agriculture)

Radiostrontium

High Low nutrient statusLow organic matter content

Limited competition with calcium in root uptake

Podzol sandy soils

Low High nutrient statusMedium to high organic matter content

Strong competition with calcium in root uptake

Umbric gley soils, peaty soils

35

Thus differences in radioecological sensitiv-ities of soils explain why in some areas of lowdeposition high concentrations of radiocaesium arefound in plants and mushrooms harvested fromseminatural ecosystems and, conversely, why areasof high deposition can show only low to moderateconcentrations of radiocaesium in plants. This isillustrated in Fig. 3.23, in which the variability inactivity concentrations of radiocaesium and radio-strontium in plants is shown for a normalizedconcentration in soil.

3.3.4.4. Dynamics of radionuclide transfer to crops

In 1986 the 137Cs content in plants, which wasat its maximum in that year, was primarilydetermined by aerial contamination. During thefirst post-accident year (1987), the 137Cs content in

plants dropped by a factor of three to one hundred(depending on soil type) as roots became thedominant contamination route.

For meadow plants in the first years afterdeposition, 137Cs behaviour was considerablyinfluenced by the radionuclide distribution betweensoil and mat. In this period, 137Cs uptake from matsignificantly exceeded (up to eight times) that fromsoil. Further, as a result of mat decomposition andradionuclide transfer to soil, the contribution of matdecreased rapidly, and in the fifth year after thedeposition it did not exceed 6% for automorphoussoils and 11% for hydromorphous soils [3.41].

In most soils the transfer rate of 137Cs to plantshas continued to decrease since 1987, although therate of decrease has slowed, as can be seen fromFig. 3.24 [3.55]. A decrease with time similar to thatshown in Fig. 3.24 has been observed in many

(a)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Less than 80 81–140 141–200 201–300 More 300

Potassium content (mg/kg)

Sands

Sandy loam

Clay loam

Tag (137Cs) (10–3 m2/kg)

(b)

0

2

4

6

8

0 2 4 6 8 10 12

Calcium content (mg-equ/100 g)

Tag (90Sr) (10–3 m2/kg)

Tag = 3.9Ca–1

FIG. 3.22. (a) Transfer of 137Cs into oat grain in soddypodzolic soils of various textures with varying potassiumcontents [3.61] and (b) transfer of 90Sr into seeds of winterrye with varying concentrations of exchangeable calcium indifferent soils [3.53].

0.10

1.00

10.00

100.00

1

1

1

2

2

2

2

3

3

33

Strontium-90Caesium-137

gk/qB

Wheat seedsNatural grass (hay)

FIG. 3.23. Variation in the concentrations of 137Cs and 90Srin two plant species with soil type; the data refer to a soildeposition of 1 kBq/m2 [3.54]. 1: peat soil; 2: soddypodzolic soil; 3: chernozem soil.

1986 1990 1994 1998 20021988 1992 1996 2000 200

10

100

1000

Grain

Potato

Year

gk/qB

FIG. 3.24. Changes with time of 137Cs concentrations ingrain and potato produced in contaminated districts of theBryansk region of the Russian Federation (Bq/kg) [3.55].

36

studies of plant root uptake in different crops, as canbe seen in Figs 3.25 and 3.26 for cereals and naturalgrasses, respectively, growing in two different soiltypes [3.56]. Two experimental points forchernozem soil (18 and 20 years) were obtainedfrom the measurements made in 1980–1985 (i.e.after 137Cs global fallout and before the Chernobylaccident) (Fig. 3.25). Values of 137Cs TFs for cerealsas well as for potato and cow’s milk obtained about20 years following global fallout do not differ signif-icantly from those observed eight to nine years andlater after the Chernobyl fallout in remote areaswith dominant sandy, sandy loam and chernozemsoils [3.56, 3.57]. The difference between Tag valuesrelevant to cereals grown on fertilized soil is muchlower than the difference for natural grasses.

For the transfer of radiocaesium from soil toplants, a decrease with time is likely to reflect: (a)physical radionuclide decay; (b) the downward

migration of the radionuclide out of the rootingzone; and (c) physicochemical interactions with thesoil matrix that result in decreasing bioavailability.In many soils, the ecological half-lives of the plantroot uptake of radiocaesium can be characterizedby two components: (a) a relatively fast decrease,with a half-life between 0.7 and 1.8 years,dominating for the first four to six years, leading to areduction of concentration in plants by about anorder of magnitude compared with 1987; and (b) aslower decrease with a half-life of between sevenand 60 years [3.45, 3.55, 3.57, 3.58]. The dynamics ofthe decrease of 137Cs availability in the soil–plantsystem are considerably influenced by soilproperties, and as a result the rates of decreasing137Cs uptake by plants can differ by a factor of threeto five [3.41].

Some caution should be exercised, however, ingeneralizing these observations, because some dataindicate almost no decrease in the root uptake ofradiocaesium with time beyond the first four to sixyears, which suggests that there is no reduction inbioavailability in soil within the time period ofobservation. Furthermore, the prediction ofecological half-lives that exceed the period ofobservation can be highly uncertain. Theapplication of countermeasures aimed at reducingthe concentration of radiocaesium in plants will alsomodify the ecological half-life.

Compared with radiocaesium, the uptake of90Sr by plants has usually not shown such a markeddecrease with time. In the areas close to theChernobyl nuclear power plant, the gradualdissolution of fuel particles has enhanced thebioavailability of 90Sr, and therefore there has beenan increase with time in 90Sr uptake by plants(Fig. 3.27 [3.39]).

In remote areas, where strontium radio-nuclides were predominantly deposited incondensed form and in lesser amounts as finedispersed fuel particles, the dynamics of long termtransfer of 90Sr to plants were similar to those ofradiocaesium, but with different ecological half-lives for plant root uptake. This difference isassociated with various mechanisms of soil transferfor these two elements. The fixation of strontium bysoil components depends less on the clay content ofthe soil than that of caesium (see Table 3.5). Moregenerally, the values of 90Sr transfer parametersfrom soil to plants depend less on the soil propertiesthan the transfer parameters for radiocaesium[3.37]. An example of the time dependence of 90Sruptake by plants is given in Fig. 3.28 [3.56].

1.000

0.100

0.010

0.0010 2 4 6 8 10 12 14 16 18 20

Years after fallout

(1)(2)

Tag2 = 0.53 exp(–ln 2t/0.9) + 0.018

Tag1 = 1.2 exp(–ln 2t/0.8) + 0.035

T ag

(Cs)

(10–

3 m

2 /kg

)

FIG. 3.25. Dynamics of the 137Cs Tag for cereals. 1: sandyand sandy loam soil, Bryansk region, Russian Federation;2: chernozem soil, Tula and Orel regions, Russian Federa-tion [3.56].

100.00

10.00

1.00

0.10

0.010 2 4 6 8 10 12 14 16 18

Years after fallout

(1)

(2)

Tag2 = 6.0 exp(–ln 2t/0.9) + 0.10

Tag1 = 200 exp(–ln 2t/1.0) + 2.2

T ag

(Cs)

(10–

3 m

2 /kg

)

FIG. 3.26. Dynamics of the 137Cs Tag (dry weight) fornatural grasses. 1: sandy and sandy loam soil, Bryanskregion, Russian Federation; 2: chernozem soil, Tula andOrel regions, Russian Federation [3.56].

37

3.3.4.5. Radionuclide transfer to animals

Animals take up radionuclides throughcontaminated forage and direct soil ingestion. Milkand meat were major contributors to the internalradiation dose to humans after the Chernobylaccident, both in the short term, due to 131I, and inthe long term, due to radiocaesium. In intensivelymanaged agricultural ecosystems, high levels ofcontamination of animal food products can beexpected only for a few weeks, or at most a fewmonths, after a pulse of fallout. In these circum-stances the extent of interception and retention onplant surfaces largely determines both the duration

and the level of contamination of animal derivedfood products. An exception is found where veryhigh deposition occurs or where plant uptake is highand sustained, both of which occurred in some areasafter the Chernobyl accident.

The levels of radiocaesium in animal foodproducts can be high and persist for a long time,even though the original deposition may not havebeen very high. This is because: (a) soils often allowsignificant uptake of radiocaesium; (b) some plantspecies accumulate relatively high levels of radio-caesium, for example ericaceous species and fungi;and (c) areas with poor soils are often grazed bysmall ruminants, which accumulate higher caesiumactivity concentrations than larger ruminants[3.35].

The contamination of animal products byradionuclides depends on their behaviour in theplant–soil system, the absorption rate and metabolicpathways in the animal and the rate of loss from theanimal (principally in urine, faeces and milk).Although absorption can occur through the skinand lungs, oral ingestion of radionuclides in feed,and subsequent absorption through the gut, is themajor route of uptake of most radionuclides.Absorption of most nutrients takes place in therumen or the small intestine at rates that vary fromalmost negligible, in the case of actinides, to 100%for radioiodine, and varying from 60% to 100% forradiocaesium, depending on the form [3.31].

After absorption, radionuclides circulate inthe blood. Some accumulate in specific organs; forexample, radioiodine accumulates in the thyroid,and many metal ions, including 144Ce, 106Ru and110mAg, accumulate in the liver. Actinides andespecially radiostrontium tend to be deposited inthe bone, whereas radiocaesium is distributedthroughout the soft tissues [3.36, 3.37, 3.50, 3.59,3.60].

The transfer of radionuclides to animalproducts is often described by transfer coefficientsdefined as the equilibrium ratio between the radio-nuclide activity concentration in milk, meat or eggsdivided by the daily dietary radionuclide intake.Transfer coefficients for radioiodine and radio-caesium to milk, and for radiocaesium to meat, aregenerally lower for large animals such as cattle thanfor small animals such as sheep, goats and chickens.The transfer of radiocaesium to meat is higher thanthat to milk.

The long term time trend of radiocaesiumcontamination levels in meat and milk, an exampleof which is displayed in Fig. 3.29, follows that for

1986 1988 1990 1992 1994 1996 1998 2000 2002

Year

20

15

10

5

0

TF ((

Bq

/kg)

/(kB

q/m

2 ))

FIG. 3.27. Dynamics of the 90Sr TF into natural grass fromsoddy podzolic soil in the CEZ [3.39].

100.00

10.00

1.00

0.10

0.011 3 5 7 9 11 13 15

Years after fallout

(1)

(2)

Tag2 = 0.30 exp(–ln 2t/4.0) + 0.11

Tag1 = 18 exp(–ln 2t/4.1) + 3.8

T ag

(Sr)

(10–

3 m

2 /kg

)

Tag3 = 0.12 exp(–ln 2t/3.3) + 0.034(3)

FIG. 3.28. Dynamics of the 90Sr aggregated TF for naturalgrasses (1: sandy and sandy loam soil, Bryansk region,Russian Federation) and cow’s milk (2: sandy and sandyloam soil, Bryansk region, Russian Federation; 3:chernozem soil, Tula and Orel regions, Russian Federa-tion) [3.56].

38

vegetation and can be divided into two phases [3.55,3.57, 3.58]. For the first four to six years after thedeposition of the radiocaesium there was an initialfast decrease with an ecological half-life of between0.8 and 1.2 years. For later times, only a smalldecrease has been observed [3.55, 3.56].

There are differing rates of 137Cs transfer tomilk in areas with different soil types, as demon-strated over nearly two decades after the accident(Fig. 3.30) in milk from the Bryansk, Tula and Orelregions of the Russian Federation, where fewcountermeasures have been used. The transfer of137Cs to milk is illustrated using the Tag, whichnormalizes the data for different levels of soilcontamination; this makes comparison among soiltypes easier. The transfer to milk declines in theorder peat bog > sandy and sandy loam >chernozem and grey forest soils. Both the dynamicsof 137Cs activity concentration in milk and itsdependence on soil type are similar to those innatural grasses (see Fig. 3.26) sampled in areaswhere cattle graze.

Similar long term data are available forcomparing the transfer of 137Cs to beef in theRussian Federation for different soil types. Theyalso show higher transfer in areas with sandy/sandyloam soils compared with chernozem soils(Fig. 3.31); there has been little decline in 137Cstransfer over the past decade.

The long term dynamics of 90Sr in cow’s milksampled in Russian areas with dominant soddypodzolic and chernozem soils (see Fig. 3.28) aredifferent from those of 137Cs. The graphs for 90Sr inmilk do not contain the initial decreasing portionwith an ecological half-life of about one year, asshown in the graphs for 137Cs, which are presumedto reflect fixation of caesium in the soil matrix. Incontrast, the 90Sr activity concentration in cow’smilk gradually decreases with an ecological half-lifeof three to four years; the second component (ifany) has not yet been identified. The physical andchemical processes responsible for these timedynamics obviously include diffusion andconvection with vertical transfer of 90Sr into soil, aswell as its radioactive decay. However, the chemicalinteractions with the soil components may differsignificantly from those known for caesium.

Meat

Milk

10 000

1000

100

101986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Year

gk/qB

FIG. 3.29. Changes with time in mean 137Cs activityconcentrations in meat and milk produced in contaminateddistricts of the Bryansk region of the Russian Federation(Bq/kg) [3.55].

10.00

1.00

0.10

0.010 2 4 6 8 10 12 14 16 18

Years after fallout

(1)

(2)

Tag2 = 0.34 exp(–ln 2t/1.6) + 0.78

Tag1 = 13 exp(–ln 2t/1.6) + 0.78

T ag

(Cs)

(10–

3 m

2 /kg

)

(a)

10.0

1.0

0.1

0 2 4 6 8 10 12 14 16

Years after fallout

(1)(2)

Tag2 = 3 exp(–ln 2t/1.8) + 0.09

Tag1 = 7 exp(–ln 2t/1.7) + 0.12

T ag

(Cs)

(10–

3 m

2 /kg

)

(b)

FIG. 3.30. (a) Dynamics of the 137Cs aggregated TF forcow’s milk. 1: peat bog soil, Bryansk region, RussianFederation; 2: chernozem soil, Tula and Orel regions,Russian Federation [3.56]. (b) Dynamics of 137Cs aggre-gated TF for cow’s milk (sandy and sandy loam soil,Bryansk region, Russian Federation). 1: 137Cs soil deposi-tion <370 kBq/m2; 2: 137Cs soil deposition >370 kBq/m2

[3.56].

39

By combining information on radionuclidetransfer with spatially varying information ingeographic information systems, it is possible toidentify zones in which a specified average activityconcentration in milk is likely to be exceeded. Anexample is shown in Fig. 3.32.

A significant amount of production in theformer USSR is confined to the grazing of privatelyowned cows on poor, unimproved meadows. Owingto the poor productivity of these areas, radiocaesiumuptake is relatively high compared with that on landused by collective farms. As an example of thedifference between farming systems, changes in 137Csactivity concentrations in milk from private andcollective farms in the Rovno region of Ukraine areshown in Fig. 3.33. The activity concentrations inmilk from private farms exceeded the action levelsuntil 1991, when countermeasures wereimplemented that resulted in a radical improvement.

3.3.5. Current contamination of foodstuffs and expected future trends

Table 3.6 shows summarized data of measuredcurrent (2000–2003) activity concentrations ofradiocaesium in grain, potato, milk and meatproduced in highly and less highly contaminatedareas covering many different types of soil withwidely differing radioecological sensitivities inBelarus, the Russian Federation and Ukraine.Caesium-137 activity concentrations are consist-ently higher in animal products than in plantproducts.

Currently, due to natural processes andagricultural countermeasures, radiocaesium activityconcentrations in agricultural food productsproduced in areas affected by the Chernobyl falloutare generally below national, regional (EU) andinternational action levels [3.64, 3.65]. However, insome limited areas with high radionuclide contami-nation (parts of the Gomel and Mogilev regions inBelarus and the Bryansk region in the RussianFederation) or poor organic soils (the Zhytomyrand Rovno regions in Ukraine), radiocaesiumactivity concentrations in food products, especiallymilk, still exceed the national action levels of about100 Bq/kg. In these areas remediation may still bewarranted (see Section 4).

Contaminated milk from privately ownedcows with 137Cs activity concentrations exceeding100 Bq/L (the current permissible level for milk)was being produced in more than 400, 200 and 100Ukrainian, Belarusian and Russian settlements,

100.00

10.00

1.00

0.10

0.010 2 4 6 8 10 12 14

Years after fallout

(1)

(2)

Tag2 = 0.77 exp(–ln 2t/0.9) + 0.12

Tag1 = 17 exp(–ln 2t/0.9) + 1.0

T ag

(Cs)

(10–

3 m

2 /kg

)

FIG. 3.31. Dynamics of 137Cs aggregated TF for beef. 1:sandy and sandy loam soil; 2: chernozem soil [3.56].

FIG. 3.32. Isolines of different levels of probability ofexceeding 100 Bq/L of 137Cs in milk (for 1991) in theKaluga region, Russian Federation [3.54]. The red colourindicates a high probability, the pink and green coloursindicate medium and low probabilities, respectively.

0

500

1000

1500

2000

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Bq

/L

Private farmsCollective farms

TPL

FIG. 3.33. Typical dynamics of 137Cs activity concentra-tions in milk produced on private and collective farms inthe Rovno region of Ukraine with a comparison with thetemporary permissible level (TPL) [3.62].

40

respectively, 15 years after the accident. Levels ofmilk contamination higher than 500 Bq/L occur insix Ukrainian, five Belarusian and five Russiansettlements (in 2001).

The concentrations and transfer coefficientsshown in the above mentioned figures and tablesshow that there has been only a slow decrease inradiocaesium activity concentrations in most plantand animal foodstuffs during the past decade. Thisindicates that radionuclides must be close toequilibrium within the agricultural ecosystems,although continued reductions with time areexpected, due to continuing radionuclide migrationdown the soil profile and to radioactive decay (evenif there was an equilibrium established between137Cs in the labile and non-labile pools of soil).Given the slow current rates of decline, and thedifficulties in quantifying long term effective half-lives from currently available data because of highuncertainties, it is not possible to conclude thatthere will be any further substantial decrease overthe next decades, except due to the radioactivedecay of both 137Cs and 90Sr, which have half-lives ofabout 30 years.

Radionuclide activity concentrations infoodstuffs can increase through fuel particle disso-

lution, changes in the water table as a consequenceof change of management of currently abandonedland or cessation of the application of counter-measures.

3.4. FOREST ENVIRONMENT

3.4.1. Radionuclides in European forests

Forest ecosystems were one of the majorseminatural ecosystems contaminated as a result offallout from the Chernobyl plume. The primaryconcern from a radiological perspective is the longterm contamination of the forest environment andits products with 137Cs, owing to its 30 year half-life.In the years immediately following contamination,the shorter lived 134Cs isotope was also significant.In forests, other radionuclides such as 90Sr and theplutonium isotopes are of limited significance forhumans, except in relatively small areas in andaround the CEZ. As a result, most of the availableenvironmental data concern 137Cs behaviour andthe associated radiation doses.

Forests provide economic, nutritional andrecreational resources in many countries.

TABLE 3.6. MEAN AND RANGE OF CURRENT CAESIUM-137 ACTIVITY CONCENTRATIONS INAGRICULTURAL PRODUCTS ACROSS CONTAMINATED AREAS OF BELARUS [3.49], THERUSSIAN FEDERATION [3.55] AND UKRAINE [3.63] (data are in Bq/kg fresh weight for grain, potato and meat and in Bq/L for milk)

Caesium-137 soil deposition range Grain Potato Milk Meat

Belarus

>185 kBq/m2 (contaminated districts of the Gomel region)

30 (8–80) 10 (6–20) 80 (40–220) 220 (80–550)

37–185 kBq/m2 (contaminated districts of the Mogilev region)

10 (4–30) 6 (3–12) 30 (10–110) 100 (40–300)

Russian Federation

>185 kBq/m2 (contaminated districts of the Bryansk region)

26 (11–45) 13 (9–19) 110 (70–150) 240 (110–300)

37–185 kBq/m2 (contaminated districts of the Kaluga, Tula and Orel regions)

12 (8–19) 9 (5–14) 20 (4–40) 42 (12–78)

Ukraine

>185 kBq/m2 (contaminated districts of the Zhytomyr and Rovno regions)

32 (12–75) 14 (10–28) 160 (45–350) 400 (100–700)

37–185 kBq/m2 (contaminated districts of the Zhytomyr and Rovno regions)

14 (9–24) 8 (4–18) 90 (15–240) 200 (40–500)

41

Figure 3.34 shows the wide distribution of forestsacross the European continent. Following theChernobyl accident, substantial radioactive contam-ination of forests occurred in Belarus, the RussianFederation and Ukraine, and in countries beyondthe borders of the former USSR, notably Finland,Sweden and Austria (see Fig. 3.5). The degree offorest contamination with 137Cs in these countriesranged from >10 MBq/m2 in some locations tobetween 10 and 50 kBq/m2, the latter range beingtypical of 137Cs deposition in several countries ofwestern Europe.

Since the Chernobyl accident it has becomeapparent that the natural decontamination offorests is proceeding extremely slowly. The netexport of 137Cs from forest ecosystems was less than1%/a [3.66, 3.67], so it is likely that, without artificialintervention, it is the physical decay rate of 137Csthat will largely influence the duration over whichforests continue to be affected by the Chernobylfallout. Despite the fact that the absolute naturallosses of 137Cs from forests are small, recycling ofradiocaesium within forests is a dynamic process inwhich reciprocal transfers occur on a seasonal, orlonger term, basis between biotic and abioticcomponents of the ecosystem. To facilitateappropriate long term management of forests, areliable understanding of these exchange processesis required. Much information on such processeshas been obtained from experiments and fieldmeasurements, and many of these data have beenused to develop predictive mathematical models[3.68].

3.4.2. Dynamics of contamination during the early phase

Forests in the USSR located along thetrajectory of the first radioactive plume werecontaminated primarily as a result of drydeposition, while further away, in countries such asAustria and Sweden, wet deposition occurred andresulted in significant hot spots of contamination.Other areas in the USSR, such as the Mogilevregion in Belarus and Bryansk and some otherregions in the Russian Federation, were alsocontaminated by deposition with rain.

Tree canopies, particularly at forest edges, areefficient filters of atmospheric pollutants of allkinds. The primary mechanism of tree contami-nation after the Chernobyl accident was directinterception of radiocaesium by the tree canopy,which intercepted between 60% and 90% of theinitial deposition [3.66]. Within a 7 km radius of thereactor this led to very high levels of contaminationon the canopies of pine trees, which, as a conse-quence, received lethal doses of radiation from thecomplex mixture of short and long lived radionu-clides released in the accident. Gamma dose rates inthe days and weeks immediately following theaccident were in excess of 5 mGy/h in the area close

FIG. 3.34. Forest map of Europe. The darkest colour,green, indicates a proportion of 88% forest in the area,while yellow indicates less than 10% [3.69].

AoL (litter layer)

AoF (organic)

AoH (organic)

A (mineral)

B (mineral)

Deposition(wet/dry)Canopy

interception

Biologicaluptake

Stem flowThrough flowLeaf/needle fall

Soil m

igration

FIG. 3.35. Major storages and fluxes in radionuclides ofcontaminated forest ecosystems [3.70].

42

to the reactor. The calculated absorbed gamma doseamounted to 80–100 Gy in the needles of pine trees.This small area of forest became known as the RedForest, as the trees died and became a reddishbrown colour, which was the most readilyobservable effect of radiation damage on organismsin the area (see Section 6).

The contamination of tree canopies wasreduced rapidly over a period of weeks to monthsdue to wash-off by rainwater and the naturalprocess of leaf/needle fall (Fig. 3.35). Absorption ofradiocaesium by leaf surfaces also occurred,although this was difficult to measure directly. Bythe end of the summer of 1986, approximately 15%of the initial radiocaesium burden in the treecanopies remained, and by the summer of 1987 thishad been further reduced to approximately 5%.Within this roughly one year period, therefore, thebulk of radiocaesium was transferred from the treecanopy to the underlying soil.

During the summer of 1986 radiocaesiumcontamination of forest products such asmushrooms and berries increased, which led toincreased contamination of forest animals such asdeer and moose. In Sweden activity concentrationsof 137Cs in moose exceeded 2 kBq/kg fresh weight,while those in roe deer were even higher [3.71].

3.4.3. Long term dynamics of radiocaesium in forests

Within approximately one year after the initialdeposition, the soil became the major repository ofradiocaesium contamination within forests. Subse-quently, trees and understorey plants becamecontaminated due to root uptake, which hascontinued as radiocaesium has migrated into thesoil profile. Just as for potassium, the nutrientanalogue rate of radiocaesium cycling within forestsis rapid and a quasi-equilibrium is reached a fewyears after atmospheric fallout [3.72]. The upper,organic rich, soil layers act as a long term sink butalso as a general source of radiocaesium for contam-ination of forest vegetation, although individualplant species differ greatly in their ability toaccumulate radiocaesium from this organic soil(Fig. 3.36).

Release of radiocaesium from the system viadrainage water is generally limited due to itsfixation on micaceous clay minerals [3.67]. Animportant role of forest vegetation in the recyclingof radiocaesium is the partial and transient storageof radiocaesium, particularly in perennial woody

components such as tree trunks and branches, whichcan have a large biomass. A portion of radiocaesiumtaken up by vegetation from the soil, however, isrecycled annually through leaching and needle/leaffall, resulting in the long lasting biological availa-bility of radiocaesium in surface soil. The storedamount of radiocaesium in the standing biomass offorests is approximately 5% of the total activity in atemperate forest ecosystem, with the bulk of thisactivity residing in trees.

Due to biological recycling and storage ofradiocaesium, migration within forest soils is limitedand the bulk of contamination in the long termresides in the upper organic horizons (Fig. 3.37).Slow downward migration of radiocaesium

1.E–04

1.E–03

1.E–02

1.E–01

1.E+00

1.E+01

1.E+02

90th percentile

Median

10th percentile

Soil Tree

Under

store

yFu

ngi

Game

FIG. 3.36. Calculated percentage distributions of radiocae-sium in specified components of coniferous forest ecosys-tems [3.73].

0.0

5.0

10.0

15.0

20.0

25.0

0 500 1000 1500 2000 2500 3000

1992

1993

1995

1996

1997

Soi

l dep

th (c

m)

Caesium-137 (Bq/kg)

FIG. 3.37. Soil profiles of radiocaesium in a Scots pineforest near Gomel in Belarus, 1992–1997 [3.74]. The hori-zontal line indicates the boundary between organic andmineral soil layers.

43

continues to take place, however, although the rateof migration varies considerably with soil type andclimate.

The hydrological regime of forest soils is animportant factor governing radionuclide transfer inforest ecosystems [3.75]. Depending on the hydro-logical regime, the radiocaesium Tag for trees,mushrooms, berries and shrubs can vary over arange of more than three orders of magnitude. Theminimum Tag values were found for automorphic(dry) forests and soils developed on even slopesunder free surface runoff conditions. The maximumTag values are related to hydromorphic forestsdeveloped under prolonged stagnation of surfacewaters. Among other factors influencing radionu-clide transfer in forests, the distribution of rootsystems (mycelia) in the soil profile and the capacityof different plants for radiocaesium accumulationare of importance [3.76].

The vertical distribution of radiocaesiumwithin soil has an important influence on thedynamics of uptake by herbaceous plants, trees andmushrooms. It also influences the change inexternal gamma dose rate with time. The upper soillayers provide increasing shielding from radiation asthe peak of the contamination migrates downwards(Fig. 3.38). The most rapid downward verticaltransfer was observed for hydromorphic forests[3.75].

Once forests become contaminated withradiocaesium, any further redistribution is limited.Processes of small scale redistribution include resus-pension [3.78], fire [3.79] and erosion/runoff, butnone of these processes are likely to result in anysignificant migration of radiocaesium beyond thelocation of initial deposition.

3.4.4. Uptake into edible products

Edible products obtained from forests includemushrooms, fruits and game animals. In forestsaffected by the Chernobyl deposition, each of theseproducts became contaminated. The highest levelsof contamination with radiocaesium have beenobserved in mushrooms, due to their great capacityto accumulate some mineral nutrients as well asradiocaesium. Mushrooms provide a common andsignificant food source in many of the affectedcountries, particularly in the countries of the formerUSSR. Changes with time in the contamination ofmushrooms reflect the bioavailability of 137Cs in thevarious relevant nutrient sources utilized by thedifferent mushroom species.

Some mushroom species exploit specific soillayers for their nutrition, and the dynamics ofcontamination of such species have been related tothe contamination levels of these layers [3.80]. Thehigh levels of contamination in mushroom speciesare reflected in generally high soil to mushroomtransfer coefficients. However, these transfer coeffi-cients (Tag) are also subject to considerablevariability and can range from 0.003 to 7 m2/kg (i.e.by a factor of approximately 2000 [3.81]). There aresignificant differences in the accumulation of radio-caesium in different species of mushroom (seeFig. 3.39) [3.82]. In general, the saprotrophs andwood degrading fungi, such as the honey fungus

7 MBq/m2

4 MBq/m2

0.7 MBq/m2

1988 1989 1990 1991 1992 1993 1994 1995 1996

Dos

e ra

te (�

Gy/

h)

18

16

14

12

10

8

6

4

2

0

Year

FIG. 3.38. Gamma dose rates in air at three forest locationswith different 137Cs soil depositions in the Bryansk regionof the Russian Federation, 150 km north-east of Chernobyl[3.77].

M P S

Nutritional type

5

0

–5

–10

Ln(T

ag)

FIG. 3.39. Variation in the logarithm of Tag with differentnutritional types of mushroom [3.82]. M: mycorrhizal;P: parasitic; S: saprotrophic nutritional type.

44

(Armillaria mellea), have a low level of contami-nation, while those fungi forming symbioses withtree roots (mycorrhizal fungi such as Xerocomusand Lactarius) have a high uptake. The degree ofvariability of mushroom contamination is illustratedin Fig. 3.40, which also indicates the tendency for aslow decrease in contamination during the 1990s.

Contamination of mushrooms in forests isoften much higher than that of forest fruits such asbilberries. This is reflected in the Tag for forestberries, which ranges from 0.02 to 0.2 m2/kg [3.81].Due to the generally lower radiocaesium levels andthe relative masses consumed, forest berries pose asmaller radiological hazard to humans than domushrooms. However, both products contributesignificantly to the diet of grazing animals andtherefore provide a second route of exposure ofhumans via game. Animals grazing in forests andother seminatural ecosystems often produce meatwith high radiocaesium levels. Such animals includewild boar, roe deer, moose and reindeer, but alsodomestic animals such as cattle and sheep, whichmay graze marginal areas of forests.

Most data on the contamination of gameanimals such as deer and moose have been obtainedfrom western European countries in which thehunting and eating of game is commonplace.Significant seasonal variations occur in the bodycontent of radiocaesium in these animals due to theseasonal availability of foods such as mushroomsand lichens, the latter being particularly importantas a component of the diet of reindeer. Good time

series measurements have been obtained from theNordic countries and Germany. Figure 3.41 shows acomplete time series of annual average radio-caesium activities for moose from 1986 to 2003 forone hunting area in Sweden, and Fig. 3.42 showsindividual measurements of 137Cs activity concen-trations in the muscle of roe deer in southernGermany. A major factor for the contamination ofgame, and roe deer in particular, is the high concen-tration of radiocaesium in mushrooms. The Tag formoose ranges from 0.006 to 0.03 m2/kg [3.81]. Themean Tag for moose in Sweden has been falling sincethe period of high initial contamination, indicatingthat the ecological half-life of radiocaesium inmoose is less than 30 years (i.e. less than thephysical half-life of 137Cs).

3.4.5. Contamination of wood

Most forests in Europe and the former USSRaffected by the Chernobyl accident are planted andmanaged for the production of timber. The exportof contaminated timber, and its subsequentprocessing and use, could give rise to radiationdoses to people who would not normally be exposedin the forest itself. Uptake of radiocaesium fromforest soils into wood is rather low; aggregated TFsrange from 0.0003 to 0.003 m2/kg. Hence wood usedfor making furniture or the walls and floors ofhouses is unlikely to give rise to significant radiationexposure of people using these products [3.85].However, the manufacture of consumer goods such

0

500 000

1 000 000

1 500 000

2 000 000

2 500 000

3 000 000

3 500 000

4 000 000

4 500 000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Year

Xerocomusbadius

Russulapaludosa

Suillusluteus

Cantharelluscibarius

Boletusedulis

0

Bq

/kg

dry

wei

ght

FIG. 3.40. Caesium-137 activity concentrations (Bq/kg dry weight) in selectedmushroom species harvested in a pine forest in the Zhytomyr region ofUkraine, approximately 130 km south-west of Chernobyl. The soil depositionof 137Cs at this site in 1986 was 555 kBq/m2. From Ref. [3.68].

45

as paper involves the production of both liquid andsolid waste that can become significantly contami-nated with radiocaesium. The handling of this wasteby workers in paper pulp factories can give rise toradiation doses within the industry [3.86].

Use of other parts of trees such as needles,bark and branches for combustion may involve theproblem of disposal of radioactive wood ash. Thispractice has increased in recent years due to theupsurge in biofuel technology in the Nordiccountries, and the problem of radiocaesium in woodash has become significant because the radio-caesium activity concentration in ash is a factor of50–100 times higher than in the original wood. Fordomestic users of firewood in contaminated regions,a buildup of ash in the home and/or garden may alsogive rise to external exposure to gamma radiationfrom radiocaesium [3.85].

3.4.6. Expected future trends

Much effort has been put into developingmathematical models that make use of the largearray of measurements of radiocaesium contami-nation in forests since 1986 [3.68]. These models areuseful in helping to improve our understanding ofthe way the Chernobyl contamination behaves inforest ecosystems. Furthermore, they can also beused to provide forecasts of future trends ofcontamination, which can assist when makingdecisions about the future management of contami-nated regions.

Predictive models of radiocaesium behaviourin forests are intended to quantify the fluxes anddistributions in the ecosystem over time. Forecastscan be made for specific ecological compartmentssuch as the wood of trees and edible products suchas mushrooms. Figures 3.43 and 3.44 show examplesof such forecasts obtained using a variety of models.Figure 3.43 shows predictions of the evolution ofradiocaesium activity in wood for two distinct typesof forest ecosystem with two age classes of trees.This illustrates the importance of both soilconditions and the stage of tree development at thetime of deposition in controlling the contaminationof harvestable wood. Figure 3.44 shows a summaryof 50 year forecasts for a pine forest in theZhytomyr region of Ukraine, approximately 130 kmsouth-west of Chernobyl. The figure shows thedegree of variability among the predictions made by11 different models and also the inherent variabilitywithin data collected from a single forest site. Theuncertainty in both monitoring data and amongmodels makes the task of forecasting future trendsof forest contamination rather difficult.

3.4.7. Radiation exposure pathways associated with forests and forest products

Contaminated forests can give rise toradiation exposures of workers in the forest and inassociated industries, as well as of members of thegeneral public. Forest workers receive directradiation exposure during their working hours, dueto the retention of radiocaesium in the tree canopyand the upper soil layers. Similarly, members of thepublic can receive external exposures from woodproducts, for example furniture or wooden floors,but, in addition, they may be exposed as a result ofthe consumption of game, wild mushrooms andberries containing radiocaesium. Forest marginsmay also be used to graze domestic animals such as

8916

9178 8891

98910991

19912991 1

3994991

9915 6991

79918991 1

9990002 02

10 20020023

Year

Cae

sium

-137

(Bq

/kg)

900

800

700

600

500

400

300

200

100

0

FIG. 3.41. The average concentration of 137Cs in moose inone hunting area in Sweden, based on approximately 100animals per year [3.83].

0

500

1000

1500

2000

2500

3000

Date

1 May 1986

25 Jan. 1989

22 Oct. 1991

18 Jul. 1994

13 Apr. 1997

8 Jan. 2000

4 Oct. 2002

Bq

/kg

dry

wei

ght

FIG. 3.42. Caesium-137 activity concentrations in themuscle of roe deer (Capreolus capreolus) harvested in aforest close to Bad Waldsee, southern Germany. The totaldeposition of 137Cs at this site in 1986 was 27 kBq/m2

[3.84].

46

cattle and sheep. This can lead to the milk of theseanimals becoming contaminated and to humanexposure as a result of the consumption of dairyproducts and meat. A further exposure pathwayresults from the collection and use of firewood fordomestic purposes. This can give rise to exposuresboth in the home and in the garden if wood ash isused as a domestic fertilizer. Also, the industrial useof forest products for energy production can give

rise to exposure both of workers and of members ofthe public. Quantitative information on humanradiation doses associated with forests and forestproducts is given in Ref. [3.85] and in Section 6 ofthis report.

Another set of important exposure pathwaysresults from the harvesting, processing and use oftimber and wood products from contaminatedforest areas. Timber and wood products becomesources of potential exposure once they areexported from the forest, often over considerabledistances and sometimes across national borders.The relative importance of these exposure pathwayshas been evaluated and quantified [3.85].

3.5. RADIONUCLIDES IN AQUATIC SYSTEMS

3.5.1. Introduction

Radioactive material from Chernobyl affectedsurface water systems in many parts of Europe. Themajority of the radioactive fallout, however, wasdeposited in the catchment of the Pripyat River,which forms an important component of theDnieper River–reservoir system, one of the largersurface water systems in Europe [3.13]. After theaccident, therefore, there was particular concernover contamination of the water supply for the areaalong the Dnieper cascade of reservoirs covering adistance of approximately 1000 km to the Black Sea(see Figs 3.6–3.9). Other large river systems inEurope, such as the Rhine and Danube, were alsoaffected by fallout, although the contaminationlevels in those rivers were not radiologicallysignificant [3.5, 3.6].

Initial radionuclide concentrations in riverwater in parts of Belarus, the Russian Federationand Ukraine were relatively high compared bothwith other European rivers and with the safetystandards for radionuclides in drinking water. Thecontamination was due to direct fallout on to riversurfaces and runoff of contamination fromcatchment areas. During the first few weeks afterthe accident, activity concentrations in river watersdeclined rapidly, because of the physical decay ofshort lived isotopes and absorption of radionuclideson to catchment soils and bottom sediments. In thelonger term, the long lived 137Cs and 90Sr comprisedthe major component of contamination of aquaticecosystems. Although the levels of theseradionuclides in rivers were low after the initial

0 10 20 30 40 50

Time after deposition (years)

0.0

2.0

4.0

6.0

8.0

10.0

1

2

3

4

Cae

sium

-137

in w

ood

(Bq

/kg)

FIG. 3.43. Predicted 137Cs activity concentration in woodfor different types of forest soil and ages of trees calculatedusing a computer model, FORESTLAND, for a depositionof 1 kBq/m2 [3.87]. 1, 2: automorphic soil, 3, 4: semi-hydromorphic soil; 1, 3: initial age 20 years; 2, 4: initial age80 years.

0

500

1000

1500

2000

2500

3000

3500

1986 1988 1990 1992 1994 1996 1998 2000

Year

Max.

Median

Min.

Bq

/kg

dry

wei

ght

FIG. 3.44. Summary of predictions of pine wood contami-nation with 137Cs in the Zhytomyr region of Ukraine madeby use of 11 models within the IAEA’s BIOMASSprogram. Caesium-137 soil deposition was about555 kBq/m2. Max., Median and Min. indicate maximum,median and minimum values of pooled model predictions,respectively. The points show means of measured values,and the broken lines indicate the maximum and minimumvalues of measurements [3.88].

47

peak, temporary increases in activity concentrationsduring flooding of the Pripyat River caused seriousconcern in areas using water from the Dniepercascade.

Lakes and reservoirs were contaminated byfallout on the water surface and by transfers ofradionuclides from the surrounding catchmentareas. Radionuclide concentrations in waterdeclined rapidly in reservoirs and in those lakeswith significant inflow and outflow of water (openlake systems). In some cases, however, activityconcentrations of radiocaesium in lakes remainedrelatively high due to runoff from organic soils inthe catchment. In addition, internal cycling of radio-caesium in closed lake systems (i.e. lakes with littleinflow and outflow of water) led to much higheractivity concentrations in their water and aquaticbiota than were typically seen in open lakes andrivers.

Bioaccumulation of radionuclides (particu-larly radiocaesium) in fish resulted in activityconcentrations (both in the most affected regionsand in western Europe) that were in some casessignificantly above the permissible levels forconsumption [3.89–3.94]. In some lakes in Belarus,the Russian Federation and Ukraine theseproblems have continued to the present day andmay continue for the foreseeable future. Freshwaterfish provide an important source of food for manyinhabitants of the contaminated regions. In theDnieper cascade in Ukraine, commercial fisheriescatch more than 20 000 t of fish per year. In someparts of western Europe, particularly parts ofScandinavia, radiocaesium activity concentrationsin fish are still relatively high [3.95].

The marine systems closest to Chernobyl arethe Black Sea and the Baltic Sea — both severalhundred kilometres from the site. Radioactivity inthe water and fish of these seas has been intensivelystudied since the Chernobyl accident. Since theaverage deposition to these seas was relatively low,and owing to the large dilution in marine systems,radionuclide concentrations were much lower thanin freshwater systems [3.96].

3.5.2. Radionuclides in surface waters

3.5.2.1. Distribution of radionuclides between dissolved and particulate phases

Retention of radionuclide fallout bycatchment soils and river and lake sediments playsan important role in determining subsequent

transport in aquatic systems. The fraction of a radio-nuclide that is adsorbed to suspended particles(which varies considerably in surface waters)strongly influences both its transport and its bioac-cumulation. Most 90Sr is present in the dissolvedphase (0.05–5% in the solid phase), but in the nearzone a significant proportion of strontium falloutwas in the form of fuel particles. The soils of theCEZ are heavily contaminated with 90Sr (seeFig. 7.7), and some of it is washed off during floodevents when the low lying areas become inundated.

In the Pripyat River, during the first decadeafter the accident approximately 40–60% of radio-caesium was found in the particulate phase [3.97],but estimates in other systems [3.98] vary from 4%to 80%, depending on the composition and concen-tration of the suspended particles and on the waterchemistry. Fine clay and silt particles absorb radio-caesium more effectively than larger, less reactivesand particles. Sandy river beds, even close to thereactor, were relatively uncontaminated, but fineparticles transported radiocaesium over relativelylarge distances. The settling of fine particles in thedeep parts of the Kiev reservoir led to high levels ofcontamination of bed sediments [3.99].

Measurements of the distribution of radio-nuclides between the dissolved and particulatephases in Pripyat River water showed that thestrength of adsorption to suspended particlesincreases in the following order: 90Sr, 137Cs,transuranic elements (239,240Pu, 241Am) [3.100].There is a possibility that natural organic colloidsmay determine the stability of transuranic elementsin surface water and in their transport from contam-inated soil; such colloids have less effect on 90Sr and137Cs [3.101].

Generally in marine systems, lower particlesorption capacities and higher concentrations ofcompeting ions (i.e. higher salinity) tend to makeparticle sorption of radionuclides less significantthan in freshwaters. In the Baltic Sea after theChernobyl accident less than 10% of 137Cs wasbound to particles and the average particulatesorbed fraction was approximately 1% [3.102,3.103]. In the Black Sea the particulate boundfraction of 137Cs was less than 3% [3.96].

3.5.2.2. Radioactivity in rivers

Initial radioactivity concentrations in riversclose to Chernobyl (the Pripyat, Teterev, Irpen andDnieper Rivers) were largely due to directdeposition of radioactivity on to the river surface.

48

The highest concentrations of radionuclides wereobserved in the Pripyat River at Chernobyl, wherethe 131I activity concentration was up to 4440 Bq/L(Table 3.7). In all water bodies the radioactivitylevels declined rapidly during the first few weeks,due to decay of short lived isotopes and absorptionof nuclides to catchment soils and river bedsediments.

Over longer time periods after the falloutoccurred, relatively long lived 90Sr and 137Cs retainedin catchment soils are slowly transferred to riverwater by erosion of soil particles and by desorptionfrom soils. The rates of transfer are influenced by theextent of soil erosion, the strength of radionuclidebinding to catchment soils and migration down thesoil profile. An example time series of 90Sr and 137Csactivity concentrations in the water of the PripyatRiver near Chernobyl is shown in Fig. 3.45.

After the Chernobyl accident, watermonitoring stations were established within theexclusion zone and along the major rivers todetermine the concentrations of radionuclides andtheir total fluxes. Measurements from these stationsallow estimates to be made of radionuclide fluxes of90Sr and 137Cs into and out of the CEZ. Themigration of 137Cs has decreased markedly with timeand shows relatively little change from upstream todownstream of the CEZ (see Fig. 3.46(a)).

In contrast, the transboundary migration of90Sr has fluctuated yearly depending on the extentof annual flooding along the banks of the PripyatRiver (Fig. 3.46(b)). There is also a significant fluxfrom the CEZ — fluxes downstream of the zone aremuch higher than those upstream. Note, however,that the extent of washout of radionuclides by theriver system is only a very small percentage of thetotal inventory contained in the catchment area.

The decline in 90Sr and 137Cs activity concen-trations occurred at a similar rate for different riversin the vicinity of Chernobyl and in rivers in westernEurope [3.108]. Measurements of 137Cs activityconcentration in different European rivers(Fig. 3.47) show a range of approximately a factor of

TABLE 3.7. MAXIMUM RADIONUCLIDEACTIVITY CONCENTRATIONS (DISSOLVEDPHASE) MEASURED IN THE PRIPYAT RIVERAT CHERNOBYL [3.91, 3.104, 3.105]

Maximum concentration (Bq/L)

Caesium-137 1591

Caesium-134 827

Iodine-131 4440

Strontium-90 30

Barium-140 1400

Molybdenum-99 670

Ruthenium-103 814

Ruthenium-106 271

Cerium-144 380

Cerium-141 400

Zirconium-95 1554

Niobium-95 420

Plutonium-241 33

Plutonium-239, 240 0.4

0.01

0.10

1.00

10.00

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1

1

2

Bq

/L

1 Strontium-902 Caesium-137, dissolved

Year

FIG. 3.45. Monthly averaged 90Sr and 137Cs activity concen-trations in the Pripyat River near Chernobyl [3.106].

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0Áåëàÿ Ñîðîêà

×åðíîáûëü

Belaya Soroka

Chernobyl

0.02.04.06.08.0

10.012.014.016.018.020.0

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Year

Cae

sium

-137

(TB

q)

Str

ontiu

m-9

0 (T

Bq

)

(a)

(b)

FIG. 3.46. Annual fluxes of 137Cs (a) and 90Sr (b) in thePripyat River at Belaya Soroka, near the Belarus–Ukraineborder (inlet to the CEZ), and downstream of Chernobyl(outlet of the CEZ) [3.107].

49

30, even when differences in fallout have beenaccounted for. In small catchments [3.67, 3.112,3.113], highly organic soils (particularly saturatedpeat soils) released up to an order of magnitudemore radiocaesium to surface waters than somemineral soils. Thus rivers in Finland with large areasof wet organic soils in the catchment have higherradiocaesium concentrations (per unit ofradioactive fallout) than rivers with predominantlymineral catchments [3.109, 3.111].

3.5.2.3. Radioactivity in lakes and reservoirs

In the affected areas of Belarus, the RussianFederation and Ukraine many lakes were signifi-cantly contaminated by radionuclides. In most lakesradionuclides were well mixed throughout the lakewater during the first days to weeks after the falloutoccurred. In deep lakes such as Lake Zurich (meandepth 143 m), however, it took several months forfull vertical mixing to take place [3.114]. In someareas of northern Europe lakes were covered withice at the time of the accident and maximum activityconcentrations in lake waters were only observedafter the ice melted.

Radionuclides deposited to a lake or reservoirare removed through water outflow and by transferto bed sediments. As in rivers, radiocaesium activityconcentrations in lakes declined relatively rapidlyduring the first weeks to months after the fallout.This was followed by a slower decline over a periodof years as radiocaesium became more stronglyabsorbed to catchment soils and lake sediments andmigrated to deeper layers in the soil and sediments.Figure 3.48 illustrates the temporal change in 137Csactivity concentration in lakes using measurements

from Lake Vorsee, a small shallow lake inGermany.

Inputs to lakes also result from transport ofradionuclides from contaminated catchment soils.In the longer term (secondary phase), 137Cs activityconcentrations in Lake Vorsee remained muchhigher than in most other lakes due to inputs of137Cs from organic soils in the catchment andremobilization from bed sediments (Fig. 3.48[3.93]). In Devoke Water (UK), radiocaesiumflowing from organic catchment soils maintainedactivity concentrations in the water that wereapproximately an order of magnitude higher than innearby lakes with mineral catchments [3.112]. Insome cases, lakes in western Europe with organiccatchments had activity concentrations in water andfish similar to those in the more highly contaminatedareas of Belarus and Ukraine.

Long term contamination can also be causedby remobilization of radionuclides from bedsediments [3.115]. In some shallow lakes wherethere is no significant surface inflow and outflow ofwater, the bed sediments play a major role incontrolling radionuclide activity concentration inthe water. Such lakes have been termed ‘closed’lakes [3.105, 3.116]. The more highly contaminatedwater bodies in the Chernobyl affected areas are theclosed lakes of the Pripyat floodplain within theCEZ. During 1991 137Cs activity concentrations inthese lakes were up to 74 Bq/L (Lake Glubokoye)and 90Sr activity concentrations were between 100and 370 Bq/L in six of the 17 water bodies studied[3.105]. Seventeen years after the accident therewere still relatively high activity concentrations inthe closed lakes in the CEZ [3.117] and at quitelarge distances from the reactor; for example,during 1996 Lakes Kozhanovskoe and Svyatoe in

0 5 10 15

Time since accident (years)

KymijokiKokemaenjokiOulujokiKemijokiTornionjokiDora BalteaDnieperSozhIputBesedPripyat (Mozyr)DanubePripyat (Chernobyl)

Cae

sium

-137

in w

ater

per

Bq

/m2

of fa

llout

(m–1

)

0.1

0.01

0.001

0.0001

0.00001

FIG. 3.47. Caesium-137 activity concentration in differentrivers per unit of deposition [3.109–3.111].

0.01

0.1

1

10

100

1000

10 000

0 5 10 15 20

Time (years)

Water

Pike (predatory)

Small Cyprinidae (non-predatory)

Cae

sium

-137

in w

ater

(Bq

/L) a

nd fi

sh (B

q/k

g)

FIG. 3.48. Time series of 137Cs in Lake Vorsee, Germany[3.93].

50

the Bryansk region of the Russian Federation(approximately 200 km from Chernobyl) contained0.6–1.5 Bq/L of 90Sr and 10–20 Bq/L of 137Cs(Fig. 3.49). Activity concentrations in water werehigher than in many lakes close to Chernobyl,because of remobilization from sediments in theseclosed lakes [3.116]. The Russian intervention levelfor drinking water of 11 Bq/L for 137Cs [3.119] isshown for comparison.

(a) Chernobyl cooling pond

The Chernobyl cooling pond covers an area ofapproximately 23 km2 and contains approximately149 × 106 m3 of water. It is located between theformer Chernobyl nuclear power plant and thePripyat River. The total inventory of radionuclides

in the pond is in excess of 200 TBq (about 80% is137Cs, 10% 90Sr, 10% 241Pu and less than 0.5% eachis of 238Pu, 239Pu, 240Pu and 241Am), with the deepsediments containing most of the radioactivity. The90Sr annual flux to the Pripyat River from thecooling pond via groundwater was estimated in arecent study to be 0.37 TBq [3.120]. This is a factorof 10–30 less than the total annual 90Sr fluxes in thePripyat River in recent years. Thus the cooling pondis not a significant source of 90Sr contamination ofthe Pripyat River. Radionuclide activity concentra-tions in the cooling pond water (Fig. 3.50) arecurrently low, at 1–2 Bq/L. Seasonal variations of137Cs concentration are caused by changes in algaeand phytoplankton biomass [3.121].

(b) Reservoirs of the Dnieper cascade

The Dnieper cascade reservoirs were signifi-cantly affected, due to both atmospheric fallout andriverine inputs from the contaminated zones (seeFig. 3.6). The different affinities of 137Cs and 90Sr forsuspended matter influenced their transportthrough the Dnieper system. Caesium-137 tends tobecome fixed on to clay sediments, which aredeposited in the deeper sections of the reservoirs,particularly in the Kiev reservoir (Fig. 3.51). Owingto this process, very little 137Cs flows through thecascade of reservoirs, and consequently the presentconcentration entering the Black Sea is indistin-guishable from the background level.

However, although the 90Sr activity concen-tration decreases with distance from the source

0

10

20

30

40

1992 1994 1996 1998 2000 2002

Year

Svyatoe

Kozhanovskoe

IL, DIL

Cae

sium

-137

(Bq

/L)

FIG. 3.49. Dynamics of 137Cs activity concentration in thewater of Lakes Svyatoe and Kozhanovskoe (RussianFederation), approximately 200 km from Chernobyl[3.118].

0.1

1.0

10.0

100.0

1000.0

Date

Caesium-137

Strontium-90

Con

cent

ratio

n (B

q/L

)

5 Jan. 1986 5 Jan. 1988 4 Jan. 1990 4 Jan. 1992 3 Jan. 1994 3 Jan. 1996 2 Jan. 1998 2 Jan. 2000 1 Jan. 2002

FIG. 3.50. Monthly averaged 137Cs and 90Sr activity concentrations in the water of the Chernobyl cooling pond[3.121].

51

(mainly due to dilution), about 40–60% passesthrough the cascade and reaches the Black Sea.Figure 3.52 shows the trend in average annual 90Sractivity concentration in the Dnieper reservoirssince the accident. As 137Cs is trapped by sedimentsin the reservoir system, activity concentrations inthe lower part (Novaya Kakhovka) of the systemare orders of magnitude lower than in the Kievreservoir (Vishgorod). In contrast, 90Sr is notstrongly bound by sediments, so activity concentra-tions in the lower part of the river–reservoir systemare similar to those measured in the Kiev reservoir.

The peaks in 90Sr activity concentration in thereservoirs of the Dnieper cascade (Fig. 3.52) werecaused by flooding of the most contaminatedfloodplains in the CEZ; for example, flooding of thePripyat River, caused by blockages of the river byice in the winter of 1990–1991, led to temporarysignificant increases in 90Sr in this system, but didnot significantly affect 137Cs levels. Activity concen-trations of 90Sr in the river water increased fromabout 1 to 8 Bq/L for a five to ten day period [3.105].Similar events took place during the winter flood of1994, during summer rainfall in July 1993 andduring the high spring flood in 1999 [3.122].

(c) Radionuclide runoff from catchment soils

Small amounts of radionuclides are erodedfrom soils and transferred to rivers, lakes andeventually the marine system. Such transfers cantake place through erosion of surface soil particlesand by runoff in the dissolved phase. Studies of

nuclear weapon tests and of Chernobyl 90Sr in rivers[3.109, 3.110, 3.123, 3.124] suggest long term lossrates of about 1–2%/a or less from the terrestrialenvironment to rivers. Thus, in the long term, runoffof radionuclides does not significantly reduce theamount of radioactivity in the terrestrial system,although it does result in continuing (low level)contamination of river and lake systems.

3.5.2.4. Radionuclides in freshwater sediments

Bed sediments are an important long termsink for radionuclides. Radionuclides can becomeattached to suspended particles in lakes, which thenfall and settle on bed sediments. Radionuclides inlake water can also diffuse into bed sediments.These processes of radionuclide removal from lakewater have been termed ‘self-cleaning’ of the lakeor reservoir [3.114].

In the Chernobyl cooling pond approximatelyone month after the accident, most of the radioac-tivity was found in bed sediments [3.91, 3.97]. In thelong term, approximately 99% of the radiocaesiumin a lake is typically found in the bed sediment. Inmeasurements in Lake Svyatoe (Kostiukovichyregion, Belarus) during 1997, approximately 3 × 109

Bq of 137Cs was in the water and 2.5 × 1011 Bq was insediments [3.125]. In Lake Kozhanovskoe in theRussian Federation, approximately 90% of theradiostrontium was found in the bed sedimentsduring 1993–1994 [3.126].

In the rapidly accumulating sediments of theKiev reservoir, the layer of maximum radiocaesium

Dnieper River

Contaminated areas (kBq/m2)

Less than 37

37–74

74–185

185–370

370–555

555–925

Pripyat River

Teterev River

Irpen River

Vishgorod

Kiev hydroelectric power plant

>925

FIG. 3.51. Caesium-137 in the bottom sediments of the Kiev reservoir [3.97].

52

concentration is now buried several tens ofcentimetres below the sediment surface (Fig. 3.53).In more slowly accumulating sediments, however,the peak in radiocaesium activity concentrationremains near the sediment surface. Peaks in thesediment layer contamination in 1988 and 1993reflect the consequences of high summer rainfallfloods and soil erosion events.

Close to Chernobyl, a high proportion of thedeposited radioactive material was in the form of

fuel particles (see Section 3.1). Radionuclidesdeposited as fuel particles are generally less mobilethan those deposited in a dissolved form. In thesediments of Lake Glubokoye in 1993, most fuelparticles remained in the surface 5 cm of sediment[3.126]. Fuel particle breakdown was at a muchlower rate in lake sediments than in soils. Studies inthe cooling pond have shown that the half-life offuel particles in sediments is approximately 30years, so by 2056 (70 years after the Chernobylaccident) one quarter of the radioactive materialdeposited as fuel particles in the cooling pond willstill remain in fuel particle form [3.39].

3.5.3. Uptake of radionuclides to freshwater fish

Consumption of freshwater fish is animportant part of the aquatic pathway for thetransfer of radionuclides to humans. Although thetransfer of radionuclides to fish has been studied inmany countries, most attention here is focused onBelarus, the Russian Federation and Ukraine,because of the higher contamination of waterbodies in these areas.

3.5.3.1. Iodine-131 in freshwater fish

There are limited data on 131I in fish.Iodine-131 was rapidly absorbed by fish in the Kievreservoir, with maximum concentrations in fishbeing observed in early May 1986 [3.91]. Activityconcentrations in fish muscle declined from around6000 Bq/kg fresh weight on 1 May 1986 to 50 Bq/kgfresh weight on 20 June 1986. This represents a rateof decline similar to that of the physical decay of131I. Owing to the rapid physical decay, 131I activityconcentrations in fish became insignificant a fewmonths after the accident.

3.5.3.2. Caesium-137 in freshwater fish and other aquatic biota

During the years following the Chernobylaccident there have been many studies of the levelsof radiocaesium contamination of freshwater fish.As a result of high radiocaesium bioaccumulationfactors, fish have remained contaminated in someareas, despite low radiocaesium levels in water.Uptake of radiocaesium into small fish wasrelatively rapid, the maximum concentration beingobserved during the first weeks after the accident[3.93, 3.95]. Due to the slow uptake rates of radio-caesium in large predatory fish (pike, eel),

1

10

100

1000

1987 1989 1991 1993 1995 1997 1999 2001

Vishgorod Novaya Kakhovka

0

100

200

300

400

500

600

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Year

Vishgorod Novaya Kakhovka

Bq

/m3

Bq

/m3

Year

(a)

(b)

FIG. 3.52. Annually averaged 137Cs (a) and 90Sr (b)activity concentrations in the water of the Kiev reservoir(Vishgorod) near the dam and in the Kakhovka reservoirof the Dnieper cascade [3.107].

0 5000 10 000 15 000 20 000 25 000 30 000

0–2

8–10

16–18

24–26

32–34

40–42

48–50

56–58

64–66

72–74

Z (cm)

Cs , bottom

1988 high summer rain

1993 high summer rain fld

137

Bq/kg

Cs , bottom

1986



137

FIG. 3.53. Activity concentrations of 137Cs in the deep siltdeposits in the upper part of the Kiev reservoir, 1998[3.106].

53

maximum activity concentrations were notobserved until six to 12 months after the falloutevent [3.93, 3.127] (Fig. 3.48).

In the Chernobyl cooling pond, 137Cs activityconcentrations in carp, silver bream, perch and pikewere about 100 kBq/kg fresh weight in 1986,declining to a few tens of kBq/kg in 1990 [3.89, 3.91]and 2–6 kBq/kg in 2001. In some closed lakes in thevicinity of the Chernobyl nuclear power plant[3.121] the 137Cs activity concentration in predatoryfish 15 years after the accident was 10–27 kBq/kgfresh weight. Typical changes with time in 137Cs intwo fish species over 16 years after the accident areillustrated in Fig. 3.54.

In the Kiev reservoir, 137Cs activity concentra-tions in fish were 0.6–1.6 kBq/kg fresh weight (in1987) and 0.2–0.8 kBq/kg fresh weight (for 1990–1995), and declined to 0.2 kBq/kg or less for adultnon-predatory fish in 2002. Values for predatoryfish species were 1–7 kBq/kg during 1987 and0.2-1.2 kBq/kg from 1990 to 1995 [3.106].

In the lakes of the Bryansk region of theRussian Federation, approximately 200 km fromChernobyl, 137Cs activity concentrations in anumber of fish species varied within the range of0.2–19 kBq/kg fresh weight during the period 1990–1992 [3.126, 3.150]. In shallow closed lakes such asLake Kozhanovskoe (Bryansk region of the RussianFederation) and Lake Svyatoe (Kostiukovichy

region in Belarus), 137Cs activity concentrations infish have declined slowly in comparison with fish inrivers and open lake systems, due to the slowdecline in 137Cs activity concentrations in the waterof the lakes [3.92, 3.116].

In western Europe, lakes in some parts ofFinland, Norway and Sweden were particularlyheavily contaminated. About 14 000 lakes inSweden had fish with 137Cs activity concentrationsabove 1500 Bq/kg fresh weight (the Swedishguideline value) in 1987 [3.90]. In some alpine lakesin Germany, 137Cs activity concentrations in pikewere up to 5000 Bq/kg fresh weight shortly after theChernobyl accident [3.93]. In Devoke Water in theUK Lake District, perch and brown trout containedaround 1000 Bq/kg fresh weight in 1988, decliningslowly to a few hundreds of Bq/kg in 1993 [3.129].

Bioaccumulation of radiocaesium in fish isdependent on a number of factors. The presence ofpotassium in a lake or river influences the rate ofaccumulation of radiocaesium in fish because of itschemical similarity to caesium [3.130]. Stronginverse relationships were observed between thelake water potassium concentration and the 137Csactivity concentration in fish following nuclearweapon testing [3.128, 3.130] and the Chernobylaccident [3.94]. In the long term, activity concentra-tions in predatory fish were significantly higher thanin non-predatory fish, and large fish tended to havehigher activity concentrations than small fish. Thehigher activity concentration in large fish is termedthe ‘size effect’ [3.127, 3.131] and is due to metabolicand dietary differences. In addition, older, largerfish were exposed to higher levels of 137Cs in thewater than younger, smaller fish.

The differences in the bioaccumulation ofradiocaesium in different fish species can be signif-icant; for example, in Lake Svyatoe in Belarus, thelevels in large pike and perch (predatory fish) werefive to ten times higher than in non-predatory fishsuch as roach. Similarly, bioaccumulation factors inlakes with a low potassium concentration can beone order of magnitude higher than in lakes with ahigh potassium concentration. Thus it was observed[3.94] that fish from lakes in the agricultural areas ofBelarus (where runoff of potassium fertilizer issignificant) had lower bioaccumulation factors thanfish from lakes in seminatural areas.

3.5.3.3. Strontium-90 in freshwater fish

Strontium behaves, chemically and biologi-cally, in a similar way to calcium. Strontium is most

0

100

200

300

400

500

600

700

800

900

1000

5891 1689 1

7898891 1

989 1099

1991 9129 3991

49919915 6991

9917 991

8 99910002

0

200

400

600

800

1000

1200

1400

1600

1800

9158 6891

78918891

9891 9109 1991

2991 9139 4991

59916991

7991 9189 9991

0002

Year

Year

Bq

/kg

fres

h w

eigh

tB

q/k

g fr

esh

wei

ght

(a)

(b)

FIG. 3.54. Averaged 137Cs activity concentrations in non-predatory (bream (a)) and predatory (pike (b)) fish; thefish are from the Kiev reservoir [3.106].

54

strongly bioaccumulated in low calcium (‘soft’)waters. The relatively low fish–water bioaccumu-lation factors for 90Sr (of the order of 102 L/kg) andthe lower fallout of this isotope meant that 90Sractivity concentrations in fish were typically muchlower than those of 137Cs. In the Chernobyl coolingpond, 90Sr activity concentrations were around2 kBq/kg (whole fish) in fish during 1986, comparedwith around 100 kBq/kg for 137Cs in 1993 [3.91]. In2000, for the most contaminated lakes aroundChernobyl, the maximum level of 90Sr concentrationin the muscles of predatory and non-predatory fishvaried between 2 and 15 Bq/kg fresh weight. In2002–2003, 90Sr in fish in reservoirs of the Dniepercascade was only 1–2 Bq/kg, which is close to thepre-Chernobyl level. Freshwater molluscs showedsignificantly higher bioaccumulation of 90Sr thanfish. In the Dnieper River, molluscs had approxi-mately ten times more 90Sr in their tissues than infish muscle [3.132]. Similarly, the bioaccumulationof 90Sr in the bones and skin of fish is approximatelya factor of ten times higher than in muscle [3.130].

3.5.4. Radioactivity in marine ecosystems

Marine ecosystems were not seriously affectedby fallout from Chernobyl, the nearest seas to thereactor being the Black Sea (around 520 km) andthe Baltic Sea (about 750 km). The primary route ofcontamination of these seas was atmosphericfallout, with smaller inputs from riverine transportoccurring over the years following the accident.Surface deposition of 137Cs was approximately2.8 PBq over the Black Sea [3.96, 3.133] and 3.0 PBqover the Baltic Sea [3.105].

3.5.4.1. Distribution of radionuclides in the sea

Radioactive fallout on to the surface of theBlack Sea was not uniform and mainly occurred

during 1 and 3 May 1986 [3.105, 3.133]. In the BlackSea surface water concentrations of 137Cs rangedfrom 15 to 500 Bq/m3 in June–July 1986, although by1989 horizontal mixing of surface waters hadresulted in relatively uniform concentrations in therange of 41–78 Bq/m3 [3.105], which by 2000 haddeclined to between 20 and 35 Bq/m3 [3.96].

In addition to the caesium isotopes, short livedradionuclides such as 144Ce and 106Ru wereobserved. The inventory of 137Cs in the water of theBlack Sea due to the Chernobyl deposition doubledthe existing inventory of 137Cs from global falloutfrom atmospheric nuclear weapon testing toapproximately 3100 TBq. The amount of 90Srincreased by 19% in comparison with the pre-Chernobyl period and was estimated to be about1760 TBq [3.96, 3.105]. Vertical mixing of surfacedeposited radioactivity also reduced the maximumconcentrations observed in water over the monthsto years after the fallout. Removal of radioactivityto deeper waters steadily reduced 137Cs activityconcentrations in the surface (0–50 m) layer of theBlack Sea. The present situation with regard to theBlack Sea marine environment is shown in Table 3.8[3.96].

A significant proportion of the 137Cs, 90Sr and239,240Pu in the Black Sea originated from nuclearweapon testing rather than from the Chernobylaccident. The riverine radionuclide input to theBlack Sea was much less significant than directatmospheric fallout to the sea surface. Over theperiod 1986–2000, riverine input of 137Cs was only4–5% of the atmospheric deposition, although 90Srriverine inputs were more significant, being approx-imately 25% of the total inputs from atmosphericdeposition [3.96, 3.134]. For the Baltic Sea, riverineinputs were at a similar level as for the Black Sea,being approximately 4% and 35% of atmosphericfallout for 137Cs and 90Sr, respectively [3.135]. Thegreater relative riverine input of 90Sr is due to itsweaker adsorption to catchment soils and lake and

TABLE 3.8. RADIONUCLIDES IN VARIOUS SAMPLES TAKEN FROM THE BLACK SEA COASTDURING 1998–2001 [3.96]

Environmental sample Caesium-137 Strontium-90Plutonium-239,

240

Sea water (Bq/m3) 14–29 12–28 (2.4–28) × 10–3

Beach sand and shells (Bq/kg) 0.9–8.0 0.5–60 (shell) (80–140) × 10–3

Seaweeds, Cystoseira barbata (Bq/kg fresh weight) 0.2–2.3 0.4–0.9 (9.0–14) × 10–3

Mussels, Mytilus galloprovincialis (tissue, Bq/kg fresh weight) 0.3–1.7 0.02–3.2 (1.5–2.5) × 10–3

Fish, Sprattus sprattus, Trashurus (Bq/kg fresh weight) 0.2–6.0 0.02–0.7 (0.3–0.5) × 10–3

55

river sediments and to lower 90Sr atmosphericfallout (compared with 137Cs) at large distancesfrom the Chernobyl reactor site. Sedimentationprocesses in the marine environment, as in thefreshwater environment, are an important factor inthe ‘self-purification’ of the aquatic ecosystem.However, the sedimentation rate for the Black Seais relatively low [3.96].

Data presented in Fig. 3.55 demonstrate that,in the central deep basin of the Black Sea, theChernobyl deposition is covered by a layer of lessthan 1 cm of sediment formed since the accident[3.96].

Due to dilution and sedimentation, theconcentration of 137Cs quickly declined, reducingthe seawater contamination at the end of 1987 totwo to four times lower than that observed in thesummer of 1986. The average 137Cs activity concen-tration in the Baltic Sea estimated in Ref. [3.136] forthe initial period after deposition was approxi-mately 50 Bq/m3, with maximum values two to fourtimes greater being observed in some areas of thesea.

3.5.4.2. Transfers of radionuclides to marine biota

Bioaccumulation of radiocaesium and radio-strontium in marine systems is generally lower thanin freshwater, because of the much higher contentof competing ions in saline water. The lower bioac-cumulation of 137Cs and 90Sr in marine systems, andthe large dilution in these systems, meant thatactivity concentrations in marine biota after theChernobyl accident were relatively low. Table 3.8gives examples of 137Cs, 90Sr and 239,240Pu in waterand marine biota of the Black Sea during the period1998–2001 [3.96]. Detailed data on Baltic Sea fishcontamination during the post-Chernobyl decadesare available in Ref. [3.136], which shows that mostspecies of fish had a relatively low level of radio-caesium contamination, in most cases in the rangeof 30–100 Bq/kg or less during the period up to1995.

3.5.5. Radionuclides in groundwater

3.5.5.1. Radionuclides in groundwater: Chernobyl exclusion zone

Sampling of groundwater in the affected areasshowed that radionuclides can be transferred fromsurface soil to groundwater. However, the level ofthe groundwater contamination in most areas

(excluding locations of radioactive waste storageand the Chernobyl shelter industrial site) is low.Furthermore, the rates of migration from the soilsurface to groundwater are also very low. Someareas in the CEZ with relatively fast radionuclidemigration to the aquifers were found in areas withmorphological depressions [3.137]. Horizontalfluxes of radionuclides in groundwaters are alsovery low because of the slow flow velocity ofgroundwaters and high retardation of radionuclides[3.138].

Short lived radionuclides are not expected toaffect groundwater supplies, because groundwaterresidence times are much longer than the physicaldecay time of short lived nuclides. The onlysignificant transfer of radionuclides to groundwaterhas occurred within the CEZ. In some wells duringthe past ten years the 137Cs activity concentrationhas declined, while that of 90Sr has continued toincrease in shallow groundwaters (Fig. 3.56).Transfer of radionuclides to groundwater hasoccurred from radioactive waste disposal sites in the

0 500 1000 1500 2000

0–0.15

0.30–0.50

0.70–0.90

1.00–1.20

1.40–1.60

1.80–2.00

2.25–2.50

2.75–3.00

Caesium-137 activity (Bq/kg)

Slic

e (c

m)

FIG. 3.55. Caesium-137 profile in the bottom sediment ofthe Black Sea (core BS-23/2000), taken during the IAEABlack Sea expedition in 2000 [3.96].

8 D

ec. 1

988

8 D

ec. 1

989

8 D

ec. 1

990

8 D

ec. 1

991

7 D

ec. 1

992

7 D

ec. 1

993

7 D

ec. 1

994

7 D

ec. 1

995

6 D

ec. 1

996

6 D

ec. 1

997

6 D

ec. 1

998

6 D

ec. 1

999

5 D

ec. 2

000

Act

ivity

con

cent

ratio

n (B

q/L

)

100.00

10.00

1.00

0.10

0.01

Caesium-137Strontium-90

FIG. 3.56. Caesium-137 and 90Sr in shallow groundwater inthe Red Forest area near the Chernobyl industrial site[3.139].

56

CEZ. After the accident, FCM and radioactivedebris were temporarily stored at industrial sites atthe power station and in areas near the floodplain ofthe Pripyat River. In addition, trees from the RedForest were buried in shallow unlined trenches. Atthese waste disposal sites, 90Sr activity concentra-tions in groundwaters are, in some cases, of theorder of 1000 Bq/L [3.140]. The health risks fromgroundwater consumption by hypothetical residentsreturning to these areas, however, were low incomparison with external radiation and radiationdoses from the intake of foodstuffs [3.138].

Although there is a potential for off-sitetransfer of radionuclides from the disposal sites,Bugai et al. [3.138] concluded that this will not besignificant in comparison with washout of surfacedeposited radioactivity. Studies have shown thatgroundwater fluxes of radionuclides are in thedirection of the Pripyat River, but the rate of radio-nuclide migration is very low and does not present asignificant risk to the Dnieper reservoir system. Off-site transport of groundwater contamination aroundthe shelter is also expected to be insignificant,because radioactivity in the shelter is separatedfrom groundwaters by an unsaturated zone of 5–6 mthickness, and groundwater velocities are low[3.138]. It is predicted that the maximum subsurface90Sr transport rate from waste disposal sites tosurface water bodies will occur from 33 to 145 yearsafter the accident. The maximum cumulativetransport from all the sources described above isestimated to be 130 GBq over approximately 100years, or 0.02%/a of the total inventory within thecontaminated catchments. Integrated radionuclidetransport for a 300 year period is estimated byBugai et al. [3.138] to be 15 TBq, or 3% of the totalinitial inventory of radioactive material within thecatchments (Fig. 3.57).

The water level of the Chernobyl cooling pondsignificantly influences groundwater flows aroundthe Chernobyl site. Currently, the water level of thecooling pond is kept artificially high, at 6–7 m abovethe average water level in the Pripyat River.However, this will change when the cooling systemsat the Chernobyl nuclear power plant are finallyshut down and the pumping of water into the pondis terminated. As the pond dries out, the sedimentswill be partly exposed and subject to dispersal.Recent studies suggest that the best strategy forremediation of the cooling pond is to allow thewater level to decline naturally, with some limitedaction to prevent secondary wind resuspensionusing phytoremediation techniques [3.141].

When the water level in the cooling ponddeclines to that of the river water surface level, thiswill lead to reduction of groundwater fluxes fromthe Chernobyl industrial site towards the river. Thiswill also reduce radionuclide fluxes from the mainradioactive waste disposal sites and the shelter tothe Dnieper cascade. The groundwater fluxes of 90Srfrom the Chernobyl shelter to the Pripyat Riverhave been modelled within the framework ofenvironmental impact assessment studies for theNSC to be erected above the shelter [3.142] (seeFig. 3.58). It has been predicted that it would takeapproximately 800 years for 90Sr to reach thePripyat River. With its half-life of 29.1 years, theactivity of 90Sr would reduce to an insignificant levelduring this time. Thus infiltration of 90Sr from theshelter will not cause harmful impacts on thePripyat River. Caesium-137 moves much moreslowly than 90Sr, and even after 2000 years its plumeis predicted to be only 200 m from the shelter.

Owing to its high adsorption to the soil matrix,239Pu migrates at a much slower rate than 90Sr or137Cs; however, its half-life is much longer (24 000

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350

Time (years)

Total groundwater transport of 90Sr to the Pripyat River

1

2 3

4

5

Str

ontiu

m-9

0 (G

Bq

/a)

1. Total transport2. Catchment of Lake Azbuchin3. Catchment of Pripyat bay4. Budbaza temporary waste disposal/storage site5. Chernobyl nuclear power plant industrial site

FIG. 3.57. Prediction of 90Sr transport via the groundwaterpathway to the Pripyat River in the Chernobyl nuclearpower plant near zone [3.138].

800 900 1000 1100 1200 1300 1400 1500 1600 1700

110

100

90

80

Hei

ght

ab

ove

sea

leve

l (m

)

1�x 1010

1�x 109

1�x 108

1�x 107

1�x 106

1�x 105

1�x 104

1�x 103

1�x 102

Distance (m)

800 900 1000 1100 1200 1300 1400 1500 1600 1700

Bq/m3

FIG. 3.58. Predicted 90Sr groundwater concentration(Bq/m3) in the vicinity of the Chernobyl shelter without theNSC after 100 years [3.142].

57

years). The maximum groundwater 239Pu influxfrom the shelter into the Pripyat River is predictedto be 2 Bq/s. When this influx is fully mixed with theaverage Pripyat River discharge of 400 m3/s, theresulting 239Pu concentration in the river would beonly 0.005 Bq/m3, as compared with the current239Pu level of 0.25 Bq/m3 [3.142]. In Ukraine theregulatory limit for 239Pu in water is 1 Bq/m3. Thusinfiltration of 239Pu from the shelter, even withoutthe NSC, will not cause any significant impact onthe Pripyat River.

3.5.5.2. Radionuclides in groundwater: outside the Chernobyl exclusion zone

The most detailed current studies ofgroundwater contamination in the far zone (beyondthe CEZ) [3.137, 3.143] have concluded that tenyears after the initial surface ground pollution, thelevels of 137Cs and 90Sr in groundwater of the upperhorizons of the aquifer were 40–50 mBq/L aroundKiev and 20–50 mBq/L in the Bryansk region of theRussian Federation and the majority of the contam-inated areas in Belarus. In these areas, far from theChernobyl reactor (in Belarus and the RussianFederation), the 137Cs activity concentration ofwater in the saturated zone of soils had a significantcorrelation with the 137Cs soil deposition. In most ofthe studied area the activity concentration ingroundwater (per unit of 137Cs soil deposition) wassignificantly lower than in most river and lakesystems. All studies reported that the radionuclideconcentration in the contaminated area outside theCEZ never exceeded the safety level forconsumption of water and was usually severalorders of magnitude below it.

After fallout from nuclear weapon testing, itwas observed that 90Sr in Danish groundwater was

approximately ten times lower than in surfacestreams [3.144]. Reference [3.144] also shows thatafter the Chernobyl accident, although there weremeasurable quantities of 137Cs in streams, activityconcentrations in groundwater were belowdetection limits.

3.5.5.3. Irrigation water

In the Dnieper River basin there is more than1.8 × 106 ha of irrigated agricultural land. Almost72% of this territory is irrigated with water from theKakhovka reservoir and other Dnieper reservoirs.Accumulation of radionuclides in plants onirrigated fields can take place via root uptake ofradionuclides introduced with irrigation water anddue to direct incorporation of radionuclides throughleaves due to sprinkling. However, in the case of theirrigated lands of southern Ukraine, radionuclidesin irrigation water did not add significant radioac-tivity to crops in comparison with that which hadbeen initially deposited in atmospheric fallout andsubsequently taken up in situ from the soil [3.145].

3.5.6. Future trends

3.5.6.1. Freshwater ecosystems

For the rivers and reservoirs of the Dniepersystem, the intensity of runoff of radionuclides willgradually reduce. In the worst case scenario, hydro-logical runoff during the next 50 years [3.146] wouldcause average concentrations of 137Cs and 90Srapproaching pre-accident levels. Contaminationlevels of the water and the main consumer fishspecies in the reservoirs of the middle and lowerDnieper River will approach background levels(Fig. 3.59). At the same time, in the isolated (closed)

0

100

200

300

400

500

600

700

800

900

1000

1996 2004 2012 2020 2028 2036 2044 2052

Year

Kiev reservoir

Kakhovka reservoir

Bq

/m3

(a)

0

100

200

300

400

500

600

700

800

900

1000

1996 2004 2012 2020 2028 2036 2044 2052

Year

Kiev reservoir

Kakhovka reservoir

Bq

/m3

(a)

FIG. 3.59. Predicted concentrations of 90Sr in water of the upper and downstream reservoirs for the worst (a) and best (b)probabilistic hydrological scenarios expected for the Pripyat River basin [3.146].

58

water bodies of the contaminated territories,increased contents of 137Cs, both in water andaquatic biota, will be maintained for severaldecades.

Recent data [3.95, 3.147] show that, at present,137Cs activity concentrations in surface water andfish are declining quite slowly. The effectiveecological half-life in water and young fish hasincreased from one to four years during the first fiveyears after the accident to six to 30 years in recentyears. Future contamination levels can be estimatedwith the use of an estimated long term decline ofradiocaesium activity concentrations in water andfish with an effective ecological half-life (Teff) of

approximately 20 years, although there is widevariation in the rates of decline [3.125].

Activity concentrations of radiocaesium inwater are, at present, relatively low (1 Bq/L atmost), except in the shallow closed lakes in the CEZand in other highly contaminated areas. Activityconcentrations are expected to continue to declineslowly during the coming decades. In some lakes,however, 137Cs activity concentrations in both waterand fish are expected to remain relatively high forsome decades, as illustrated in Tables 3.9 and 3.10.Activity concentrations of 90Sr in water were alsoestimated using a predicted Teff of 20 years. Thismay, again, be slightly conservative, as long term

TABLE 3.9. CAESIUM-137 ACTIVITY CONCENTRATIONS IN WATER IN VARIOUS CHERNOBYLAFFECTED LAKES AROUND EUROPE AND PREDICTIONS FOR 30, 50 AND 70 YEARS AFTERTHE ACCIDENT [3.125]

Measured 137Cs (Bq/L) (year of measurement)

Predicted 137Cs (Bq/L)

2016 2036 2056

Lake Kozhanovskoe, Russian Federation 7.0 (2001) 4.2 2.1 1.0

Kiev reservoir, Ukraine 0.028 (1998) 0.015 0.007 0.004

Chernobyl cooling pond 2.5 (2001) 1.5 0.8 0.4

Lake Svyatoe, Belarusa 4.7 (1997) 2.4 1.2 0.6

Lake Vorsee, Germany 0.055 (2000) 0.032 0.016 0.008

Devoke Water, UK 0.012 (1998) 0.006 0.003 0.002

a This lake had a countermeasure applied in 1998. The prediction is for levels in the absence of countermeasures.

TABLE 3.10. CAESIUM-137 ACTIVITY CONCENTRATIONS (PER UNIT FRESH WEIGHT) IN FISHIN VARIOUS CHERNOBYL AFFECTED LAKES AROUND EUROPE AND PREDICTIONS FOR 30, 50AND 70 YEARS AFTER THE ACCIDENT [3.125]

Fish speciesMeasured 137Cs (Bq/kg) (year of measurement)

Predicted 137Cs (Bq/kg fresh weight)

2016 2036 2056

Lake Kozhanovskoe, Russian Federation

Goldfish 10 000 (1997) 5 200 2 600 1 300

Kiev reservoir, Ukraine Perch 300 (1997) 160 80 40

Chernobyl cooling pond Perch 18 000 (2001) 11 000 5 400 2 700

Lake Svyatoe, Belarusa Perch 104 000 (1997) 54 000 27 000 14 000

Lake Vorsee, Germany Pike 174 (2000) 100 50 25

Lake Høysjøen, Norway Trout 390 (1998) 210 100 50

Devoke Water, UK Trout 370 (1996–1998) 200 100 50

a This lake had a countermeasure applied in 1998. The prediction is for levels in the absence of countermeasures.

59

rates of decline of 90Sr from weapons testing had aTeff of about ten years [3.148]. Similar to 137Cs,activity concentrations of 90Sr in water are expectedto decline from their current low levels during thecoming decades (Table 3.11).

Fuel particle breakdown took place at a muchslower rate in lake sediments than in soils [3.149].The half-life of fuel particles in sediments in thecooling pond is approximately 30 years [3.39], andhence radionuclides in fuel particles will remain intheir original form for many years.

3.5.6.2. Marine ecosystems

At present, radionuclides (mainly radio-caesium) in marine systems are at much lowerconcentrations than those observed in freshwatersystems. Activity concentrations in sea water andmarine biota in the Black Sea are expected tocontinue to decline (see Table 3.8). This is mainlydue to physical decay, but continued transfers toseabed sediments and further dilution will alsocontribute to the decline.

3.6. CONCLUSIONS

The highest radionuclide deposition occurredin Belarus, the Russian Federation and Ukraine, buthigh depositions also occurred in a number of otherEuropean countries.

Most of the strontium and plutonium radionu-clides were deposited close to the reactor and wereassociated with fuel particles. The environmentalmobility of these radionuclides was lower than thatof the fallout associated with condensed particles,which predominated in other areas, although the

bioavailability of 90Sr has increased with time as thefuel particles have partially dissolved.

Most of the originally released radionuclideshave disappeared, due to radioactive decay; 137Cs iscurrently of most concern. In the long term future(more than 100 years) only plutonium isotopes and241Am will remain.

The deposition in urban areas in the nearestcity of Pripyat and surrounding settlements couldhave initially given rise to a substantial externaldose to the inhabitants, which was averted by theevacuation measures. The deposition of radioactivematerial in other urban areas has providedsubstantial contributions to the dose to humansduring the years after the accident and up to thepresent.

During the first weeks to months after theaccident, the transfer of short lived radioiodineisotopes to milk was rapid and high, leading tosubstantial doses to humans in the former USSR.Due to the emergency situation and the short half-life of 131I, there are few reliable data on the spatialdistribution of deposited radioiodine. Currentmeasurements of 129I may assist in estimating 131Ideposition better and thereby improve thyroid dosereconstruction.

The high concentrations of radioactivesubstances in surface water directly after the accidentreduced rapidly, and drinking water and water usedfor irrigation have very low concentrations ofradionuclides today.

Due to radioactive decay, rain and wind,human activities, and countermeasures, surfacecontamination in urban areas by radioactivematerial has been substantially reduced. Externaldoses in urban areas, compared with open areas, arereduced by shielding effects.

TABLE 3.11. STRONTIUM-90 ACTIVITY CONCENTRATIONS IN WATER IN VARIOUSCHERNOBYL AFFECTED LAKES AND RIVERS AND PREDICTIONS FOR 30, 50 AND 70 YEARSAFTER THE ACCIDENT [3.125]

Measured 90Sr (Bq/L) (year of measurement)

Predicted 90Sr (Bq/L)

2016 2036 2056

Pripyat River 0.28 (1998) 0.15 0.08 0.04

Kiev reservoir 0.16 (1998) 0.09 0.04 0.02

Chernobyl cooling pond 2.0 (2001) 1.2 0.6 0.3

Lake Glubokoye, CEZ 120 (2004) 80–90 40–60 20–30

60

At present, in most of the settlementssubjected to radioactive contamination, theradiation dose rate above solid surfaces hasreturned to the pre-accident background level.Elevated dose rates remain mainly in areas ofundisturbed soil.

From the summer of 1986 onwards, 137Cs wasthe dominant radionuclide of concern in agricul-tural products (milk and meat). During the first fewyears, substantial amounts of food were discardedfrom human consumption. The highest activityconcentrations of 137Cs have been found in foodproducts from forest areas, especially inmushrooms, berries, game and reindeer. High 137Csactivity concentrations in fish occur in lakes withslow or no turnover of water, particularly if the lakeis also shallow and mineral nutrient poor.

The importance of 90Sr in food products islower than that of 137Cs because of its lowerdeposition and because milk is the only majoranimal food product to which it is transferred.Strontium accumulation in the bones of agriculturalanimals and fish occurs but does not typically leadto radiation doses to humans.

There have been large long term variations in137Cs activity concentrations in food products, duenot only to deposition levels but also to differencesin soil types and management practices. In manyareas there are still food products, particularly fromextensive agricultural production systems andforests, with 137Cs activity concentrations exceedingthe intervention limits. Large land areas in theformer USSR are still excluded from agriculturalproduction for radiological reasons.

The major and persistent problems in theaffected areas occur in extensive agriculturalsystems with soils with a high organic content andwhere animals graze on unimproved pastures. Thisparticularly affects rural residents in the formerUSSR, who are commonly subsistence farmers withprivately owned dairy cows.

In general, there was an initial substantialreduction in the transfer of 137Cs to vegetation andanimals, as would be expected, due to weathering,physical decay, migration of radionuclides down thesoil column and reductions in bioavailability.However, in the past decade there has been littlefurther obvious decline, and long term effectivehalf-lives have been difficult to quantify.

There has been a particularly slow decreasesince deposition in 137Cs activity concentrations insome products from forests, and some species ofmushrooms are expected to have high 137Cs activity

concentrations for decades to come. Under certainweather and ecological conditions, the biomass ofmushrooms in autumn can be much higher thannormal, leading to relatively high seasonal increasesin 137Cs activity concentrations in game. Thus itmust not always be assumed that 137Cs activityconcentrations in animals will remain as they arenow or decline each year.

Radiocaesium in timber is of minorimportance, although doses in the timber industryhave to be considered. Wood ash can contain higheramounts of 137Cs. Forest fires have increased the airactivity concentrations in local areas, but not to ahigh extent.

Due to dilution, there were never highconcentrations of 137Cs in marine fish in the BlackSea or the Baltic Sea.

3.7. FURTHER MONITORING AND RESEARCH NEEDED

Updated mapping of 137Cs deposition inAlbania, Bulgaria and Georgia should beperformed in order to complete the study of post-Chernobyl contamination of Europe.

Improved mapping of 131I deposition, basedboth on historical environmental measurementscarried out in 1986 and on recent measurements of129I in soil samples in areas where elevated thyroidcancer incidence has been detected after theChernobyl accident, would reduce the uncertaintyof the thyroid dose reconstruction needed for deter-mination of radiation risks.

Long term monitoring of 137Cs and 90Sractivity concentrations in agricultural vegetable andanimal products produced in areas with various soiland climate conditions and different agriculturalpractices should be performed for decades to comewithin focused research programmes at selectedsites.

The study of the distribution of 137Cs andplutonium radionuclides in the urban environment(Pripyat, Chernobyl and some other contaminatedtowns) in the future would improve the modellingof human external exposure and inhalation of radio-nuclides for possible application to any futurenuclear or radiological accident or malicious action.

The continued long term monitoring ofspecific forest products such as mushrooms andgame needs to be carried out in those areas in whichforests were significantly contaminated. The resultsfrom such monitoring are being used by the relevant

61

authorities in affected countries to provide advice tothe general public on the continued use of forestsfor recreation and the gathering of wild foods.

In addition to the general monitoring of forestproducts, required for radiation protection, moredetailed, scientifically based, long term monitoringof specific forest sites is required to provide anongoing and improved understanding of the longterm dynamics and persistence of radiocaesiumcontamination and its variability. Such monitoring isalso necessary to improve the existing predictivemodels. Monitoring programmes are being carriedout in several of the more severely affectedcountries, such as Belarus and the RussianFederation, and it is important that these continuefor the foreseeable future if current uncertainties inlong term forecasts are to be reduced.

Aquatic systems have been intensively studiedand monitored during the years after the Chernobylaccident, and transfers and bioaccumulation of themost important long term contaminants, 90Sr and137Cs, are now well understood. There is thereforelittle urgent need for major new researchprogrammes on radionuclides in aquatic systems.There is, however, a requirement for continued (butperhaps more limited) monitoring of the aquaticenvironment and for further research in somespecific areas, as detailed below.

Predictions of the future contamination ofaquatic systems with 90Sr and 137Cs would beimproved by continued monitoring of radioactivityin key systems (the Pripyat–Dnieper system, theseas, and selected rivers and lakes in the moreaffected areas and western Europe). This wouldcontinue the time series measurements of activityconcentrations in water, sediments and fish andenable the refinement of predictive models forthese radionuclides.

Although they are currently of minor radio-logical importance in comparison with 90Sr and137Cs, further studies of transuranic elements in theChernobyl accident area would improve predictionsof environmental contamination in the very longterm (hundreds to thousands of years). Furtherempirical studies of transuranic elements and 99Tcare unlikely to have direct implications for radio-logical protection in the Chernobyl affected areas,but would further add to our knowledge of theenvironmental behaviour of these very long livedradionuclides.

Future plans to reduce the water level of theChernobyl cooling pond will have significant impli-cations for its ecology and the behaviour of radionu-

clides/fuel particles in newly exposed sediments.Specific studies on the cooling pond shouldtherefore continue. In particular, further study offuel particle dissolution rates in aquatic systemssuch as the cooling pond would improve knowledgeof these processes.


[3.1] INTERNATIONAL NUCLEAR SAFETYADVISORY GROUP, Summary Report on thePost-accident Review Meeting on the ChernobylAccident, Safety Series No. 75-INSAG-1, IAEA,Vienna (1986).

[3.2] IZRAEL, Y.A., et al., Chernobyl: RadioactiveContamination of the Environment, Gidrometeo-izdat, Leningrad (1990).

[3.3] IZRAEL, Y.A., Radioactive Fallout AfterNuclear Explosions and Accidents, Elsevier,Amsterdam (2002).

[3.4] INTERNATIONAL ADVISORY COMMIT-TEE, The International Chernobyl Project:Technical Report, IAEA, Vienna (1991).

[3.5] UNITED NATIONS, Sources, Effects and Risksof Ionizing Radiation (Report to the GeneralAssembly), Scientific Committee on the Effects ofAtomic Radiation (UNSCEAR), UN, New York(1988) 309–374.

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[3.131] HADDERINGH, R.H., VAN AERSSEN,G.H.F.M., RYABOV, I.N., KOULIKOV, O.A.,BELOVA, N., “Contamination of fish with 137Csin Kiev reservoir and old river bed of Pripyat nearChernobyl”, Freshwater and Estuarine Radio-ecology (DESMET, G., et al., Eds), Elsevier,Amsterdam (1997) 339–351.

[3.132] KRYSHEV, I.I., SAZYKINA, T.G., Accumula-tion factors and biogeochemical aspects ofmigration of radionuclides in aquatic ecosystemsin the areas impacted by the Chernobyl accident,Radiochim. Acta 66–67 (1994) 381–384.

[3.133] EREMEEV, V.N., IVANOV, L.M., KIRWAN,A.D., MARGOLINA, T.M., Amount of 137Cs and134Cs radionuclides in the Black Sea produced bythe Chernobyl accident, J. Environ. Radioact. 27(1995) 49–63.

[3.134] KANIVETS, V.V., VOITSEKHOVITCH, O.V.,SIMOV, V.G., GOLUBEVA, Z.A., The post-Chernobyl budget of 137Cs and 90Sr in the BlackSea, J. Environ. Radioact. 43 (1999) 121–135.

[3.135] NIELSEN, S.P., et al., The radiological exposureof man from radioactivity in the Baltic Sea, Sci.Total Environ. 237–238 (1999) 133–141.

[3.136] EUROPEAN UNION, The RadiologicalExposure of the Population of the EuropeanCommunity to Radioactivity in the Baltic Sea,Rep. EUR 19200 EN, Office for Official Publica-tions of the European Communities, Luxembourg(2000).

[3.137] SHESTOPALOV, V.M. (Ed.), ChernobylDisaster and Groundwater, Balkema, Leiden(2002).

[3.138] BUGAI, D.A., WATERS, R.D., DZHEPO, S.P.,SKALSKY, A.S., Risks from radionuclidemigration to groundwater in the Chernobyl 30-kmzone, Health Phys. 71 (1996) 9–18.

[3.139] VOITSEKOVITCH, O.V., SHETOPALOV, V.M.,SKALSKY, A.S., KAIVETS, V.V., Monitoring ofRadioactive Contamination of Surface GroundWater Following the Chernobyl Accident,Ukrainian Hydrometeorological Institute, Kiev(2001) (in Russian).

[3.140] VOITSEKHOVITCH, O.V., SANSONE, U.,ZHELEZNYAK, M., BUGAI, D., “Water qualitymanagement of contaminated areas and its effectson doses from aquatic pathways”, The Radiolog-ical Consequences of the Chernobyl Accident(Proc. Int. Conf. Minsk, 1996), Rep. EUR 16544EN, Office for Official Publications of theEuropean Communities, Luxembourg (1996) 401–410.

[3.141] VANDENHOVE, H. (Ed.), PHYTOR, Evalua-tion of Willow Plantation for the Phytorehabilita-

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tion of Contaminated Arable Lands and FloodPlane Areas, Final Report, Rep. SCK•CEN ERBIC15-CT98 0213, SCK•CEN, Mol (2002).

[3.142] BECHTEL INTERNATIONAL SYSTEMS,ELECTRICITÉ DE FRANCE, BATTELLEMEMORIAL INSTITUTE, EnvironmentalImpact Assessment: New Safe ConfinementConceptual Design: Chernobyl Nuclear PowerPlant Unit 4, Bechtel, EDF, Battelle, SanFrancisco, CA (2003).

[3.143] UNITED NATIONS DEVELOPMENTPROGRAMME, Water Evaluation and Predic-tion in the Area Affected by the ChernobylAccident (the Bryansk Region), Final Report ofProject RUS/95/004, UNDP, Moscow (2001).

[3.144] HANSEN, H.J.M., AARKROG, A., A differentsurface geology in Denmark, the Faroe Islandsand Greenland influences the radiologicalcontamination of drinking water, Water Res. 24(1990) 1137–1141.

[3.145] FOOD AND AGRICULTURE ORGANIZA-TION OF THE UNITED NATIONS, INTER-NATIONAL ATOMIC ENERGY AGENCY,Guidelines for Agricultural CountermeasuresFollowing an Accidental Release of Radio-

nuclides, Technical Reports Series No. 363, IAEA,Vienna (1994).

[3.146] ZHELEZNYAK, M., SHEPELEVA, V., SIZO-NENKO, V., MEZHUEVA, I., Simulation ofcountermeasures to diminish radionuclide fluxesfrom the Chernobyl zone via aquatic pathways,Radiat. Prot. Dosim. 73 (1997) 181–186.

[3.147] SMITH, J.T., et al., Chernobyl’s legacy in food andwater, Nature 405 (2000) 141.

[3.148] CROSS, M.A., SMITH, J.T., SAXÉN, R., TIMMS,D.N., An analysis of the time dependent environ-mental mobility of radiostrontium in Finnish rivercatchments, J. Environ. Radioact. 60 (2002) 149–163.

[3.149] KONOPLEV, A.V., et al., “Physico-chemical andhydraulic mechanisms of radionuclide mobiliza-tion in aquatic systems”, The Radiological Conse-quences of the Chernobyl Accident (Proc. Int.Conf. Minsk, 1996), Rep. EUR 16544 EN, Officefor Official Publications of the European Commu-nities, Luxembourg (1996) 121–135.

[3.150] FLEISHMAN, D.G., NIKIFOROV, V.A.,SAULUS, A.A., KOMOV, V.T., 137Cs in fish ofsome lakes and rivers of the Bryansk region andnorth-west Russia in 1990–1992, J. Environ.Radioact. 24 (1994) 145–158.

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4. ENVIRONMENTAL COUNTERMEASURES AND REMEDIATION

The need for the application of urgentprotective actions became evident very soon afterthe Chernobyl accident occurred. A wide range ofcountermeasures was applied for protecting thepublic from radiation, from urgent evacuation in1986 of the inhabitants from the area of highestradioactive contamination to long term monitoringof radionuclides in foodstuffs in many Europeancountries. The whole spectrum of the appliedcountermeasures and their effectiveness have beenconsidered in a number of international reports[4.1–4.7].

The main subject of this section is the counter-measures that have been applied to theenvironment in order to reduce the radiologicalimpact on humans. At the time of the Chernobylaccident the philosophy of radiation protection ofnon-human species had not been sufficientlydeveloped to be practically applied for the purposesof justifying appropriate countermeasures. Suchpolicies are currently still under development [4.8].

This section does not consider specifically theemergency and mitigatory actions applied to thedamaged reactor aimed at reducing radioactivereleases to the environment; these aspects havebeen covered elsewhere [4.2].

Environmental countermeasures have beenapplied since 1986 to urban, agricultural, forest andaquatic ecosystems. Most of these countermeasureswere driven by relevant international and nationalradiological criteria.

4.1. RADIOLOGICAL CRITERIA

Countermeasures, termed protective actionsat the emergency stage and remedial actions at thepost-emergency stage, are actions taken to reducethe level of exposure as much as is reasonablyachievable. A fundamental aspect of radiationprotection philosophy is to optimize the doseaverted against the costs of applying the counter-measure. However, the costs and benefits ofcountermeasures are not always quantifiable inpurely monetary terms. The advantages of counter-measures often include reassurance and a decreasein anxiety in the affected population. However,

countermeasures may also have negative conse-quences, either directly to ecosystems (e.g.disruption of nutrient cycles) or to sectors of thepopulation either economically or due to disruptionof normal life.

4.1.1. International radiological criteria and standards

At the time of the Chernobyl accident in 1986,the relevant international radiation protectionstandards for protection of the public and workerswere contained in International Commission onRadiological Protection (ICRP) Publication 26[4.9]. Specific recommendations on the protectionof the public in the event of a major radiationaccident were given in ICRP Publication 40 [4.10].The corresponding IAEA Basic Safety Standards,based on ICRP recommendations, were issued in1982 [4.11]. The basic principles of modernradiation protection — justification, optimizationand dose limitation — and the clear distinctionbetween protection in normal and interventionsituations were contained in these documents. Atthat time, the annual limit for occupationalexposure was equal to 50 mSv and that for publicexposure was 5 mSv. The latter value was perceivedas a safe level of human exposure.

Special limits for public radiation protectionin the event of nuclear or radiological emergencieswere not specifically established in thesedocuments, and instead it was recommended:

(a) By almost all means to reduce humanaccidental exposure below doses that mayresult in deterministic health effects (acuteradiation syndrome, radiation damage toparticular organs or tissues);

(b) To intervene (i.e. to apply and subsequentlywithdraw countermeasures aimed at reducingstochastic health effects (cancer, geneticanomalies)) based on an optimizationassessment taking into account both thecollective dose reduction achieved by theapplication of the countermeasures and theassociated economic and social interventioncosts.

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The most relevant ICRP guidance [4.10]recommended some generic two level criteria forintervention in the early accident phase — forsheltering, 5–50 mSv of whole body dose or 50–500 mSv to particular organs; for administration ofstable iodine aimed at thyroid protection againstintake of radioiodines, 50–500 mSv to the thyroid;for evacuation, 50–500 mSv of whole body dose or500–5000 mSv to particular organs. For the interme-diate accident phase, the generic criteria of 5–50 mSv of whole body dose or 50–500 mSv toparticular organs were recommended for control offoodstuff contamination with radionuclides, and 50–500 mSv of whole body dose for relocation.

Afterwards, in connection with publicconcerns over the radiological consequences of theChernobyl accident, new additional internationalregulations were developed. Thus in 1989 the CodexAlimentarius Commission approved guidancelevels for radionuclides in food moving in interna-tional trade for the first year after a major nuclearaccident (see Table 4.1) [4.12].

New international basic radiation protectionstandards for the protection of the public andworkers were developed by the ICRP in 1990 afterresearch data had shown that radiation risk coeffi-cients for stochastic human health effects weresubstantially higher than previously thought. Theannual limits of exposure were substantially (by afactor of 2.5–5) reduced and established equal to20 mSv for workers and 1 mSv for members of thegeneral public [4.13]. The latter value is currentlyperceived as a safe level of human exposure.

Special limits for public protection in theevent of nuclear or radiological emergencies werenot established in these documents. Appropriatespecific recommendations were developed later on

intervention for the protection of the public in aradiological emergency [4.14]. In this guidance theoptimization concept was confirmed as the basicone applicable in the event of an emergency andfurther elaborated with regard to dose averted asthe consequence of intervention (see Fig. 4.1). TheICRP discarded the previous two level interventioncriteria and recommended instead some inter-vention levels (in terms of averted effective dose) —50 mSv for sheltering, 500 mSv (thyroid dose) foradministration of stable iodine, 500 mSv forevacuation, 1000 mSv (lifetime dose) for relocationand 10 mSv/a for the control of foodstuffs.

A more recent ICRP publication (Publication82) [4.15] considered public radiation protection inconditions of prolonged radiation exposure, such asin areas contaminated due to the Chernobylaccident. In this document, the ICRP generallyrecommends retaining the optimization principle,but also suggests generic radiological criteria formaking decisions on countermeasure application. Inparticular, it proposes the value of the ‘existingannual dose’, including external and internal dosesfrom natural and human-made radionuclides, of10 mSv as the generic dose below which inter-vention is not usually expedient. This does notexclude intervention at lower doses if site specificoptimization analysis proves it to be expedient.Inter alia, the ICRP recommended a generic inter-vention exemption level for radionuclides incommodities dominating human exposure equal to1 mSv/a. This criterion could be applied for justifi-cation of the reference levels for radionuclides infood.

TABLE 4.1. GUIDELINE LEVELS FOR RADIO-NUCLIDES IN FOOD FOLLOWING ACCI-DENTAL NUCLEAR CONTAMINATION, FORUSE IN INTERNATIONAL TRADE [4.12]

Food for general consumption

(Bq/g)

Milk and infant food

(Bq/g)

Caesium-134, 137 1 1

Iodine-131 1 0.1

Strontium-90 0.1 0.1

Plutonium-239, americium-241

0.01 0.001

Time after start of accident

t1 t2

Avertable

dose (�E)

Dos

e p

er u

nit

time

(E(t)

)

FIG. 4.1. Avertable dose and effective dose accumulatedper unit time as a function of time when the protectivemeasure is introduced at time t1 and lifted again at time t2.

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4.1.2. National radiological criteria and standards

Limitations on human exposure caused by theChernobyl accident, including standards for radio-nuclides in food, drinking water, timber, etc., wereintroduced soon after the accident, first by theUSSR but also by many other European countries(i.e. Nordic countries, EU countries and easternEuropean countries [4.1]).

In accordance with the Standards of RadiationSafety [4.16] in force in 1986, the USSR Ministry ofHealth introduced a temporary limit of averageequivalent whole body dose of 100 mSv for the first

year after the Chernobyl accident (from 26 April1986 until 26 April 1987), then 30 mSv for thesecond year and 25 mSv in each of 1988 and 1989[4.3]. In all, until 1 January 1990, a dose to thegeneral public not exceeding 173 mSv was allowedfrom the radioactive fallout of the Chernobylaccident.

In order to limit the internal exposure ofmembers of the population, temporary permissiblelevels (TPLs) of radionuclide content in foodproducts and drinking water were introduced in theUSSR. Table 4.2 presents the TPLs for the mainfood products [4.3, 4.17]. The first TPL set approved

TABLE 4.2. TEMPORARY PERMISSIBLE LEVELS (Bq/kg) OF RADIONUCLIDE CONTENT INFOOD PRODUCTS AND DRINKING WATER ESTABLISHED IN THE USSR (1986–1991) AFTER THECHERNOBYL ACCIDENT [4.3, 4.17]

TPL

4104–88 129–252 TPL-88 TPL-91

Date of adoption 6 May 1986 30 May 1986 15 December 1987 22 January 1991

Radionuclide Iodine-131 Beta emitters Caesium-134 and caesium-137

Caesium-134 and caesium-137

Strontium-90

Drinking water 3700 370 18.5 18.5 3.7

Milk 370–3700 370–3700 370 370 37

Dairy products 18 500–74 000 3700–18 500 370–1850 370–1850 37–185

Meat and meat products — 3700 1850–3000 740 —

Fish 37 000 3700 1850 740 —

Eggs — 37 000 1850 740 —

Vegetables, fruit, potato, root crops

— 3700 740 600 37

Bread, flour, cereals — 370 370 370 37

TABLE 4.3. ACTION LEVELS (Bq/kg) FOR CAESIUM RADIONUCLIDES IN FOOD PRODUCTSESTABLISHED AFTER THE CHERNOBYL ACCIDENT [4.3, 4.5]

Action level

Codex Alimentarius Commission

EU BelarusRussian

FederationUkraine

Year of adoption 1989 1986 1999 2001 1997

Milk 1000 370 100 100 100

Infant food 1000 370 37 40–60 40

Dairy products 1000 600 50–200 100–500 100

Meat and meat products 1000 600 180–500 160 200

Fish 1000 600 150 130 150

Eggs 1000 600 — 80 6 Bq/egg

Vegetables, fruit, potato, root crops 1000 600 40–100 40–120 40–70

Bread, flour, cereals 1000 600 40 40–60 20

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by the USSR Ministry of Health on 6 May 1986concerned 131I activity concentrations in foodstuffsand was aimed at limiting the thyroid dose tochildren to 300 mGy. The next TPL set, adopted on30 May 1986, concerned the content of all betaemitters in food products caused by surface contam-ination, with particular attention given to ecologi-cally mobile and long lived caesium radionuclides.Later, TPLs introduced in 1988 (TPL-88) and 1991(TPL-91) concerned the sum of 134Cs and 137Csactivities. The TPL-91 for caesium radionuclideswas supplemented by TPLs for 90Sr.

Annual consumption by rural inhabitants ofthe usual food ration, if all components containedcaesium radionuclides at the level of TPL-86, wouldcause an internal dose of less than 50 mSv (atTPL-88 it would be less than 8 mSv and at TPL-91 itwould be less than 5 mSv).

Action levels for 131I in food established insome European countries in May 1986 varied withinthe range of 500–5000 Bq/kg. Later, the authoritiesof the EU established two values for caesium radio-nuclides in imported food, one for milk and infantfood and another for all other food products (seeTable 4.3) [4.3, 4.5]. Similar values were introducedin Nordic countries, with an exception for wild foods(reindeer meat, game, freshwater fish, forestberries, fungi and nuts), which are importantproducts for some local populations and especiallyfor indigenous people. Thus in the first monthSweden imposed action levels of 5 kBq/kg for 131Iand 10 kBq/kg for 137Cs in imported food; fordomestic foods the respective values were 2 and1 kBq/kg. In the middle of May, action levels of300 Bq/kg for 137Cs in all food and 2 kBq/kg for 131Iin milk and dairy products were introduced. Forwild foods produced or consumed in the Nordiccountries, the action levels varied between 1500 and6000 Bq/kg in different countries and time periods.

Along with the standards for food products,standards were introduced by the USSR for agricul-tural raw material, wood (see Section 4.3) andherbs, and for beta contamination of differentsurfaces [4.3].

The general policy of the USSR, and later ofthe authorities in the separate republics, was toreduce both the radiological criteria and the TPLsalong with the natural improvement of radiologicalconditions due to radionuclide decay andpenetration/fixation in soil. Gradual TPL reductionhas been used as an instrument to force producersto apply technologies that decrease radionuclidecontent in products in order to limit associated

human exposure. The TPLs were established byexperts balancing the desire to reduce internal dosein populations with the need to maintain profitableagricultural production and forestry in thecontrolled areas. Different reference levels fornumerous groups of food products were establishedwith the aim of not restricting consumption of anyfoods unless the dose criterion might be exceeded.

By the end of 1991 the USSR had split intoseparate countries, among them Belarus, theRussian Federation and Ukraine, which had beenstrongly affected by the Chernobyl accident.Afterwards each country implemented its ownpolicy of radiation protection of the public. Owingto the acceptance by the ICRP in 1990 of the annualeffective dose limit for the public in regulatedsituations (practices) equal to 1 mSv, this level wasconsidered by the authorities of the three countriesas safe also in post-emergency conditions. Thereforeit is still used in national legislations as an inter-vention level of annual dose caused by Chernobylfallout for the introduction of countermeasures,including long term remediation measures.

Current national TPLs for food products,drinking water and wood in the three countries arecomparable with each other (see Table 4.3), and allof them are substantially lower than both the EUmaximum permissible levels for import [4.5] and theCodex Alimentarius Commission’s guidance levelsfor radionuclides in food moving in internationaltrade [4.12].

The State authorities in the three countrieshave struggled to meet the established TPLs forproducts and the dose criteria by implementation ofenvironmental countermeasures as described belowand by inspection of foods throughout each country.

4.2. URBAN DECONTAMINATION

Decontamination of settlements was one ofthe main countermeasures applied to reduceexternal exposure of the public and cleanupworkers during the initial stage of response to theChernobyl accident. The immediate purpose ofsettlement decontamination was the removal ofradiation sources distributed in urban environmentsinhabited by humans.

Analysis of the sources of external exposure indifferent population groups living in contaminatedareas revealed that a significant fraction of dose isreceived by people from sources located in soil, oncoated surfaces such as asphalt and concrete and to

72

a small extent on building walls and roofs. This iswhy most effective decontamination technologiesinvolved removal of the upper soil layer.

The decontamination efficiency can be charac-terized by means of the following parameters: thedose rate reduction factor (DRRF), which is therelative reduction of dose rate above a surfacefollowing decontamination, and the dose reductionfactor (DRF), which is the reduction of theeffective external dose to an individual fromgamma emitting radionuclides deposited in theenvironment.

4.2.1. Decontamination research

In order to ensure high decontaminationeffectiveness and to keep the associated costs low,several research projects have been implementedaimed at determining the values of the DRRF andDRF for particular decontamination technologiesapplied to different surfaces and artefacts in thehuman environment [4.18–4.20]. Reports fromthese experimental and theoretical studies containvalidated models of urban decontamination and setsof model parameters and practical recommenda-tions for cleanup in different time periods afterurban radioactive contamination. A preliminaryremediation assessment based on well developedcost–benefit techniques is recommended in order tojustify decontamination and to optimize its imple-mentation.

According to these and other studies, thecontributions of different urban surfaces to thehuman external dose and the associated opportu-nities for dose reduction are determined bysettlement and house design, construction material,the habits of the populations, the mode of radionu-clide deposition (dry or wet), the radionuclide andphysicochemical composition of the fallout, andtime (see Section 3.2).

Following dry deposition, street cleaning,removal of trees and shrubs and ploughing ofgardens are efficient and inexpensive means ofachieving very significant reductions in dose andwould rate highly in a list of short term remediationpriorities. Roofs are important contributors to dose,but the cost of cleaning roofs is high and thiscountermeasure would not rank highly in a list ofpriorities. Walls contribute little to dose, areexpensive and difficult to decontaminate and wouldtherefore carry a very low rating.

In the case of wet deposition, gardens andlawns, both in the short term and the long term,

would be given first priority, because a considerablereduction in dose (~60%) can be achieved atrelatively low cost. Street cleaning would also be ofbenefit.

While planning decontamination for the longterm, it is important to take into account the contri-bution of external dose to the total (external andinternal) dose. In areas dominated by clay soils,transfer of caesium radionuclides in the food chainand the associated internal doses are low. In theseareas the relative decrease in the total dose is closeto the DRF value. In contrast, in sandy and peatysoil areas, where long term internal exposuredominates, the relative decrease in the total dosedue to village decontamination is expected to beless significant.

4.2.2. Chernobyl experience

Large scale decontamination was performedbetween 1986 and 1989 in the cities and villages ofthe USSR most contaminated after the Chernobylaccident. This activity was performed usually bymilitary personnel and included washing of buildingswith water or special solutions, cleaning ofresidential areas, removal of contaminated soil,cleaning and washing of roads, and decontaminationof open water supplies. Special attention was paid tokindergartens, schools, hospitals and other buildingsfrequently visited by large numbers of persons. Intotal, about one thousand settlements were treated;this included cleaning tens of thousands ofresidences and public buildings and more than athousand agricultural farms [4.18, 4.21, 4.22].

In the early period following the accident,inhalation of resuspended radioactive particles ofsoil and nuclear fuel could contribute significantlyto internal dose. To suppress dust formation,dispersion of organic solutions over contaminatedplots was used in order to create an invisiblepolymer film after drying. This method wasimplemented at the Chernobyl nuclear power plantand in the CEZ during the spring and summer of1986. Streets in cities were watered to prevent dustformation and to remove radionuclides to thesewerage system. The effectiveness of early decon-tamination efforts in 1986 still remains to bequantified. However, according to Los andLikhtarev [4.23] daily washing of streets in Kievdecreased the collective external dose to itsthree million inhabitants by 3000 man Sv, anddecontamination of schools and school areas savedanother 600 man Sv.

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Depending on the decontamination technol-ogies used, the dose rate over different measuredplots was reduced by a factor of 1.5–15. However,the high cost of these activities hindered theircomprehensive application on contaminated areas.Due to these limitations, the actual effectiveness ofthe decrease in annual external dose was 10–20%for the average population and ranged from about30% for children visiting kindergartens and schoolsto less than 10% for outdoor workers (herders,foresters, etc.). These data were confirmed byindividual external dose measurements conductedbefore and after large scale decontaminationcampaigns in 1989 in the Bryansk region of theRussian Federation [4.18].

Regular monitoring of decontaminated plotsin settlements over five years showed that after 1986there was no significant recontamination and thatthe exposure rate was decreasing over the longterm, as described in Section 5.1 of this report. Theaverted collective external dose to 90 000inhabitants of the 93 most contaminated settlementsof the Bryansk region was estimated to be about1000 man Sv [4.18].

Since 1990 large scale decontamination in thecountries of the former USSR has been stopped, butparticular contaminated plots and buildings withmeasured high contamination levels have beenspecifically cleaned. Some decontaminationactivities still continue in Belarus, aimed mostly atpublic buildings and areas: hospitals, schools,recreation areas, etc. However, in some contami-nated Belarusian villages, cleanup of dwellings andfarms has also been performed [4.22].

Another area of continuing decontaminationactivity is the cleanup of industrial equipment andpremises contaminated as a result of ventilationsystems being operated during the release/deposition period in 1986 and immediatelyafterwards. Some 20 to 30 industrial buildings andventilation systems have been decontaminatedannually in Belarus [4.22].

4.2.3. Recommended decontamination technologies

In accordance with present radiationprotection methodology, a decision on intervention(decontamination) and selection of optimal decon-tamination technologies should be made givingconsideration to the costs of all actions and to socialfactors. The calculated cost should address thevarious decontamination technologies for which an

assessment of the averted dose has been made. Thebenefit (averted collective effective dose) anddetriment (expenses, collective dose to decontami-nation workers) are to be compared for each decon-tamination technology by means of a cost–benefitanalysis [4.9] or multiattribute analysis [4.24], whichmay include qualitative social factors.

The priorities that different procedures wouldbe given in a decontamination strategy should beenvironment specific. Nevertheless, based onaccumulated experience and research, the followinggeneric set of the major simple decontaminationprocedures can be recommended for the long term:

(a) Removal of the upper 5–10 cm layer(depending on the activity–depth distribution)of soil in courtyards in front of residentialbuildings, around public buildings, schools andkindergartens, and from roadsides inside asettlement. The removed, most contaminated,layer of soil should be placed into holesspecially dug on the territory of a privatehomestead or on the territory of a settlement.The clean soil from the holes should be used tocover the decontaminated areas. Such atechnology excludes the formation of specialburial sites for radioactive waste.

(b) Private fruit gardens should be treated bydeep ploughing or removal of the upper5-10 cm layer of soil. By now, vegetablegardens have been ploughed many times, andthe activity distribution in soil will be uniformin a layer 20–30 cm deep.

(c) Covering the decontaminated parts ofcourtyards, etc., with a layer of clean sand, or,where possible, with a layer of gravel toattenuate residual radiation (see item (a)).

(d) Cleaning or replacement of roofs.

These procedures can be applied both fordecontaminating single private gardens and housesand for decontaminating settlements as a whole. Itis evident that, in the latter case, the influence of thedecontamination on further reduction in externalradiation dose will be greater. Achievable decon-tamination factors for various urban surfaces arepresented in Table 4.4. Detailed data on theefficiency, technology, necessary equipment, costand time expenses, quantity of radioactive waste,and other parameters of decontaminationprocedures are contained in Ref. [4.25].

Radioactive waste generated from urbandecontamination should be disposed of in

74

accordance with established regulatory require-ments. In the event of large scale decontamination,temporary storage should be arranged in specialisolated areas from which future activity releaseinto the environment will be negligible. The siteshould be marked by the international symbol ofradiation hazard.

4.3. AGRICULTURAL COUNTERMEASURES

The implementation of agricultural counter-measures after the Chernobyl accident has beenextensive, both in the most severely affectedcountries of the former USSR and in westernEurope. The main aim of agricultural counter-measures was the production of food products withradionuclide activity concentrations below actionlevels2. The application of countermeasures inintensive agricultural production systems waslargely confined to Belarus, the Russian Federationand Ukraine, although some food bans wereinitially applied in western Europe. Many counter-measures were used extensively in the first fewyears after the accident, and their applicationcontinues today. In addition, in these threecountries countermeasures have been applied toprivate food production from unimprovedmeadows, where high 137Cs activity concentrationshave persisted for many years [4.3, 4.4, 4.7].

High and persistent transfer of 137Cs has alsooccurred in many contaminated areas of westernEurope. In these countries countermeasures have

largely been focused on animal food products, forexample for grazing animals on unimprovedpastures.

4.3.1. Early phase

From 2–5 May 1986 about 50 000 cattle, 13 000pigs, 3300 sheep and 700 horses were evacuatedfrom the CEZ together with the people [4.26]. Inthe CEZ more than 20 000 agricultural anddomestic animals, including cats and dogs,remaining after the evacuation were killed andburied. Due to a lack of forage for the evacuatedanimals and difficulties in managing the largenumber of animals in the territories to which theyhad been moved, many of the evacuated animalswere also slaughtered [4.27, 4.28]. In the acuteperiod after the accident it was not possible todifferentiate between the different levels of contam-ination of animals, and in the period May–July 1986the total number of slaughtered animals reached95 500 cattle and 23 000 pigs.

Many carcasses were buried and some werestored in refrigerators, but this produced greathygiene, practical and economic difficulties.Condemnation of meat was an immediatelyavailable and effective countermeasure to reduceingested dose from animal products and was widelyused in the USSR and elsewhere. However, this wasvery expensive and resulted in large quantities ofcontaminated waste.

In the first weeks after the accident, the mainaim of countermeasure application in the USSR wasto lower 131I activity concentrations in milk or toprevent contaminated milk from entering the foodchain. The following were recommendations [4.29]on how to achieve this:

2 Referred to in the countries of the former USSRas temporary permissible levels (TPLs).

TABLE 4.4. ACHIEVABLE DECONTAMINATION FACTORS (DIMENSIONLESS)FOR VARIOUS URBAN SURFACES [4.25]

Technique DRRF

Windows Washing 10

Walls Sandblasting 10–100

Roofs Hosing and/or sandblasting 1–100

Gardens Digging 6

Gardens Removal of surface 4–10

Trees and shrubs Cutting back or removal ~10

Streets Sweeping and vacuum cleaning 1–50

Streets (asphalt) Lining >100

75

(a) Exclusion of contaminated pasture grassesfrom the animals’ diet by changing frompasture to indoor feeding of uncontaminatedfeed;

(b) Radiation monitoring at processing plants andsubsequent rejection of milk in which 131Iactivity concentrations were above the actionlevel (3700 Bq/L at that time);

(c) Processing rejected milk (mainly convertingmilk to storable products such as condensed ordried milk, cheese or butter).

In the first few days after the accident thecountermeasures were largely directed towardsmilk from collective farms, and few private farmerswere involved. Information on countermeasures formilk was only given to managers and localauthorities and was not distributed to the privatefarming system of the rural population. Thisresulted in limited application of countermeasures,especially for privately produced milk in ruralsettlements, resulting in a low effectiveness in someareas.

Within a few weeks of the accident, feeding ofanimals with ‘clean’ fodder began because this hadthe potential to reduce 137Cs in cattle to acceptablelevels within a period of 1–2 months. However, thiscountermeasure was not in widespread use at thisstage, partly due to a lack of availability of uncon-taminated feed early in the growing season.

As early as the beginning of June 1986 mapswere constructed of the density of radioactivedeposition in the contaminated regions. Thisallowed estimates to be made of the extent of thecontamination of pasture and identification ofwhere contaminated milk would be found.

During the growing period of 1986, whenthere was still substantial surface contamination ofplants, the major countermeasures in agriculturewere of a restrictive nature. In the first few monthsseverely contaminated land was taken out of useand recommendations were developed on suitablecountermeasures that would allow continuedproduction on less heavily contaminated land. Inthe more heavily affected regions, a ban wasimposed on keeping dairy cattle. To reduce contam-ination levels in crops, an effective method was todelay harvesting of forage and food crops.Radiation control of products was introduced ateach stage of food production, storage andprocessing [4.3, 4.30].

Based on a radiological survey performedfrom May to July 1986, approximately 130 000,

17 300 and 57 000 ha of agricultural land wereinitially excluded from economic use in Belarus, theRussian Federation and Ukraine, respectively[4.31].

From June 1986 other countermeasures aimedat reducing 137Cs uptake into farm products wereimplemented as follows:

(i) Banning cattle slaughter in regions where137Cs contamination levels exceeded 555 kBq/m2 (animals had to be fed clean food for1.5 months before slaughter);

(ii) Minimizing external exposure and formationof contaminated dust by omitting someprocedures normally used in crop production;

(iii) Limiting the use of contaminated manure forfertilization;

(iv) Preparation of silage from maize instead ofhay;

(v) Restricting the consumption of milk producedin the private sector;

(vi) Obligatory radiological monitoring of agricul-tural products;

(vii) Obligatory milk processing.

Decontamination by removal of the top soillayer was not found to be appropriate for agricul-tural lands because of its high cost, destruction ofsoil fertility and severe ecological problems relatedto burial of the contaminated soil.

As early as August–September 1986 eachcollective farm received maps of contaminationlevels of their agricultural land and guidance onpotential contamination of products, includinginstructions on the farming of private plots [4.3,4.30].

In western Europe advice was initially givenon avoiding the consumption of drinking waterfrom local supplies in some countries.

Sweden received some of the highest levels ofdeposition outside of the countries of the formerUSSR. Initially, Sweden imposed action levels on131I and 137Cs activities in imported and domesticfoods (see Section 4.1.2). A range of otherresponses were applied: (a) cattle were not put on topasture if the ground deposition exceeded 10 kBq/m2 of 131I and 3 kBq/m2 of radiocaesium; (b) advicewas given not to consume fresh leafy vegetables andto wash other fresh vegetables; (c) restrictions wereplaced on the use of sewage sludge as fertilizer forsoil; (d) deep ploughing was recommended; and (e)a higher cutting level for harvesting of grass wasadvised.

76

In Norway, crops in fields were monitoredafter harvesting, and those with radiocaesium above600 Bq/kg fresh weight were discarded and ploughedin. Also, hay and silage harvested in June weremonitored, and that with activity concentrationsexceeding the guidelines was not used as forage.

In Germany some milk in Bavaria wasdiverted into food processing plants to be convertedinto milk powder. It was intended to use the milkpowder as feed for pigs, but this was not done due tothe high radiocaesium content.

In the UK advice was issued for the regulationof the consumption of red grouse, and restrictionswere imposed on the movement and slaughter ofupland sheep from a number of the more contami-nated areas of the UK.

In Austria there was advice not to feed freshgrass to cows for a short period in May 1986 [4.32].

4.3.2. Late phase

Radiological surveys of agricultural productsshowed that by the end of 1986 four regions of theRussian Federation (Bryansk, Tula, Kaluga andOrel), five regions of Ukraine (Kiev, Zhytomyr,Rovno, Volyn and Chernigov) and three regions ofBelarus (Gomel, Mogilev and Brest) had foodproducts that exceeded the action levels for radio-caesium. In the more contaminated areas of theGomel, Mogilev, Bryansk, Kiev and Zhytomyrregions in the first year after the accident, theproportion of grain and milk exceeding the actionlevels was about 80% [4.3, 4.7, 4.26].

Additionally, in the early 1990s in Ukraine,101 285 ha of agricultural land was withdrawn fromagricultural use (about 30% of this area had a 137Cscontamination level above 555 kBq/m2). Privatelyowned cattle were moved with the people fromsome settlements. Provision of ‘clean’ foodstuffsproduced in the collective sector or imported from‘clean’ regions was organized for those residents notresettled.

In the Russian Federation in 1987–1988further evacuations of agricultural animals werecarried out, but on a more elective basis than inUkraine. All sheep in the areas contaminated atover 555 kBq/m2 were removed, because of the hightransfer of radiocaesium to these ruminants. Ofcattle in the regions above 555 kBq/m2, 6880animals were removed, but many families retainedtheir animals.

In Belarus in 1989, 52 settlements wererelocated after decontamination and counter-

measure use were found to be inadequate to lowerdoses to an acceptable level. Additionally, in 1991under two new laws, some people were allowed toresettle away from contaminated areas, and somesettlements were moved. In total, 470 settlementswere moved. In all these resettlements, the agricul-tural animals accompanied their owners to the newlocations where possible.

Application of countermeasures in contami-nated areas had two major radiation protectionaims. The first was to guarantee foodstuffproduction corresponding to the action levels and toensure an annual effective dose to local inhabitantsof less than 1 mSv. The second was to minimize thetotal flux of radionuclides in agriculturalproduction. Generally, the earlier agriculturalcountermeasures were applied, the more costeffective they were [4.33].

From 1987 high radiocaesium activity concen-trations in agricultural products were only observedin animal products; application of countermeasuresaimed at lowering 137Cs activity concentrations inmilk and meat was the key focus of the remediationstrategy for intensive agriculture. Potatoes and rootvegetables were being produced with acceptablylow radiocaesium levels. In the second year after theaccident the radiocaesium activity concentration ingrain was much lower than in the first year, andcountermeasure application ensured that most grainwas below the action levels. By 1991 less than 0.1%of grain in all three countries had radiocaesiumcontents above 370 Bq/kg.

The most difficult issue remaining was theproduction of milk in compliance with thestandards. However, large scale application of arange of countermeasures (described below) madeit possible to achieve a sharp decrease in theamount of animal products with radiocaesiumactivity concentrations above the action levels in allthree countries. Changes with time of milk and meatexceeding the action levels can be seen in Fig. 4.2. Itshould be noted that the values of the action levelshave been reduced with time in each of the threecountries, so the data are not directly comparable.Changes in the action levels in each country areshown in Fig. 4.3.

The differences in the time trend shown inFig. 4.2 among the countries mainly relate tochanges in the action levels but also to the scale ofcountermeasure application. This is particularlyclear for Russian milk, where radiocaesiumactivity concentrations rose after 1997 due to areduction in countermeasure use. The recent

77

reduction in the amounts of meat above the actionlevels in Ukraine and Belarus is because animalsare monitored before slaughter to ensure that themeat is below the required level. In the RussianFederation, where animals are also monitoredbefore slaughter, the concentration data arehigher, because they refer to both privately andcollectively produced meat.

The maximum effect from countermeasureapplication was achieved in 1986–1992. Thereafter,because of financial constraints in the mid-1990s,the use of agricultural countermeasures wasdrastically reduced. However, by optimizingavailable resources, 137Cs countermeasureeffectiveness remained at a level sufficient to

maintain an acceptable 137Cs content in most animalproducts (Fig. 4.2).

4.3.3. Countermeasures in intensive agricultural production

The main countermeasures used in the USSR,and later in the three independent countries, arebriefly described below. The priority was onchemical amendments to improve soil fertility andto reduce the uptake of radiocaesium by crops andplants used for fodder. The extent to which eachmeasure was used varied among the three countries.The recommendations on countermeasures havebeen repeatedly revised and updated [4.35–4.37].

1

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68918891

09912991 1

499 9916 8991

00022002

4002

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Belarus

(a)

1

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68918891

09912991

49916991

89910002

2002

Year

Russian Federation

Ukraine

Belarus

(b)

t (1

000)

t

FIG. 4.2. Amounts of milk (a) and meat (b) exceeding the action levels in the Russian Federation (collective and private),Ukraine and Belarus (only milk and meat entering processing plants) after the Chernobyl accident [4.26].

0

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150

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Year

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Ukraine

Belarus

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Year

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Belarus

TPL

for

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t (B

q/k

g)

TPL

for

milk

(Bq

/L)

FIG. 4.3. Changes with time in the action levels (TPL) in the USSR and later in the three independent countries [4.34].

78

4.3.3.1. Soil treatment

Soil treatment reduces uptake of radio-caesium (and radiostrontium). The procedure caninvolve ploughing, reseeding and/or the applicationof nitrogen, phosphorus, potassium (NPK)fertilizers and lime. Ploughing dilutes theradioactive contamination originally in the uppersoil layers, where most plant roots absorb theirnutrients. Both deep and shallow ploughing wereused extensively, and skim and burial ploughingwere also used. The use of fertilizers increases plantproduction, thereby diluting the radioactivity in theplant. In addition, the use of fertilizers reduces rootuptake into plants by decreasing the Cs:K ratio inthe soil solution [4.30].

When soil treatment includes all the abovemeasures it is commonly called radicalimprovement; this has been found to be the mostefficient and practical countermeasure for meadowscontaminated by Chernobyl fallout. In the first fewyears after the accident the focus was on radicalimprovement, including greatly increased fertili-zation rates. Commonly, high value legumes andcereal grasses were grown on the treated land. Thenature of the treatment and the efficiency of theradical improvement of hay meadows and pasturesstrongly depend on the type of meadow and the soilproperties. Traditional surface improvement,involving soil discing, fertilization and surfaceliming, was less effective. Some marshy plots weredrained, deep ploughed, improved and used asgrassland. In the 1990s there was a greater focus onsite specific characteristics to ensure that the soiltreatment used was the most appropriate and

effective for the prevailing conditions. With time,repeated fertilization of already treated soils wasnecessary, but the appropriate application rateswere carefully assessed. However, actual rates ofapplication were sometimes constrained by availa-bility of funds [4.30, 4.38].

Areas that received additional fertilizers ineach of the three most affected countries are shownin Fig. 4.4; areas receiving radical improvement areshown in Fig. 4.5. The average amount of additionalpotassium fertilizers added was about 60 kg/ha ofK2O annually between 1986 and 1994. In the mid-1990s the productivity of arable land fell because aworsening economic condition prevented the imple-mentation of countermeasures at the previous rates;this resulted in an increasing proportion of contami-nated products. In some areas of the Russian

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7000

8000

Year

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Ukraine

Belarus

1986–1990 1991–1995 1996–2000 2001–2003

(a) (b)

ha (1

000)

FIG. 4.4. Changes in the extent of agricultural areas treated with liming (a) and mineral fertilizers (b) in the countries mostaffected by the Chernobyl accident [4.34].

0

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Year

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Ukraine

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ha (1

000)

FIG. 4.5. Areas of radical improvement in the countriesmost affected by the Chernobyl accident [4.34].

79

Federation this halted the previous decrease in theamounts of milk and meat exceeding the radiationsafety standards (see Fig. 4.2); for example, in themore contaminated areas, such as Novozybkov(Bryansk region), because of insufficient use ofpotassium fertilizers, 137Cs activity concentrations inagricultural products in 1995–1996 increased bymore than 50% compared with the period ofoptimal countermeasure application (1991–1992).

The effectiveness of soil treatment isinfluenced by soil type, nutrient status and pH, andalso by the plant species selected for reseeding. Inaddition, the application rates of NPK fertilizersand lime affect the reduction achieved. Severalstudies have shown that the reduction factorsachieved for soil–plant transfer of radiocaesiumfollowing radical improvement, liming and fertili-zation were in the range of two to four for poor,sandy soils and three to six for more organic soils.An added benefit was the reduction in external doserate by a factor of two to three due to the dilution ofthe surface contamination layer after ploughing.

Even though the radiological problemsassociated with 90Sr are less acute than those of137Cs, some countermeasures have been developedand a reduction of two to four in the soil–planttransfer of radiostrontium following discing,ploughing and reseeding has been achieved.

Despite these countermeasures, in the morehighly contaminated areas of the Bryansk regionthe radiocaesium contamination of 20% of thepasture and hay on farms still exceeded the actionlevels in 1997–2000. Concentrations of 137Cs in hayvaried between 650 and 66 000 Bq/kg dry weight.

4.3.3.2. Change in fodder crops grown on contaminated land

Some plant species take up less radiocaesiumthan others, as can be seen from experimental datacollated in Belarus from 1997 until 2002 (Fig. 4.6).The extent of the difference is considerable, andfodder crops such as lupin, peas, buckwheat andclover, which accumulate high amounts of radio-caesium, were completely or partly excluded fromcultivation.

In Belarus rapeseed is grown on contaminatedareas with the aim of producing two products:edible oil and protein cake for animal fodder.Varieties of rapeseed are grown that have a twofoldto threefold lower 137Cs and 90Sr uptake rate thanother varieties. When the rapeseed is grown,additional fertilizers (liming with 6 t/ha and fertili-

zation with N90P90K180) are used to reduce radio-caesium and radiostrontium uptake into the plantby a factor of about two. This reduces contami-nation of the seed that is used for the protein cake.During processing of the rapeseed, both radio-caesium and radiostrontium are effectivelyremoved, and negligible amounts remain. Theproduction of rapeseed oil in this way has proved tobe an effective, economically viable way to usecontaminated land and is profitable for both thefarmer and the processing industry. During the pastdecade the area under rapeseed cultivation hasincreased fourfold to 22 000 ha [4.40].

4.3.3.3. Clean feeding

The provision of uncontaminated feed orpasture to previously contaminated animals for anappropriate period before slaughter or milking(‘clean’ feeding) effectively reduces radionuclidecontamination, respectively, in meat and milk at arate that depends on the animal’s biological half-lifefor each radionuclide. Radiocaesium activityconcentration in milk responds rapidly to changes indiet, as the biological half-life is a few days. Formeat the response time is longer, due to the longerbiological half-life in muscle [4.28].

Clean feeding reduces uptake of the contami-nating radionuclides; it has been one of the mostimportant and frequently used countermeasuresafter the Chernobyl accident for meat from agricul-tural animals in both the countries of the formerUSSR and western Europe. Official estimates of thenumber of cattle treated are between 5000 and20 000 annually in the Russian Federation and20 000 in Ukraine (supported by the government up

0

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Carrot Cabbage Tomato Potato Haricot Table Cucumber Radish Peabeet

Per

cent

age

com

par

ed w

ith p

eas

FIG. 4.6. Comparison of 137Cs uptake in different crops,normalized to that of peas [4.39].

80

to 1996) [4.3]. Clean feeding is routinely used in allthree countries for meat production and iscombined with live monitoring of animals, so that ifanimal flesh is above the action levels the animalscan be returned to the farm for further cleanfeeding.

4.3.3.4. Administration of caesium binders

Hexacyanoferrate compounds (commonlyreferred to as Prussian blue) are highly effectiveradiocaesium binders. They may be added to thediet of dairy cows, sheep and goats, as well as tomeat producing animals, to reduce radiocaesiumtransfer to milk and meat by reducing absorption inthe gut. They have a low toxicity and are thereforesafe to use. Many different formulations of hexa-cyanoferrates have been developed in differentcountries, partly to identify the most effectivecompound and partly to produce a cheaper, locallyavailable product. Hexacyanoferrate compoundscan achieve reduction factors in animal products ofup to ten [4.41].

Prussian blue can be added to the diet ofanimals as a powder, incorporated into pelletedfeed during manufacturing or mixed with sawdust.A locally manufactured hexacyanoferrate calledferrocyn (a mixture of 5% KFe[Fe(CN)6] and 95%Fe4[Fe(CN)6]) has been developed in the RussianFederation. It has been administered as 98% purepowder, salt licks (10% ferrocyn) and in sawdustwith 10% adsorbed ferrocyn (called bifege) [4.42].

The number of cattle treated annually withPrussian blue in each of the three countries is shownin Fig. 4.7. In addition, slow release boli containinghexacyanoferrate have been developed that areintroduced into the animals’ rumen and graduallyrelease the caesium binder over a few months. Theboli, originally developed in Norway, consist of a

compressed mixture of 15% hexacyanoferrate, 10%beeswax and 75% barite [4.43].

Prussian blue has been used to reduce the137Cs contamination of animal products since thebeginning of the 1990s. Prussian blue applicationhas been especially useful and effective insettlements where there is a lack of meadowssuitable for radical improvement. In initial trials,Prussian blue reduced 137Cs transfer from fodder tomilk and meat by a factor of 1.5–6.0 [4.44]. InBelarus a special concentrate with Prussian blue isdistributed at a rate of 0.5 kg of concentrate per cowdaily, and an average value of three for thereduction factor for milk has been achieved.

Prussian blue has not been used as extensivelyin Ukraine as in the Russian Federation andBelarus, and its use was confined to the early 1990s.This is because in Ukraine no local source ofPrussian blue is available and the cost of purchasingit from western Europe was considered to be toohigh. Therefore, instead, locally available claymineral binders have been used on a small scale.These were cheaper but somewhat less effectivethan Prussian blue.

4.3.4. Summary of countermeasure effectiveness in intensive production

The effectiveness of the different agriculturalcountermeasures in use on farms is summarized inTable 4.5. The reduction factors (ratio of radio-caesium activity concentration in the product beforeand after countermeasure application) achieved byeach measure are given.

4.3.5. Countermeasures in extensive production

Extensive production in the three countries ofthe former USSR is largely confined to the grazingof privately owned cattle on poor, unimprovedmeadows. Owing to the poor productivity of theseareas, radiocaesium uptake is relatively highcompared with land used by collective farms.Radical improvement of meadows used by privatelyowned cattle has been applied in all three countriessince the early 1990s. Clean feeding is not generallyused by private farmers, although, on occasions,collective farms may supply private farmers withuncontaminated feed or pastures. Prussian blue isused by private farmers in both the RussianFederation and Belarus. In the Russian Federationall three Prussian blue delivery systems are used,according to availability and preference [4.46].

0

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30

35

Russia

Ukraine

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Year

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ber

of t

reat

ed c

attle

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0)

1991

1992

1993

1994

1995

1996

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1998

1999

2000

2001

2002

2003

FIG. 4.7. Changes with time in the use of Prussian blue inthe three countries of the former USSR (provided byForum participants from official national sources).

81

In extensive systems such as upland grazedareas in western Europe, the most commonly usedcountermeasures for free ranging animals havebeen clean feeding, administration of caesiumbinders, monitoring of live animals, managementrestrictions and changes in slaughter times. Many ofthese countermeasures were still in use in 2004. Theapplication of long term countermeasures has beenmost extensive in Norway and Sweden, but longterm countermeasures have also been applied in theUK and Ireland.

AFCF is a highly effective hexacyanoferratecompound achieving up to a fivefold reduction inradiocaesium in lamb and reindeer meat and up to athreefold reduction in cow’s milk and a fivefoldreduction in goat’s milk. The use of AFCF has beentemporarily authorized in the EU and in some othercountries. AFCF as a caesium binder is effective inextensive production systems, in contrast to manyother countermeasures whose applicability islimited. Boli are particularly favourable for infre-quently handled free grazing animals, as the boli canbe administered when animals are gathered forroutine handling operations. For use in extensivesystems, the boli can be given a protective surfacecoating of wax to delay the onset of AFCF release,

so that effectiveness is increased at the time whenanimals are collected for slaughter [4.47]. It hasbeen estimated that the use of boli as a counter-measure for sheep was 2.5 times as cost effective asfeeding with uncontaminated feed [4.48]. Salt lickscontaining AFCF have also been used, but are lesseffective [4.49].

Management regimes have been modified forsome animals in contaminated areas; for example,slaughter times are modified to ensure that the 137Csactivity concentrations are relatively low. In the UKthe movement and slaughter of upland sheep arerestricted in some areas. The animals are monitoredto ensure that their 137Cs activity concentrations arebelow the action level before they are slaughtered.

Live monitoring of animal derived products(monitoring of live animals and/or of milk andtissues after slaughter) has been used to ensure thatcountermeasures have been effective. The use ofmonitoring is also important in maintaining publicconfidence in the products from affected areas.

An example of the long term consequences ofthe accident can be seen in Fig. 4.8, which shows thenumber of reindeer in Sweden that had radio-caesium activity concentrations above the actionlevel and the number of slaughtered animals. The

TABLE 4.5. SUMMARY OF THE REDUCTION FACTORS ACHIEVED WITH THEDIFFERENT COUNTERMEASURES USED IN THE THREE COUNTRIES OF THEFORMER USSR [4.30, 4.34, 4.40, 4.45]

Caesium-137 Strontium-90

Normal ploughing (first year) 2.5–4.0 —

Skim and burial ploughing 8–16 —

Liming 1.5–3.0 1.5–2.6

Application of mineral fertilizers 1.5–3.0 0.8–2.0

Application of organic fertilizers 1.5–2.0 1.2–1.5

Radical improvement:First applicationFurther applications

1.5–9.0a

2.0–3.01.5–3.51.5–2.0

Surface improvement:First applicationFurther applications

2.0–3.0a

1.5–2.02.0–2.51.5–2.0

Change in fodder crops 3–9 —

Clean feeding 2–5 (time dependent) 2–5

Administration of caesium binders 2–5 —

Processing milk to butter 4–6 5–10

Processing rapeseed to oil 250 600

a For wet peat, up to 15 with drainage.

82

high number of slaughtered animals in the first yearwas in part due to the low action level of 300 Bq/kgfresh weight, which was subsequently increased to1500 Bq/kg from 1987. The decline has beenachieved partly by extensive use of counter-measures, including clean feeding and change ofslaughter time.

4.3.6. Current status of agricultural countermeasures

Currently in all three countries of the formerUSSR clean feeding remains an important counter-measure to ensure that meat from intensive farmscan be marketed.

In Belarus, fertilization with phosphorus–potassium is used on collective farms, and milkabove the action level from the farms is processedinto butter. Radical improvement is used on privatefarms together with Prussian blue for milk.Rapeseed production is currently limited byprocessing capacity, although this may be increasedin the future.

In Ukraine the only remaining countermeasureused on intensive systems is clean feeding of meatproducing animals prior to slaughter. Any milkabove the action level is used within the settlements,partially to feed pigs. All other countermeasures aredirected at private farmers. These countermeasurescurrently comprise the radical improvement ofmeadows and the use of clay mineral caesiumbinders for privately produced milk.

In the Russian Federation, fertilizers (largelypotassium) are supplied to intensive farms. For

private farms, Prussian blue is provided forprivately produced milk and, on request, forprivately produced meat intended for market.

In all contaminated settlements a service forthe monitoring of local produce exists, although thecapacity and availability of the service varies.

In western Europe countermeasures foranimals in extensive systems are still used inNorway and Sweden, and the movement andslaughter of upland sheep are still restricted incertain areas of the UK.

4.3.7. A wider perspective on remediation, including socioeconomic issues

Experience after the Chernobyl accident hasshown that account has to be taken, in developingrestoration strategies, of a wide range of differentissues to ensure the long term sustainability of largeand varied types of contaminated areas [4.51]. Theselection of robust and practicable restorationstrategies should take into account not only radio-logical criteria but also: (a) practicability, includingeffectiveness, technical feasibility and the accepta-bility of the countermeasure; (b) cost–benefit; (c)ethical and environmental considerations; (d)requirements for effective public communication;(e) the spatial variation in many of these factors;and (f) the contrasting needs of people in urban,rural and industrial environments [4.52]. When notonly radiological factors but also social andeconomic factors are taken into account, betteracceptability of countermeasures by the public canbe achieved.

A number of European Commission (EC) andUnited Nations projects have applied some of theabove considerations in trying to provideappropriate information to, and interaction with,people in contaminated territories and in involvingthem in making decisions about responding toenhanced radiation doses and about ways of livingsustainably in contaminated areas. In particular, thisintroduces the possibility of self-help and theopportunity for people to decide for themselveswhether they wish to modify their behaviour toreduce their doses. The EC ETHOS project [4.53,4.54] identified the dissemination of a practicalradiological culture within all segments of thepopulation as a prerequisite, especially for profes-sionals in charge of public health. The EC TacisProgramme ENVREG project [4.55] in Belarus andUkraine sought to minimize the environmental andsecondary medical effects resulting from the

0

20 000

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1968

8/7

19

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888/9

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9/1

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Part of slaughter above the action level

Num

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eind

eer

per

yea

r

FIG. 4.8. Change with time in the number of reindeer inSweden with radiocaesium activity concentrations abovethe action level and in the number of slaughtered animals[4.50].

83

Chernobyl accident by improving the publicperception and awareness of these effects.

Most recently, the EC CORE project [4.56]was initiated to address long term rehabilitation andsustainable development in the Bragin, Chechersk,Slavgorod and Stolin areas of Belarus. COREcommunity projects include health care, radio-logical safety, information and education. Inaddition, critical socioeconomic constraints arebeing addressed, specifically using a creditingsystem for small businesses and farmers, the costeffective production of ‘clean’ products, thecreation of a rural entrepreneurs’ centre and thepromotion of community economic initiatives.

The Chernobyl debate is increasingly aboutsocioeconomic issues and the communication oftechnical information in an understandable way.The ETHOS, ENVREG and CORE projects allhave a strong community focus and targetChernobyl affected communities and other localstakeholders. Feedback from the communitiesshould indicate which approaches are provingsuccessful and to what extent. The holisticphilosophy of these projects of considering bothenvironmental and social problems is in line withthe recent United Nations initiative known asStrategy for Recovery [4.57].

4.3.8. Current status and future of abandoned land

In this section the extent of recovery ofabandoned land is summarized for each of the threecountries of the former USSR. In 2004, 16 100,11 000 and 6095 ha of previously abandoned land inBelarus, the Russian Federation and Ukraine,respectively, were returned to economic use [4.26].In general, there is currently little effort beingdevoted to any further rehabilitation of abandonedareas.

4.3.8.1. Exclusion and resettlement zones in Belarus

The CEZ covers a total of 215 000 ha inBelarus. The people who used to reside there wereevacuated in 1986. Since May 1986, lands in theCEZ have been taken out of agricultural and otherproduction. The Polessye State RadioecologicalReserve (PSRR) was set up by a government decreein 1988 and comprises mainly the CEZ but alsoincludes some other areas with high levels of trans-uranium radionuclide contamination. Access to thePSRR is forbidden and very few, mostly old, people

are currently present, without permission, in thearea. Pursuant to the law on the legal regime ofterritories contaminated as a result of theChernobyl nuclear power plant accident [4.58],most of the land in the CEZ cannot be brought backinto economic production within a millennium,because of contamination with long lived trans-uranium radionuclides. In the CEZ only activitiesrelated to ensuring radiation safety, fighting forestfires, preventing the transfer of radioactivesubstances, protecting the environment andscientific research and experimental work arepermitted.

While the CEZ (i.e. the Bragin, Khoiniki andNarovlya areas of the Gomel region) is the mostcontaminated area adjacent to the Chernobylnuclear power plant, a further resettlement zonewas identified in the early 1990s from which morepeople were evacuated; this zone covers a total areaof 450 000 ha.

A total area of agricultural land of 265 000 hareceived a deposition of 137Cs at levels in excess of1480 kBq/m2 and/or of 90Sr in excess of 111 kBq/m2

and/or of plutonium isotopes in excess of3.7 kBq/m2. All this land is excluded from agricul-tural use.

The remaining abandoned agricultural land inthe resettlement zone could be used for agriculturein the future. The present state of the ecosystemsand the economic infrastructure of the resettlementzone are characterized by a general deterioration inthe former agricultural lands, drainage systems androads. Due to lack of drainage, there has also been agradual elevation in the water table. Normalecological succession has led to an increase in thenumber of perennial weeds and shrubs. Unlike inthe CEZ, in the resettlement zone limited access forcertain maintenance activities, such as the activitiesneeded to maintain roads, electricity transmissionlines, etc., is permitted.

In Belarus it is considered to be important tobring lands back to agricultural use, if possible. Atthe request of collective and State farms, ifsupported by local authorities, surveys of formeragricultural lands were conducted to determinewhether it is possible to rehabilitate the land foragricultural use. This was based on radiologicalconsiderations only.

By 2001 a total of 14 600 ha of previouslywithdrawn land had been returned to use [4.34], andrecently this has been increased to about 16 000 ha.This land is closely adjacent to populatedsettlements. In these rehabilitated sites the soil

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fertility has been restored and a variety of counter-measures has been used to minimize radiocaesiumand radiostrontium uptake based on officialguidelines [4.37].

Most of the agricultural and other land of theresettlement zone was transferred to the authorityof the Ministry of Forestry. This is because much ofthe resettlement zone is considered suitable forforest production.

According to an assessment by Bogdevitch etal. [4.59], a total of about 35 000 ha of the morefertile agricultural land may be suitable for furtherrehabilitation. However, economic support forrecovery and use of countermeasures has declinedsignificantly over recent years. Use of counter-measures is now confined to radical improvement ofmeadows, feeding of Prussian blue to cattle, limingand fertilization.

Methodologies for the rehabilitation ofabandoned land are being developed and improved,in particular with respect to economic evaluation.The main obstacles to the renewed agricultural useof abandoned land are the destroyed infrastructure,the high production cost and the low marketdemand for the agricultural goods. A large scalerehabilitation of excluded land will only be possibleif there is a general improvement in the economicsituation of the country.

4.3.8.2. Rehabilitation of contaminated lands in Ukraine

The first priority was the rehabilitation of landon which people are living. Consideration has sincebeen given to the potential rehabilitation ofabandoned areas. Such areas can be rehabilitated ifthis procedure is expedient with respect toeconomic and social criteria. The main condition forhuman occupancy of such areas without restrictionsis that the additional annual effective dose shouldnot exceed 1 mSv.

The efficiency of countermeasures isdetermined by the following criteria:

(a) Radiological: reduction of radionuclidecontent in local products and in the associatedindividual and collective dose.

(b) Economic: increased product market value.(c) Social and psychological: public opinion on a

given countermeasure.

In 2004, on the basis of radiological criteriaalone, a significant part of the abandoned agricul-tural lands (more than 70%) could be returned toeconomic use. When economic and social criteriaare assessed, the amount of land that could berehabilitated declines (see Table 4.6). Table 4.6

TABLE 4.6. REHABILITATION OF ZONES OF OBLIGATORYRESETTLEMENT (OUTSIDE THE CHERNOBYL EXCLUSION ZONE)a

Area Abandoned land (ha)Can be rehabilitated judged on radiological, economic

and social criteria (ha)

Kiev region

1998–2000 (done) — 3475

2001–2005 — 4720

Total 29 342 8205

Zhytomyr region

1998–2000 (done) — 2620

2001–2005 — 4960

Total 71 943 7580

a Provided by Forum participants from official national sources.

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shows a scheme for rehabilitation based ontechnical criteria over a seven year period The firstphase, from 1998 until 2000, was implemented, butthat for the second phase was not, due to changingeconomic and social conditions.

In the CEZ, the limiting radionuclide is now90Sr rather than 137Cs. On the basis of radiologicalconsiderations, the south-west part of the zone canbe used without restrictions. However, in reality,legal restrictions, the lack of a suitable infra-structure and consideration of economic and social–psychological factors prevent its rehabilitation.

The same restrictions apply to the otherabandoned areas, where legal restrictions are also inforce that, together with deteriorating economicconditions, currently prevent the application ofcountermeasures in the remaining identifiedabandoned areas. The pressure to bring theabandoned land back into production is alsoreduced by the current abundance of agriculturallyproductive land in Ukraine and the presence insouthern Ukraine of land that is much moreproductive.

Some people have returned to abandonedareas to live, and others live outside them but usethe land for agricultural activities such as hayproduction. Countermeasures are not being appliedin the abandoned areas, but there is sanitary andregulatory control of these activities.

4.3.8.3. Abandoned zones in the Russian Federation

Areas in the Russian Federation with highlevels of radioactive soil contamination wereabandoned in stages from 1986 until 1989, and intotal 17 000 ha of agricultural land was excludedfrom economic use. The abandoned areas belongedto 17 rural settlements with about 3000 inhabitants(at the time of the accident) and 12 collective farms.

In 1987–1989 considerable efforts were madeto keep the highly contaminated areas in economicuse, and hence most of the abandoned areas weresubjected to intensive countermeasure application.However, these efforts were only partiallysuccessful, and the land was gradually abandoned;in the 1990s, the intensity of countermeasureapplication was reduced. Overall, about 11 000 hawas returned to agricultural use by 1995. Thesedecisions to return land to agricultural use weremade individually for each contaminated field.Special attention was paid to highly contaminatedfields surrounded by fields with relatively low levels

of contamination, because there was a naturalinclination to use these fields. The assessments werebased on Russian radiation safety standards,including standards governing the quality of agricul-tural products (TPL-93) [4.60].

Between 1995 and 2004 there was no furtherrehabilitation of the abandoned areas. Officiallythey are abandoned but, unofficially, some localpeople are living in these areas and using them foragricultural production, but without the benefit ofcountermeasures.

Recently, a technical project of gradualrehabilitation of the remaining abandoned areas, inwhich the mean 137Cs soil deposition varies from1540 to 3500 kBq/m2, has been proposed by theRussian Institute of Agricultural Radiology andAgroecology. The criteria for agriculturalproduction include ensuring that 137Cs activityconcentrations would be less than the TPL, as wellas a requirement that application of counter-measures for each contaminated field would beoptimized. During the first planned stage, up to2015, it is proposed to produce grain and potatoesusing agricultural workers who live elsewhere butwould come into the contaminated area asnecessary. Soil based countermeasures (liming,potassium fertilization) should allow the productionof plant products with sufficiently low levels of 137Cson most of the abandoned area. From 2015 theimplementation of animal breeding is planned, andfrom 2025 the re-establishment of populatedsettlements could commence. Thus by 2045 allabandoned land could be used once more, althoughapplication of different countermeasures would beneeded up to 2055 to ensure that annual doses tothe local inhabitants were less than 1 mSv.

4.4. FOREST COUNTERMEASURES

Countermeasures for forested areas contami-nated with radionuclides are only likely to beimplemented if they can be accepted by foresters orlandowners on a practical basis (i.e. actions arelikely to fit in with normal forest managementpractices). For countermeasures to be successfulthey must also be accepted by the general public. Asforest countermeasures are labour consuming andexpensive, they cannot be implemented quickly andmust be planned carefully. They are likely to be longterm activities and their beneficial effects take timeto be realized.

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4.4.1. Studies on forest countermeasures

Generally, prior to the Chernobyl accidentcountermeasures to offset doses due to large scalecontamination of forests had not been given verymuch attention. Several international projects inthe 1990s gave rise to a number of publications inwhich suggestions and recommendations weremade for possible countermeasures to be appliedin forests [4.61–4.64]. However, in the threecountries of the former USSR, actions had alreadybeen taken to restrict activities in the morecontaminated zones, which included significantareas of forestry [4.65]. These actions were, ingeneral, rather simple and involved restrictions onbasic activities such as accessing forests andgathering wild foods and firewood. A majorquestion remains as to whether any more complexor technologically based countermeasures can beapplied in practice, and whether the ideasdeveloped by researchers will remain astheoretical possibilities rather than as methodsthat can be applied in real forests on a realisticscale. The following section describes some of themore feasible countermeasures that have beendevised for forests contaminated with radio-caesium. This is illustrated in Section 4.4.3 bystudies in which countermeasures have actuallybeen put into practice.

4.4.2. Countermeasures for forests contaminated with radiocaesium

There are several categories of counter-measure that are, in principle, applicable to forestecosystems [4.66, 4.67]. A selection of these isshown in Table 4.7. These can be broadlycategorized into (a) management based and (b)technology based countermeasures.

4.4.2.1. Management based countermeasures

Under the broad heading of managementbased countermeasures, the principal remedialmethods applied after the Chernobyl accidentinvolved restrictions on various activities normallycarried out in forests. Restriction of access tocontaminated forests and restriction of the use offorest products were the main countermeasuresapplied in the USSR and later in the threeindependent countries [4.65]. These restrictions canbe categorized as follows:

(a) Restricted access, including restrictions onpublic and forestworker access. This has beenassisted by the provision of information fromlocal monitoring programmes and educationon issues such as food preparation [4.65].

(b) Restricted harvesting of food products by thepublic. The most commonly obtained foodproducts include game, berries andmushrooms. The relative importance of thesevaries from country to country. In the threecountries of the former USSR, mushrooms areparticularly important and can often beseverely contaminated.

(c) Restricted collection of firewood by thepublic. This not only exposes people to in situgamma radiation while collecting firewoodbut can also lead to further exposures in thehome and garden when the wood is burnedand the ash is disposed of, sometimes beingused as a fertilizer.

(d) Alteration of hunting practices. Theconsumption of fungi by animals such as roedeer leads to strong seasonal trends in theirbody content of radiocaesium (see Section3.3). Thus excessive exposures can be avoidedby eating the meat only in seasons in whichfungi are not available as a food source for theanimals.

(e) Fire prevention is a fundamentally importantpart of forest management under any circum-stances, but it is also important after a largescale deposition to avoid secondary contami-nation of the environment, which could resultfrom burning of trees and especially forestlitter, which is one of the major repositories ofradiocaesium in the forest system (see Section3.3). One of the ways in which forest fires canbe avoided is by minimizing human presencein the forest, so this countermeasure isstrongly linked to restricting access, asdescribed above.

4.4.2.2. Technology based countermeasures

This category of countermeasures includes theuse of machinery and/or chemical treatments toalter the distribution or transfer of radiocaesium inforests. Many mechanical operations are carried outas part of normal forestry practice; examples ofthese have been described by Hubbard et al. [4.69]with reference to their use as countermeasures.Similarly, applications of fertilizers and pesticidesmay be made at different times in the forest

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TABLE 4.7. SELECTED COUNTERMEASURES THAT HAVE BEEN CONSIDERED FOR APPLICA-TION IN CONTAMINATED FORESTS [4.68]

Countermeasure Category Caveat Benefit Cost

Normal operation Management — No loss of productivity or amenity

No dose reduction and negative social costs

Minimum management: forest fire protection, disease protection and necessary hunting

Management — Creation of nature reserve and reduced worker dose

Worker dose, loss of productivity, negative social costs and costs for hunting

Delayed cutting of mature trees

Management/agrotechnical

Marginal feasibility Reduced contamination of wood due to:— Radioactive decay— Fixation of caesium

in soil— Loss from soil and

wood

Delay in revenue

Early clear cutting and replanting or self-regeneration

Management/agrotechnical

Must consider tree age at time of contamination; possibly in combination with soil mixing

Reduced tree contamination:— Lower soil–tree

transfer— Delayed harvest

time— Alternative tree

crop

Higher dose to workers during replanting and operational costs

Soil improvement: harrowing after thinning or clear cutting

Agrotechnical Cost effectiveness is dependent on the area to be treated; possibly in combination with fertilizer application

Improved tree growth, therefore growth dilution; dilutes radionuclide activity concentrations in the soil surface layer and decreases them in mushrooms, berries and understorey game

Operational costs, worker doses and environmental or ecological costs (e.g. nitrate and other nutrients lost)

Application of phosphorus–potassium fertilizer and/or liming

Agrotechnical Phosphorus–potassium: may only be effective for caesium, especially effective for younger standsLime: particularly useful for 90Sr

Reduction of uptake to trees, herbs, etc., maybe better growth and dilution effect and higher fixation

Cost of fertilizer, worker dose and negative ecological effects

Limiting public access Management Note: people normally residing in forests not considered

Reduction in dose, possible increase in public confidence

Loss of amenity/social value, loss of food and negative social impacts

Salt licks Agrotechnical — Reduction in caesium uptake by grazing animals

Continuing cost of providing licks

Ban on hunting Management — Reduction in dose due to ingestion of game

Need to find alternative supply of meat

Ban on mushroom collection

Management — Reduction in internal dose

Need to find alternative mushroom supply

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cropping cycle as part of normal managementpractice. However, the cost effectiveness of manytechnological countermeasures is questionable,especially when applied on a large scale [4.68]. Thusit is to be expected that such countermeasures willbe restricted to small scale cases only, if they arefeasible at all. Such cases might include small areasof urban woodland, such as parkland, which arelikely to be visited by many more people thanextensive and remote forest areas.

Technological countermeasures might includemechanical removal of leaf litter or scraping of soillayers, clear cutting and ploughing, and theapplication of calcium- and potassium-containingfertilizers. It is evident, however, that any of thesemethods can damage the ecological functioning ofthe forest when applied outside of the normalschedule of forestry operations. This, and the higheconomic costs of such operations, means that thepractical use of such techniques as countermeasuresremains largely speculative, and such measures havenot been applied after the Chernobyl accident otherthan in small scale experiments. Indeed, the resultsof cost–benefit calculations indicate that themanagement options likely to result in the leastoverall detriment are those which limit access andconsumption of forest foods. Options that involvetechnological intervention, application of chemicalsor altering the harvesting patterns in forests areunlikely to be used in practice.

4.4.3. Examples of forest countermeasures

Case studies in which forest countermeasures,particularly technology based countermeasures,have actually been applied in practice are rare. Thisillustrates the difficulty of implementing practicalremedial measures in forests, in contrast toagriculture, in which the application of fertilizers, inparticular, has been used with some success (seeSection 4.3). In practice, restrictive counter-measures were applied in the USSR, and later in thethree independent countries, as well as in a limitednumber of other countries, such as Sweden.

In the Bryansk region of the RussianFederation, individual restrictions on forestry andon the population living near forests wererecommended according to the level of 137Csdeposition. For forests receiving depositions greaterthan 1480 kBq/m2, access was only allowed forforest conservation, fire fighting and control ofpests and diseases. All forestry activity was stopped,and public access, including for collection of forest

plants, was prohibited. In forests receivingdepositions between 555 and 1480 kBq/m2,collection of forest products was also prohibited,but limited forestry activities continued. Atdeposition levels between 185 and 555 kBq/m2,harvesting of trees was continued on the basis ofradiological surveys that were used to identifyindividual areas in which external doses to forestryworkers and contamination of wood wereacceptable. However, the collection of berries andmushrooms by the public was only permitted inforests with deposition levels less than 74 kBq/m2.

One of the major effects of the restrictionsthat were enforced on a large scale up to 1990 was anegative impact on rural populations. At thebeginning of 1990 the population began gatheringmushrooms and berries again over the wholeBryansk region. However, in areas where theoriginal 137Cs deposition was between 555 and1480 kBq/m2, restrictions on gathering forest foodproducts are still in force. This example illustrates amajor difficulty in implementing countermeasuresinvolving restrictions on public activities thatinevitably lead to a disturbance of normal societalbehaviour patterns. Furthermore, wood productionis still under the official control of local forestauthorities [4.65]; the currently applicablepermissible levels for contamination of wood andforest products in the Russian Federation are shownin Table 4.8. Similar restrictions and permissiblelevels have been implemented in different regionsof Belarus, notably the Gomel and Mogilev regions.

The use of caesium binders, particularlyPrussian blue, in domestic animals has been one ofthe more effective techniques used to reduce dosesfrom contaminated forests in the three countries ofthe former USSR. The principles underlying thismethod are described in Section 4.3; they areequally applicable to the problem of marginalgrazing of domestic animals in forests. Typically,reductions in 137Cs activity concentrations of afactor of five in milk and a factor of three in meatcan be achieved at optimum dosage [4.65].

One example of intervention in normal forestrelated practices in countries outside the formerUSSR is the case of roe deer hunting in Sweden. In1988 the average muscle content of roe deer shot inthe autumn was 12 000 Bq/kg in the Gävle area. Theintervention level for such foodstuffs in Sweden is1500 Bq/kg. Such high levels of contamination ofroe deer meat were due to the preferentialconsumption of fungi by the deer in the autumn. Asa result of experiments, the Swedish authorities

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recommended a change of hunting season for roedeer to the spring; this change was appliedvoluntarily by the hunting community in the early1990s. As a result, the radiocaesium content in roedeer meat in Gävle was reduced by approximatelysix times. The recommendation to shift the huntingseason to the spring has remained in place until thepresent day [4.71].

In addition, the management of reindeer bythe Sami people in northern Sweden has beenaltered in a variety of ways to help reduce the radio-caesium content of animals before slaughter. Thisincludes provision of clean fodder for sufficient timeto reduce the body burden below the interventionlevel. A similar result can be achieved by alteringthe time of slaughter, sometimes in combinationwith feeding of clean fodder [4.72].

4.5. AQUATIC COUNTERMEASURES

There are a number of different interventionmeasures that can be employed following fallout ofradioactive material to reduce doses to the publicvia the surface water pathway. These actions may begrouped into two main categories: those aimed atreducing doses from radionuclides in drinking water

and those aimed at reducing doses from theconsumption of contaminated aquatic foodstuffs.

In the context of the atmospheric fallout ofradionuclides to both terrestrial and aquatic systems,it has been shown [4.73–4.75] that doses from terres-trial foodstuffs are in general much more significantthan doses from drinking water and aquaticfoodstuffs. However, in the Dnieper River system,the river water transported radionuclides to areasthat were not significantly contaminated by atmos-pheric fallout. This created a significant stress in thepopulation and a demand to reduce radionuclidefluxes from the affected zone via the aquatic system.Many remediation measures were put in place but,because actions were not taken on the basis of dosereduction, most of these measures were ineffective.Moreover, radiation exposures of workers imple-menting these countermeasures were high.

Measures to reduce doses via drinking watermay, however, be required, particularly in the shortterm (timescale of weeks) after fallout, whenactivity concentrations in surface waters arerelatively high. Owing to the importance of shortlived radionuclides, early intervention measures,particularly the changing of supplies, can signifi-cantly reduce radiation doses to the population.Measures to reduce doses due to freshwaterfoodstuffs may be required over longer timescalesas a result of the bioaccumulation of radionuclidesin the aquatic food chain.

Reviews of aquatic countermeasures (e.g.Refs [4.76–4.79]) have considered both direct(restrictions) and indirect intervention measures toreduce doses:

(a) Restrictions on water use or changing toalternative supplies;

(b) Restrictions on fish consumption;(c) Water flow control measures (e.g. dykes and

drainage systems);(d) Reduction of uptake by fish and aquatic

foodstuffs from contaminated water;(e) Preparation of fish prior to consumption.

There is no evidence that countermeasureswere required, or applied, in marine systems afterthe Chernobyl accident.

4.5.1. Measures to reduce doses at the water supply and treatment stage

Restrictions were placed on the use of waterfrom the Dnieper River for the first year after the

TABLE 4.8. TEMPORARY PERMISSIBLELEVELS FOR CAESIUM-137 IN WOOD ANDFOREST FOOD PRODUCTS IN THE RUSSIANFEDERATION [4.70]

TPL (Bq/kg)

Round wood, including bark 11 100

Unsawn timber with bark removed 3 100

Sawn wood (planks) 3 100

Construction wood 370

Wood used for pulp and paper production

3 100

Wood products for household use and industrial processing

2 200

Wood products for packing and food storage

1 850

Firewood 1 400

Mushrooms and berries (fresh weight) 1 480

Mushrooms and berries (dry weight) 7 400

Medical plants and medical raw material 7 400

Seeds of trees and bushes 7 400

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accident. Abstraction of drinking water for Kievwas switched to the Desna River with use of apipeline built during the first weeks after theaccident. A summary of the measures taken by theUkrainian authorities to switch to alternativesupplies from less contaminated rivers and fromgroundwater can be found in Refs [4.76, 4.79].

Radionuclides may be removed from drinkingwater supplies during the water treatment process.Suspended particles are removed during watertreatment, and filtration can remove dissolvedradionuclides. In the Dnieper waterworks station,activated charcoal and zeolite were added to waterfiltration systems. It was found that activatedcharcoal was effective in removing 131I and 106Ru,and zeolite was effective in removing 137Cs, 134Csand 90Sr. These sorbents were effective for the firstthree months, after which they became saturatedand their efficiency declined [4.80, 4.81]. Theaverage removal of these radionuclides from water(dissolved phase) was up to a factor of two.

After the accident, the upper gates of the Kievreservoir dam were opened to release surface water.It was believed at the time that the surface waterwas relatively low in radionuclide content, becausesuspended particles had sunk to deeper waters.Therefore, the release of water would allow room inthe reservoir to contain runoff water from theinflowing rivers, which was believed to be highlycontaminated. In fact, because of directatmospheric deposition to the reservoir surface, thesurface waters in the reservoir were much morecontaminated than the deep waters. As noted byVoitsekhovitch et al. [4.80], “a better approach tolowering the water level within the Kiev reservoirwould have been to open the bottom dam gates andclose the surface gates. This would have reduced thelevels of radioactivity in downstream drinking waterin the first weeks after the accident.” Although thiscountermeasure was not efficiently implementedafter the Chernobyl accident, regulation of flow,given the correct information on contamination,could effectively reduce activity concentrations indrinking water, as it takes some time (days or more)for lakes and reservoirs to become fully mixed.

In a large river–reservoir system such as theDnieper, control of water flows in the system cansignificantly reduce transfers of radioactive materialdownstream [4.82]. In the Dnieper River, the time ittakes for water to travel from the Kiev reservoir tothe Black Sea varies between three and ten months.Over the time that the water takes to traveldownstream, radioactive pollution is reduced by

decay of short lived radionuclides and transfers toreservoir bed sediments (particularly of radio-caesium) [4.82].

4.5.2. Measures to reduce direct and secondary contamination of surface waters

Standard antisoil erosion measures can beused to reduce runoff of radionuclides attached tosoil particles. Note, however, that typically less than50% of radiocaesium and less than 10% of radio-strontium and radioiodine were in the particulatephase, and this limits the potential effectiveness ofthis countermeasure. It should also be noted thatthe dissolved, rather than particulate, form of theseradionuclides is important in determining activityconcentrations in drinking water and freshwaterbiota.

Dredging of canal bed traps to interceptsuspended particles in contaminated rivers wascarried out in the Pripyat River [4.79]. These canalbed traps were found to be highly inefficient for tworeasons: (a) the flow rates were too high to trap thesmall suspended particles carrying much of theradionuclide contamination; and (b) a significantproportion of the radionuclide activity (and most ofthe ‘available’ activity) was in dissolved form andthus would not have been intercepted by thesediment traps.

One hundred and thirty zeolite-containingdykes were constructed on smaller rivers andstreams around Chernobyl in order to interceptdissolved radionuclides. These were found to bevery ineffective: only 5–10% of the 90Sr and 137Cs inthe small rivers and streams was adsorbed by thesezeolite barriers [4.80]. In addition, the rivers andstreams on which they were placed were later foundto contribute only a few per cent to the total radio-nuclide load in the Pripyat–Dnieper system.

After the Chernobyl accident, spring floodingof the highly contaminated Pripyat floodplainresulted in increases in 90Sr activity concentrationsin the Pripyat River from annual average activityconcentrations of around 1 Bq/L to a maximum ofaround 8 Bq/L for a flood event covering an approx-imately two week period [4.83]. In 1993 a dyke wasconstructed around the highly contaminatedfloodplain on the left bank of the Pripyat. Thisprevented flooding of this area and proved effectivein reducing 90Sr wash-off to the river during floodevents [4.80]. A second dyke was constructed on theright bank of the Pripyat in 1999. The annualaverage 90Sr activity concentration in Kiev reservoir

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water, however, was below 1 Bq/L in all years from1987 onwards. The radiological significance of the90Sr activity concentrations in Kiev reservoir water,even during the short flood events, is therefore verylow, although it has been argued that the avertedcollective dose to the large number of users of theriver–reservoir system is significant.

It is potentially possible to increase thesedimentation of radionuclides from lakes andreservoirs by the introduction of a strongly sorbingmaterial such as a zeolite or an (uncontaminated)mineral soil. This method has not been tested. Usinga model for the removal of radiocaesium from lakesby settling of suspended particles, Smith et al. [4.78]identified two problems with this method: (a) large,deep lakes would require extremely large amountsof sorbent; and (b) secondary contamination of thelake by remobilization of activity from thecatchment and/or bottom sediments would requirerepeat applications in most systems.

4.5.3. Measures to reduce uptake by fish and aquatic foodstuffs

Bans on the consumption of freshwater fishhave been applied in the limited zones affected bythe Chernobyl accident [4.84]. In some areas,selective bans on the more contaminated predatoryfish have been applied. It is believed that such bansare often ignored by fishermen. Bans on the sale offreshwater fish were applied in some areas ofNorway [4.85]. Farmed fish could be used as analternative source of freshwater fish in areasaffected by fishing bans, since farmed fish fed withuncontaminated food do not accumulate radionu-clides significantly [4.86].

The addition of lime to reduce radionuclidelevels in fish was tested in 18 Swedish lakes [4.87].The results of the experiments showed that liminghad no significant effect on the uptake of 137Cs infish in comparison with control lakes. Although theuptake of 90Sr was not studied in these experiments,it is expected that increased calcium concentrationin lakes may have an effect on the 90Sr concen-tration in fish. Experience of lake liming, inconjunction with artificial feeding of fish inUkraine, has been summarized by Voitsekhovitch[4.79].

It is known that the concentration factor forradiocaesium in fish is inversely related to thepotassium content of the surrounding water. After

the Chernobyl accident, potassium was added to 13lakes in Sweden, either as potash or as an additive inmixed lime [4.87]. The results of the potashtreatment were somewhat inconclusive, with a smallreduction in activity concentrations in perch fryobserved during the two year experiment. It wasfound that in lakes with short water retention timesit was difficult to maintain high levels of K+ in thelake.

In an experiment on Lake Svyatoe (a closedlake) in Belarus, Kudelsky et al. [4.88, 4.89] addedpotassium chloride fertilizer on to the frozen lakesurface. Results showed a significant (factor ofthree) overall reduction in 137Cs concentration infish during the first years after the experiment.However, as expected, the 137Cs in the waterincreased by a factor of two to three after thecountermeasure application. It is likely thatpotassium treatment is only feasible in lakes withvery long water residence times, which allowincreased potassium concentrations to bemaintained. Also, the increased 137Cs in water isunlikely to be acceptable in lakes that have waterabstracted for drinking.

Manipulation of the aquatic food web byintensive fishing was carried out in four lakes inSweden [4.87], and as a complementary measure inan additional three lakes. This resulted in areduction of the fish population by about 5–10 kg/ha. The species reduced were mainly pike, perchand roach. No effect of intensive fishing on 137Csconcentrations in fish was observed. Fertilizationwas carried out in two Swedish lakes usingOsmocoat (5% phosphorus and 15% nitrogen). Theconcentrations of total phosphorus generallyshowed no change in the long term mean value: itappears that the fertilization treatment was notcarried out sufficiently effectively. No effect wasobserved on 137Cs activity concentrations in fish.

Different methods of food preparation mayaffect the quantity of radionuclides in consumedfood [4.90]. Ryabov suggested bans on theconsumption of smoked and dried fish, becausethese processes increase concentrations of radionu-clides (per unit of weight consumed) [4.84]. Otherpreparation processes may reduce radionuclidelevels in fish by approximately a factor of two. Aneffective measure to reduce the consumption ofradiostrontium is to remove the bony parts of fishprior to cooking, since strontium is mainly concen-trated in the bones and skin. Various other foodpreparation methods are discussed in Ref. [4.91].

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4.5.4. Countermeasures for groundwater

There is no evidence that measures have everbeen taken to protect groundwater supplies after anatmospheric deposition of radioactivity.Groundwater residence times are long enough thatshorter lived radionuclides such as 131I will havedecayed long before they affect drinking water.Only very small amounts of radiostrontium andradiocaesium percolate from surface soils togroundwater after atmospheric deposition. A study[4.77] has shown that, after the Chernobylaccident, exposure to 90Sr and 137Cs via thegroundwater pathway was insignificant incomparison with other pathways (food, externalexposure, etc.).

Measures were taken to protect groundwaterfrom seepage of radionuclides from the shelter andfrom radioactive waste sites in the CEZ. Thesemeasures focused mainly on the construction ofengineering and geochemical barriers around thelocal hot spots to reduce groundwater fluxes to theriver network. Actions to stop precipitation fromentering the shelter, and drainage of rainwatercollected in the bottom rooms of the shelter, havealso to be considered as preventive measures toreduce groundwater contamination around theChernobyl nuclear power plant industrial site.

4.5.5. Countermeasures for irrigation water

As discussed previously, irrigation did not addsignificantly to the radionuclide contamination ofcrops that had previously been affected by theatmospheric deposition of radionuclides. Thus, inpractice, no countermeasures were directly appliedto irrigation waters. However, the experiencedescribed in Ref. [4.79] shows that the change fromsprinkling to drainage irrigation of agriculturalplants (e.g. vegetables) can reduce the transfer ofradionuclides from water to crops by several times.This, in combination with improved fertilization ofirrigated lands, can effectively reduce radionuclidelevels in crops irrigated with water from reservoirsaffected by radioactive pollution.

4.6. CONCLUSIONS AND RECOMMENDATIONS

The Chernobyl accident prompted the intro-duction of an extensive set of short and long termenvironmental countermeasures by the authorities

in the most affected countries to reduce its negativeconsequences. Unfortunately, there was not alwaysopenness and transparency towards the public, andinformation was withheld. This can, in part, explainsome of the problems experienced later in commu-nication with the public, and the mistrust of thecompetent authorities. Similar behaviour in manyother countries outside Belarus, the RussianFederation and Ukraine led to a distrust inauthority that, in many countries, has promptedinvestigations on how to deal with such majoraccidents in an open and transparent way and onhow the affected people can be involved in decisionmaking processes.

The unique experience of countermeasureapplication after the Chernobyl accident hasalready been widely used both at the national andinternational levels in order to improve prepar-edness against future nuclear and radiologicalemergencies [4.12, 4.14, 4.41, 4.91, 4.92].

4.6.1. Conclusions

(a) The Chernobyl accident prompted the intro-duction of an extensive set of short and longterm environmental countermeasures by theUSSR and, later, independent countryauthorities, aimed at reducing the accident’snegative consequences. The countermeasuresinvolved large amounts of human, economicand scientific resources.

(b) When social and economic factors along withthe radiological factors are taken into accountduring the planning and application ofcountermeasures, better acceptability of thesemeasures by the public is achieved.

(c) The unprecedented scale and long term conse-quences of the Chernobyl accident requiredthe development of some additional nationaland international radiation safety standards,to take account of changes of radiationexposure conditions.

(d) Countermeasures applied in the early phase ofthe Chernobyl accident were only partiallyeffective in reducing radioiodine intake viamilk, because of the lack of timely informationabout the accident and advice on appropriateactions, particularly for private farmers.

(e) The most effective countermeasures in theearly phase were exclusion of contaminatedpasture grasses from animal diets andrejection of milk (with further processing)based on radiation monitoring data. Feeding

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animals with ‘clean’ fodder was effectivelyperformed in some affected countries. Theslaughtering of cattle was unjustified from aradiological point of view and had greathygienic, practical and economic implications.

(f) The greatest long term problem has been radio-caesium contamination of milk and meat. Inthe USSR, and later in the three independentcountries, this has been addressed by thetreatment of land used for fodder crops, cleanfeeding and application of caesium binders toanimals, which enabled most farming practicesto continue in affected areas.

(g) Decontamination of settlements was widelyapplied in contaminated regions of the USSRduring the first years after the Chernobylaccident as a means of reducing the externalexposure of the public; this was cost effectivewith regard to external dose reduction whenits planning and implementation werepreceded by a remediation assessment basedon cost–benefit considerations and externaldosimetry data.

(h) The decontamination of urban environmentshas produced a considerable amount of lowlevel radioactive waste, which creates aproblem of disposal. However, secondarycontamination of cleaned up plots has notbeen observed.

(i) The following forest related restrictionswidely applied in the USSR and later in thethree independent countries and partially inScandinavia have reduced human exposuredue to residence in radioactively contami-nated forests and the use of forest products:

(i) Restrictions on public and forest workeraccess as a countermeasure againstexternal exposure.

(ii) Restricted harvesting by the public offood products such as game, berries andmushrooms contributed to a reduction ininternal dose. In the affected countriesmushrooms are a common dietarycomponent, and therefore this restrictionhas been particularly important.

(iii) Restricted collection of firewood by thepublic to prevent exposures in the homeand garden when the wood is burned andthe ash is disposed of or used as afertilizer.

(iv) Alteration of hunting practices, aimed atavoiding consumption of meat with highseasonal levels of radiocaesium.

(v) Fire prevention, especially in areas withlarge scale radionuclide deposition, inorder to avoid secondary contaminationof the environment.

(j) Experience has shown that forest restrictionscan result in significant negative social conse-quences, and advice from the authorities tothe general public may be ignored as a result.This situation can be offset by the provision ofsuitable educational programmes targeted atthe local scale to explain the purpose of thesuggested changes in the use of some forestareas.

(k) It is unlikely that any technology based forestcountermeasures (i.e. the use of machineryand/or chemical treatments to alter the distri-bution or transfer of radiocaesium in forests)will be practicable on a large scale.

(l) Numerous countermeasures put in place inthe months and years after the accident toprotect water systems from transfers of radio-nuclides from contaminated soils were, ingeneral, ineffective and expensive and led torelatively high exposures of the workersimplementing the countermeasures.

(m) The most effective countermeasure foraquatic pathways was the early restriction ofdrinking water abstraction and the change toalternative supplies. Restrictions on theconsumption of freshwater fish have provedeffective in Scandinavia and Germany;however, in Belarus, the Russian Federationand Ukraine such restrictions may not alwayshave been adhered to.

(n) It is unlikely that any future countermeasuresto protect surface waters will be justifiable interms of economic cost per unit of dosereduction. It is expected that restrictions onthe consumption of fish will be retained in afew cases (in closed lakes) for several moredecades.


4.6.2.1. Countries affected by the Chernobyl accident

(a) Long term remediation measures andcountermeasures in the areas contaminatedwith radionuclides should be applied if theyare radiologically justified and optimized.

(b) Authorities and the general public should beparticularly informed on radiation risk factors

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and the technological possibilities to reducethem in the long term by means ofremediation and countermeasures. Localauthorities and the public should be involvedin related discussions and decision making.

(c) In the long term after the Chernobyl accident,remediation measures and regular counter-measures should be maintained where theyremain efficient and justified — mainly inagricultural areas with poor (sandy and peaty)soils and resulting high radionuclide transferfrom soil to plants.

(d) Particular attention must be given to privatefarms in several hundred settlements and toabout 50 intensive farms in Belarus, theRussian Federation and Ukraine, where radio-nuclide concentrations in milk still exceed thenational action levels.

(e) Emphasis should be on the most efficient longterm remediation measures; these are theradical improvement of pastures andgrasslands and the draining of wet peaty areas.The most efficient regular agriculturalcountermeasures are the pre-slaughter cleanfeeding of animals accompanied by in vivomonitoring, the application of Prussian blue tocattle and the enhanced application of mineralfertilizers in plant cultivation.

(f) Restricting harvesting of wild food productssuch as game, berries, mushrooms and fishfrom closed lakes by the public still may beneeded in areas where their activity concen-trations exceed the national action levels.

(g) Advice should continue to be given onindividual diets, as a way of reducingconsumption of highly contaminated wildfood products, and on simple cookingprocedures to remove radioactive caesium.

(h) It is necessary to identify sustainable ways tomake use of the most affected areas thatreflect the radiation hazard, but also to revivetheir economic potential for the benefit of thecommunity.

4.6.2.2. Worldwide

(a) The unique experience of countermeasureapplication after the Chernobyl accidentshould be carefully documented and used forthe preparation of international guidance forauthorities and experts responsible forradiation protection of the public and theenvironment.

(a) Practically all the long term agriculturalcountermeasures implemented on a largescale on contaminated lands of the three mostaffected countries can be recommended foruse in the event of future accidents. However,the effectiveness of soil basedcountermeasures varies at each site. Analysisof soil properties and agricultural practicesbefore application is therefore of greatimportance.

(b) Recommendations on the decontamination ofthe urban environment in the event of largescale radioactive contamination should bedistributed to the owners and operators ofnuclear facilities that have the potential forsubstantial accidental radioactive release(nuclear power plants and reprocessingplants) and to authorities in adjacent regions.

4.6.2.3. Research

(a) Generally, the physical and chemicalprocesses involved in environmental counter-measures and remediation technologies, bothof a mechanical nature (radionuclide removal,mixing with soil, etc.) and a chemical nature(soil liming, fertilization, etc.), are understoodsufficiently to be modelled and applied insimilar circumstances worldwide. Much lessunderstood are the biological processes thatcould be used in environmental remediation(e.g. reprofiling of agricultural production,bioremediation, etc.). These processes requiremore research.

(b) An important issue that requires more socio-logical research is the perception by the publicof the introduction, performance andwithdrawal of countermeasures in the event ofan emergency, as well as the development ofsocial measures aimed at involving the publicin these processes at all stages, beginning withthe decision making process.

(c) There is still substantial diversity in the inter-national and national radiological criteria andsafety standards applicable to the remediationof areas affected by environmental contami-nation with radionuclides. The experience ofradiological protection of the public after theChernobyl accident has clearly shown theneed for further international harmonizationof appropriate radiological criteria and safetystandards.

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[4.91] FOOD AND AGRICULTURE ORGANIZA-TION OF THE UNITED NATIONS, INTER-NATIONAL ATOMIC ENERGY AGENCY,Guidelines for Agricultural CountermeasuresFollowing an Accidental Release of Radionu-clides, Technical Reports Series No. 363, IAEA,Vienna (1994).

[4.92] FOOD AND AGRICULTURE ORGANIZA-TION OF THE UNITED NATIONS, INTER-NATIONAL ATOMIC ENERGY AGENCY,INTERNATIONAL LABOUR ORGANISA-TION, OECD NUCLEAR ENERGY AGENCY,PAN AMERICAN HEALTH ORGANIZA-TION, WORLD HEALTH ORGANIZATION,International Basic Safety Standards for Protec-tion against Ionizing Radiation and for the Safetyof Radiation Sources, Safety Series No. 115,IAEA, Vienna (1996).

99

5. HUMAN EXPOSURE LEVELS

5.1. INTRODUCTION

5.1.1. Populations and areas of concern

Following the Chernobyl accident, bothworkers and the general public were affected byradiation that carried a risk of adverse healtheffects. UNSCEAR selected the following threecategories of exposed populations: (a) workersinvolved in the accident, either during theemergency period or during the cleanup phase; (b)the inhabitants of contaminated areas who wereevacuated in 1986; and (c) the inhabitants ofcontaminated areas who were not evacuated [5.1].

In this section consideration is given primarilyto members of the general public exposed to radio-nuclides deposited in the environment. The workersinvolved in the emergency response to the accidentor in the cleanup following the accident andexposed predominantly on-site (i.e. at theChernobyl nuclear power plant and in the CEZ) arenot considered here. For information on Chernobylworker populations, the reader is referred to thecomprehensive material provided by UNSCEAR[5.1, 5.2] and by the Chernobyl Forum in its reportconsidering the human health effects [5.3].

Information on the radiation doses receivedby members of the general public, both thoseevacuated from the accident area and those wholive permanently in contaminated areas, is requiredfor the following health related purposes:

(a) Substantiation of countermeasures andremediation programmes;

(b) Forecast of expected adverse health effectsand justification of corresponding healthprotection measures;

(c) Information for the public and the authorities; (d) Epidemiological and other medical studies of

radiation caused adverse health effects.

In this section the methodologies and dataspecifically required for the estimation of meandoses to population groups living in particularsettlements and selected by the factors influencingeither external or internal dose or both arepresented. These factors are usually age, sex,occupation, food habits, etc. Dose distributionsamong group members and collective doses are also

considered. Individual doses to members of thepublic, used mainly in analytical epidemiologicalstudies, are presented in the Chernobyl Forumreport on the health consequences of the Chernobylaccident [5.3]. On these subjects, substantialprogress has been achieved since publication of thecomprehensive UNSCEAR report in 2000 [5.1].

As mentioned in Section 3.1, atlases havebeen prepared that show the deposition of 137Cs andother radionuclides throughout the former USSRand other countries of Europe [5.4, 5.5]. Theseindicate that the most affected countries areBelarus, the Russian Federation and Ukraine. Inaddition, the countries of Austria, Bulgaria, Finland,Greece, Italy, Norway, Republic of Moldova,Slovenia, Sweden and Switzerland had areas thatcan be considered to have been ‘contaminated’ —that is, at the level of more than 37 kBq/m2 (>1 Ci/km2) of 137Cs (see Table 3.2).

5.1.2. Exposure pathways

Following the Chernobyl accident there wereseveral pathways by which humans were exposed toradioactive material (Fig. 5.1). The main pathwaysare listed below in the approximate time sequencein which the doses were received:

(a) External dose from cloud passage;(b) Internal dose from inhalation during cloud

passage and of resuspended material;(c) External dose from radionuclides deposited

upon soil and other surfaces;

FIG. 5.1. Pathways of exposure of humans to environ-mental releases of radioactive material.

100

(d) Internal dose from the consumption ofcontaminated food and water.

Under most exposure conditions for membersof the general public the two most importantpathways are dose from radiation from the decay ofradionuclides deposited upon the soil and othersurfaces and dose from the ingestion of contami-nated food and water. If persons are evacuatedquickly after passage of the initial cloud, then themost important pathways are the first two in the list,because the latter two pathways have beenprevented.

5.1.3. Concepts of dose

Methods of calculating radiation dose havebeen refined over the years, and specific conceptshave evolved [5.1, 5.6]. The fundamental measure ofradiation dose to an organ or tissue is the absorbeddose, which is the amount of energy absorbed bythat organ or tissue divided by its weight. The inter-national unit of absorbed dose is the gray (Gy),which is equal to one joule per kilogram. Since thisis a rather large amount of dose, it is common to useunits of mGy (one thousandth of a gray) or µGy(one millionth of a gray).

Since many organs and tissues were exposedas a result of the Chernobyl accident, it has beenvery common to use an additional concept, effectivedose, which is the sum of the products of absorbeddose to each organ multiplied by a radiationweighting factor and a tissue weighting factor. Theformer varies by radiation type and is related to thedensity of ionizations created; the latter is anapproximation of the relative probability that anabsorbed dose to a particular organ might lead to

the production of a cancer. The sum of all tissueweighting factors is equal to 1.0.

The concepts mentioned above are applied toindividuals. Where many individuals have beenexposed to an event, such as happened following theChernobyl accident, an additional concept, thecollective dose, can be used. The collective dose isthe sum of the doses to all individuals within aparticular group, which may be the residents of aparticular country or the persons involved in sometype of activity, such as cleaning up the conse-quences of the accident. This concept is most oftenapplied to effective doses, and the common unit ofthe collective effective dose is the man-Sv.

Finally, UNSCEAR has employed the conceptof dose commitment to examine the long termconsequences of a practice or accident [5.1]; forexample, at the very moment that the Chernobylaccident occurred, it can be considered that a dosecommitment occurred at the moment of the releaseof the radioactive material. This is true even thoughit will take many years for the doses to be receivedby the persons alive at that time and by persons notyet born or conceived.

5.1.4. Background radiation levels

Living organisms are continually exposed toionizing radiation from natural sources, whichinclude cosmic rays and terrestrial radionuclides(such as 40K, 238U, 232Th and their progeny, including222Rn (radon)). Table 5.1 shows the average annualdose and typical dose range worldwide from naturalsources.

In addition to natural sources, radiationexposure occurs as a result of human activities.Table 5.2 shows the annual individual effective

TABLE 5.1. RADIATION DOSES FROM NATURAL SOURCES [5.1]

Worldwide average annual effective dose (mSv)

Typical range (mSv)

External exposure

Cosmic rays 0.4 0.3–1.0

Terrestrial gamma rays 0.5 0.3–0.6

Internal exposure

Inhalation (mainly radon) 1.2 0.2–10

Ingestion 0.3 0.2–0.8

Total 2.4 1–10

101

doses in 2000 on a worldwide basis. Diagnosticmedical exposure is the largest non-natural sourceof radiation. The residual global effects of theChernobyl accident are now very small but, ofcourse, are higher in European countries andespecially in areas of Belarus, the RussianFederation and Ukraine.

5.1.5. Decrease of dose rate with time

To calculate the radiation dose for particulartime periods, it is necessary to predict the decreaseof dose rate with time. The most obviousmechanism acting to cause such a decrease is theradioactive decay of the radionuclides. AdditionalDRRFs are usually called ecological half-lives; forexample, external gamma exposure rates decreasewith time due to the weathering of long lived radio-nuclides such as 137Cs into the soil and subsequentmigration down the soil column, which results inincreased absorption of the emitted radiationswithin the soil. Typically, a two componentexponential function describes this process [5.7,5.8].

The availability of 137Cs for ingestion alsodecreases with time at a rate faster than radioactivedecay. This additional long term decrease is duemainly to the adsorption of 137Cs to soil particlesfrom which the caesium atoms are no longer biolog-ically available. As with the external dose rate, thedecrease of 137Cs in milk or in humans living in areascontaminated by the Chernobyl accident also shows

a two component exponential decrease with time[5.9, 5.10].

5.1.6. Critical groups

In all situations that involve the exposure oflarge segments of the population to natural orhuman-made radioactive material, there is always asignificant spread in the radiation dose received byvarious members of the population living within thesame geographical area. Those individuals with thehigher doses are frequently called the critical group,and these persons may have doses twice or evenhigher than the average dose to all members of thepopulation considered. Usually such persons can beidentified in advance, and, in some cases, specialprotective measures may be considered.

For external dose, members of the criticalgroup are those who spend a considerable amountof time outdoors, either for occupational or recrea-tional reasons; also, people living and/or working inbuildings with minimal shielding might be membersof the critical group. For exposure to radioiodineisotopes, the critical group is often infants drinkinggoat’s milk. Infants have a thyroid gland weighingonly two grams that concentrates roughly 30% ofthe radioiodine consumed; goats are more efficientthan cows at secreting radioiodine into milk. Forexposure to radiocaesium, critical groups have beenidentified as those who consume large quantities oflocal animal products such as milk and meat andwild products such as game meat, mushrooms, wildberries and lake fish.

TABLE 5.2. EFFECTIVE DOSES IN 2000 FROM NATURAL AND HUMAN SOURCES [5.1]

Worldwide average annual per caput effective dose (mSv)

Range or trend in exposure

Natural background 2.4 Typical range of 1–10 mSv

Diagnostic medical examinations 0.4 Ranges from 0.04 to 1 mSv at the lowest and highest levels of health care

Atmospheric nuclear testing 0.005 Has decreased from a maximum of 0.15 mSv in 1963; higher in the northern hemisphere

Chernobyl accident 0.002 Has decreased from a maximum of 0.04 mSv in 1986 (in the northern hemisphere); higher at locations nearer the accident site

Nuclear power production 0.0002 Has increased with expansion of the nuclear programme but decreased with improved practice

102

5.2. EXTERNAL EXPOSURE

5.2.1. Formulation of the model for external exposure

In any situation of human external exposurecaused by releases of radioactive substances into theenvironment, the following three types of data arenecessary for assessment of organ or effectivedoses:

(a) Parameters that describe the external gammaradiation field;

(b) Parameters describing human behaviour inthis field;

(c) Conversion factors from dose in air to organor effective dose.

The basic model for human external exposurein the event of radioactive contamination of theenvironment is the model for exposure above anopen plot of undisturbed soil; the absorbed dose inair D(t) at a height of 1 m above the soil surface isused as the basic parameter to describe the radiationfield. The value of this basic parameter is influencednot only by the surface activity of deposited radio-nuclides but also by such natural factors as the initialpenetration of radionuclides in soil and theirradioactive decay, vertical migration of long livedradionuclides and the presence of snow cover.

Radiation exposure is influenced by altered ordisturbed environments. In models this factor istaken into account by using location factors. The

location factor LFi is defined as the ratio of the doserate in air at point i inside a settlement to a similarvalue above a plot of undisturbed soil [5.11].Human behaviour in the radiation field is describedby occupancy factors OFik, which represent thefraction of time spent by individuals of the kthpopulation group at the ith point of the settlementof interest. The third type of data necessary forassessment of the effective external dose areconversion factors CFk, which convert measuredvalues (the absorbed dose in air) to a parameterthat can be directly related to health effects — theeffective dose to the kth population group.

On this basis, a deterministic model for theassessment of the effective external dose rate Ek forrepresentatives of the kth population group isrepresented in Fig. 5.2.

5.2.2. Input data for the estimation of effective external dose

Numeric values for the parameters listedabove have been determined from long termdosimetric investigations in the most highly contam-inated regions after the Chernobyl accident.

5.2.2.1. Dynamics of external gamma dose rate over open undisturbed soil

Immediately after the accident, externalgamma exposure rates were relatively high, andcontributions from many short lived radionuclideswere important. Thus in the contaminated areasoutside the Chernobyl nuclear power plantboundaries the initial dose rate over lawns andmeadows ranged between 3 and 10 µGy/h in areascontaminated at about 37 kBq/m2 (1 Ci/km2) of137Cs and up to 10 000 µGy/h within the CEZ withhigher deposition levels. Exposure rates decreasedrapidly, due to the radioactive decay of short livedradionuclides, as shown in Fig. 5.3.

Owing to different isotopic compositions ofradionuclide fallout in different geographical areas[5.8, 5.13, 5.14], the contribution of short livedradionuclides to the overall dose rate was highlyvariable. In the CEZ, 132Te + 132I, 131I and 140Ba +140La dominated during the first month and then95Zr + 95Nb for another half year before 137Cs and134Cs became dominant (Fig. 5.4). In contrast, in thefar zone only the radioiodine isotopes dominatedduring the first month; afterwards 137Cs and 134Csdominated, with a moderate contribution from103Ru and 106Ru (Fig. 5.5). Since 1987 more than

= ∑ ∫ dtLFCFOFEi

k

LF

Locationfactorover soil

( )tD

Dose conversionfactor

ikOF

Occupancyfactor

ikCF

= ∑ ∫E ii

ikik

i

Dose rate

tD

External dose to humans

DD ( )t( )t

FIG. 5.2. Model of external exposure of the kth populationgroup (i is a location index) [5.9].

103

90% of the dose rate in air has come from thegamma radiation of long lived 137Cs and 134Cs. Thusthe radionuclide composition of the depositedactivity was a major factor in determining theexternal exposure of the population in the earlyperiod of time after the accident. Model estimatesof the gamma dose rate in free air (90% confidenceinterval) based on the radionuclide composition of

the deposited activity agree well with the measuredvalues during the first month after deposition (seeFig. 5.6).

The influence of radionuclide migration intosoil on the gamma dose rate has been determinedusing gamma spectrometric analyses of over 400 soilsamples taken during 1986–1999 in the contami-nated areas of Germany (Bavaria), the Russian

Time after the accident (days)

0.1

1.0

10.0

100.0

1000.0

1 10 100 1000 10 000

North-west direction, CEZSouth direction, CEZFar zone (>100 km)

Ab

sorb

ed d

ose

rate

in a

ir (n

Gy/

h p

er 1

kB

q/m

2 of

137

Cs)

FIG. 5.3. Dynamics of standardized dose rate in air overundisturbed soil after the Chernobyl accident in differentgeographical areas [5.12].


North-west direction, CEZ

Co

ntrib

utio

n to

ab

sorb

ed d

ose

rat

e in

air

1 m

ab

ove

gro

und

(%)

Cs-137; Cs-134; Cs-136

Zr-95 + Nb-95

Te-132 + I-132

I-131; I-133Ba-140 + La-140

Ru-103; Ru-106

1 10 100

100

80

60

40

20

0

FIG. 5.4. Relative contribution of gamma radiation fromindividual radionuclides to the external gamma dose rate inair during the first year after the Chernobyl accident(north-west direction, CEZ) [5.12].


0

20

40

60

80

100

1 10 100

Cs-137; Cs-134; Cs-136

Te-132 + I-132

Ru-103; Ru-106

Ba-140 + La-140

I-131; I-133

Zr-95 + Nb-95

Far zone (>100 km)

Con

trib

utio

n to

ab

sorb

ed d

ose

rate

in a

ir 1

m a

bov

e gr

ound

(%)

FIG. 5.5. Relative contribution of gamma radiation fromindividual radionuclides to the external gamma dose rate inair during the first year after the Chernobyl accident (farzone — more than 100 km from the Chernobyl nuclearpower plant) [5.12].


0

1

2

3

4

5

6

0 5 10 15 20 25 30 35

Mean

5%

95%

Dos

e ra

te (r

elat

ive

units

)

FIG. 5.6. Dose rate in air during the first days after theaccident in several rural settlements in the Bryansk andTula regions of the Russian Federation (normalized to thedose rate on 10 May 1986). Points indicate dose rate meas-urements and curves represent calculated values accordingto the isotopic composition [5.7].

104

Federation, Sweden and Ukraine [5.7, 5.8, 5.15].The analysis also included data on the 137Cs distri-bution in soil at sites in the north-east region of theUSA, whose contamination was attributed tonuclear tests at the Nevada test site [5.16], and inBavaria (Germany), where contamination was dueto global fallout. The last two data sets wereobtained 20 to 30 years after deposition; this allowsfor long term predictions to be applied to theChernobyl depositions. The measurement sites wereconsidered to be representative of reference sites(i.e. open, undisturbed fields).

For a few years after the accident, the doserate over open plots of undisturbed soil decreasedby a factor of 100 or more compared with the initiallevel (see Fig. 5.3). At that time, the dose rate wasmainly determined by gamma radiation of caesiumradionuclides (i.e. 137Cs (half-life 30 years) and 134Cs(half-life 2.1 years), and later, one decade and moreafter the accident, mainly the longer lived 137Cs).Long term studies of external gamma exposurerates during the past 17 years have shown that theexternal gamma exposure rate is decreasing fasterthan that due to radioactive decay alone. Golikov etal. [5.7] and Likhtarev et al. [5.8] have calculated areference function for 137Cs gamma radiation doserate that has 40–50% of the exposure ratedecreasing with an ecological half-life of 1.5–2.5years and the remaining 50–60% decreasing with anecological half-life of 40–50 years, as indicated inFig. 5.7. The latter value is rather uncertain. Itcorresponds to an effective half-life that takes intoaccount both the radioactive decay of 137Cs and itsgradual deepening in soil after 17–19 years.

5.2.2.2. Dynamics of external gamma dose rate in anthropogenic areas

In settlements in urban and rural areas, thecharacteristics of the radiation field differ consid-erably from those over an open plot of undisturbedland, which is used as the reference site and startingpoint for calculation of external dose to people fromdeposited activity. These differences are attrib-utable to varying source distributions as a result ofdeposition, runoff, weathering and shielding. Allsuch effects can be summarized by the term‘location factors’.

Location factors for typical western Europeanbuildings have been assessed [5.11, 5.17, 5.18].Gamma spectrometric measurements performed inGermany and Sweden [5.19–5.22] allowed the

determination of location factors in urban environ-ments and their variation with time over severalyears after the Chernobyl accident. The character-istic feature, and advantage, of these investigationsis that they began immediately after the accident,whereas systematic investigations of location factorsin the contaminated areas of Belarus, the RussianFederation and Ukraine began two to three yearsafter the accident. The results of one such laterinvestigation in Novozybkov (in the Bryansk regionof the Russian Federation) are presented in Fig. 3.12(Section 3).

5.2.2.3. Behaviour of people in the radiation field

The influence of the behaviour of differentsocial population groups on the level of exposurecan be taken into account if the frequency withwhich people of the kth population group remain atthe location of the ith type is known. The timesspent in various types of location (indoor, outdoorson streets or in yards, etc.) by members of differentpopulation groups have been assessed on the basisof responses to a questionnaire. Data collectedincluded age, sex, occupation, information aboutdwelling, etc. An example of the results is shown inTable 5.3, where values of occupancy factors for thesummer period are presented for different groups ofthe rural populations of Belarus, the RussianFederation and Ukraine [5.15].


0.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15 20 25 30 35

95%5%Median

‘Chernobyl’ caesium Bryansk region (Russian Federation)

Caesium fromNevada test site(north-west USA) Global fallout

from Bavaria (Germany)

r(t) = 0.38 exp(–0.693 t/2.4y) + 0.39 exp(-0.693 t/37y)

Dos

e ra

te (r

elat

ive

units

)

FIG. 5.7. Reduction of the 137Cs gamma dose rate in air dueto caesium migration in undisturbed soil relative to thedose rate caused by a plane source on the air–soil interface(from Ref. [5.7]).

105

5.2.2.4. Effective dose per unit gamma dose in air

Mean values of conversion factors CFk, whichconvert the gamma dose rate in air to the effectivedose rate in a member of population (age) group k,were obtained for the three groups of population byuse of phantom experiments [5.15] and MonteCarlo calculations [5.23]. The values were 0.75 Sv/Gy for adults, 0.80 Sv/Gy for schoolchildren (7–17 years) and 0.90 Sv/Gy for pre-school children (0–7 years). For the calculation of effective doses,conversion factors CFk were used that areindependent of the location and time after theaccident.

5.2.3. Results

5.2.3.1. Dynamics of external effective dose

Shortly after the deposition of the fallout thegamma radiation field was dominated by emissionsfrom short lived radionuclides, as discussed above(see Figs 5.4 and 5.5). As the mixtures at differentlocations varied widely, the radionuclidecomposition of the deposited activity was a majorfactor in determining the external exposure of thepopulation during the early period after theaccident.

Another relevant parameter in the midtermperiod is the dependence of location factors ontime, due to the relatively fast migration processesof radionuclides during this period. The dose rateover different urban surfaces caused by gammaradiation of 137Cs decreased during the first yearsafter deposition, with an exponential half-life of oneto two years (see Fig. 3.12). In the five to sevenyears after deposition, the change in dose rate withtime had stabilized — this was due to the decay of

the short lived radionuclides and the fixation ofcaesium radionuclides within the soil column.

According to measurements and evaluationswithin the first year after the accident, the externaldose rate had decreased by a factor of approxi-mately 30, mainly due to radioactive decay of shortlived radionuclides (see Fig. 5.8). During thefollowing decade the external dose rate decreasedbecause of the radioactive decay of 134Cs and 137Csand the migration of radiocaesium into the soil.Afterwards, the external dose rate was mainly dueto 137Cs. In the long term, radiocaesium becomesfixed within the soil matrix, and this results in a slowmigration into the soil and, correspondingly, in aslow decrease of the external dose rate. On the basisof such measurements, it is predicted that, of thetotal external dose to be accumulated during 70years following the accident, about 30% wasaccumulated during the first year and about 70%during the first 15 years (Fig. 5.8) [5.7].

5.2.3.2. Measurement of individual external dose with thermoluminescent dosimeters

In general, before the Chernobyl accident,individual external doses were measured only foroccupational exposures. After the Chernobylaccident, individual external doses to members ofthe population were also measured. For thispurpose thermoluminescent dosimeters weredistributed to the inhabitants of the more contami-nated areas of Belarus, the Russian Federation andUkraine [5.24–5.28]. Inhabitants wore thermolumi-nescent dosimeters for about one month in thespring and summer periods. Examples of suchresults are presented in Figs 5.9 and 5.10 for ruraland urban areas, respectively. According to theseresults it can be concluded that the urban

TABLE 5.3. VALUES OF OCCUPANCY FACTORS FOR THE SUMMER PERIOD FOR DIFFERENTGROUPS OF THE RURAL POPULATIONS OF THE RUSSIAN FEDERATION, BELARUS ANDUKRAINEa [5.15]

Location Indoor workers Outdoor workers Pensioners SchoolchildrenPre-school

children

Inside houses 0.65/0.77/0.56 0.50/0.40/0.46 0.56/0.44/0.54 0.57/0.44/0.75 0.64/—/0.81

Outside houses (living area)

0.32/0.19/0.40 0.27/0.25/0.29 0.40/0.42/0.41 0.39/0.45/0.21 0.36/—/0.19

Outside settlements 0.03/0.04/0.04 0.23/0.35/0.25 0.04/0.14/0.05 0.04/0.11/0.04 0/—/0

a The first number corresponds to data for the Russian Federation, the second is for Belarus and the third is for Ukraine[5.15].

106

population has been exposed to a lower dose by afactor of 1.5–2 compared with the rural populationliving in areas with similar levels of radioactivecontamination. This arises because of the bettershielding features of urban buildings and differentoccupational habits.

The critical group in relation to externalirradiation is composed of individuals in anoccupation or with habits that result in spending asignificant amount of time outside in areas ofundisturbed soil, in forests or meadows, and whoalso live in houses with the least protectiveproperties. At present, the average external doseto any population group does not exceed theaverage dose in a settlement by more than a factorof two. Typical critical groups are foresters (factor1.7), herders (factor 1.6) and field crop workers(factor 1.3) living in one-storey wooden houses[5.9, 5.15].

Analysis of the results of measurements ofinhabitants of settlements showed that the distri-bution of individual doses can be described by a log-normal function [5.7]. Figure 5.11 presents acomparison of model calculations with individualthermoluminescence measurements performed in1993 in four villages of the Bryansk region (565measurements). The distributions of the ratio ofindividual external doses to the mean value ofmeasured doses in each of the villages are almostidentical. Thus the resulting log-normal distributionwith a geometric standard deviation of about 1.5(attributed mainly to the stochastic variability ofindividual doses) may be assumed to be typical forrural settlements in the zone of the Chernobylaccident.


0.01

0.10

1.00

10.00

100.00

0.01 0.10 1.00 10.00 100.00

Effective dose rate

Accumulated effective dose

Effe

ctiv

e d

ose

rate

(10–

6 S

v/h)

and

acc

umul

ated

effe

ctiv

e d

ose

(10–

3 S

v) p

er 1

MB

q/m

2 of

137

Cs

FIG. 5.8. Model prediction of the time dependence of theexternal effective gamma dose rate and the accumulatedexternal effective dose to the urban population of theBryansk region of the Russian Federation [5.7].

Time after the accident (years)5 10 15 20

0

50

100

150

200

250

Veprin

Smyalch

Mea

n ef

fect

ive

mon

thly

dos

e to

vill

age

resi

den

ts (m

Sv)

FIG. 5.9. Results of thermoluminescence measurements ofmean monthly doses among inhabitants living in woodenhouses in the Veprin and Smyalch villages (Bryansk regionof the Russian Federation) in different time periodsfollowing deposition [5.28].

Year

0

50

100

150

200

1989 1990 1991 1992 1993

Inhabitants living in wooden housesInhabitants living in brick houses

Mea

n ef

fect

ive

mon

thly

dos

e (1

0–6

Sv)

FIG. 5.10. Effective dose rates for indoor workers inNovozybkov (Russian Federation). The points with errorbars represent average values and 95% confidenceintervals (+/– two standard errors) of thermoluminescencemeasurements [5.28].

107

5.2.3.3. Levels of external exposure

To illustrate actual levels of external exposureand differences in the level of exposure amongvarious population groups, Table 5.4 presentscalculated values of effective external doses duringdifferent time intervals for rural and urbanpopulations in the Russian Federation and Ukraine,and Table 5.5 presents the ratio of average effectivedoses in separate population groups to the meandose in a settlement. Calculations of dose fordifferent time intervals were performed on the basisof the model described above for the assessment ofexternal dose in a population.

At present, the average annual external doseto residents of a rural settlement with a current 137Cssoil deposition of ~700 kBq/m2 (~20 Ci/km2) is0.9 mSv. For the critical group, the dose valueexceeds the annual dose limit of 1 mSv set for thepopulation under normal conditions. The externaldose due to Chernobyl deposition accumulated tothe present time is 70–75% of the total lifetime dose(70 years) for persons born in 1986 and living all thetime in contaminated areas.

Individual dose/mean dose in village

0

5

10

15

20

25

30

35

40

0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0

Veprin

Kozhany

Smyalch

Vnukovichi

Rel

ativ

e fr

eque

ncy

(%)

FIG. 5.11. Frequency distributions of monthly effectiveexternal doses to individual persons as measured in thesummer of 1993 with thermoluminescent dosimeters infour villages of the Bryansk region of the Russian Federa-tion (points) and calculated by the stochastic model(curve). Doses are normalized to the arithmetic mean ofthe individual doses determined for each of the villages(from Ref. [5.7]).

TABLE 5.4. AVERAGE NORMALIZED EFFECTIVE EXTERNAL DOSE TO THE ADULTPOPULATION IN THE INTERMEDIATE (100 km < DISTANCE < 1000 km) ZONE OF CHERNOBYLCONTAMINATION

PopulationE/s137 (mSv ◊ kBq–1 ◊ m–2 of 137Cs)a

1986 1987–1995 1996–2005 2006–2056 1986–2056

Russian Federation Rural 14 25 10 19 68

[5.7, 5.28] Urban 9 14 5 9 37

Ukraine [5.8] Rural 24 36 13 14 88

Urban 17 25 9 10 61

a s137 is given as for 1986.

TABLE 5.5. RATIO OF AVERAGE EFFECTIVE EXTERNAL DOSES IN SEPARATE POPULATIONGROUPS TO THE MEAN DOSE IN A SETTLEMENT [5.9]

Type of dwelling Indoor workers Outdoor workers Herders, foresters Schoolchildren

Wooden 0.8 1.2 1.7 0.8

One to two storey, brick 0.7 1.0 1.5 0.9

Multistorey 0.6 0.8 1.3 0.7

108

5.3. INTERNAL DOSE

5.3.1. Model for internal dose

The general form of models used to calculateinternal dose is shown in Fig. 5.12 [5.9]. The mainpathways of radionuclide intake into the body of aperson of age k are inhalation, with averageinhalation rate IRk of air with time dependentconcentration ACr of radionuclide r, and ingestionof the set of f food products and water withconsumption rates CRfk with time dependentspecific activity SAfr.

Data on air concentrations and food activityconcentrations have been discussed in previoussections and will be summarized briefly below. Dataon food consumption rates are taken from theliterature [5.2, 5.10] or from special surveys of theaffected populations [5.29, 5.30]. Other data neededfor dosimetric calculations are taken from publica-tions of the International Commission on Radio-logical Protection for age specific inhalation rates[5.31] and for age specific dose coefficients [5.32].The latter values are for both inhalation andingestion and give the dose per unit radionuclideinhaled or ingested. These values are calculated interms of committed dose; that is, the dose that willbe received over the next 50 years for adults or untilage 70 for younger persons. For most radionuclides,but not for 90Sr or 239Pu, the biological residencetime within the body is short, and the committeddose is only slightly larger than the dose accruedover the course of one year. Strontium andplutonium nuclides, and a few others, are

metabolized slowly, and the full committed dose isnot actually received for many years.

Another method of calculating internal dose isto use direct measurements of the radionuclide ofinterest in the human body. This was done for 131I inthe human thyroid in the three most affectedcountries [5.33–5.35] and for 137Cs (e.g. Refs [5.10,5.36]). Especially for the thyroid, direct measure-ments are not sufficient to calculate doses, and suchinformation must be supplemented by suitableintake models to determine the past and futureconcentration of the radionuclide in the body andits organs.

Predictions of future intakes of long livedradionuclides into the body must be made in orderto predict future doses. Information on the longterm transfer of the important radionuclide 137Csfrom the environment to the human body can bemade on the basis of experience with this radionu-clide in global and local fallout [5.1]. Also, enoughtime has now passed since the Chernobyl accidentthat measurements specific to Chernobyl can beused to predict the future course of concentration of137Cs in foods and the human body; for example,Likhtarev et al. [5.10] on the basis of 126 000samples of milk collected during 1987–1997observed a two component exponential loss curvewith 90% of 137Cs activity disappearing with a half-life of 2.9 ± 0.3 years and 10% with 15 ± 7.6 years.The second value is very uncertain, due to the shorttime of observation compared with the radiologicalhalf-life of 137Cs of 30 years. These data are ingeneral agreement with those observed in theRussian Federation [5.37, 5.38].

5.3.2. Monitoring data as input for the assessment of internal dose

A unique feature of Chernobyl relatedmonitoring of human internal exposure was theextensive application of whole body measurementsof radionuclide content in the human body and itsorgans (mainly thyroid); these measurements wereperformed along with regular measurements ofradionuclides in food, drinking water and othercomponents of the environment. This combinationof various kinds of monitoring data allowedsubstantial improvement in the precision of thereconstruction of internal dose.

To assess internal dose from inhalation, the airconcentration measurements described in aprevious section have been used. The mostimportant aspect was assessment of dose for the

( )∑ ∫=r

rrkkk dttACDCIRE

Inhalation

kIR( )tACr

fkCR( )tSAfr

rkDC

rkCD

( )∑ ∫=r

frfkrkk dttSACRCDE

Ingestion

∑

=

Airconcentration

Inhalationrate

Inhalation dosecoefficient

Food specificactivity

Foodconsumption rate

Ingestion dosecoefficient

f∑

FIG. 5.12. Model for calculation of internal exposure forpersons exposed to Chernobyl fallout [5.9].

109

first days after the accident, when the concentrationof radionuclides in air was relatively high. Later, theassessment of doses via inhalation was needed inrelation to the resuspension of radionuclides withlow mobility in the food chain, such as plutonium.

Assessment of radionuclide intake with foodand drinking water was primarily based on thenumerous measurements of 131I, 134,137Cs and 90Sr,which have been performed all over Europe andespecially in the three most affected countries(Belarus, the Russian Federation and Ukraine).Gamma spectroscopy for 131I and 134,137Cs and radio-chemical analyses for 90Sr have been the main typesof measurement. In some laboratories betaspectroscopy was successfully applied to determinedifferent radionuclides in samples; when radionu-clide composition was well known, total betaactivity measurements were also made. In most ofthe measurements, 137Cs in raw animal products(milk, meat, etc.) was determined; the number ofthese measurements performed since 1986 andavailable for dose estimation comprises a fewmillion. Generic data on radionuclide measure-ments in food are presented in the sectionspertaining to the terrestrial environment.

Activity concentrations of soluble radio-nuclides (mainly 131I, 134,137Cs, 90Sr) in drinking waterwere determined in 1986 both in surface andunderground sources (see Section 3.5). Later, theseactivity concentrations declined to relatively lowlevels, and their contribution to internal dose wasusually negligible compared with that associatedwith the intake of food.

In May–June 1986, 131I activities weremeasured in the thyroids of residents of areas withsubstantial radionuclide deposition. In total, morethan 300 000 131I measurements in the thyroid wereperformed in the three most affected countries, anda substantial number of measurements were alsoperformed in other European countries. Specialattention was paid to measurements of children andadolescents. After careful calibration, data on largescale measurements were used as the main basis forthe reconstruction of thyroid dose.

Most of the numerous whole body measure-ments performed since 1986 in different Europeancountries have been aimed at the determination of134,137Cs. The number of measurements exceededone million, most of which were performed in thethree most affected countries. The measurementdata were widely used both for model validationconcerning radionuclide intake and evaluation ofthe effectiveness of countermeasures. In the most

contaminated regions of Belarus, the RussianFederation and Ukraine, whole body measurementdata were used to obtain more precise estimates ofhuman doses both for radiation protection purposesand as part of epidemiological studies.

Strontium-90 and plutonium radionuclides,which do not emit gamma radiation that is readilydetectable by whole body counters, have beenmeasured in excreta samples, and, since the 1990s, insamples taken at autopsy. Several hundred samplesof human bone tissue have been analysed byradiochemical methods for 90Sr/90Y content.Activities of plutonium radionuclides have beensuccessfully determined in several tens of samplesof human lungs, liver and bones [5.39, 5.40].

Reduced monitoring programmes forradiation protection purposes, and specifically forthe justification of remediation efforts, arecontinuing in the affected areas.

5.3.3. Avoidance of dose by human behaviour

In addition to the countermeasures employedto reduce levels of contamination in urban environ-ments and in agricultural foodstuffs, changes inhuman habits after the accident were also effectivein reducing doses to residents of the contaminatedareas. The most obvious and highly effectivemethod immediately after the accident would havebeen to stop the consumption of milk to reduce theintake of 131I. The effectiveness of this is not welldocumented, and it is only in some of the moreaffected regions that the residents of the threecountries were advised of this option in a timelymanner.

The longer term option of reducing theconsumption of food products known to be morehighly contaminated by 134,137Cs appears to havebeen more successful, at least during 1987–1993[5.10, 5.41]. Such foods were typically locallyproduced milk and beef or of the ‘wild’ variety,including game meat, mushrooms and berries.Later, due to deteriorating economic conditions andthe gradual reduction of the public’s caution overwild food products, such self-imposed restrictionsbecame less widespread.

5.3.4. Results for doses to individuals

5.3.4.1. Thyroid doses due to radioiodines

One of the major impacts of the accident wasexposure of the human thyroid. Doses were

110

accumulated rather quickly due to the rapid transferof iodine through the food chain and the short half-life of 131I of eight days; other radioiodines ofinterest in terms of thyroid dose also have shorthalf-lives. The importance of thyroid doses wasrecognized by national authorities throughout theworld, and early efforts focused on this issue.Estimates of country average individual thyroiddoses to infants and adults have been provided byUNSCEAR [5.2]. Attention has been paid tothyroid dose reconstruction since the early 1990s,when an increase of thyroid cancer morbidity wasdiscovered in children and adolescents residing inareas of Belarus, the Russian Federation andUkraine contaminated with Chernobyl fallout [5.1,5.3, 5.42].

In association with radioepidemiologicalstudies, the main patterns of thyroid dose formationwere clarified and published in the 1990s [5.33–5.35]and summarized in Ref. [5.1]. Nevertheless,important new work in this area has appearedrecently [5.43–5.45]. The general approach tointernal dose reconstruction has been elaborated inRef. [5.46].

Methodologies of thyroid dose reconstructionfor the Chernobyl affected populations developedin parallel in Belarus, the Russian Federation andUkraine, with the participation of US and EUexperts; these methodologies have a number ofcommonalities and some substantial distinctionsthat complicate their desired integration. Firstly, inall three countries there are many tens of thousandsof 131I thyroid measurements available, although ofdifferent quality, that are used as the basic data forthyroid dose reconstruction. In the RussianFederation, additionally, data on 131I in milk wereused. Owing to the use of human and environmental131I measurements, the reconstructed doses arerealistic rather than conservative.

Another commonality is the use of several agegroups living in one settlement or in a group of closesettlements as a unit for mean thyroid dose recon-struction. When there is a substantial number ofhuman and environmental 131I measurementsavailable in a settlement, they are used for dosereconstruction. The subsidiary quantities used fordose reconstruction in the settlements wherehistorical 131I measurements are not available are137Cs soil deposition values as indicators ofradioactive contamination in the area.

However, the methodologies for thyroid dosereconstruction for settlements withoutenvironmental or human 131I measurements are

substantially different in the three countries. InUkraine, where most of the radioiodine wasdeposited in dry weather conditions, Likhtarev et al.[5.45] developed a model with linear dependence ofthyroid dose on 137Cs soil deposition. In Belarus,where both dry and wet deposition of radioiodinesoccurred, a semiempirical model based on non-linear dependence of thyroid dose on 137Cs soildeposition was developed by Gavrilin et al. [5.35]and widely applied. In another recently publishedpaper devoted to the same problem, acomprehensive radioecological model ofradioiodine environmental transfer was developedand successfully applied for thyroid dosereconstruction [5.44]. In the Russian Federation,where wet deposition of radioiodines dominated, alinear semiempirical model of dependence of 131Iactivity concentration in milk and of thyroid doseon 137Cs soil deposition of more than 37 kBq/m2 wasdeveloped [5.43] and applied [5.47]. Despitedifferences in the applied methodologicalapproaches, the general agreement, except for areasof low contamination, is satisfactory [5.3].

The thyroid doses resulting from theChernobyl accident comprise four contributions: (a)internal dose from intakes of 131I; (b) internal dosefrom intakes of short lived radioiodines (132I, 133Iand 135I) and of short lived radiotelluriums (131Teand 132Te); (c) external dose from the deposition ofradionuclides on the ground; and (d) internal dosefrom intakes of long lived radionuclides such as134Cs and 137Cs.

For most residents of the Chernobyl affectedareas, the internal thyroid dose resulting fromintakes of 131I is by far the most important and hasreceived almost all of the attention. The dose from131I was mainly due to the consumption of freshcow’s milk and, to a lesser extent, of greenvegetables; children on average received a dose thatwas much higher than that received by adults,because of their small thyroid mass and aconsumption rate of fresh cow’s milk that wassimilar to that of adults.

An example of age and sex dependence of themean thyroid dose to inhabitants of a settlement,based on 60 000 measurements of 131I in thyroidsperformed in Ukraine in May 1986, is presented inFig. 5.13 [5.48]. The mean thyroid dose to infants islarger by a factor of about seven than to youngadults (19–30 years) residing in the same rural orurban settlements; this ratio decreases monotoni-cally with age as an exponential function, with somedeviation in adolescents. Differences in age

111

dependence between males and females seem to beinsignificant. Similar patterns were revealed bothfrom Belarusian and Russian measurements of 131Iin the thyroid [5.34, 5.35].

As the rural population living in contaminatedareas depends more on local agricultural productionthan does an urban population, thyroid dosescaused predominantly by the consumption ofcontaminated milk and dairy products are higher inrural than in urban populations by a factor of abouttwo [5.1].

Although the largest contribution to thyroiddose resulted from intakes of 131I, it is alsoimportant to take into consideration the internaldose from short lived radioiodines (132I, 133I and135I). Among members of the public, the highestrelative contribution to the thyroid doses from shortlived radionuclides was expected among theresidents of Pripyat. This cohort was exposed toradioiodines via inhalation only and was evacuatedabout 1.5 days after the accident. Analysis of directthyroid and lung spectrometric measurementsperformed on 65 Pripyat evacuees has shown thatthe contribution of short lived radionuclides tothyroid dose is about 20% for persons who did notemploy stable iodine to block their thyroids andmore than 50% for persons who took KI pills soonafter the accident [5.49]. The total thyroid doseamong the Pripyat evacuees, however, wasrelatively small compared with populationsconsuming contaminated food.

For populations permanently residing incontaminated areas, the contribution of short livedradionuclides to thyroid dose was minor, as most ofthe thyroid exposure resulted from the week longconsumption of contaminated milk and otherfoodstuffs. During transport of radioiodines along

food chains, short lived radioiodines decayed, andthe contribution of short lived radioiodines isestimated to have been of the order of 1% of the 131Ithyroid dose [5.49, 5.50].

The distribution of individual thyroid doses isillustrated in Table 5.6 for children and adolescentsresiding in the northern regions of Ukraine (i.e. theKiev, Zhytomyr and Chernigov regions) mostaffected by radiation after the Chernobyl accident[5.45]. The dose distributions presented in Table 5.6are based on about 100 000 human thyroid measure-ments. The range of thyroid dose in all groups iswide, between less than 0.2 Gy and more than10 Gy. The latter dose group includes about 1% ofyounger children, less than 0.1% of children of fiveto nine years, and less than 0.01% of adolescents.Doses to adults are lower by a factor of about 1.5than those to adolescents (see Fig. 5.13). In all agegroups presented in Table 5.6, and especially in theyounger ones, doses were high enough to cause bothshort term functional thyroid changes and thyroidcancer in some individuals [5.1, 5.3, 5.42].

Similar data for Belarus and the RussianFederation are available [5.35, 5.47]. Substantiallymore detail on the calculation of thyroid doses toindividuals is provided in the dosimetry section ofthe Chernobyl Forum report on health effects [5.3].

Generally, it can be stated that adequatemethodologies for thyroid dose reconstruction forpeople who resided in the spring of 1986 in thecontaminated areas of Belarus, the RussianFederation and Ukraine have been developed andpublished. These estimates of both individual andcollective doses are being widely used by researchscientists and national health authorities both inforecasts of thyroid morbidity and in radioepidemi-ological studies.

5.3.4.2. Long term internal doses from terrestrial pathways

Inhabitants of areas contaminated with radio-nuclides in 1986 are still experiencing internalexposure due to consumption of local foodstuffscontaining 137Cs and, to a lesser extent, 90Sr.According to model estimates and direct humanmeasurements [5.39], inhalation of plutonium radio-nuclides and 241Am does not significantly contributeto human dose in this context.

Generic dose conversion parameters havebeen developed to reconstruct the past, assess thecurrent and forecast future average effectiveinternal doses. Examples for the adult rural

1

10

0 5 10 15 20

Rel

ativ

e d

ose

Age (years)

MaleFemale

FIG. 5.13. Age–sex dependence of the mean thyroid dose toinhabitants of a settlement standardized to the mean doseto adults from the same settlement [5.48].

112

population of a settlement located in the interme-diate (100 km < distance < 1000 km) zone ofcontamination based on experimental data andmodels developed in the Russian Federation andUkraine are given in Table 5.7 [5.9, 5.10, 5.15].Values for each indicated time period are givenseparately for various soil types as the ratios of themean internal dose (E) to the mean 137Cs soildeposition in a settlement as of 1986 (s137)(µSv · kBq-1 · m-2).

In a series of experimental whole bodymeasurements and associated annual internal dosecalculations it was found that long term doses tochildren caused by ingestion of food containingcaesium radionuclides are usually lower by a factorof about 1.1 to 1.5 than those to adults andadolescents (see, for example, Refs [5.51, 5.52]).

The mean internal doses to residents of ruralsettlements strongly depend on soil properties. Forassessment purposes, soils are classified into three

TABLE 5.6. DISTRIBUTION OF INDIVIDUAL THYROID DOSES FOR AGE GROUPS OFCHILDREN AND ADOLESCENTS FROM THE KIEV, ZHYTOMYR AND CHERNIGOV REGIONSOF UKRAINE, BASED ON IODINE-131 IN THYROID MEASUREMENTS [5.45]

Category and age group Number of measurementsPer cent of children with thyroid dose (Gy) in interval

£0.2 >0.2–1 >1–5 >5–10 >10

Settlements not evacuated

Rural areas

1–4 years 9 119 40 43 15 1.7 0.9

5–9 years 13 460 62 31 6.5 0.44 0.07

10–18 years 26 904 73 23 3.7 0.16 <0.01

Urban areas

1–4 years 5 147 58 33 7.5 1.0 0.7

5–9 years 11 421 82 15 2.6 0.23 0.04

10–18 years 24 442 91 7.7 1.4 0.12 <0.01

Evacuated settlements

1–4 years 1 475 30 45 22 2.7 1.0

5–9 years 2 432 55 36 8.4 0.6 0.08

10–18 years 4 732 73 23 3.6 0.13 0.02

TABLE 5.7. RECONSTRUCTION AND PROGNOSIS OF THE AVERAGE EFFECTIVE INTERNALDOSE TO THE ADULT RURAL POPULATION IN THE INTERMEDIATE (100 km < DISTANCE< 1000 km) ZONE OF CHERNOBYL CONTAMINATION

Soil typeE/s137 (mSv ◊ kBq–1 ◊ m–2 of 137Cs)a

1986 1987–1995 1996–2005 2006–2056 1986–2056

Russian Federation [5.9]

Soddy podzolic sandyBlack

9010

605

121

161

18017

Ukraine [5.10, 5.15]

Peat bog 19 167 32 31 249

Sandy 19 28 5 5 57

Clay 19 17 3 3 42

Black 19 6 1 1 27

a s137 is given as for 1986.

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major soil types: (a) black or chernozem soil; (b)podzol soil (including both podzol sandy and podzolloam soils); and (c) peat bog or peat soil. Due to theenvironmental behaviour of 137Cs, internal exposureexceeds external dose in areas with peaty soil.Contributions due to internal and external exposureare comparable in areas with light sandy soil, andthe contribution of internal exposure to the total(external and internal) dose does not exceed 10% inareas with dominantly black soil. According tonumerous studies, the contribution of 90Sr to theinternal dose regardless of natural conditions isusually less than 5%.

The parameters obtained from independentsets of Russian and Ukrainian data significantlydiffer for some soil types and time periods (seeTable 5.7). Some of these discrepancies can beexplained by the different meteorologicalconditions (mainly dry deposition in Ukraine andwet deposition in the Russian Federation) thatoccurred in different parts of the Chernobylaffected areas and by different food consumptionhabits.

Multiplication of the parameters presented inTable 5.7 by the mean 137Cs soil deposition (as of1986) gives an estimate of the internal effective dosecaused by radiation from 137Cs and 134Cs (for theRussian Federation, also from 90Sr and 89Sr) but notfrom radioiodines. Dose estimates are given on theassumption that countermeasures against internalexposure were not applied. In broad terms, the mostimportant factors controlling internal dose to therural population are the dominant soil type and theamount of 137Cs deposition.

In towns and cities, internal dose is partiallydetermined by radioactive contamination offoodstuffs produced in surrounding districts.

However, importation of foodstuffs from non-contaminated areas has significantly reduced theintake of radionuclides, and internal doses receivedby urban populations are typically a factor of two tothree less than in rural settlements with an equallevel of radioactive contamination.

The deviation in dose to critical groupscompared with settlement average values varies bya factor of about three for internal exposure. Thegroup most subjected to internal exposure from137Cs is adults consuming both locally producedagricultural animal foods (e.g. milk, dairy products,etc.) and natural foods (e.g. mushrooms, lake fish,berries, etc.) in amounts exceeding averageconsumption rates.

At present, inhabitants of areas of lowcontamination (less than 0.04 MBq/m2 of 137Cs) arereceiving up to 0.004 mSv/a from ingestion of localfoods in black soil areas, up to 0.04 mSv/a in sandysoil areas and about 0.1 mSv/a in villages located inpeaty soil areas. In the period 2002–2056, they willreceive an additional internal dose of less than0.1 mSv in black soil areas, up to 0.7 mSv in sandysoil areas and about 1–2 mSv in villages located inpeaty soil areas.

To avoid the presentation of dosimetric dataon a site by site basis, mean effective doses to adultresidents of rural and urban localities have beendetermined as a function of soil 137Cs deposition andpredominant soil type; such data are given inTables 5.8 and 5.9. The 137Cs soil deposition issubdivided into two ranges: 0.04–0.6 MBq/m2

(1-15 Ci/km2) and above 0.6 MBq/m2 (i.e. 0.6–4MBq/m2 (15–100 Ci/km2)) in 1986. The level0.04 MBq/m2 is considered as a conventional borderbetween ‘non-contaminated’ and ‘contaminated’areas. In areas contaminated with 137Cs above

TABLE 5.8. PAST (1986–2000) AND FUTURE (2001–2056) MEAN CHERNOBYL RELATEDEFFECTIVE INTERNAL DOSES (mSv) TO ADULT RESIDENTS OF AREAS WITH CAESIUM-137SOIL DEPOSITION ABOVE 0.04 MBq/m2 (1 Ci/km2) IN 1986 [5.53]

PopulationCaesium-137 in soil

(MBq/m2)

Soil type/time period

Black Podzol Peat

1986–2000 2001–2056 1986–2000 2001–2056 1986–2000 2001–2056

Rural 0.04–0.6 1–10 0.1–1 3–30 0.5–7 8–100 2–30

0.6–4 — 30–100 7–50 —

Urban 0.04–0.6 1–8 0.1–0.6 2–20 0.3–5 6–80 1–20

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0.6 MBq/m2, application of active countermeasures(i.e. agricultural restrictions, decontaminationmeasures, recommendations to restrictconsumption of locally gathered natural foods(forest mushrooms and berries, lake fish, etc.)) hasbeen mandatory.

Dosimetric models predict that by 2001 theresidents had already received at least 75% of theirlifetime internal dose due to 137Cs, 134Cs, 90Sr and89Sr (see Table 5.8). In the coming years (2001–2056) they will receive the remaining 25% (i.e. lessthan 1 mSv for black soil, up to 7 mSv for podzol soiland up to 30 mSv for peat soil). In the more contam-inated podzol soil areas, an effective dose of up to50 mSv can still be expected.

As can be seen from Table 5.9, the moreelevated internal doses in some of the settlementsare above the national action level of 1 mSv/a. Forsome population groups in contaminated areas, wildfoods (forest mushrooms, game, forest berries, fish)can make an important contribution to dose [5.9,5.15, 5.30]. Studies of 137Cs intake of the ruralpopulation in the Bryansk region of the RussianFederation indicated that natural foods contributedabout 20% of total uptake in 1987, but up to 80% in1994–1999 [5.29]. The relative contribution of wildfoods to internal dose has risen gradually because ofthe substantial reduction of radionuclide content inagricultural foods derived from vegetables andanimals, combined with a much slower decrease inthe contamination of wild foods. In the latterperiod, the highest contributions to 137Cs intake(and, by inference, internal dose) came from forestmushrooms, followed by forest berries, game andlake fish.

Similar trends were found in residents ofKozhany (Bryansk region), located on the coast of ahighly contaminated lake, where natural foodscontributed an average of 50–80% of 137Cs intake[5.30]. Men were more likely to eat natural foods

than women, and there was a positive correlationbetween consumption of mushrooms and fish thatindicated a liking by many inhabitants for ‘gifts ofnature’. The average annual internal dose due to137Cs was estimated to be 1.2 mSv for men and 0.7mSv for women in 1996.

5.3.4.3. Long term doses from aquatic pathways

Human exposure via the aquatic pathwayoccurs as a result of consumption of drinking water,fish and agricultural products grown using irrigationwater from contaminated water bodies. Use ofwater bodies as a source of drinking water forlivestock and flooding of agricultural land can alsolead to human exposure via terrestrial pathways.

In the middle and lower areas of the DnieperRiver catchment, which were not significantlysubjected to direct radionuclide contamination in1986, a significant proportion (10–20%) of theChernobyl related exposures was attributed toaquatic pathways [5.53]. Although these doses were,in fact, estimated to be very low, there was aninadequate appreciation by the local population ofthe risks of using water from contaminated aquaticsystems. This created an (unexpected) stress in thepopulation concerning the safety of the watersupply system. In areas close to Chernobyl,radiation exposures via the aquatic pathway aremuch higher, but are again minor in comparisonwith terrestrial pathways.

Three pathways of exposure due to aquaticsystems need to be considered [5.53]:

(a) Consumption of drinking water from rivers,lakes, reservoirs and wells in the contaminatedareas. The most significant exposures viaconsumption of drinking water resulted fromthe use of water from the Dnieper River basin,and, in particular, the reservoirs of the

TABLE 5.9. ANNUAL (2001) MEAN CHERNOBYL RELATED EFFECTIVEINTERNAL DOSES (mSv) TO ADULT RESIDENTS OF AREAS WITHCAESIUM-137 SOIL DEPOSITION ABOVE 0.04 MBq/m2 (1 Ci/km2) IN 1986 [5.53]

PopulationCaesium-137 in soil

(MBq/m2)

Soil type

Black Podzol Peat

Rural 0.04–0.6 0.004–0.06 0.03–0.4 0.1–2

0.6–4 — 0.4–2 —

Urban 0.04–0.6 0.003–0.04 0.02–0.2 0.1–1

115

Dnieper River system. The Dnieper cascade isa source of drinking water for more than eightmillion people. The main consumers ofdrinking water from the Dnieper River live inthe Dnipropetrovsk and Donetsk regions. InKiev, water from the Dnieper and DesnaRivers is used by about 750 000 people. Theremaining part of the population use watermainly derived from groundwater sources.

(b) Consumption of fish. The Dnieper Riverreservoirs are used intensively for commercialfishing. The annual catch is more than 25 000 t.There was no significant decrease in fishing inmost of these reservoirs during the firstdecade after the accident. During the first twoto three years, however, restrictions wereplaced on the consumption of fish from theKiev reservoir. In some smaller lakes, both inthe former USSR and in parts of westernEurope, fishing was prohibited during the firstmonths and even years after the accident.

(c) Consumption of agricultural products grownon land irrigated with water from the Dnieperreservoirs. In the Dnieper River basin there ismore than 1.8 × 106 ha of irrigated agriculturalland. Almost 72% of this territory is irrigatedwith water from the Kakhovka reservoir in theDnieper River–reservoir system. Accumu-lation of radionuclides in plants in irrigatedfields can take place because of root uptake ofthe radionuclides introduced with irrigationwater and due to direct incorporation of radio-nuclides through leaves following sprinklerirrigation. However, recent studies haveshown that, in the case of irrigated land insouthern Ukraine, irrigation water did not addsignificant amounts of radioactive material tocrops in comparison with that which had beeninitially deposited in atmospheric fallout andsubsequently taken up from the soil.

The contribution of aquatic pathways to thedietary intake of 137Cs and 90Sr is usually quite small,even in areas that were seriously affected byChernobyl fallout. For the relatively large ruralpopulation that consumes fish from local rivers andlakes, however, exposures could be significant. Inaddition, collective doses to the large urban andrural populations using water from the Pripyat–Dnieper River–reservoir system were relativelyhigh. Owing to the high fallout within the catchmentof the Pripyat and Dnieper Rivers, this system has

been intensively monitored, and doses via aquaticpathways have been estimated [5.53].

Contaminated rivers could potentially haveled to significant doses in the first months after theaccident through consumption of drinking water,mainly through contamination with short livedradionuclides. The most significant individual dosewas from 131I and was estimated to be up to 0.5–1.0 mSv for the citizens of Kiev during the first fewweeks after the Chernobyl accident [5.53].

After the end of the first month following theaccident, the main contributors to doses via aquaticpathways became 137Cs and 90Sr. Estimated dosesdue to these radionuclides in the Dnieper River–reservoir system were made on the basis ofmonitoring data and predictions of floodfrequencies. A worst case scenario of a series of highfloods during the first decade after the accident(1986–1995) was assumed. Estimates were thatindividual doses via aquatic pathways would nothave exceeded 1–5 mSv/a. Thus long term doses viathe drinking water pathway were small incomparison with doses (mainly from short livedradionuclides) in the early phase [5.53].

The contribution of different exposurepathways to dose is shown in Fig. 5.14 for the villageof Svetilovichy in the Gomel region of Belarus. Inthis case, consumption of freshwater fish forms animportant part of the diet, and hence doses via thispathway can be significant for some individuals.

5.4. TOTAL (EXTERNAL AND INTERNAL) EXPOSURE

The generalized data for both external andinternal (not including dose to the thyroid)

External from soil

50.3%

External from shore4.0%

External from swimming

0.01%

Internal from food ingestion

23.9%

Internal from fish ingestion

20.6%Internal from drinking water

1.2%

FIG. 5.14. Contributions of different pathways to theeffective dose to the critical group of the population ofSvetilovichy in the Gomel region of Belarus [5.53, 5.54].

116

exposures of the general public presented inTables 5.4 and 5.9, respectively, have beensummarized in Table 5.10 in order to estimatebroadly the mean individual total (external andinternal) effective doses accumulated by residentsof radioactively contaminated areas during 1986–2000 and to forecast doses for 2001–2056. Table 5.11gives estimates of the annual total dose in 2001. Inboth tables data are given for levels of 137Cs soildeposition existing in 1986 in currently inhabitedareas of Belarus, the Russian Federation andUkraine, separately for rural and urban populationsand for different soil types, with no account taken ofcurrent countermeasures. Both accumulated andcurrent annual total doses are presented for adults,since, in the long term, children generally receivelower external and internal doses from 137Csenvironmental contamination (in contrast tothyroid internal doses from radioiodine intake),because of their occupancy (see Tables 5.3 and 5.5),food habits and metabolic features.

As can be seen from Table 5.10, bothaccumulated and predicted mean doses in

settlement residents vary over two orders ofmagnitude depending on the radioactive contami-nation of the area, soil type and settlement type.Thus in 1986–2000 the dose range was from 2 mSv intowns located in black soil areas, up to 300 mSv invillages located in areas with podzol sandy soil.According to the forecast, the doses expected in2001–2056 are substantially lower than the dosesalready received (i.e. in the range of 1–100 mSv). Intotal, if countermeasures were not applied, thepopulations of some of the more contaminatedvillages in Belarus and the Russian Federationwould receive lifetime effective doses of up to400 mSv, not including dose to the thyroid.However, intensive application of countermeasuressuch as settlement decontamination and agriculturalcountermeasures has reduced dose levels by a factorof about two. For comparison, a worldwide averagelifetime dose from natural background radiation isabout 170 mSv, with a typical range of 70–700 mSvin various regions.

Based on local demographic data [5.51], 137Cssoil deposition maps (see Section 3.1) and the

TABLE 5.10. PAST (1986–2000) AND FUTURE (2001–2056) MEAN CHERNOBYL RELATED TOTALEFFECTIVE DOSES (mSv) TO ADULT RESIDENTS OF AREAS WITH CAESIUM-137 SOIL DEPOSI-TION ABOVE 0.04 MBq/m2 (1 Ci/km2) IN 1986 [5.53]

PopulationCaesium-137

in soil (MBq/m2)

Soil type

Black Podzol Peat

1986–2000 2001–2056 1986–2000 2001–2056 1986–2000 2001–2056

Rural 0.04–0.6 3–40 1–14 5–60 1–20 10–150 3–40

0.6–4 — 60–300 20–100 —

Urban 0.04–0.6 2–30 1–9 4–40 1–13 8–100 2–20

TABLE 5.11. ANNUAL (2001) MEAN CHERNOBYL RELATED TOTAL EFFECTIVE DOSES (mSv) TOADULT RESIDENTS OF AREAS WITH CAESIUM-137 SOIL DEPOSITION ABOVE 0.04 MBq/m2 (1 Ci/km2) IN 1986 [5.53]

Population Caesium-137 in soil (MBq/m2)Soil type

Black Podzol Peat

Rural 0.04–0.6 0.05–0.8 0.1–1 0.2–2

0.6–4 — 1–5 —

Urban 0.04–0.6 0.03–0.4 0.05–0.6 0.1–1

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current level of countermeasure application (seeSection 4), the vast majority of the five millionpeople currently residing in the contaminated areasof Belarus, the Russian Federation and Ukraine(see Table 3.2) — that is, in the early 2000s —receive annual effective doses of less than 1 mSv(i.e. less than the national action levels in the threecountries). For comparison, a worldwide averageannual dose from natural background radiation isabout 2.4 mSv, with a typical range of 1–10 mSv invarious regions [5.1].

The number of residents of the contaminatedareas in the three most affected countries thatcurrently receive more than 1 mSv annually can beestimated to be about 100 000 persons. As the futurereduction of both the external dose rate and radio-nuclide (mainly 137Cs) activity concentrations infood will be rather slow (see Sections 5.2 and 3.3–3.5), the reduction of human exposure levels isexpected to be slow (i.e. about 3–5%/a withcurrently applied countermeasures).

5.5. COLLECTIVE DOSES

5.5.1. Thyroid

A summary of the collective doses to thethyroid for the three most contaminated countries,based on the thyroid dose reconstruction techniquesdescribed in Section 5.3.4.1, is shown in Table 5.12.The total thyroid collective dose is 1.6 × 106 man Gy,with nearly half received by the group of personsexposed in Ukraine. The present estimate of thecollective thyroid dose does not differ from thatmade in Ref. [5.1].

5.5.2. Total (external and internal) dose from terrestrial pathways

Estimates of collective dose accumulated in1986–2005 via the terrestrial pathways of externalirradiation and ingestion of contaminated foods aregiven in Table 5.13 for the three most affectedcountries. The total collective dose was estimated tobe 43 000 man Sv in 1986–1995, including24 000 man Sv from external exposure and 19 000man Sv from internal exposure, according toUNSCEAR [5.1], annex J, table 34. According tothe models of exposure dynamics presented above[5.7], the estimated collective effective externaldoses in 1986–2005 are about a factor of 1.2 higher,and collective effective internal doses are higher bya factor of 1.1–1.5 (depending on soil properties andapplied countermeasures), than those obtained in1986–1995. In total, the collective dose increased by9000 man Sv, or by 21%, during the second decade,compared with the first decade, after the accident,

TABLE 5.12. COLLECTIVE THYROID DOSESIN THE THREE COUNTRIES MOST CONTAM-INATED BY THE CHERNOBYL ACCIDENT[5.1]

Collective thyroid dose (103 man Gy)

Russian Federation 300

Belarus 550

Ukraine 740

Total 1600

TABLE 5.13. ESTIMATED COLLECTIVE EFFECTIVE DOSES IN 1986–2005 TO THE POPULATIONSOF THE CONTAMINATED AREAS OF BELARUS, THE RUSSIAN FEDERATION AND UKRAINE(CAESIUM-137 SOIL DEPOSITION IN 1986 MORE THAN 37 kBq/m2)a

Population (millions of people)

Collective dose (103 man Sv)

External Internal Total

Belarus 1.9 11.9 6.8 18.7

Russian Federation 2.0 10.5 6.0 16.5

Ukraine 1.3 7.6 9.2 16.8

Total 5.2 30 22 52

a Excluding thyroid dose. (Modified from Ref. [5.1], annex J, table 34, using dosimetric models presented in this report.)

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and reached 52 000 man Sv. This is in goodagreement with the predictions made byUNSCEAR in 1988 [5.2].

The recent estimate of collective dose basedon both human and environmental measurementsimplicitly accounts for substantial, but not specified,amounts of collective dose saved by the institutionof countermeasures that included evacuation,relocation, prohibition on the use of foodstuffs andlonger term remediation of contaminated areas.

5.5.3. Internal dose from aquatic pathways

The most important aquatic system (theDnieper River basin) occupies a large area with apopulation of about 32 million people who use thewater for drinking, fishing and irrigation. Estimateshave been made of the collective dose to peoplefrom these three pathways for a period of 70 yearsafter the accident (i.e. from 1986 to 2056) [5.55,5.56]. A long term hydrological scenario has beenanalysed using a computer model [5.57]. Historicaldata were used to account for the natural variabilityin river flow. Dose assessment studies were carriedout to estimate the collective dose from the threepathways [5.58]. The results of the calculations aregiven in Table 5.14.

Dose estimates for the Dnieper River systemshow that if there had been no action to reduceradionuclide fluxes to the river, the collective dosecommitment for the population of Ukraine (mainlydue to radiocaesium and radiostrontium) couldhave reached 3000 man Sv. Protective measures (seeSection 4) carried out during 1992–1993 on the leftbank floodplain of the Pripyat River decreasedexposure by approximately 700 man Sv. Otherprotective measures on the right bank in the CEZ(during 1999–2001) will further reduce collectivedoses by 200–300 man Sv [5.59].


5.6.1. Conclusions

(a) The collective effective dose (not includingdose to the thyroid) received by about fivemillion residents living in the areas of Belarus,the Russian Federation and Ukraine contami-nated by the Chernobyl accident (137Csdeposition on soil of >37 kBq/m2) wasapproximately 40 000 man Sv during theperiod 1986–1995. The groups of exposed

TABLE 5.14. COLLECTIVE DOSE COMMITMENT (CDC70) DUE TO STRONTIUM-90 ANDCAESIUM-137 FLOWING FROM THE PRIPYAT RIVER TO THE DNIEPER RIVER ANDDOWNSTREAM [5.56, 5.58]

RegionPopulation

(millions of people)Strontium-90 CDC 70

(man-Sv)Caesium-137 CDC70

(man-Sv)Ratio 90Sr CDC70/

137Cs CDC70

Chernigov 1.4 4 2 2

Kiev 4.5 290 190 1.5

Cherkassy 1.5 115 50 2.3

Kirovograd 1.2 140 40 3.5

Poltava 1.7 130 60 2.2

Dnepropetrovsk 3.8 610 75 8

Zaporozhe 2 320 35 9

Nikolaev 1.3 150 20 8

Kharkov 3.2 60 4 15

Lugansk 2.9 15 1 15

Donetsk 5.3 330 20 17

Kherson 1.2 100 20 5

Crimea 2.5 175 5 35

Total 32.5 2500 500 5

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persons within each country received anapproximately equal collective dose. Theadditional amount of collective effective doseprojected to be received between 1996 and2006 is about 9000 man Sv.

(b) The collective dose to the thyroid was nearly2 × 106 man Gy, with nearly half received bypersons exposed in Ukraine.

(c) The main pathways leading to humanexposure were external exposure from radio-nuclides deposited on the ground and theingestion of contaminated terrestrial foodproducts. Inhalation and ingestion of drinkingwater, fish and products contaminated withirrigation water were generally minorpathways.

(d) The range in thyroid dose in differentsettlements and in all age–gender groups islarge, between less than 0.1 Gy and more than10 Gy. In some groups, and especially inyounger children, doses were high enough tocause both short term functional thyroidchanges and thyroid cancer effects in someindividuals.

(e) The internal thyroid dose from the intake of131I was mainly due to the consumption offresh cow’s milk and, to a lesser extent, ofgreen vegetables; children, on average,received a dose that was much higher thanthat received by adults, because of their smallthyroid masses and consumption rates of freshcow’s milk that were similar to those of adults.

(f) For populations permanently residing incontaminated areas and exposed predomi-nantly via ingestion, the contribution of shortlived radioiodines (i.e. 132I, 133I and 135I) tothyroid dose was minor (i.e. about 1% of the131I thyroid dose), since short lived radio-iodines decayed during transport of the radio-iodines along the food chains. The highestrelative contribution (20–50%) to the thyroiddose to the public from short lived radionu-clides was received by the residents of Pripyatthrough inhalation; these residents wereevacuated before they could consume contam-inated food.

(g) Both measurement and modelling data showthat the urban population was exposed to alower external dose by a factor of 1.5–2compared with the rural population living inareas with similar levels of radioactivecontamination. This arises because of thebetter shielding features of urban buildings

and different occupational habits. Also, as theurban population depends less on localagricultural products and wild foods than therural population, both effective and thyroidinternal doses caused predominantly byingestion were lower by a factor of two tothree in the urban than in the ruralpopulation.

(h) The initial high rates of exposure declinedrapidly due to the decay of short lived radio-nuclides and to the movement of radio-caesium into the soil profile. The latter causeda decrease in the rate of external dose due toincreased shielding. In addition, as caesiummoves into the soil column it binds to soilparticles, which reduces the availability ofcaesium to plants and thus to the human foodchain.

(i) The great majority of dose from the accidenthas already been accumulated.

(j) Persons who received effective doses (notincluding dose to the thyroid) higher than theaverage by a factor of two to three were thosewho lived in rural areas in single storey homesand who ate large amounts of wild foods suchas game meats, mushrooms and berries.

(k) The long term internal doses to residents ofrural settlements strongly depend on soilproperties. Contributions due to internal andexternal exposure are comparable in areaswith light sandy soil, and the contribution ofinternal exposure to the total (external andinternal) dose does not exceed 10% in areaswith predominantly black soil. The contri-bution of 90Sr to the internal dose, regardlessof natural conditions, is usually less than 5%.

(l) The long term internal doses to childrencaused by ingestion of food containingcaesium radionuclides are usually lower by afactor of about 1.1–1.5 than those in adults andadolescents.

(m) Both accumulated and predicted mean dosesin settlement residents vary in the range oftwo orders of magnitude, depending on theradioactive contamination of the area,predominant soil type and settlement type. Inthe period 1986–2000 the accumulated doseranged from 2 mSv in towns located in blacksoil areas up to 300 mSv in villages located inareas with podzol sandy soil. The dosesexpected in the period 2001–2056 are substan-tially lower than the doses already received(i.e. in the range of 1–100 mSv).

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(n) If countermeasures had not been applied, thepopulations of some of the more contami-nated villages could have received lifetime (70years) effective doses of up to 400 mSv.Intensive application of countermeasures suchas settlement decontamination and agricul-tural countermeasures has substantiallyreduced the doses. For comparison, aworldwide average lifetime dose from naturalbackground radiation is about 170 mSv, with atypical range of 70–700 mSv in various regionsof the world.

(o) The vast majority of the approximately fivemillion people residing in the contaminatedareas of Belarus, the Russian Federation andUkraine currently receive annual effectivedoses of less than 1 mSv (equal to the nationalaction levels in the three countries). Forcomparison, a worldwide average annual dosefrom natural background radiation is about2.4 mSv, with a typical range of 1–10 mSv invarious regions of the world.

(p) The number of residents of the contaminatedareas in the three most affected countries thatcurrently receive more than 1 mSv annuallycan be estimated to be about 100 000 persons.As the future reduction of both the externaldose rate and the radionuclide (mainly 137Cs)activity concentrations in food is predicted tobe rather slow, the reduction in the humanexposure levels is also expected to be slow (i.e.about 3–5%/a with current countermeasures).

(q) Based upon available information, it does notappear that the doses associated with hotparticles were significant.

(r) The assessment of the Chernobyl Forumagrees with that of UNSCEAR [5.1] in termsof the dose received by the populations of thethree most affected countries: Belarus, theRussian Federation and Ukraine.


(a) Large scale monitoring of foodstuffs, wholebody counting of individuals and provision ofthermoluminescent dosimeters to members ofthe general public are no longer necessary.The critical groups in areas of high contami-nation and/or high transfer of radiocaesium tofoods are known. Representative members ofthese critical groups should be monitored withdosimeters for external dose and with wholebody counting for internal dose.

(b) Sentinel or marker individuals in more highlycontaminated areas not scheduled for furtherremediation might be identified for continuedperiodic whole body counting and monitoringof external dose. The goal would be to followthe expected continued decrease in externaland internal dose and to determine whethersuch decreases are due to radioactive decayalone or to further ecological elimination.



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6. RADIATION INDUCED EFFECTS ON PLANTS AND ANIMALS

6.1. PRIOR KNOWLEDGE OF RADIATION EFFECTS ON BIOTA

The effects of radiation on plants and animalshave long been of interest to scientists; in fact, muchof the information on the effects on humans hasevolved from studies on plants and animals.Additional research followed the development ofnuclear energy and concerns about the possibleimpacts of increased, but authorized, discharges ofwaste radionuclides into the terrestrial and aquaticenvironments. The magnitude of these authorizedreleases has always been controlled on the basis ofthe limitation of human exposure, but it has beenrecognized that animals and plants have also beenexposed — frequently to a higher degree thanhumans. By the mid-1970s, sufficient informationhad been accrued on the effects of ionizingradiation on plants and animals that several author-itative reviews had been compiled to summarize thefindings [6.1–6.4].

Some broad generalizations about the effectsof radiation exposure can be gleaned from theresearch that has been conducted over the past 100years. Foremost are the relatively large differencesin doses required to cause lethality among varioustaxonomic groups (Fig. 6.1). Considerable variationin response occurs within a taxon due to enhancedradiosensitivity of some individuals or life stages.Wide ranges in doses are also observed within agroup or taxon when progressing from minor tosevere effects.

Figure 6.2 summarizes information on thedoses required to be delivered over a short timeperiod to produce damage of different degrees invarious plant communities, soil invertebrates androdents. Within the plant kingdom, trees aregenerally more sensitive than shrubs, which in turnare more sensitive than herbaceous species.Primitive forms such as lichens, mosses andliverworts are more resistant than vascular plants.Radiation resistant plants frequently havemolecular and cellular characteristics that enhancetheir ability to tolerate radiation stress, anddifferences in plant community response can beexplained, in part, by the early work of Sparrow[6.8]. He showed that characteristics such as large

chromosomes, normal (rather than diffuse) centro-meres, small chromosome number, uninucleatedcells, diploid or haploid cells, sexual reproduction,long intermitotic time and slow rates of meiosis areassociated with high radiosensitivity in plants, butthat sensitivity can be modified in time due toseasonal processes (e.g. dormancy or the onset ofgrowth in spring; Table 6.1).

Scientific reviews (e.g. Ref. [6.3]) haveindicated that mammals are the most sensitiveorganisms and that reproduction is a more sensitiveendpoint than mortality. For acute exposures of

Viruses

Molluscs

Protozoa

Bacteria

Moss, lichen, algae

Insects

Crustaceans

Reptiles

Amphibians

Fish

Higher plants

Birds

Mammals

1 10 100 1000 10 000

Acute lethal dose range (Gy)

FIG. 6.1. Acute dose ranges that result in 100% mortality invarious taxonomic groups. Humans are among the mostsensitive mammals, and therefore among the most sensitiveorganisms [6.5].

Moss–lichen

Grassland

Tropical rain forest

Old fields

Shrubs

Deciduous forest

Soil invertebrates

Rodents

Coniferous forest

0.01 0.1 1 10 100 1000 10 000

Minor effects

Intermediate to severe effects

Dose (Gy)

FIG. 6.2. Range of short term radiation doses (deliveredover 5–60 d) that produced effects in various plant commu-nities, rodents and soil invertebrates. Minor effects includechromosomal damage, changes in productivity, reproduc-tion and physiology. Intermediate effects include changesin species composition and diversity through selectivemortality. Severe effects (massive mortality) begin at theupper range of intermediate effects [6.6, 6.7].

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mammals, mortality generally occurs at doses above3 Gy, while reproduction is affected at doses below0.3 Gy. Chronic exposures alter the responses, withmortality occurring at greater than 0.1 Gy/d andreproduction effected at less than 0.01 Gy/d.Among aquatic organisms, fish are the mostsensitive, with gametogenesis and embryodevelopment being the more sensitive stages.Effects on animal populations can be reduced bytheir mobility (in terms of moving from areas ofhigh exposure to areas of low exposure). Compara-tively stationary soil invertebrates do not have suchabilities and can receive substantial doses relative tothe rest of the animal kingdom, particularly becausesoil is a sink for most radioactive contamination.

The response of a plant or animal to radiationdepends on the dose received as well as its radiosen-sitivity. The former is largely determined by itshabitat preference in relation to the evolving distri-bution of radioactive contaminants as a function oftime, as well as the organism’s propensity toaccumulate radionuclides in its organs and tissues.Owing to their particular use of the habitat, plantsand animals within a contaminated area mayreceive radiation doses that can be substantiallyhigher than those of humans occupying the samearea (e.g. humans gain some shielding from housingand may obtain food and water from less contami-nated sources [6.3]).

Although all exposures to ionizing radiationhave the potential to damage biological tissue,protraction of a given total absorbed dose in time

can, depending on the dose rate, result in areduction in response due to the intervention ofcellular and tissue repair processes. This has led tothe conventional, but somewhat artificial,distinction between so called acute and chronicradiation exposure regimes. In general, an acuteradiation exposure is one that usually occurs at ahigh dose rate and in a short period of time relativeto that within which obvious effects occur. Chronicexposures are taken to be continuous in time, oftenover a significant portion of an organism’s lifespan,or throughout some particular life stage (e.g.embryonic development) and usually at a suffi-ciently low dose rate that the cumulative dose doesnot produce acute effects.

The earlier reviews noted above wereconsistent in concluding that it is unlikely that therewill be any significant detrimental effects:

(a) To terrestrial and aquatic plant populations,and aquatic animal populations at chronicdose rates of less than 10 mGy/d; or

(b) To terrestrial animal populations at dose ratesof less than 1 mGy/d.

It should be emphasized, however, that thesedose rates were not intended for use as limits in anysystem to provide for the protection of theenvironment; they were simply the dose rates belowwhich the available evidence, admittedly limited inthe range of organisms and biological responsesinvestigated, indicated little likelihood of any

TABLE 6.1. PRINCIPAL NUCLEAR CHARACTERISTICS AND FACTORSINFLUENCING THE SENSITIVITY OF PLANTS TO RADIATION [6.5, 6.8]

Factors increasing sensitivity Factors decreasing sensitivity

Large nucleus (high DNA content) Small nucleus (low DNA content)

Much heterochromatin Little heterochromatin

Large chromosomes Small chromosomes

Acrocentric chromosomes Metacentric chromosomes

Normal centromere Polycentric or diffuse centromere

Uninucleate cells Multinucleate cells

Low chromosome number High chromosome number

Diploid or haploid nuclei High polypolid

Sexual reproduction Asexual reproduction

Long intermitotic time Short intermitotic time

Long dormant period Short or no dormant period

Slow meiosis Fast meiosis

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significant response. The above dose rates are withreference to population level effects, not to impactson individual organisms.

More recent reviews of the effects of radiationexposure on individual organisms carried out in theframework of two EC projects, FASSET(Framework for the Assessment of EnvironmentalImpact) and EPIC (Environmental Protection fromIonising Contaminants in the Arctic), haveproduced broadly consistent conclusions [6.9–6.11].Although minor effects may be seen at lower doserates in sensitive cell systems or individuals ofsensitive species (e.g. haematological cell counts inmammals, immune response in fish, growth in pinesand chromosome aberrations in many organisms),the threshold dose rate for significant effects inmost studies is about 0.1 mGy/h (2.4 mGy/d).Detrimental responses then increase progressivelywith increasing dose rate and usually become clearat greater than 1 mGy/h (24 mGy/d) given over alarge fraction of the lifespan. The significance of theminor morbidity and cytogenetic effects on theindividual, or on populations more generally, seenat dose rates of less than 2.4 mGy/d has yet to bedetermined [6.11].

The recently compiled EPIC database coversa very wide range of radiation dose rates (frombelow 10–5 Gy/d up to more than 1 Gy/d) to wildflora and fauna observed in northern parts of theRussian Federation and in the Chernobyl contami-nated areas [6.10]. The general conclusion from theEPIC database is that the threshold for determin-istic radiation effects in wildlife lies somewhere inthe range of 0.5–1 mGy/d for chronic low linearenergy transfer radiation.

These broad conclusions concerning theimpact of radiation on plants and animals providean appropriate context within which to consider theavailable information on the effects that have beenobserved from the increased radiation exposuresfollowing the accident at Chernobyl.

6.2. TEMPORAL DYNAMICS OF RADIATION EXPOSURE FOLLOWING THE CHERNOBYL ACCIDENT

It is critical to frame any discussion ofChernobyl environmental effects within the specifictime period of interest. Effects observed now, nearly20 years after the accident, are drastically differentfrom those that occurred during the first 20 days.Three distinct phases of radiation exposure have

been identified in the area local to the accident[6.4]. In the first 20 days, radiation exposures wereessentially acute because of the large quantities ofshort lived radionuclides present in the passingcloud of contamination (99Mo, 132Te/132I, 133Xe, 131Iand 140Ba/140La). Most of these short lived, highlyradioactive nuclides were deposited on to plant andground surfaces, resulting in the accumulation oflarge doses that measurably affected biota. Highexposures of the thyroids of vertebrate animals alsooccurred during the first days and weeks followingthe accident from the inhalation and ingestion ofradioactive iodine isotopes or their radioactiveprecursors.

The measured exposure rates on the day ofthe accident in the immediate vicinity of thedamaged reactor are shown in Fig. 6.3. Theseexposure rates were mainly due to gamma radiationfrom deposited radionuclides and range up to about20 Gy/d. However, for surface tissues and smallbiological targets (e.g. mature needles and growingbuds of pine trees), there was a considerableadditional dose rate from the beta radiation of thedeposited radionuclides. Taking into account thehigh dose rates during the relatively short exposureperiod from the short lived radioisotopes, this firstphase of 20–30 days can be generally characterizedas an acute exposure regime that had pronouncedeffects on biota.

The second phase of radiation exposureextended through the summer and autumn of 1986,during which time the short lived radionuclidesdecayed and longer lived radionuclides weretransported to different components of theenvironment by physical, chemical and biological

100COOLING POND

1 km

TOWN OF PRIPYAT

REACTOR1

10

100

100

1

0.1

RIVER PRIPYAT

FIG. 6.3. Measured exposure rates in air on 26 April 1986in the local area of the Chernobyl reactor. Units of isolinesare R/h (1 R/h is approximately 0.2 Gy/d) [6.12].

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processes. Dominant transport processes includedrain induced transfer of radionuclides from plantsurfaces on to soil, and bioaccumulation throughplant tissues. Although the dose rates at the soilsurface declined to much less than 10% of the initialvalues, due to radioactive decay of the short livedisotopes (see Fig. 5.3), damaging total doses werestill accumulated. The modifying effect of radionu-clide wash-off by rain on radiation damage ofconifers is shown in Fig. 6.4.

In general, approximately 80% of the totalradiation dose accumulated by plants and animalswas received within three months of the accident,and over 95% of this was due to beta radiation [6.4].This finding agrees with earlier studies on theimportance of beta radiation, relative to the gammacomponent, to the total dose from radioactive

fallout; for example, when a 10 h old mixture offresh fission products was experimentally depositedon cereal plants at differing stages of growth, at adensity of 7 GBq/m2, the ratio of resulting beta andgamma dose rates, measured with thermolumi-nescent dosimeters, varied from 1 to 130 [6.13].

Measurements made with thermoluminescentdosimeters on the soil surface at sites within theCEZ indicated that the ratio of beta dose to gammadose was about 26:1 (i.e. 96% of the total dose wasfrom beta radiation). For a gamma dose rate of0.01 mGy/h at the soil surface, 15 days after theaccident, the total cumulative dose in the firstmonth from beta and gamma radiation wasestimated to be 0.5 ± 0.2 Gy, and 0.6 and 0.7 Gy atthe end of the second and third months, respectively[6.14].

In the third (and continuing) phase ofradiation exposure, dose rates have been chronic,less than 1% of the initial values, and derivedmainly from 137Cs contamination. With time, thedecay of the short lived radionuclides and themigration of much of the remaining 137Cs into thesoil have meant that the contributions to the totalradiation exposure from beta and gammaradiations have tended to become morecomparable. The balance does depend, however, onthe degree of bioaccumulation of 137Cs in organismsand the behaviour of the organism in relation to themain source of external exposure (i.e. the soil).Aside from the spatial heterogeneity in the doserate arising from the initial deposition, largevariations in the radiation exposure of differentorganisms occurred at different times due to theirhabitat niche (e.g. birds in the canopy versusrodents on the ground). Immigration of animalsinto the CEZ and reproduction of those plants andanimals that are present means that new animalsand plants are constantly being introduced into theradioactively contaminated conditions that existaround Chernobyl today. The current conditionsare presented in Section 6.8.

6.3. RADIATION EFFECTS ON PLANTS

Doses received by plants from the Chernobylfallout were influenced by the physical properties ofthe various radionuclides (i.e. their half-lives,radiation emissions, etc.), the physiological stage ofthe plant species at the time of the accident and thedifferent species dependent propensities to take upradionuclides into critical plant tissues. The

FIG. 6.4. A small conifer, the upper portion damaged bythe initial deposition of radiation on to the crown of theplant, and the lower part of the plant damaged by the irra-diation of surface deposited material subsequently washedfrom the plant’s crown, leaving the middle section of theplant unaffected (photograph courtesy of T. Hinton, 1991).

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occurrence of the accident in late April heightenedthe damaging effects of the fallout because itcoincided with the period of accelerated growth andreproduction in plants. The deposition of betaemitting contamination on critical plant tissuesresulted in their receiving a significantly larger dosethan animals living in the same environment [6.13,6.15]. Large apparent inconsistencies in dose–response observations occurred when the betaradiation component was not appropriatelyaccounted for [6.16].

Within the CEZ, deposition of total betaactivity and associated doses to plants weresufficient (0.7–3.9 GBq/m2) to cause short termsterility and reduction in the productivity of somespecies [6.15]. By August 1986, crops that had beensown prior to the accident began to emerge. Growthand development problems were observed in plantsgrowing in fields with contamination densities of0.1–2.6 GBq/m2 and with estimated dose ratesinitially received by plants reaching 300 mGy/d.Spot necroses on leaves, withered tips of leaves andinhibition of photosynthesis, transpiration andmetabolite synthesis were detected, as well as anincreased incidence of chromosome aberrations inmeristem cells [6.17]. The frequency of variousanomalies in winter wheat exceeded 40% in 1986–1987, with some abnormalities apparent for severalyears afterwards [6.18].

Coniferous trees were already known to beamong the more radiosensitive plants, and pineforests 1.5–2 km west of the Chernobyl nuclearpower plant received a sufficient dose (>80 Gy) tocause mortality [6.19] at dose rates that exceeded20 Gy/d [6.12]. The first signs of radiation injury inpine trees in close proximity to the reactor were

yellowing and needle death, which appeared withintwo to three weeks. During the summer of 1986 thearea of radiation damage expanded in the north-west direction up to 5 km; serious damage wasobserved at a distance of 7 km. The colour of thedead pine stands resulted in the forest beingreferred to as the Red Forest.

Tikhomirov and Shcheglov [6.19] andArkhipov et al. [6.20] found that mortality rate,reproduction anomalies, stand viability and re-establishment of pine tree canopies were dependenton absorbed dose. Acute irradiation of Pinussilvestris at doses of 0.5 Gy caused detectablecytogenetic damage; at more than 1 Gy, growthrates were reduced and morphological damageoccurred; and at more than 2 Gy, the reproductiveabilities of trees were altered. Doses of less than 0.1Gy did not cause any visible damage to the trees.Table 6.2 shows the variation in activity concen-tration and dose among pine trees within the CEZ.The radiosensitivity of spruce trees was observed tobe greater than that of pines. At absorbed doses aslow as 0.7–1 Gy, spruce trees had malformedneedles, buds and shoot growth [6.22].

Of the absorbed dose to critical parts of trees,90% was due to beta radiation from the depositedradionuclides and 10% to gamma radiation. Asearly as 1987, recovery processes were evident inthe surviving tree canopies and young forests werere-established in the same place as the perishedtrees by replanting in reclamation efforts [6.20]. Inthe decimated pine stands, a sudden invasion ofpests occurred that later spread to adjoining areas.The deceased pine stands have now been replacedby grassland, with a slow invasion of self-seedingdeciduous trees. Four distinct zones of radiation

TABLE 6.2. RADIOACTIVE CONTAMINATION (kBq/kg) OF CONIFEROUS TREES AS AFUNCTION OF DISTANCE FROM THE CHERNOBYL REACTOR (AZIMUTH 205–260°), WITHCORRESPONDING ESTIMATES OF THE AIR DOSE RATE (mGy/h) IN OCTOBER 1987 AND THEACCUMULATED EXTERNAL DOSE (Gy) [6.21]

Distance from the Chernobyl nuclear power plant (km)

Air dose rate

(mGy/h)a

External dose (Gy)a

Activity concentration in needles (kBq/kg)

Caesium-144 Ruthenium-106 Zirconium-95 Niobium-95 Caesium-134 Caesium-137

2.0 2.2 126 13 400 4100 800 1500 1500 4100

4.0 0.10 5 150 60 8 15 17 72

16.0 3.5 × 10–4 0.014 1.5 0.6 0.1 0.17 0.18 0.55

a Dose rate and dose of gamma radiation at 1 m height from the soil surface.

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induced damage to conifers were discernable(Table 6.3).

6.4. RADIATION EFFECTS ON SOIL INVERTEBRATES

Although between 60% and 90% of the initialfallout was captured by the forest canopy and otherplants [6.19], within weeks to a few months theprocesses of wash-off by rain and leaf fall moved themajority of the contamination to the litter and soillayers (see Section 3.4 for more details), where soiland litter invertebrates were exposed to highradiation levels for protracted time periods. Thepotential for impact on soil invertebrates was partic-ularly large, since the timing of the accidentcoincided with their most radiosensitive life stages:reproduction and moulting following their winterdormancy.

Within two months of the accident, thenumber of invertebrates in the litter layer of forests3–7 km from the nuclear reactor was reduced by afactor of 30 [6.14], and reproduction was stronglyaffected (larvae and nymphs were absent). Doses ofapproximately 30 Gy (estimated from thermolumi-nescent dosimeters placed in the soil) hadcatastrophic effects on the invertebrate community,causing mortality of eggs and early life stages, aswell as reproductive failure in adults. Within a year,reproduction of invertebrates in the forest litterresumed, due, in part, to the migration of inverte-brates from less contaminated sites. After 2.5 years,the ratio of young to adult invertebrates in the litterlayer, as well as the total mass of invertebrates perunit area, was no different from control sites;

however, species diversity remained markedlylower [6.14].

The diversity of invertebrate species withinthe soil facilitates an analysis of community leveleffects (i.e. changes in species composition andabundance); for example, only five species of inver-tebrates were found in ten soil cores taken frompine stands in July 1986 at a distance of 3 km fromthe Chernobyl nuclear power plant, compared with23 species at a control site 70 km away. The meandensity of litter fauna was reduced from 104individuals per 225 cm2 core at the control locationto 2.2 at the 3 km site. Six species were found in allten cores taken from the control site, whereas nospecies was found in all ten cores from the 3 kmlocation [6.23]. The number of invertebrate speciesfound at the heavily contaminated sites was onlyhalf that of controls in 1993, and complete speciesdiversity did not recover until 1995, almost ten yearsafter the accident [6.14].

Compared with invertebrates within the forestlitter layer, those residing in arable soil were notaffected so much. A fourfold reduction inearthworm numbers was found in arable soils, butno catastrophic mortality of any group of soil inver-tebrates was observed. There was no reduction insoil invertebrates below a 5 cm depth in the soil.Radionuclides had not yet migrated into deeper soillayers, and the overlying soil shielded the inverte-brates from beta radiation, the main contributor(94%) to the total dose. The dose to invertebrates inforest litter was threefold to tenfold higher than thatto those residing in surface soil [6.14].

Although researchers are unclear if sterility ofinvertebrates occurred in the heavily contaminated

TABLE 6.3. ZONES AND CORRESPONDING DAMAGE TO CONIFEROUS FORESTS IN THE AREAAROUND THE CHERNOBYL NUCLEAR POWER PLANT [6.22]

Zone and classificationExternal gamma dosea

(Gy)Air dose ratea

(mGy/h)Internal dose to

needles (Gy)

Conifer death (4 km2): complete death of pines, partial damage to deciduous trees

>80–100 >4 >100

Sublethal (38 km2): death of most growth points, death of some coniferous trees, morphological changes to deciduous trees

10–20 2–4 50–100

Medium damage (120 km2): suppressed reproductive ability, dried needles, morphological changes

4–5 0.4–2 20–50

Minor damage: disturbances in growth, reproduction and morphology of coniferous trees

0.5–1.2 <0.2 <10

a Dose rate and dose of gamma radiation at 1 m height from the soil surface.

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sites at Chernobyl [6.14], the 30 Gy cumulative dosereported for Chernobyl field studies is within therange of experimental doses used to control pestinsects by external irradiation. A recent reviewindicated that most insect, mite and tick familiesrequire a sterilization dose of less than 200 Gy[6.24], although the sterilization dose for someinsects and related arthropods is much lower andranges widely among and within orders. As wasfound for plants [6.8], radiosensitivity of insects isrelated to the average interphase nuclear volume[6.24].

6.5. RADIATION EFFECTS ON FARM ANIMALS

Ruminants, both domesticated (cattle, goats,sheep) and wild (elk, deer), generally receive highdoses in radioactively contaminated environmentsbecause they consume large amounts of vegetation,and many radionuclides accumulate in their bodies;for example, each day a single cow consumes about30% of the grass from an area of 150 m2. Ingestionof radionuclides leads to exposure of the gut, thethyroid and other body organs. Injuries to cattle area major fallout consequence for rural populations,because of livestock loss but also because of theassociated social and psychological implications[6.25, 6.26].

In the period shortly after the accident,domestic livestock within the CEZ were exposed tohigh levels of radioactive iodine (131I and 133I, withhalf-lives of 8 d and 21 h, respectively); this resultedin significant internal and external doses from betaand gamma radiation (Table 6.4). A thyroid dose of76 Gy from the two isotopes of iodine is sufficient tocause serious damage to the gland [6.27]. The soilsof Ukraine and Belarus are naturally low in stable

iodine, cobalt and manganese. In conditions ofendemic deficiency of stable iodine, the transfer ofradioactive iodine from blood to the thyroid glandmay be two to three times higher than normal[6.15]. These conditions accentuated the conse-quences of the accident.

Depressed thyroid function in cattle wasrelated to the dose received (69% reduction infunction with a thyroid dose of 50 Gy, and 82%reduction in animals that received a dose of280 Gy). The concentration of thyroid hormones inthe blood of animals was lower than the physio-logical norm during the whole lactation period.Radiation damage to the thyroid gland wasconfirmed by histological studies (i.e. hyperplasia ofconnective tissue and sometimes adipose tissue,vascular hyperaemia and necrosis of epithelium).Animals with practically no thyroid tissue wereobserved in Ukraine. Disruptions of the hormonalstatus in calves born to cows with irradiated thyroidglands were especially pronounced [6.28]. Similareffects were observed in cattle evacuated from theBelarusian portion of the CEZ [6.26].

Although most livestock were evacuated fromthe area after the accident, several hundred cattlewere maintained in the more contaminated areasfor a two to four month period. By the autumn of1986, some of these animals had died; othersshowed impaired immune responses, lowered bodytemperatures and cardiovascular disorders.Hypothyroidism lasted until 1989, and may havebeen responsible for reproductive failures inanimals that had received a thyroid dose of more than180 Gy [6.26]. The offspring of highly exposed cowshad reduced weight, reduced daily weight gains andsigns of dwarfism. Reproduction returned to normal inthe spring of 1989. Haematological parameters werenormal for animals kept in areas with 137Cs contami-nation of 0.2–1.4 MBq/m2 (5–40 Ci/km2) [6.28].

TABLE 6.4. DOSES TO CATTLE THAT STAYED IN THE 30 km ZONE OF CHERNOBYL FROM 26APRIL TO 3 MAY 1986 [6.21]

Distance from the Chernobyl nuclear power plant (km)

Surface activity (108 Bq/m2)

Absorbed dose (Gy)

Thyroid Gastrointestinal tract Whole body internal

3 8.4 300 2.5 1.4

10 6.1 230 1.8 1.0

14 3.5 260 1.0 0.6

12 2.4 180 0.7 0.4

35 1.2 90 0.4 0.2

131

Chronic radiation damage was observed inover 2000 sheep and 300 horses (3–8 years old)removed from the highly contaminated Khoinikiarea of Belarus 1.5 years after the accident [6.26].Doses were not estimated. In sheep, a depression ofgeneral condition, emaciation, heavy breathing,decrease of temperature and other abnormalitieswere found. Leukopaenia, erythropaenia, thrombo-cytopaenia and eosinophilia, increase in blood sugarconcentrations 1.5–2 times higher than normal, anda significant decrease of thyroid hormone concen-trations compared with normal levels wereobserved. The offspring weight and fleece clip yieldof irradiated sheep were half as much as, or lessthan, those of healthy individuals. In horses, thedamage resulted in depression of general condition,oedema, leukopaenia, thrombocytopaenia,eosinophilia and myelocytosis. Seventy per cent ofthe animals had thyroid hormone concentrations inblood serum that were lower than the detectionlevels of the assay methods [6.26].

Numerous news reports of radiation inducedteratogenesis (birth defects) in cattle and pigsoccurred in regions where total doses did notexceed 0.05 Gy/a. Scientific evidence indicates thatincreased birth defects are not distinguishable frombackground frequencies at such low doses [6.25].Additionally, data for 1989 show that livestock birthdefects in the contaminated area of the Zhytomyrregion were no higher than in the uncontaminatedareas of the same region. Photographs of a sixfooted calf were widely disseminated and theabnormality was attributed to the accident. The calf,however, was born in June 1986, and thus theprocess of differentiation and organ formationwithin the womb finished prior to the accident; thismuch publicized observation of teratogenesis wastherefore caused by factors other than radiationfrom the Chernobyl accident.

6.6. RADIATION EFFECTS ON OTHER TERRESTRIAL ANIMALS

Four months after the accident, surveys andautopsies of wildlife and abandoned domesticanimals that remained within the 10 km radius ofthe Chernobyl nuclear power plant were conducted[6.14]. Fifty species of birds were identified,including some rare species; all appeared normal inappearance and behaviour. No dead birds werefound. Swallows and house sparrows were found tobe producing progeny that also appeared normal.

Forty-five species of mammals from six orders wereobserved, and no unusual appearances orbehaviours were noted.

Some wildlife and domestic animals were shotand autopsied in August and September 1986. Dogsand chickens showed signs of chronic radiationsyndrome (reduced body mass, reduced fat reserves,increase in mass of lymph nodes, liver and spleen,haematomas present in liver and spleen andthickening of the lining of the lower intestine). Noeggs were found in the nests of chickens or in theirovaries.

During the autumn of 1986, the number ofsmall rodents on highly contaminated research plotsdecreased by a factor of two to ten. Estimates ofabsorbed dose during the first five months after theaccident ranged from 12 to 110 Gy for gamma and580 to 4500 Gy for beta radiation. The numbers ofanimals were recovering by the spring of 1987,mainly due to immigration from less affected areas.In 1986 and 1987 the percentage of pre-implan-tation deaths in rodents from the highly contami-nated areas increased twofold to threefoldcompared with controls. Resorption of embryosalso increased markedly in rodents from theaffected areas; however, the number of progeny perfemale did not differ from controls [6.29].

6.7. RADIATION EFFECTS ON AQUATIC ORGANISMS

Cooling water for the Chernobyl nuclearpower plant was obtained from the 21.7 km2 human-made reservoir located south-east of the plant site.The cooling reservoir became heavily contaminatedfollowing the accident (see Section 3.5 for details)with over 6.5 ± 2.7 × 1015 Bq of a mixture of radio-nuclides in the water and sediments [6.30]. Aquaticorganisms were exposed to external exposure fromradionuclides in water and contaminated bottomsediments and irradiation from contaminatedaquatic plants. Internal exposure occurred asorganisms took up radioactively contaminated foodand water or inadvertently consumed contaminatedsediments. The resultant doses to aquatic biota overthe first 60 days following the accident are depictedin Fig. 6.5.

The maximum dose rates for aquaticorganisms (excluding fish) were reported in the firsttwo weeks after the accident, when short livedisotopes (primarily 131I) contributed 60–80% of thedose. During the second week, the contribution of

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short lived radionuclides to doses to aquaticorganisms decreased by a factor of two. Maximumdose rates to fish were delayed (Fig. 6.5), due to thetime required for their food webs to becomecontaminated with longer lived radionuclides(mostly 134,137Cs, 144Ce/144Pr, 106Ru/106Rh and 90Sr/90Y). Differences in dose rates among fish speciesoccurred due to their trophic positions. Non-predatory fish (carp, goldfish, bleak) reachedestimated peak dose rates of 3 mGy/d from internalcontamination in 1986, followed by significantreductions in 1987. Dose rates in predatory fish(perch), however, increased in 1987 and did notstart to decline until 1988 [6.21]. Accumulated doseswere highest for the first generation of fish born in1986 and 1987. Bottom dwelling fish (goldfish, silverbream, bream, carp) that received significantexposure from the bottom sediments receivedaccumulated total doses of approximately 10 Gy.

In 1990 the reproductive capacity of youngsilver carp was analysed [6.31]. The fish were in liveboxes within the cooling pond at the time of theaccident. By 1988 the fish reached sexual maturity.Over the entire post-accident period they received adose of 7–8 Gy. Biochemical analyses of muscles,liver and gonads indicated no difference from thecontrols. The amount of fertilized spawn was 94%;11% of the developing spawn were abnormal.Female fertility was 40% higher than the controls,but 8% of the irradiated sires were sterile. The levelof fluctuating asymmetry in offspring did not differ

from the controls, although the level of cytogeneticdamage (22.7%) significantly exceeded the controls(5–7%). In contrast, Pechkurenkov [6.32] reportedthat the number of cells with chromosomeaberrations in 1986–1987 in carp, flat bream andsilver carp was within the norm. It is worth notingthat the cooling pond was subject not only toradioactive contamination but also to chemicalpollution.

Recent reviews of the chronic effects ofionizing radiation on reproduction in fish, with theChernobyl data included (Table 6.5), have beensummarized.

6.8. GENETIC EFFECTS IN ANIMALS AND PLANTS

Quality data concerning the incidence ofChernobyl related induced mutations in plants andanimals are relatively sparse. An increasedmutation level was apparent in 1987 in the form ofvarious morphological abnormalities observed inCanada flea-bane, common yarrow and mousemillet plants. Examples of abnormalities includeunusual branching of stems, doubling of the numberof racemes, abnormal colour and size of leaves andflowers, and development of ‘witches’ brooms’ inpine trees. Similar effects in the 5 km radius circlenear the reactor also appeared in deciduous trees(leaf gigantism, changes in leaf shape; see Fig. 6.6).

0.1

1

10

100

0 10 20 30 40 50 60

Days post-accident

Phytoplankton

Zooplankton

Fish

Macroalgae

Benthic organisms

cGy/

d

FIG. 6.5. The dynamics of absorbed dose rate (cGy/d) oforganisms within the Chernobyl cooling pond during thefirst 60 days following the accident. Data are model resultsbased on concentrations of radionuclides in the watercolumn and lake sediments [6.21].

FIG. 6.6. Typical morphological abnormality seen onconifer trees. Such enhancement of vegetative growth andgigantism of some plant parts were not uncommon (photo-graph courtesy of T. Hinton, 1991).

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Morphological changes were observed at an initialgamma close rate of 0.2–0.3 mGy/h. At 0.7–1.3 mGy/h enhancement of vegetative reproduction(heather) and gigantism of some plant species wereobserved [6.19, 6.20, 6.34, 6.35].

Cytogenetic analysis of cells from the rootmeristem of winter rye and wheat germ of the 1986harvest demonstrated a dose dependence in thenumber of aberrant cells. A significant excess overthe control level of aberrations was observed at anabsorbed dose of 3.1 Gy, inhibition of mitoticactivity occurred at 1.3 Gy and germination wasreduced at 12 Gy [6.36]. Analysis of three successivegenerations of winter rye and wheat on the mostcontaminated plots revealed that the rate ofaberrant cells in the intercalary meristem in thesecond and third generations was higher than in thefirst.

From 1986 to 1992 mutation dynamics werestudied in populations of Arabidopsis thalianaHeynh. (L.) within the CEZ [6.37]. On all studyplots in the first two to three years after theaccident, Arabidopsis populations exhibited an

increased mutation burden. In later years, the levelof lethal mutations declined; nevertheless themutation rate in 1992 was still four to eight timeshigher than the spontaneous level. The dosedependence of the mutation rate was best approxi-mated by a power function with a power index ofless than one.

Zainullin et al. [6.38] observed elevated levelsof sex linked recessive lethal mutations in naturalDrosophila melanogaster populations living underconditions of increased background radiation due tothe Chernobyl accident. Mutation levels wereincreased in 1986–1987 in flies inhabiting contami-nated areas with initial exposure rates of 2 mGy/hand more. In the subsequent two years mutationfrequencies gradually returned to normal.

Studies of adverse genetic effects in wild micehave been reported by Shevchenko et al. [6.39] andPomerantseva et al. [6.40]. These involved micecaught during 1986–1991 within a 30 km radius ofthe Chernobyl reactor with different levels ofgamma radiation and in 1992–1993 at a site in theBryansk region of the Russian Federation. The

TABLE 6.5. CHRONIC EFFECTS OF IONIZING RADIATION ON REPRODUCTION IN FISH,DERIVED FROM THE FASSET DATABASE [6.33]

Dose rate (mGy/h)

Dose rate (mGy/d)

Effects

0–99 0–2.4 Background dose group; normal cell types, normal damage and normal mortality observed

100–199 2.4–4.8 No data available

200–499 4.8–12 Reduced spermatogonia and sperm in tissues

500–999 12–24 Delayed spawning, reduction in testes mass

1000–1999 24–48 Mean lifetime fecundity decreased, early onset of infertility

2000–4999 48–120 Reduced number of viable offspring

Increased number of embryos with abnormalities

Increased number of smolts in which sex was undifferentiated

Increased brood size reported

Increased mortality of embryos

5000–9999 120–240 Reduction in number of fish surviving to one month of age

Increased vertebral abnormalities

>10 000 >240 Interbrood time tending to decrease with increasing dose rate

Significant reduction in neonatal survival

Sterility in adult fish

Destruction of germ cells within 50 days in medaka fish

High mortality of fry; germ cells not evident

Significant decrease in number of male salmon returning to spawn

After four years, female salmon had significantly reduced fecundity

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estimated total doses of gamma and beta radiationvaried widely and reached 3–4 Gy per month in1986–1987. One endpoint was dominant lethality,measured by embryo mortality of the offspring ofwild male mice mated to unexposed femalelaboratory mice. The dominant lethality rate waselevated for a period of a few weeks followingcapture for mice sampled at the most contaminatedsite. At dose rates of about 2 mGy/h, two of 122captured males produced no offspring and wereassumed to be sterile. The remainder showed aperiod of temporary infertility and reduced testesmass, which, however, recovered with time aftercapture.

The frequencies of reciprocal translocations inmouse spermatocytes were consistent with previousstudies. For all collected mice, a dose ratedependent incidence of increased reciprocal trans-locations (scored in spermatocytes at meioticmetaphase I) was observed. The frequency of miceharbouring recessive lethal mutations decreasedwith time post-accident [6.40]. Radiation relatedgene mutation is unlikely to have any adverse effecton populations at the dose rates that prevail now.

Advances in the sophistication and associatedtechnologies of detecting molecular andchromosomal damage have occurred since the earlygenetic studies prior to the Chernobyl accident.Such advances have allowed researchers on thegenetic consequences of the Chernobyl accident toexamine endpoints not previously considered. Mostprominent, and controversial, is the mutationfrequencies in repeat DNA sequences termed‘minisatellite loci’ or expanded simple tandemrepeats (ESTRs). These are repeat DNA sequencesthat are distributed throughout the germline andthat have a high background (spontaneous)mutation rate. At present, ESTRs are considered tohave no function, although this is a matter of muchinterest and discussion [6.41, 6.42]. Minisatellitemutations have only rarely been associated withrecognizable genetic disease [6.43].

Although laboratory examination ofmutations in mouse ESTR loci shows clear evidenceof a mutational dose response [6.44, 6.45], noconvincing data on elevated levels of minisatellitemutations in plants or animals residing in theChernobyl affected areas appear to have beenpublished so far in the peer reviewed scientificliterature. In general, quantitative interpretation ofthe ESTR data is difficult because of conflictingfindings, their weak association with genetic disease,dosimetric uncertainties and methodological

problems [6.42]. This is an area of science thatrequires additional research.

6.9. SECONDARY IMPACTS AND CURRENT CONDITIONS

Prior to the accident, much of the area aroundChernobyl was covered in 30–40 year old pinestands that, from a successional standpoint,represented mature, stable ecosystems. The highdose rates from ionizing radiation during the firstfew weeks following the accident altered thebalanced community by killing sensitive individuals,altering reproduction rates, destroying someresources (e.g. pine stands), making other resourcesmore available (e.g. soil water) and opening nichesfor immigration of new individuals. All thesecomponents, and many more, were interwoven in acomplex web of action and reaction that alteredpopulations and communities of organisms.

Exposure to ionizing radiation is an environ-mental stress, in many ways similar to otherenvironmental stresses such as pollution by metalsor the destruction caused by forest fires. If suchstressors are sufficient, the community organizationis changed and generally reverts to an earliersuccessional state. However, when the stress issubsequently reduced and sufficient time passes,recovery occurs and the ecosystem again regainsstability, advancing towards a more mature state.The change in species diversity observed within thesoil invertebrate communities presented above isperhaps the most obvious published example ofcommunity level change and subsequent recoveryfollowing the Chernobyl accident. The death of pinestands close to the Chernobyl reactor and thesubsequent establishment of grasslands anddeciduous trees are striking visual examples.

Age and sex distributions, diversity and theabundance and gross physiological conditions ofsmall mammal populations in the CEZ appear to besimilar to background locations in other parts ofUkraine [6.46–6.48]. Reports on the current geneticconditions of rodents within the zone are contra-dictory; for example, Shevchenko et al. [6.39] foundsignificant disorders in spermatogenesis, whileBaker et al. [6.46] found no reproductive inhibitionor germ line mutations.

Layered on top of the impacts of the radiationexposure was the abrupt and drastic change thatoccurred when humans were removed from theCEZ. The town adjacent to the Chernobyl reactor,

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Pripyat, was abandoned when over 50 000 peoplewere evacuated. Agricultural activity, forestry,hunting and fishing within the CEZ were stoppedbecause of the radioactive contamination of theproducts. Only activities designed to mitigate theconsequences of the accident were carried out, aswell as those supporting the living conditions of thecleanup workers, including substantial roadconstruction.

For some years after the accident, the agricul-tural fields still yielded domesticated produce, andmany animal species, especially rodents and wildboars, consumed the abandoned cereal crops,potatoes and grasses as an additional source offorage. This advantage, along with the specialreserve regulations established in the CEZ (e.g. aban on hunting), tended to compensate for theadverse biological effects of the radiation andpromoted an increase in the populations of wildanimals. Significant population increases of gamemammals (wild boar, roe deer, red deer, elk, wolves,foxes, hares, beavers, etc. (Fig. 6.7)) and bird species(black grouse, ducks, etc.) were observed soon afterthe Chernobyl accident [6.49, 6.50].

More than 400 species of vertebrate animals,including 67 ichthyoids, 11 amphibians, 7 reptiles,251 birds and 73 mammals, inhabit the territory ofthe evacuated town of Pripyat and its vicinity; morethan 50 of them belong to a list of those protectedaccording to national Ukrainian and European RedBooks. The CEZ has become a breeding area forwhite tailed eagles, spotted eagles, eagle owls,cranes and black storks (Fig. 6.8) [6.51].

In the Pripyat River floodplain a developedsystem of artificial drainage channels now supportsabout a hundred families of beavers. Recognizingthe value of the abandoned land around Chernobyl,28 endangered Przhevalsky wild horses wereintroduced in 1998. After six years their number haddoubled [6.51]. In both the Ukrainian andBelarusian parts of the CEZ, State radioecologicalreserves have been created with a regime of natureprotection.

As has been shown many times before, whenhumans are removed, nature flourishes. Thisphenomenon exists in US National Parks such asYellowstone and the Grand Tetons, and at large USDepartment of Energy sites where the generalpublic has been excluded for over 50 years. Humanpresence in any environment is a disturbance to thenatural biota. Normal activities of farming, hunting,logging and road building, to name but a few,fragment, pollute and generally stress the processes

and mechanisms of natural environments. Theremoval of humans alleviates one of the morepersistent and ever growing stresses experienced bynatural ecosystems.

(a)

(b)

FIG. 6.7. Wild boar (a) and wolves (b) inhabiting the CEZare not afraid of people because of long term hunt prohibi-tion (photographs courtesy of S. Gaschak, 2004).

FIG. 6.8. A white tailed eagle chick observed recently in theCEZ. Before 1986 these rare predatory birds had rarelybeen found in this area (photograph courtesy of S.Gaschak, 2004).

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On the other hand, the absence of forestmanagement, and the associated increase in forestfires, have substantial impacts on natural commu-nities. After the human population was evacuated,both wood cutting and the construction ofmineralized fire prevention strips ceased. Thenumber of dead trees increased and createdconditions that enhanced the development of forestdiseases and pests (borers, bark beetles, etc.). Theamount of dead wood and brushwood has graduallyincreased in the unmanaged forests. Thedegradation of the forests resulted in enormousforest fires during the dry summer period of 1992,when the area of burnt forest amounted to 170 km2

(i.e. about one sixth of the woodlands) [6.52].Without a permanent residence of humans for

20 years, the ecosystems around the Chernobyl siteare now flourishing. The CEZ has become a wildlifesanctuary [6.47], and it looks like the nature park ithas become.


6.10.1. Conclusions

(a) Radiation from radionuclides released by theChernobyl accident caused numerous acuteadverse effects in the biota located in the areasof highest exposure (i.e. up to a distance of afew tens of kilometres from the release point).Beyond the CEZ, no acute radiation inducedeffects on biota have been reported.

(b) The environmental response to the Chernobylaccident was a complex interaction amongradiation dose, dose rate and its temporal andspatial variations, and the radiosensitivities ofthe different taxons. Both individual andpopulation effects caused by radiationinduced cell death have been observed inplants and animals as follows:

(i) Increased mortality of coniferous plants,soil invertebrates and mammals;

(ii) Reproductive losses in plants andanimals;

(iii) Chronic radiation syndrome in animals(mammals, birds, etc.).

No adverse radiation induced effects havebeen reported in plants and animals exposedto a cumulative dose of less than 0.3 Gy duringthe first month after the radionuclide fallout.

(c) Following the natural reduction of exposurelevels due to radionuclide decay andmigration, populations have been recoveringfrom the acute radiation effects. By the nextgrowing season after the accident, thepopulation viability of plants and animalssubstantially recovered as a result of thecombined effects of reproduction andimmigration. A few years were needed forrecovery from the major radiation inducedadverse effects in plants and animals.

(d) The acute radiobiological effects observed inthe Chernobyl accident area are consistentwith radiobiological data obtained in experi-mental studies or observed in naturalconditions in other areas affected by ionizingradiation. Thus rapidly developing cellsystems, such as meristems of plants and insectlarvae, were predominantly affected byradiation. At the organism level, young plantsand animals were found to be the mostsensitive to the acute effects of radiation.

(e) Genetic effects of radiation, in both somaticand germ cells, were observed in plants andanimals in the CEZ during the first few yearsafter the accident. Both in the CEZ andbeyond, different cytogenetic anomaliesattributable to radiation continue to bereported from experimental studiesperformed on plants and animals. Whether theobserved cytogenetic anomalies have anydetrimental biological significance is notknown.

(f) The recovery of affected biota in the CEZ hasbeen confounded by the overriding responseto the removal of human activities (e.g.termination of agricultural and industrialactivities and the accompanying environ-mental pollution in the most affected area).As a result, the populations of many plantsand animals have expanded, and the presentenvironmental conditions have had a positiveimpact on the biota in the CEZ.

6.10.2. Recommendations for future research

(a) In order to develop a system of environmentalprotection against radiation, the long termimpact of radiation on plant and animalpopulations should be further investigated inthe CEZ; this is a globally unique area for

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radioecological and radiobiological researchin an otherwise natural setting.

(b) In particular, multigenerational studies ofradiation effects on the genetic structure ofplant and animal populations might bringfundamentally new scientific information.

(c) There is a need to develop standardizedmethods for biota–dose reconstruction, forexample in the form of a unified dosimetricprotocol.

6.10.3. Recommendations for countermeasures and remediation

(a) Protective actions for farm animals in the eventof a nuclear or radiological emergency shouldbe developed and internationally harmonizedbased on modern radiobiological data,including the experience gained in the CEZ.

(b) It is likely that any technology basedremediation actions aimed at improving theradiological conditions for plants and animalsin the CEZ would have adverse impacts onbiota.


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[6.16] GRODZINSKY, D.M., KOLOMIETS, O.D.,KUTLAKHMEDOV, Y.A., Anthropogenic radio-nuclide anomaly and plants, Lybid, Kiev (1991) (inRussian).

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[6.18] GRODZINSKY, D.N., GUDKOV, I.N., “Radibio-logical effects on plants in the contaminated terri-tory”, The Chornobyl Exclusion Zone, Nat.Academy of Science of Ukraine, Kiev (2001) 325–377.

[6.19] TIKHOMIROV, F.A., SHCHEGLOV, A.I., Maininvestigation results on the forest radioecology in

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the Kyshtym and Chernobyl accidents zones, Sci.Total Environ. 157 (1994) 45–47.

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[6.24] BAKRI, A., HEATHER, N., HENDRICHS, J.,FERRIS, I., Fifty years of radiation biology inentomology: Lessons learned from IDIDAS, Ann.Entomol. Soc. Am. 98 (2005) 1–12.

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[6.46] BAKER, R.J., et al., Small mammals from themost radioactive sites near the Chornobyl nuclearpower plant, J. Mammol. 77 (1996) 155–170.

[6.47] BAKER, R.J., CHESSER, R.K., The Chernobylnuclear disaster and subsequent creation of awildlife preserve, Environ. Toxicol. Chem. 19(2000) 1231–1232.

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[6.49] GAICHENKO, V.A., KRYZANOVSKY, V.I.,STOLBCHATY, V.N., Post-accident state of theChernobyl nuclear power plant alienated zonefaunal complexes, Radiat. Biol. Ecol., Special issue(1994) 27–32 (in Russian).

[6.50] SUSCHENYA, L.M., et al. (Eds), The AnimalKingdom in the Accident Zone of the ChernobylNPP, Navuka i Technica, Minsk (1995) (inRussian).

[6.51] GASCHAK, S.P., et al., Fauna of Vertebrates inthe Chernobyl Zone of Ukraine, InternationalChornobyl Center for Nuclear Safety, RadioactiveWaste and Radioecology, Slavutych (2002) (inUkrainian).

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7. ENVIRONMENTAL AND RADIOACTIVE WASTE MANAGEMENT ASPECTS OF THE DISMANTLING

OF THE CHERNOBYL SHELTER

The destruction of the unit 4 reactor at theChernobyl nuclear power plant created radioactivecontamination and radioactive waste3 in the unit,the Chernobyl nuclear power plant site and thesurrounding area (further referred to as the CEZ).The future development of the CEZ depends on thestrategy for the conversion of unit 4 into an ecologi-cally safe system (i.e. the development of the NSC,the dismantlement of the current shelter, removal ofFCM, and eventual decommissioning of the reactorsite).

In particular, the long term strategy for unit 4involves implementation of the NSC concept tocover the unstable shelter and the relatedradioactive waste management activities at theChernobyl nuclear power plant site and the CEZ.Currently units 1, 2 and 3 (1000 MW RBMKreactors) are shut down awaiting decommissioning;two additional reactors (units 5 and 6) that had beennear completion were abandoned in 1986 followingthe accident.

This section addresses the current status ofunit 4 and the existing and future environmentalimpact associated with it and the management ofthe radioactive waste from the accident at theChernobyl nuclear power plant site and in theCEZ.

7.1. CURRENT STATUS AND THE FUTURE OF UNIT 4 AND THE SHELTER

7.1.1. Unit 4 of the Chernobyl nuclear power plant after the accident

In the course of the 1986 accident, a small partof the nuclear fuel (3.5% according to pastestimates [7.1] or 1.5% according to recentestimates [7.2]) and a substantial fraction of volatileradionuclides (see Section 3.1) were released fromthe damaged unit 4. The remainder of the damaged

nuclear fuel, more than 95% of the fuel mass at themoment of the accident, i.e. about 180 t, was left inthe remains of the reactor [7.1]. The uncertainty inthis estimate is discussed in Section 7.1.5.

The first measures taken after the accident tocontrol the fire and the radionuclide releasesconsisted of dumping neutron absorbingcompounds and fire control material into the craterformed by the destruction of the reactor [7.1] (seeFig. 7.1). The total amount of material dumped onthe reactor was approximately 5000 t, includingabout 40 t of boron compounds, 2400 t of lead,1800 t of sand and clay and 600 t of dolomite, as wellas sodium phosphate and polymer liquids [7.1].

At the Chernobyl nuclear power plant site inmid-May 1986 there were high levels of air radiationdose rate and air activity concentration, caused byrelatively uniform contamination of the area withfinely dispersed nuclear fuel and aerosols of shortlived radionuclides, and also the presence ofdispersed nuclear fuel particles or fragments. Thesefragments consisted of discrete and non-uniformmaterial from the reactor core, reactor construc-tional material and graphite.

After the accident, the debris of the destroyedreactor building was collected, along with fragmentsof the reactor core, etc., and the soil surface layer.Thousands of cubic metres of radioactive wastegenerated by this work were disposed of in thepioneer wall and the cascade wall. Construction ofwalls around the damaged reactor reduced theradiation dose rates by a factor of 10–20 [7.3]. Thecompletion of the pioneer wall and the cascade walland a significant reduction in radiation levelsallowed the shelter to be constructed.

The shelter, which was intended to provide theenvironmental containment of the damagedreactor, was erected within an extremely shortperiod of time, between May and November 1986,under conditions of high radiation exposure of thepersonnel. The steps taken to save time and costduring the construction, and the high dose ratesinside the structure, resulted in a lack of reliable andcomprehensive data on the stability of the damagedolder structures, a need for remote control

3 The radioactive waste in the CEZ does notinclude the waste associated with the decommissioning ofChernobyl nuclear power plant units 1, 2 and 3.

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concreting and the impossibility of carrying outwelding in some specific situations.

7.1.2. Current status of the damaged unit 4 and the shelter

The shelter [7.4] was constructed using steelbeams and plates as structural elements. Itsfoundation rests at some points on the originalstructural elements of unit 4, whose structuralintegrity, following the accident, is not well known.At other points it rests on debris remaining from theaccident. Thus the ability of the shelter structure towithstand natural events such as earthquakes andtornados is known only with large uncertainties. Inaddition to uncertainties on the structural stabilityat the time of its construction, structural elements ofthe shelter have degraded as a result of moistureinduced corrosion during the nearly 20 years sincethe accident.

The shelter has approximately 1000 m2 ofopenings in its surface. These openings allowapproximately 2000 m3/a of precipitation to

percolate through the radioactively contaminateddebris and eventually to pool in rooms in the lowerlevels of unit 4 (see Fig. 7.2) [7.5]. Condensationwithin unit 4 of approximately 1650 m3/a of waterand the residues from periodic spraying of 180 m3/aof liquid dust suppressant contribute to thequantities of water percolating through the unit 4debris and collecting in its basement. The collectedwater is contaminated with 137Cs, 90Sr andtransuranic elements, resulting in average concen-trations of 1.6 × 1010 Bq/m3 of 137Cs, 2.0 × 109 Bq/m3

of 90Sr, 1.5 × 105 Bq/m3 of plutonium and 6 mg/L ofuranium. About 2100 m3/a of the collected waterevaporates, and about 1300 m3/a leaks through thefoundation into the soil beneath unit 4 [7.6]. Theexisting Chernobyl nuclear power plant radioactivewaste management system is not capable of treatingliquid radioactive waste that contains transuranicelements.

The inside conditions of unit 4 (Fig. 7.3) arehazardous and present significant risks to workersand the environment. General area radiation doserates range from 2 µSv/h to 0.1 Sv/h inside the

FIG. 7.1. The destroyed reactor after the accident in 1986.

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shelter [7.5]. Individual occupational radiationexposures during current operations at unit 4 arecontrolled so that they do not exceed the dose limitof 20 mSv/a [7.7].

Unit 4 is ventilated during current activitiesthrough a monitored exhaust above the reactorroom. The unfiltered exhaust air is normally belowthe permitted limits for atmospheric discharge, anda filtration system exists for use should the exhaustair levels approach the permitted discharge limits.The ventilation system is zoned so that air flowsfrom outside the shelter through spaces withincreasing levels of contamination.

Unit 4 and the associated cascade walls havean accumulation of FCM, including large corefragments that could conceivably lead to criticalityunder flooded conditions. Such a criticality accidentis considered unlikely; however, if criticality shouldoccur, it might lead to the exposure of some workersinside unit 4 to an external dose of only a fewmillisieverts, because workers tend to avoid thespaces with criticality risk. It has been estimatedthat, in such a case, there would be no significant

consequences inside and outside the CEZ [7.5, 7.8,7.9].

A number of activities have been performedin recent years to stabilize and improve theconditions of the shelter. These include: repair ofthe unit 3/4 ventilation stack foundation andbracing; reinforcement of the B1 and B2 beams(Fig. 7.4); improvement of the physical protectionand access control system; design of an integratedautomated control system (control of buildingstructure conditions, seismic control, nuclear safetycontrol and radiation control); modernization of thedust suppression system; and additional structuralstabilization. Computerized control systems wereinstalled in the shelter [7.9] to monitor gammaradiation, neutron flux, temperature, heat flux,concentrations of hydrogen, carbon oxide and air

FIG. 7.2. Opening in the shelter allowing infiltration ofatmospheric water.

FIG. 7.3. Reactor room of unit 4 after the accident.

A

CE

F

FIG. 7.4. Major structural components of the Chernobylshelter: (A) pipe roofing; (B) southern panels; (C)southern hockey sticks; (D) B1/B2 beams; (E) mammothbeam; (F) octopus beam.

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moisture, mechanical stability of structures, etc. Thishas been achieved with significant support fromUkraine and donor countries4.

The magnitude and importance of possiblefuture radioactive releases from the shelter (in theevent of its collapse) significantly depend on theradiological and physicochemical properties of theradioactive material, including dust that may arisefrom the area inside the shelter. Now, nearly 20years after the accident, dust has penetratedconcrete walls, floors and ceilings, and is in the air inthe form of aerosols. Thus in a number of shelterpremises the fuel-containing dust has become themain source of radiation hazard. Research [7.5,7.10] shows that the typical size of these particles(activity median aerodynamic diameter) is from 1 to10 µm. Hence most of the material is expected to berespirable, which increases its potential inhalationhazard. The potential for inhalation hazard isincreased by the winds that may be generated if theshelter roof were to collapse.

Should the shelter collapse, it would alsocomplicate continuing accident recovery efforts,and the resulting radioactive dust cloud would haveadverse environmental impacts. Further analysis ofthe environmental release is sensitive to the sourceterm assumed in the dust cloud that would begenerated as a result of the collapse. Differentstudies give different possible radioactive dustreleases to the environment, ranging from about500 to 2000 kg of particulate dust, which couldcontain from 8 to 50 kg of finely dispersed nuclearfuel. Regardless of the source term assumption,almost all material that might be raised into theatmosphere by a shelter collapse is expected to bedeposited within the CEZ [7.11, 7.12].

Another concern related to the FCM is itspossible transport out of the shelter intogroundwater through the accumulated water. Thepotential for FCM to dissolve in the accumulatedwater was confirmed when bright yellow stains andfaded pieces of FCM were found on the surface ofsolidified fuel–lava streams in unit 4 [7.3];subsequent analysis proved the presence of soluble

uranium compounds. Until recently, this FCM wasconsidered to be a glassy mass that was veryinsoluble. The possibility of leaching of radionu-clides from the FCM and of mobile radionuclidessuch as 90Sr migrating and reaching the PripyatRiver was expected to be very low [7.9]. Theexpected significance of this phenomenon is notknown, and therefore monitoring of the evolvinggroundwater situation at and around the shelter isimportant.

Additional studies of the water table showedthat it has risen by up to 1.5 m in a few years toabout 4 m from the ground level, and may still berising. This effect is considered to have occurredmainly as a result of the construction of a 3.5 kmlong and 35 m deep wall around unit 4 that aimed toprotect the Kiev reservoir from potential contami-nation through groundwater [7.9].

The main potential hazard associated with theshelter is a possible collapse of its top structures andthe release of radioactive dust into theenvironment; therefore a dust suppression systemwas installed beneath the shelter roof that periodi-cally sprays dust suppression solutions and fixatives.The system has operated since January 1990, andmore than 1000 t of dust suppressant has beensprayed during this period.

7.1.3. Long term strategy for the shelter and the new safe confinement

In order to avoid a collapse of the shelter,some measures have been implemented andadditional measures are planned to strengthenunstable parts of the shelter and to extend theirstability from 15 to 40 years [7.13]. In addition, theNSC is planned to be built as a cover over theexisting shelter as a longer term solution (seeFig. 7.5). The Ukrainian Government supports theconcept of a multifunctional facility with at least 100years service life. This facility aims to reduce theprobability of shelter collapse, reduce the conse-quences of a shelter collapse, improve nuclearsafety, improve worker and environmental safety,and convert unit 4 into an environmentally safe site.The construction of the NSC is expected to allow forthe dismantlement of the current shelter, removal ofFCM from unit 4 and the eventual decommissioningof the reactor.

The specific operational aspects related to theconstruction and operation of the NSC, includingmaintenance in the long term, have not yet beenidentified. It is important to note that the NSC

4 Contributors to the work of the ChernobylShelter Fund include Austria, Belgium, Canada,Denmark, the European Commission, Finland, France,Germany, Greece, Ireland, Italy, Kuwait, Luxembourg,the Netherlands, Norway, Poland, Spain, Sweden,Switzerland, Ukraine, the UK and the USA. Additionaldonors to the Fund include Iceland, Israel, Korea,Portugal, Slovakia and Slovenia.

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design is based on the current plans for removal ofthe FCM that depend on the availability of a finalgeological disposal facility about 50 years from now[7.13]. This extended dormancy period could resultin the dispersal of the special human resourcesneeded to remove and dispose of the FCM safely.Accordingly, there are good reasons for removingthe FCM and structural material as soon as possibleafter the construction of the NSC.

7.1.4. Environmental aspects

7.1.4.1. Current status of the shelter

At present, the environmental contaminationaround the Chernobyl nuclear power plant site isdue to the initial radioactive contamination of thearea from the accidental release of 1986, the routinereleases of radionuclides through the ventilationsystem of the shelter and the engineering and otheractivities carried out in the CEZ. The main dosecontributing radionuclides within the CEZ aroundthe Chernobyl nuclear power plant site are 137Cs,90Sr, 241Am and 239,240Pu (see also Section 3); thedistribution of these radionuclides is shown inFig. 7.6 [7.2].

7.1.4.2. Impact on air

Currently, radioactive aerosol releases intothe atmosphere from the shelter are considered toresult from two main sources: controlled releasesfrom the central hall of unit 4 into the environmentthrough the exhaust ventilation system and

ventilation stack No. 2, and uncontrolled releasesthrough the leaks in the roof and walls. Ventilationstack No. 2 releases 4–10 GBq/a, which is manytimes lower than the regulatory limit of 90 GBq/a[7.9]. The uncontrolled releases depend on thelocations and areas of the openings in the externalstructures and the air transfer rate through them,which depends on many factors, such as temper-ature, barometric pressure, humidity and windspeed and direction.

As a result, the air in the immediate vicinity ofthe shelter contains finely dispersed fuel particleswith concentrations of up to 40 mBq/m3 of 137Cs atdistances less than 1 km and 2 mBq/m3 at about3 km from the shelter. The aerosol particles haveradioactive compositions similar to those of thefuel; the primary beta emitters are 90Sr and 137Cs,while the alpha emitters are mostly plutonium and241Am. Inhalation doses to individuals outside theshelter result from a combination of the ongoingshelter releases and resuspended material from theinitial accident. If a person (worker) were to spendan entire year adjacent to the shelter, a recentinhalation dose assessment indicates that releaseswould result in an annual dose of about 0.5 mSv,which would decrease to about 0.0002–0.0005 mSvbeyond a distance of 10 km [7.14]. Inhalation dosesfrom the ongoing releases outside the CEZ aresignificantly less than the dose limits for thepopulation [7.7].

7.1.4.3. Impact on surface water

The average concentrations of radionuclidesin surface water bodies are declining. In the PripyatRiver in 2003, for example, concentrations wereobserved to be 0.05 (max. 0.12) Bq/L for 137Cs and0.15 (max. 0.35) Bq/L for 90Sr [7.15]. The mainsources of radionuclides in the rivers in the CEZduring ordinary and high water seasons continue tobe runoff from the watersheds situated outside theimmediate Chernobyl nuclear power plant area,infiltrating waters from the Chernobyl nuclearpower plant cooling pond and old waterreclamation systems in the heavily contaminatedterritories. During winter and low water seasons, theradionuclide fluxes from regional groundwatercontribute the majority of the radionuclidemigration to the Pripyat River from this area.However, the values of radionuclide flux from allgroundwater into surface water are still relativelylow, and the contribution of groundwatercontamination plumes from the temporaryFIG. 7.5. Planned NSC.

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(a) kBq/m2

20 000

7500

4000

2000

750

400

200

75

40

0

· State border· Railway· Road· Towns and villages· Rivers and lakes· Exclusion zone border

Scale 1:200 000

0 2 4

km

(b) kBq/m2

20 000

7500

4000

2000

750

400

200

75

40

20

0


Scale 1:200 000

0 2 4

km

FIG. 7.6. Surface contamination by radioactive fallout within the CEZ [7.2]. (a) Caesium-137 in soils of the CEZ in 1997(kBq/m2); (b) 90Sr in soils of the CEZ in 1997 (kBq/m2); (c) 241Am in soils of the CEZ in 2000 (kBq/m2); (d) 239,240Pu in soilsof the CEZ in 2000 (kBq/m2).

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(c) kBq/m2


Scale 1:200 000

0 2 4

km

1000.0

400.0

200.0

100.0

40.0

20.0

10.0

4.0

1.0

0.4

0.1

0.0

(d) kBq/m2


Scale 1:200 000

1000.0

400.0

200.0

100.0

40.0

20.0

10.0

4.0

1.0

0.4

0.1

0.0

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radioactive waste facilities and the shelter area hasbeen identified as about 3–10% [7.15] of the annualmigration of radionuclides into the Pripyat–DnieperRiver system from the CEZ (see also Section 3.5).

7.1.4.4. Impact on groundwater

Surface contamination around the Chernobylnuclear power plant site is the cause of groundwatercontamination, with groundwater levels of 100–1000 Bq/m3 for 90Sr and about 10–100 Bq/m3 for137Cs. Radionuclide contamination of thegroundwater at the shelter site is much higher. Inrecent studies, the primary source term for radio-nuclide contamination of the groundwater isconsidered to be water accumulating inside theunderground rooms of unit 4 (as a result of precipi-tation), groundwater accumulated near the pioneerwall (because of absence of a drainage system) andother water infiltrating from the nuclear powerplant site.

In some places, 137Cs in groundwater in thesubsurface horizons near the shelter reaches 100 Bq/Land even 3000–5000 Bq/L. However, in the majorityof the shelter area, 137Cs concentrations ingroundwater are more or less similar and vary from1 to 10 Bq/L. Typical concentrations of 90Sr ingroundwater around the shelter site are in the rangefrom 2 to 160 Bq/L, with maximum concentrationsobserved during the past five years ranging from1000 to 3000 Bq/L. Estimated concentrations oftransuranic elements in the groundwater of this areaalso vary over a wide range, from 0.003 to 3–6 Bq/Lfor 238Pu and 239,241Pu, and from 0.001 to 8–10 Bq/Lfor 241Am [7.16, 7.17].

7.1.4.5. Impacts of shelter collapse without the new safe confinement

Owing to concerns about the long termstability of the shelter, estimates have been made ofthe probability of its collapse. Depending on themechanisms considered, the probability rangesfrom about 0.001 to 0.1/a [7.5, 7.18], and thereforean analysis (summarized from Ref. [7.6]) of thepotential impacts of a shelter collapse has beenperformed for scenarios without and with the NSCin place.

(a) Impact on air

Collapse of the shelter could raise a largecloud of fine dust (up to 500–2000 kg) containing 8–

50 kg of nuclear fuel particles with an activity ofabout 1.6 × 1013 Bq. This could lead to an additionalannual inhalation dose of up to 0.4 Sv near theshelter. The estimated annual doses outside theCEZ could reach 2 mSv [7.6], which would exceedthe established dose limits for the public in Ukraine[7.7].

Within the boundaries of the CEZ, thedepositions of radionuclides from such a collapsewould be, in all cases, a small fraction of the existingcontamination levels caused by the originalChernobyl accident. Typical results are shown inFig. 7.7 [7.8]. The highest relative increase in soilcontamination would occur if the wind were to blowthe plume from a shelter collapse to the south-westtowards the area that received the least impact fromthe original accident. In this case, the additionaldeposition might add about 10% to the existing soilcontamination levels. Outside the CEZ boundaries,at 50 km from the shelter, additional surfacecontamination with 137Cs, 90Sr and 238,239,240Pu due toa shelter collapse would contribute from a few to10%.

(b) Impact on surface water

In the event of a shelter collapse, additionalradioactive material could also be deposited in andnear the rivers.

As shown in Fig. 7.7, radionuclidedepositions into the Pripyat River could be as highas 1.1 × 1012 Bq of 90Sr, 2.4 × 1012 Bq of 137Cs,1.6 × 1010 Bq of 238Pu, 4.0 × 1010 Bq of 239,240Pu and5.0 × 1010 Bq of 241Am. Estimates of the maximumpossible concentrations of these radionuclides inthe Dnieper reservoirs show that the peak concen-tration of 90Sr can be expected in the Kievreservoir on the 41st day after the accidenthappens, and would be about 700 Bq/m3. Themaximum concentration of 90Sr in the Kakhovkareservoir would be about 200 Bq/m3 or less. Thisconfirms that the normative values of 90Sr inpotable water (2000 Bq/m3 [7.7]) would not beexceeded if an accident leading to the maximumimpacts were to occur at the shelter.

The maximum possible concentrations of 137Csthat can be expected in the Kiev and Kanevreservoir water, even in the worst simulatedscenarios, are three to ten times lower than thelimits for potable water. Such a collapse would notaffect the concentrations of 238Pu, 239,240Pu and241Am in the Pripyat and Dnieper Rivers [7.6].

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(a)

kBq/m2

(b)

kBq/m2

FIG. 7.7. Strontium-90 soil density of Chernobyl fallout (a) upstream of Yanov bridge, 1999, and (b) predicted from a sheltercollapse [7.6]. The distance from the shelter is given on both axes.

149

Releases from a shelter collapse could lead tosome increased exposure of people livingdownstream of the most impacted area in the CEZand who consume water and fish from thereservoirs. Radiation doses to individuals arediscussed in Ref. [7.6], in which the highest valuesare predicted to be for professional fishermen andtypical consumers.

(c) Impact on groundwater

Rainwater infiltration and condensationwithin the existing shelter have also been studied[7.6]. The radiological significance of the large poolof water in the basement of the shelter wasconfirmed. The leakage of the heavily contaminatedwater from this pool through the concrete walls andfloor of the room is a main source of the contami-nation of the vadose zone and groundwater beneaththe shelter. Under existing conditions, a positivewater balance exists and water collects in thebasement rooms.

The results of an assessment of groundwatercontamination without the NSC show that aconcentration of 90Sr in the groundwater of about4 × 109 Bq/m3 is expected to occur at distances lessthan 100 m from the shelter, and would decline to100 Bq/m3 at 600 m from the shelter. The contami-nation is predicted to reach the Pripyat River in 800years. However, the infiltration fluxes of 90Sr fromthe shelter even without the NSC are not expectedto cause significant impacts on the Pripyat River.

7.1.4.6. Impacts of shelter collapse within the new safe confinement

(a) Impact on air

Placement of the NSC over the shelter isexpected to reduce the release of dust on to the siteresulting from a collapse, thus reducing themagnitude of inhalation doses. The dust wouldlargely settle within the NSC and not be released tothe environment except through normal ventilationpathways. The amount of transported dust woulddepend on the ventilation and the confinementcapability designed into the NSC. The doses areexpected to be reduced by factors of seven to 70compared with the estimated doses in the event of ashelter collapse without the NSC, depending on thecapacity of the NSC ventilation system [7.6]. Thisleads to an expected decrease of outdoor workers’exposure by a factor of two in comparison with the

scenario of a shelter collapse without the NSC.However, some workers might be inside the NSC atthe time of the collapse; doses to these workersmight be increased because of containment of thedust.

For the small number of individuals who havechosen to reside within the CEZ, inhalation dosesare expected to be reduced by factors of 50 to 500,to no more than 1 or 2 mSv [7.6]. Even assuming theworst (95th percentile) meteorological conditionsand also assuming that the dust cloud passes overone of the larger cities, such as Slavutych, anincrease of latent fatal cancer risk projected for thepopulation in the event of a collapse with the NSC isnot expected.

Very minor additions to soil contaminationwould be caused by the discharge and deposition ofairborne radionuclides should the shelter collapseinside the NSC. Within the boundaries of the CEZ,the radionuclide deposition would be in all cases asmall fraction of the existing levels caused by theoriginal Chernobyl accident. The highest relativeincrease would occur if the wind were to blow theplume from a shelter collapse to the south-westtowards the area that received the least impact fromthe original accident; in this case, the additionaldeposition might add less than 0.2% to the existingsoil contamination levels.

(b) Impact on surface water

Emplacement of the NSC would ensure that,in the event of a collapse, additional deposition ofradionuclides on surface water would be minimal.The depositions illustrated in Fig. 7.7 would bereduced by factors of 50 to 500 [7.6], and theresulting concentrations in downstream waterswould not exceed the Ukrainian norms.

(c) Impact on groundwater

The dynamics of radionuclide migration intothe groundwater with the presence of the NSC wasevaluated assuming that the water level is reducedto zero in the basement one and a half years afterthe NSC is constructed. After NSC construction, theprecipitation fluxes are expected to be minimizedand evaporation fluxes will be higher than fluxesfrom dust suppression and condensation. Thismeans that the water level in the basement isexpected to diminish due to seepage through thewalls, and the room would therefore be empty inless than two years.

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7.1.5. Issues and areas for improvement

7.1.5.1. Influence of the source term uncertainty on environmental decisions

There is still considerable uncertaintyregarding the amount of nuclear fuel remaining inunit 4. One estimate [7.1, 7.19] is that inside unit 4there is approximately 95% of the 190 t of nuclearfuel (as uranium) that was in the reactor at the timeof the accident. Another estimate [7.12] is that thereis 60% of the original core plus the fuel in the decaypool and in the central room remaining in thefacility (212 t total, less 80 t of FCM, less 6 t ofblown out fuel = 126 t remaining). The estimatedradioactivity inside the shelter in 1995 was approxi-mately 7 × 1017 Bq [7.3]. Despite these and otherstudies, to date there is no comprehensiveinformation regarding the amount and distributionof fuel inside the shelter. This lack of knowledge isan important factor in the evaluation of the safetyand environmental consequences of unit 4 and theshelter evolution, as well as for the selection ofadequate solutions for the long term managementof the associated radioactive waste.

7.1.5.2. Characterization of fuel-containing material

The physical state of the FCM appears to bechanging with time. It appears that the FCM hasbegun to oxidize and may be decomposing into fineparticulate matter with an unknown oxidation rate,particle size and behaviour. Another relatedimportant uncertainty is on the dust distribution inthe shelter, and more specifically in the NSCatmosphere over long term operation of the facility.As estimates of the environmental impacts (e.g.transport and inhalation calculations) of long termshelter development are sensitive to theassumptions about these source term parameters, itis necessary that these parameters be further inves-tigated. This would contribute to increasedconfidence in the safety assessment results and theselection of appropriate protective measures forworkers, the public and the environment.

7.1.5.3. Removal of fuel-containing material concurrent with development of a geological disposal facility

The stabilization of the shelter andconstruction of the NSC is expected to generatesignificant amounts of long lived radioactive waste,

some of which would contain FCM. However, thereare no plans for removal of the FCM until ageological disposal facility is constructed andcommissioned. A long term management strategyfor the FCM and long lived radioactive wastetherefore needs to be developed to ensure safemanagement of this waste.

It can be concluded that there is no technicalreason to delay removal of the FCM until ageological disposal facility is available. Removal ofFCM could commence following dismantlement ofthe unstable structures of the shelter, continuingwith radioactive waste predisposal management andtemporary storage on the Chernobyl nuclear powerplant site until the geological disposal facilitybecomes available. Due to the high content of longlived radionuclides there is also no significantworker dose benefit to be obtained from waiting forthe availability of a geological disposal facility.Whether retrieved now or after 50 years, remoteretrieval and radioactive waste managementtechniques will be required to remove the FCM andrestore the unit 4 site.

7.2. MANAGEMENT OF RADIOACTIVE WASTE FROM THE ACCIDENT

In the course of remediation activities, both atthe Chernobyl nuclear power plant site and in itsvicinity, large volumes of radioactive waste weregenerated and placed in temporary near surfacewaste storage facilities located in the CEZ (Fig. 7.8)at distances of 0.5–15 km from the nuclear powerplant site. Sites for temporary waste storage of the

FIG. 7.8. Temporary radioactive waste disposal facilities inthe territory of the CEZ.

151

trench and landfill type were created from 1986 to1987, intended for radioactive waste generated afterthe accident as a result of the cleanup ofcontaminated areas, to avoid dust spread, reduceradiation levels and provide better workingconditions at unit 4 and its surroundings. Thesefacilities were established without proper designdocumentation, engineered barriers orhydrogeological investigations, which are requiredby contemporary waste safety requirements.

During the years following the accident,economic and human resources were expanded toprovide a systematic analysis and an acceptablestrategy for the management of existing radioactivewaste. However, as reported in some Ukrainianstudies [7.20], to date a broadly accepted strategyfor radioactive waste management at the Chernobylnuclear power plant site and the CEZ, andespecially for high level and long lived waste, hasnot been developed. Some of the reasons are thelarge number of and areas covered by theradioactive waste storage and disposal facilities, ofwhich only half are well studied and inventoried.This results in large uncertainties in the documentedradioactive waste inventories (volume, activity,etc.).

The existing radioactive waste from theaccident and potential radioactive waste to begenerated during the NSC construction, shelterdismantling, FCM removal and decommissioning ofunit 4 can be categorized as:

(a) Radioactive waste from the shelter and thenuclear power plant site that will be created byconstruction of infrastructure and the NSC;

(b) Accident generated transuranic waste that hasbeen mixed with radioactive waste fromoperations at Chernobyl nuclear power plantunits 1, 2 and 3;

(c) Radioactive waste in temporary radioactivewaste facilities located throughout the CEZ;

(d) Radioactive waste in existing radioactivewaste disposal facilities.

The safety and environmental issues related toeach of these categories of radioactive waste arepresented in this section. The radioactive wasteexpected to be generated during the decommis-sioning of the Chernobyl nuclear power plant units1, 2 and 3 represents an additional category that isnot the subject of this report.

The current Ukrainian legislation applies acategorization of radioactive waste in accordancewith its specific activity and radiotoxicity, specifiedin Table 7.1 [7.21].

For waste contaminated with unspecifiedmixtures of radionuclides emitting gammaradiation, use of the classification ‘low’, ‘interme-diate’ and ‘high’ activity is allowed using the airdose rate at a distance of 0.1 m, as specified in Table7.2 [7.21].

Current radioactive waste managementpractice in Ukraine does not fully comply with theabove classification; measures are therefore beingtaken to bring it into conformity with the newregulations [7.22].

TABLE 7.1. UKRAINIAN SOLID RADIOACTIVE WASTE CATEGORIZATION [7.21]

Range of specific activity (kBq/kg)

Group 1a Group 2a Group 3a Group 4a

Low activity 10–1–101 100–102 101–103 103–105

Intermediate activity 101–105 102–106 103–107 105–108

High activity >105 >106 >107 >108

a Group 1: transuranic alpha radionuclides; group 2: alpha radionuclides (excepting transuranium); group 3: beta and gammaradionuclides (excluding those in group 4); group 4: 3H, 14C, 36Cl, 45Cf, 53Mn, 55Fe, 59Ni, 63Ni, 93mNb, 99Tc, 109Cd, 135Cs, 147Pm,151Sm, 171Tm and 204Tl.

TABLE 7.2. CLASSIFICATION OF RADIO-ACTIVE WASTE WITH UNKNOWN SPECIFICACTIVITY USING THE DOSE RATE AT 0.1 mDISTANCE [7.21]

Dose rate (µGy/h)

Low activity 1–100

Intermediate activity 100–10 000

High activity >10 000

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7.2.1. Current status of radioactive waste from the accident

7.2.1.1. Radioactive waste associated with the shelter

The shelter is considered to be “the destroyedunit 4 after a radiological accident” and “a nearsurface storage facility for unconditionedradioactive waste at a stage of stabilization andreconstruction” [7.22, 7.23]. The amount and type ofwaste, debris and other radioactive material insidethe shelter is presented in Table 7.3.

In addition, soil that was heavily contaminatedby the deposition of fuel fragments and with radio-nuclides and debris from the accident (metal pieces,concrete rubble, etc.) was also collected and storedin the vicinity of unit 4:

(a) Three pioneer walls (west, north and south ofthe shelter), where contaminated soil,concrete and containers are stored and whichcontain an estimated 1700–4900 m3 of highlevel waste5 and up to 72 000 m3 of low andintermediate level waste [7.25, 7.26].

(b) The cascade wall north of the shelter, wherecore fragments, metal, concrete, core pit

equipment and accident cover material arestored (16 600 m3 of high level waste, 117 t ofreactor core elements and 53 400 m3 of lowand intermediate level waste) [7.25].

(c) The industrial site around the shelter, whereconcrete, gravel, sand, clay and contaminatedsoil are stored that contain 7000 m3 of highlevel waste and 286 000 m3 of low and inter-mediate level waste [7.27]. Other studies showthat fuel, graphite, etc., are located in thecontaminated soil [7.26].

The radioactive waste inside the pioneer andcascade walls was later covered with concrete. Thismaterial is considered to be high level waste that isnot acceptable to be disposed of in near surfacedisposal facilities. Since it cannot be retrieved easilyfor conditioning, the radioactive waste recoveredfrom these walls is to be part of a global strategy forthe decommissioning of unit 4.

TABLE 7.3. ESTIMATED INVENTORY IN THE SHELTER [7.25]

Type of radioactive waste and criteria of assessment

Category of radioactive waste

Amount

FCM Fresh fuel assemblies, spent fuel assemblies, lava type material, fuel fragments, radioactive dust

High level About 190–200 t, 700 t of graphite

Solid radioactive waste with less than 1% nuclear fuel (mass)

Fragment of the core with a dose rate at 10 cm of more than 10 mSv/h

Liquid radioactive waste Changing inventory based on precipitation (e.g. pulp, oils, suspensions with soluble uranium salts)

Low level (up to 3.7 ¥ 105 Bq/L)

2500–5000 m3

Intermediate level (more than 3.7 ¥ 105 Bq/L)

500–1000 m3

Solid radioactive waste Metal equipment and building material, for example concrete, dust, non-metal material (organic, plastic)

High level 38 000 m3 (building material), 22 240 t (metal constructions)

Low and intermediate level

300 000 m3 (building material and dust), 5000 m3 (non-metal)

5 High level waste falls into two subcategories: lowtemperature waste with a heating rate of less than2 kW/m3 and heat generating waste with a heating ratehigher than 2 kW/m3 [7.24].

153

It is estimated that the current and expectedradioactive waste from unit 4 can be categorized asshort lived low and intermediate level waste (soilfrom the construction of the NSC, constructionmaterial, concrete, metal constructions, etc.) andhigh level waste (e.g. FCM) according to Ukrainianlegislation [7.28, 7.36].

7.2.1.2. Mixing of accident related waste with operational radioactive waste

During 1986–1993, some low and intermediatelevel radioactive waste and high level waste withtransuranic elements were stored together withsome operational radioactive waste from units 1, 2and 3 in an above ground storage facility (seeFig. 7.9) at the Chernobyl nuclear power plant site.

This waste amounts to about 2500 m3, with atotal radioactivity of about 131 TBq [7.19], and isstored unconditioned. Once filled, the storagefacility was backfilled with concrete grout andcovered with a concrete roof to reduce radiationlevels and water infiltration. Thus the retrieval ofthe radioactive waste stored in this facility cannotbe easily achieved and will require particular care.Plans for such retrieval are currently under study.At present, this facility is being extended and isintended to be used for the disposal of radioactivewaste produced during the decommissioning ofunits 1, 2 and 3.

7.2.1.3. Temporary radioactive waste storage facilities

The largest volumes of radioactive wastegenerated by unit 4 remediation activities are

located in the CEZ (see Fig. 7.8). Sites fortemporary storage of radioactive waste, of thetrench and landfill type, were constructed shortlyafter the accident at distances of 0.5–15 km fromthe nuclear power plant site. They were createdfrom 1986 to 1987 and intended for radioactivewaste generated after the accident as a result of thecleanup of contaminated areas to avoid dustspread, reduce radiation levels and provide betterworking conditions at unit 4. These facilities wereestablished without design documentation,engineered barriers or hydrogeologicalinvestigations.

The total area of temporary radioactive wastefacilities is about 8 km2, with the total volume ofdisposed radioactive waste estimated to be over106 m3. The main inventories of activity are concen-trated in the Stroibaza and Ryzhy Les temporaryradioactive waste facilities along the western traceof the Chernobyl fallout (see Fig. 7.8). The specificactivity of the radioactive waste in the temporaryradioactive waste facility at Ryzhy Les is105-106 Bq/kg of 90Sr and 137Cs and 103–104 Bq/kg ofplutonium isotopes (total).

Most of the facilities are structured in the formof trenches 1.5–2.5 m deep in the local sandy soil.The radioactive material (soil, litter, wood andbuilding debris) is overlain by a layer of alluvialsand 0.2–0.5 m thick. The majority of the temporaryradioactive waste facilities consist of trenches invarious types of geological setting, in which wastewas stacked and covered with a layer of soil fromthe nearby environment. These facilities aretherefore very variable with regard to theirpotential for release, which depends on the totalradioactivity stored, the waste form (in particulartimber), the retention capacity of the substratumalong migration pathways and the location of thesites in hydrogeological settings. At least half ofthese temporary radioactive waste facilities havebeen studied (see Table 7.4) [7.19, 7.29].

There are also many other temporaryradioactive waste facilities, estimated to compriseabout 800 trench facilities each with wastedisposal volumes in the range of 8 × 102 to2 × 106 m3 [7.29, 7.30]. The inventories of thesefacilities are known for about half of them. Thefacilities are not under regulatory control.Estimates made for a few sites show that theirradioactive contents can be high (10–1000 TBq),sometimes of an order of magnitude comparablewith the total radioactivity present in soil in theCEZ (about 7000 TBq) [7.30].

FIG. 7.9. Existing above ground storage facility for solidradioactive waste at the Chernobyl nuclear power plant site.

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7.2.1.4. Radioactive waste disposal facilities

The main radioactive waste disposal facilitiesfor accident waste are the Buriakovka, Podlesnyand Kompleksny sites, which are under regulatorycontrol. These three near surface disposal sites wereestablished after the accident to dispose ofradioactive waste from remediation actions carriedout during the first year following the accident.These sites were chosen and designed for thedisposal of higher level accident waste than theradioactive waste located in the temporaryradioactive waste facilities [7.19].

Buriakovka, built in 1987, is the only disposalfacility currently in operation in the CEZ. Itcomprises 30 trenches covered with a 1 m clay layerand is located on 23.8 ha. Up to 652 800 m3 ofradioactive waste has been disposed of. After in situ

compaction, this was reduced to 530 000 m3, with atotal radioactivity of 2.5 × 1015 Bq of solid shortlived low and intermediate level waste. It consists ofmetal, soil, sand, concrete and wood contaminatedwith 90Sr, 137Cs, 134Cs, 238,239,240Pu, 154,155Eu and241Am. Radioactive waste with dose rates at 10 cmfrom the surface in the range of 0.003–10 mGy/hwas accepted in this facility.

The Podlesny vault type disposal facility wascommissioned in December 1986 and closed in1988. The facility was designed for the disposal ofhigh level waste with a dose rate 10 cm from thesurface in the range of 0.05–2.5 Gy/h. Material withdose rates above this was also disposed of in thefacility. The total radioactive waste volume of11 000 m3 of building material, metal debris, sand,soil, concrete and wood was placed in two vaults.The disposal facility was covered with concrete at its

TABLE 7.4. STATUS OF TEMPORARY RADIOACTIVE WASTE FACILITIES [7.19, 7.29]

Size (ha)

Number of trenches

Number of landfills

Radioactive waste typeRadioactive

waste volume (103 m3)

Total activity (Bq)

Sites with well known inventories

Neftebaza 53 221 4 Soil, plants, metal, concrete and bricks

104 4 ¥ 1013

Peschannoe Plato

78 2 82 Short liveda low and intermediate level waste of soil, rubble and concrete

57 7 ¥ 1012

Partially investigated sites

Stantzia Yanov

128 Known: more than 36

— Soil, plants, metal, concrete and bricks

30 >4 ¥ 1013

Ryzhy Les 227 Estimated at more than 61

Estimated at more than 8

Mainly soil, some construction and domestic material

500 Up to 4 ¥ 1014

Staraya Stroibaza

130 More than 100

— Soil, metal, concrete and wood

171 1 ¥ 1015

Novaya Stroibaza

122 — — Soil, plants, metal, concrete and bricks

150 2 ¥ 1014

Pripyat 70 — — Contaminated vehicles, machinery, wood and construction waste

16 3 ¥ 1013 Bq (1990)

Chistogalovka 6 — — Material from demolition of buildings, soil, wood and work clothes

160 4 ¥ 1012

Kopachi 125 — — Construction waste from demolition

110 3 ¥ 1013

a According to Ukrainian legislation, short lived waste is radioactive waste whose release from regulatory control isachieved earlier than 300 years after disposal; long lived waste is radioactive waste whose release from regulatorycontrol is achieved later than 300 years after disposal [7.21].

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closure. In 1990 the estimated total radioactivity ofthe disposed waste was 2600 TBq. In 2002 a re-evaluation of the facility status showed reasons tobelieve that the total activity of waste disposed atthis site may be higher than initially estimated, anda need for a re-estimation of the current inventorywas identified. Due to the uncertainties in theinventory, it is assumed that various types of wastewere disposed of, including FCM.

The Kompleksny vault type facility was basedon reconstructed facilities of the unfinished units 5and 6 at the Chernobyl nuclear power plant site.Kompleksny was in operation from October 1986until 1988 and was designed for low and interme-diate level waste corresponding to dose rates up to0.01 Gy/h at 10 cm from the surface of the wastecontainer. More than 26 200 m3 of solid waste with atotal activity of 4 × 1014 Bq was disposed of in 18 000containers and later covered with sand and clay.This waste is mainly sand, concrete, metal,construction material and bricks. Due to the highlevel of groundwater at different periods of theyear, the facility is flooded 0.5–0.7 m above itsbottom. Significant uncertainties exist associatedwith the radionuclide inventory because of the lackof data about the radioactive waste disposed of atthe site.

At present, a new near surface facility, theVektor complex, for low and intermediate levelradioactive waste processing, storage and disposal, isunder development. This complex will include [7.19]:

(a) An engineering facility for the processing ofall types of solid radioactive waste (capacity of3500 m3/a);

(b) A disposal facility for short lived solidradioactive waste (55 000 m3 total capacity);

(c) A storage facility for long lived solidradioactive material;

(d) A storage facility for FCM; (e) Intermediate storage for high level

conditioned radioactive waste to be preparedfor final disposal at the deep geologicaldisposal facility.

7.2.2. Radioactive waste management strategy

At present, no further dismantlement andcleanup of unit 4 is planned. However, estimates ofthe radioactive waste generation and subsequentmanagement options have been performed for theconstruction of the NSC and the dismantlementphase of the unstable structures of the shelter. The

preparation phase is expected to generate about390 t of solid radioactive waste and about 280 m3 ofliquid [7.6]. It also requires the removal of100 000 m3 of contaminated soil around unit 4,which may still contain fuel fragments. Preliminarystudies for the dismantlement of the shelter super-structure predict that about 1200 t of steel, with anestimated volume of radioactive waste of 1800 m3

[7.14], mainly metal and large concrete pieces, willbe removed. This waste is planned to be sortedbased upon its radiation level. High level waste,which is expected to be only a small part, is plannedto be placed in containers and stored within theNSC.

According to Ukrainian legislation [7.31], allindustrial radioactive waste is classified according tothe scheme shown in Fig. 7.10: high level and longlived waste must be disposed of in a deep geologicaldisposal facility; low and intermediate level andshort lived radioactive waste in a near surfacedisposal facility. Following these criteria, a strategyfor the management of radioactive waste from the1986 accident needs to be developed, and inparticular for the management of high level andlong lived radioactive waste.

The planned options for low level waste are tosort the waste according to its physical character-istics (soil, concrete, metal, etc.) and, possibly, todecontaminate it and/or condition it for beneficialreuse (reuse of soil for NSC foundations, melting ofmetal pieces) or send it for disposal in a newextension of the Buriakovka disposal facility [7.19]or the Vektor disposal site.

The long lived waste is planned to be placed ininterim storage. Different storage options are beingconsidered at the Chernobyl nuclear power plant orthe Vektor site, and a decision has not yet been made.After construction of the NSC, decommissioning of

Below Exemption

Level

Low and

Intermediate

Level Waste

(LILW)

High Level Waste

(HLW)High level waste

Longlived

Shortlived

Interimstorage

Geologicaldisposal

Near surfacedisposal

Low andintermediatelevel waste

Below exemptionlevel Recycle or

disposewithout radiologicalrestrictions

FIG. 7.10. Planned management of radioactive waste at theChernobyl nuclear power plant site [7.19].

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the shelter facilities is envisaged, including shelterdismantlement and further removal of FCM. Highlevel radioactive waste will be partially processed inplace and stored at a temporary storage site until adeep geological disposal site is ready. At present, thisstrategy is considered as the preferred option for highlevel radioactive waste and FCM [7.19]. Toimplement this strategy, it is planned to organize asystem for processing and temporary storage of thehigh level and long lived radioactive waste at theVektor facility complex that is now being developed.When the Vektor facility is in full operation, it maybe possible to begin the work of removing FCM andother radioactive waste from the shelter under coverof the NSC.

Such a strategic approach is foreseen in thecomprehensive programme on radioactive wastemanagement that was approved by the UkrainianGovernment [7.25]. Prior to elaboration of such aprogramme, special field studies and geologicalinvestigations must be carried out in the CEZ andits surrounding area, and in particular in the areaswith crystalline rocks that have a depth of morethan 500 m. According to Ref. [7.25], it is consideredreasonable to begin an investigation for exploringthe most appropriate geological site in this area in2006. Following such planning, the construction of adeep geological disposal facility might be completedbefore 2035–2040.

Management of future liquid radioactivewaste from the shelter is planned to be performed atthe new liquid radioactive waste treatment plant atthe Chernobyl nuclear power plant site. However,the management of liquid waste containingtransuranic elements remains an issue to beresolved.

In addition, in the strategy for management ofradioactive waste from the accident, account shouldbe taken of the management of other storage sitescontaining about 2000 pieces of contaminatedequipment (transport vehicles, helicopters, tanks,

etc.) that were used in the first months after theaccident and for which the final disposition has notbeen determined.

7.2.3. Environmental aspects

Safety concerns in relation to most of thetemporary radioactive waste facilities in the CEZneed to be viewed within the context that most ofthese facilities are located in very contaminatedareas, with surface levels of 90Sr in the range of 400–20 000 kBq/m2, 700–20 000 kBq/m2 for 137Cs and 40–1000 kBq/m2 for 239,241Pu. In this same territory, thetemporary radioactive waste facilities occupy arelatively small volume covered with several metresof soil and other geological material.

The major concern is the risk of increasedcontamination of groundwater and the possibility, inthe future, that such contamination reaches majorwater sources used as water supplies. The measure-ments reported in the French–German initiative[7.32] (see Table 7.5) clearly show that sometemporary radioactive waste facilities have asignificant influence on groundwater. In particular,flooded and partially flooded trenches are givingrise to enhanced migration, due to the absence ofengineered safety features. More favourablesettings, such as the Buriakovka site, lessen theradionuclide release variations and maintainconcentrations in groundwater at comparatively lowlevels.

For a part of the year, some temporaryradioactive waste facilities are very near or in thegroundwater table, which can affect radionuclidedispersion. It is noticeable that water table levels atthe trenches and landfills vary from about 1 to 7 mdepth and vary depending on the season. Part of thefacilities at Stantzia Yanov and Neftebaza areconstantly flooded. Flooding is also an importantconcern at the Kompleksny disposal site, where thewaste containers are flooded from 0.5 to 0.7 m from

TABLE 7.5. CONTAMINATION OF GROUNDWATER NEAR SELECTED TEMPORARY RADIO-ACTIVE WASTE STORAGE FACILITIES IN 1994–1995 [7.16] AND IN 1999 [7.23]

Strontium-90 (Bq/L)

Caesium-137 (Bq/L)

Plutonium-239, 240(Bq/L)

1994–1995 1999 1994–1995 1999 1994–1999

Ryzhy Les 100–120 000 100–230 0.1–100 0.1–2.5 0.4–0.6

Stroibaza 3–200 30–50 1–20 0.02–0.004 No data

Peschannoe Plato 3–10 2–40 0.7–3 0.02–0.1 No data

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the bottom of the disposal facility [7.19]. The degreeof contamination is monitored in these disposal sitesusing a monitoring system, established in 1986–1989, that needs upgrading.

Monitoring results of groundwater contami-nation around the temporary storage facilitiesindicated concentrations of 90Sr in the range of100–100 000 Bq/m3 [7.19, 7.33]. The highest levels ofcontamination are detected at the northern part ofthe Chernobyl nuclear power plant site,groundwater from which also runs into the PripyatRiver. Therefore, actual and potential impacts fromradionuclides exist for those radioactive wastefacilities located immediately next to the riversidein alluvial soils and which might be at regular risk offlooding during high water periods [7.20, 7.32].These types of disposal facility have been studiedduring the past five years and continue to be studiedas a basis for their step by step removal andrelocation to the properly established disposalfacilities.

As mentioned above, the rate of radionuclidemigration with groundwater is much lower than thehydraulic transport of the water itself. This meansthat, due to retardation factors and geochemicalprocesses, the majority of radionuclides beingreleased from the body of the temporaryradioactive waste facilities are accumulating in thegeological media. Taking into account theadsorption capacity of the soils and geologicalmedia surrounding the temporary radioactive waste

facilities, several studies have shown that asignificant fraction of 90Sr is still associated with thefuel matrix, which delays its release to the porewater in the soil for many years. As a result, radio-nuclide concentrations in groundwater, even forsuch mobile radionuclides as 90Sr, are very low.Plutonium isotopes (and 241Am associated withthem) have not yet been adequately studied;however, it is well known that their migrationbeyond the temporary radioactive waste sites isnegligible (Fig. 7.11).

Studies of the vertical and lateral transferrates of radionuclides demonstrated that, for thelocal soil, there is a low risk of radionuclide contam-ination in groundwater and therefore a proportion-ately low risk of significant contamination of thePripyat River in the future, as discussed also inSection 3.5 (see Fig. 3.58). It has been shown thatthe leading edge of contaminated groundwater frommost of the significant temporary radioactive wastefacilities may reach regional surface water within100 or more years, making this issue of minimalimportance in terms of radiological impact forpopulations living downstream of the Pripyat Riversystem [7.17, 7.34]. However, for the CEZ,groundwater is still an important potential sourcefor radionuclide migration in the environment, andtherefore the waste facilities have to be underregular monitoring and institutional control.

The long term strategy for the temporaryfacilities is related to the management of the

Trench No. 22-TStrontium-90 in moisturesampler (Bq/L)

Strontium-90 in well (Bq/L)

X (m)

Ele

vatio

n (m

.a.s

.l)

Trench No. 22outline

Multilevelwell profile

Tracertest site

FIG. 7.11. Spatial distribution of 90Sr (Bq/L) in the groundwater near surface trench No. 22 of the Ryzhy Les facility in October1998 [7.34].

158

associated radiological risks. The ultimate goalshould be that waste is disposed of or left intemporary radioactive waste facilities that ensuresufficient confinement of 137Cs and 90Sr to allowtheir decay without having generated significantimpacts on potential critical groups. For thosetemporary radioactive waste facilities located nearthe banks of the Pripyat River that could beinundated by floodwaters, the preferred strategy isto remove and relocate the waste into the properlyestablished disposal facilities.

For the temporary radioactive waste facilitiesin the CEZ whose inventory is not known, and forwhich the potential for future contamination ofsurrounding groundwater and surface water isuncertain, safety assessments need to be performed,taking into account radioactive decay and naturalattenuation. There is clearly a need to assess, withan increased level of confidence, the migration ofcontamination plumes and their interface withmajor water resources and supply areas (aquifers,rivers, reservoirs, local supplies for the nuclearpower plant and the CEZ). Such assessments needto consider all sources of release likely to affectthese water resources.

The safety assessment results will guidedecisions on appropriate remediation or institu-tional control measures at the temporary sites.Operational waste acceptance criteria (e.g. activityconcentrations) also need to be established toensure that potential exposures from variousscenarios remain acceptable, on the hypothesis thatresettlement in the CEZ occurs after somehundreds of years. It is obvious that institutionalcontrol at such disposal sites will need to bemaintained for a period of a few hundred years toallow 137Cs and 90Sr activities to decay to insignif-icant levels. This will require significant resourcesfor monitoring, implementation of recovery actionsand probably major restrictions on resettlement.However, long term institutional controls shouldnot be considered as an alternative to recoveryactions to improve overall safety in the CEZ.

7.2.4. Issues and areas of improvement

7.2.4.1. Radioactive waste management programme for the exclusion zone and the Chernobyl nuclear power plant

A comprehensive programme for radioactivewaste management has not yet been established for

further cleanup of contaminated areas or temporaryradioactive waste facilities at the Chernobyl nuclearpower plant and within the CEZ. As mentionedearlier, the ongoing strategy is to monitor thetemporary waste sites with the highest radiologicalrisk to the environment, so as to assess whethercleanup or environmental protection actions areneeded. In addition, options for the long termprocessing, storage and disposal of long lived andhigh level waste from the Chernobyl nuclear powerplant and the CEZ, as well as management of liquidwaste contaminated with transuranic elements, areto be selected and the necessary facilitiesdeveloped. Development of such a programmecould ensure the consistent and coordinated longterm management of all types of accident waste andhence provide protection of workers, the public andthe environment.

7.2.4.2. Decommissioning of unit 4

Two main factors need to be addressed withinthe strategy for dismantlement of the shelter anddecommissioning of unit 4: the safety implicationsof the management of associated radioactive waste(in particular of the high level waste) and the safetyimplications of delaying recovery operations. Thestrategy for the management of radioactive wastethat cannot be disposed of in near surface facilitiesneeds to be developed. Specifically, there is a needfor new waste management facilities (e.g. storage oflong lived waste, geological disposal), with consider-ation given to the capacity of these facilities andalso the possibility of using the existing facilities forthe decommissioning of the Chernobyl nuclearpower plant. Particular attention needs to be givento the establishment of an adequate infrastructureand facilities for the management of long livedwaste (in particular large quantities of soil,transuranic liquid waste and contaminated metal)and high level waste (i.e. FCM) and theirsubsequent disposal.

7.2.4.3. Waste acceptance criteria

The waste management programme beingimplemented does include criteria for thecategorization of accident radioactive waste, whichare needed for the selection of an appropriatemanagement option for individual radioactive wastestreams. Adoption of criteria for wastemanagement, based on 137Cs and alpha specificradioactivity levels in the waste, is under

159

development. Although such criteria are moreadapted to appraising the potential for waste to beaccepted in near surface facilities, the question ofestimating the acceptable specific activities forexisting waste, especially in temporary radioactivewaste facilities, remains difficult to solve. Thedevelopment of waste acceptance criteria isimportant in order to ensure protection of workersand the environment, as well as the public, in thelong term.

7.2.4.4. Long term safety assessment of existing radioactive waste storage sites

There is a need to identify the remainingtemporary radioactive waste storage facilities and toappropriately mark them to prevent inadvertentintrusion. The long term impact of these facilities onthe environment also needs to be evaluated in orderto estimate the need, where necessary, for imple-mentation of upgrading or remedial actions.

Taking into account the large number offacilities, there is also a need to prioritize the needsfor safety assessment. These assessments shouldevaluate safety in the present conditions and withconsideration of possible future resettlement.Consideration should be given to the need torestrict the number of sites that are flooded or will,in the future, need extensive control over somehundreds of years.

In order to select those facilities with higherradiological risk it is important to improvemethods for assessing the radioactive content ofthe waste in the temporary facilities, especially oflong lived radionuclides. For pragmatic reasons,this assessment should be based on a limitednumber of parameters and measures. In this way,uncertainties that affect present estimates of thepotential impact of individual facilities on theenvironment will be reduced, and a consistentassessment that takes into account all existing andpotential sources of contamination in the CEZ willbecome feasible.

7.2.4.5. Potential recovery of temporary waste storage facilities located in the Chernobyl exclusion zone

Work is under way on the development of astrategy for the management of temporary wastestorage facilities; this envisages three options for thedifferent facilities, depending on their status andradiological hazard to the environment [7.19, 7.29]:

(a) Retrievability of waste and disposal in theshort term in order to minimize environ-mental consequences and improve the safetyof workers; for example, industrial sites, theshelter, the flooded temporary storagefacilities and the Kompleksny disposal facility.

(b) Possible temporary storage of waste underinstitutional control in accordance withradiation protection requirements with a viewto future disposal; for example, the Podlesnydisposal facility and contaminated equipmentfrom the activities aimed at mitigation of theChernobyl accident.

(c) Investigation of facilities that need to bestudied in order to decide on adequate inter-vention measures; for example, temporaryradioactive waste facilities and soil from theconstruction of the NCF.

7.3. FUTURE OF THE CHERNOBYL EXCLUSION ZONE

The long term development of the CEZ is animportant and complex task that must considervarious technical, economic, social and otherfactors; various options have been considered forthe evolution of this zone. According to Likhtarevet al. [7.35], after 2015 about 55% of the territoryaround the Chernobyl nuclear power plant could beconsidered for release from radiological limitationsaccording to Ukrainian legislation. However, thefinal decision on permitting people to return to thiszone must take into account the inhomogeneouscharacter of the contaminated land, specificfeatures of radionuclide migration and accumu-lation in different portions of the local landscape,and the routine habits of the population living inthis region (hunting, fishing, berry picking,mushroom gathering, etc.).

The overall plan for the development of theCEZ is to recover the affected areas of the CEZ,redefine the CEZ and make the non-affected areasavailable for resettlement by the public. This willrequire well defined administrative controls as tothe nature of activities that may be performed in theresettled areas, prohibition of growing of food cropsand cattle grazing and the use of only clean feed forcattle. Accordingly, these resettled areas are bestsuited for an industrial site rather than for aresidential area.

For the reasons given above, the activitiesfocused on decontamination and dismantlement of the

160

shelter and on radioactive waste management in thisterritory are expected to continue, which requiresoptimal management of this area. The new conceptforesees division of the CEZ into different sections:

(a) The industrial zone is planned to include themost contaminated areas, where theChernobyl nuclear power plant, facilities forprocessing radioactive waste and mainradioactive waste storage areas are situated.Primarily industrial activities are envisaged tobe carried out here, specifically theconstruction of the NSC facilities. To providethe infrastructure for NSC construction, newroads, shipping yards, railways and othersupport structures are planned. The town ofChernobyl has been considered as an optionfor such infrastructure development [7.6]. Ifthe CEZ is selected as the site for constructionof the geological repository for high activityand long lived radioactive waste, a significantamount of drilling and mining work will haveto be performed, which will also requirespecific development of the engineering infra-structure.

(b) The sanitary restricted zone is considered tobe a buffer area between industrial and naturereserve areas.

(c) The nature reserve areas are planned to belocated where most industrial and humanactivities are prohibited, with the aim ofpreservation of the basic natural landscapesand biodiversity of the region.

The rehabilitation of the CEZ is expected tocreate optimal conditions for industrial activity andenvironmental protection for a long period of time;for example, the NSC is expected to be operationalfor at least 100 years. Different types of radioactivestorage facility must provide safe storage for 300 ormore years. A possible activity in this area may beconstruction of the main geological disposal facilityfor radioactive waste. A national engineering centremay be established for processing all categories ofradioactive material and waste to be delivered tothe geological repository from different parts ofUkraine.

Continued monitoring and support studies inthe CEZ are needed to form a basis for the reviewand optimization of the management strategy in thecontaminated territories, and also for developingbasic and practical knowledge about the dynamicsand evolution of radionuclide migration, the need

for additional engineering barriers and the imple-mentation of environmental remediation technol-ogies.

In summary, the future of the CEZ for thenext hundred years and more is envisaged to beassociated with the following activities:

(i) Construction and operation of the NSC andrelevant engineering infrastructure;

(ii) De-fuelling, decommissioning anddismantling of units 1, 2 and 3 of theChernobyl nuclear power plant and shelter;

(iii) Construction of facilities for the processingand management of radioactive waste, inparticular a deep geological repository forhigh activity and long lived radioactivematerial;

(iv) Development of nature reserves in the areathat remains closed to habitation;

(v) Maintenance of environmental monitoringand research activities.


7.4.1. Conclusions

It can be concluded that the existing uncer-tainties associated with the stability of the shelterstructures, the radioactive inventory, the insufficientconfinement, the evolving characteristics of theFCM and the conditions inside and around theshelter (e.g. groundwater conditions) createuncertain safety conditions from the point of viewof protection of workers, the public and theenvironment in the future. Therefore, continuationof the stabilization measures at the shelter andconstruction of the NSC are expected to improvesafety and prevent or mitigate accident scenariosthat would be expected to have consequencesoutside the CEZ.

It is also required that prompt solutions befound for the safe predisposal and disposalmanagement of the radioactive waste to be generatedduring this period, in particular for the management oflong lived and high level waste. Planning andevaluation of safety for the decommissioning of unit 4after the construction of the NSC is needed in order todevelop appropriate measures and to allocatenecessary resources for the conversion of the shelterinto a safe environmental system.

161

The decommissioning of unit 4 will generatesignificant amounts of radioactive waste with a widerange of characteristics that will need to be safelymanaged as part of the decommissioning and wastemanagement activities at the Chernobyl nuclearpower plant and the CEZ. A comprehensivestrategy for the management of all waste streams isneeded to ensure adequate infrastructure andcapabilities for the processing, storage and disposalof this waste. Such a strategy will also need to takeinto account the future development ofunderground and on-surface storage and disposalfacilities, some of which are flooded.

At present, studies show that the known wastefacilities do not present an unacceptable hazard tothe public; however, an assessment of their longterm impact on the public and the environment isneeded. This should be done taking into account theremaining sources of radioactive contamination inthe CEZ, and particularly those facilities that areflooded and represent higher risks.

For the less known and less studied wastefacilities it will be necessary to reduce the uncer-tainties associated with the waste inventories andfacility characteristics, assess their long term safety,monitor the dynamics of radionuclide migrationinto the environment and, where necessary,implement remediation measures. This is importantfor the successful implementation of wastemanagement activities in the CEZ and theconversion of the zone into a safe environmentalsystem.


Recognizing the ongoing effort on improvingsafety and addressing the aforementioned uncer-tainties in the existing input data, the followingmain recommendations are made regarding thedismantling of the shelter and the management ofthe radioactive waste generated as a result of theaccident.

(a) Since individual safety and environmentalassessments have been performed only forindividual facilities at and around theChernobyl nuclear power plant, a compre-hensive safety and environmental impactassessment, in accordance with internationalstandards and recommendations, thatencompasses all activities inside the entireCEZ, should be performed.

(b) During the preparation and construction ofthe NSC and soil removal, special monitoringwells are expected to be destroyed. Therefore,it is important to maintain and improve theenvironmental monitoring strategies,methods, equipment and staff qualificationneeded for the adequate performance ofmonitoring of the conditions at the Chernobylnuclear power plant site and the CEZ.

(c) The dismantling of the shelter after a delay ofabout 50 years does not seem to be a viableoption, due to the need for long termmaintenance of structure stability andintegrity, resources and knowledge. This longterm strategy raises concerns related to thepotential loss of the most experiencedpersonnel at the Chernobyl nuclear powerplant and the maintenance of a stableworkforce necessary for the safe operation ofthe NSC. It is reasonable, therefore, to beginretrieving FCM soon after dismantling theunstable structures of the shelter rather thanwaiting for the availability of a geologicaldisposal facility.

(d) Development of an integrated radioactivewaste management programme for theshelter, the Chernobyl nuclear power plantsite and the CEZ is needed to ensureapplication of consistent managementapproaches and sufficient facility capacity forall waste types. Specific emphasis needs to begiven to the characterization and classificationof waste (in particular waste with transuranicelements) from all remediation and decom-missioning activities, as well as to the estab-lishment of sufficient infrastructure for thesafe long term management of long lived andhigh level waste. Therefore, development ofan appropriate waste management infra-structure is needed in order to ensuresufficient waste storage capacity; at present,the rate and continuity of remediationactivities at the Chernobyl nuclear powerplant site and in the CEZ are being limited.

(e) A coherent and comprehensive strategy forthe rehabilitation of the CEZ is needed, withparticular focus on improving the safety of theexisting waste storage and disposal facilities.This will require development of a prioriti-zation approach for remediation of the sites,based on safety assessment results, aimed atmaking decisions about those sites at whichwaste will be retrieved and disposed of and

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those sites at which the waste will be allowedto decay in situ.



[7.2] KASHPAROV, V.A., et al., Territory contamina-tion with the radionuclides representing the fuelcomponent of Chernobyl fallout, Sci. TotalEnviron. 317 (2003) 105–119.

[7.3] BOROVOY, A., BOGATOV, S., PASUKHIN,E., Current status of the shelter and its impact onthe environment, Radiokhimiya 41 (1999) 368–378(in Russian).

[7.4] NOVOKSHCHENOV, V., The Chernobylproblem, Civ. Eng. 72 (2002) 74–83.

[7.5] BOROVOY, A. (Ed.), Object Shelter SafetyAnalysis Report, Chernobyl nuclear power plant(2002) (in Russian).

[7.6] STATE SPECIALIZED ENTERPRISE ‘CHER-NOBYL NUCLEAR POWER PLANT’, Envi-ronmental Impact Assessment, New SafeConfinement Conceptual Design: ChernobylNuclear Power Plant — Unit 4, State SpecializedEnterprise ‘Chernobyl Nuclear Power Plant’, Kiev(2003).

[7.7] Radiation Safety Norms of Ukraine, Rep. NRSU-97, Ministry of Health of Ukraine, Kiev (1998).

[7.8] GMAL, B., MOSER, E.F., PRETZSCH, G.,QUADE, U., Criticality Behaviour of the Fuel-containing Masses inside the Object “Shelter” ofthe Chernobyl NPP, Unit 4, GRS Rep. A – 2414,Gesellschaft für Anlagen- und Reaktorsicherheit,Cologne (1997).

[7.9] OECD NUCLEAR ENERGY AGENCY, Cher-nobyl: Assessment of Radiological and HealthImpacts, 2002 Update of Chernobyl: Ten YearsOn, OECD, Paris (2002).

[7.10] BOGATOV, S., BOROVOY, A., Assessment ofInventory and Determination of Features of DustContained in the Shelter, Preprint of ISTC ShelterReport, Chernobyl (2000) (in Russian).

[7.11] PRETZSCH, G., “Radiological consequences of ahypothetical roof breakdown accident of theChernobyl sarcophagus”, One Decade after Cher-nobyl: Summing up the Consequences of theAccident, IAEA-TECDOC-964, Vol. 2, IAEA,Vienna (1997) 591–597.

[7.12] SCIENCE AND TECHNOLOGY CENTER INUKRAINE, Comprehensive Risk Assessment ofthe Consequences of the Chornobyl Accident,Science and Technology Center in Ukraine, Kiev(1998).

[7.13] STATE SPECIALIZED ENTERPRISE ‘CHER-NOBYL NUCLEAR POWER PLANT’, SIPProject, Shelter Transformation Safety, DigestPrepared by the State Specialized Enterprise‘Chernobyl Nuclear Power Plant’ InformationDepartment, Slavutych (2004).

[7.14] SCHMIEMAN, E.A., et al., Conceptual design ofthe Chernobyl new safe confinement — Anoverview, Can. Nucl. Soc. Bull. 25 2 (2004) 9–16.

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[7.19] Integrated Radioactive Waste Programme at theStage of Shutdown of the Chernobyl NPP andTransformation of the Shelter into an Environ-mentally Safe System, Ministry of Fuel andEnergy, Administration of the Exclusion Zone,State Committee of Nuclear Regulation, Ministryof Environment and Natural Resources, andMinistry of Health of Ukraine (2004) (inUkrainian).

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[7.21] Basic Sanitary Rules of Radiation Safety ofUkraine, Ministry of Health of Ukraine, Kiev(2000).

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[7.25] Concept of Radioactive Waste Management at theShelter, Approved by the State Commission onIssues on Complex Solution of Problems ofChernobyl NPP on 15 November 1999 (1999) (inUkrainian).

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CONTRIBUTORS TO DRAFTING AND REVIEW

Alexakhin, R. Russian Institute of Agricultural Radiology and Agroecology, Russian Federation

Anspaugh, L. University of Utah, United States of America

Balonov, M. International Atomic Energy Agency

Batandjieva, B. International Atomic Energy Agency

Besnus, F. Institut de radioprotection et de sûreté nucléaire, France

Biesold, H. Gesellschaft für Anlagen- und Reaktorsicherheit, Germany

Bogdevich, I. Belarusian Research Institute of Soil Science and Agrochemistry, Belarus

Byron, D. International Atomic Energy Agency

Carr, Z. World Health Organization

Deville-Cavelin, G. Institut de radioprotection et de sûreté nucléaire, France

Ferris, I. Food and Agriculture Organization of the United Nations

Fesenko, S. Russian Institute of Agricultural Radiology and Agroecology, Russian Federation

Gentner, N. United Nations Scientific Committee on the Effects of Atomic Radiation

Golikov, V. Institute of Radiation Hygiene of the Ministry of Public Health, Russian Federation

Gora, A. International Radioecology Laboratory, Ukraine

Hendry, J. International Atomic Energy Agency

Hinton, T. University of Georgia, United States of America

Howard, B. Centre for Ecology and Hydrology, United Kingdom

Kashparov, V. Ukrainian Institute of Agricultural Radiology, Ukraine

Kirchner, G. Institut für Angewandten Strahlenschutz, Germany

LaGuardia, T. TLG Services, Inc., United States of America

Linsley, G. Consultant, United Kingdom

Louvat, D. International Atomic Energy Agency

Moberg, L. Swedish Radiation Protection Authority, Sweden

Napier, B. Pacific Northwest National Laboratory, United States of America

Prister, B. Ukrainian Institute of Agricultural Radiology, Ukraine

Proskura, M. Ministry for Emergencies and Affairs of Population Protection from the Consequences of the Chernobyl Catastrophe, Ukraine

Reisenweaver, D. International Atomic Energy Agency

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Schmieman, E. Pacific Northwest National Laboratory, United States of America

Shaw, G. Imperial College of Science, Technology and Medicine, United Kingdom

Shestopalov, V. National Academy of Sciences, Ukraine

Smith, J. Centre for Ecology and Hydrology, United Kingdom

Strand, P. International Union of Radioecology, Norway

Tsaturov, Y. Russian Federal Service for Hydrometeorology and Environmental Monitoring, Russian Federation

Vojtsekhovich, O. Hydrometeorological Scientific Research Institute, Ukraine

Woodhead, D. Consultant, United Kingdom

Consultants Meetings

Vienna, Austria: 30 June–4 July 2003, 15–19 December 2003, 26–30 January 2004, 14–18 June 2004, 18–22 October 2004, 29 November–3 December 2004, 31 January–4 February 2005

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INTERNATIONAL ATOMIC ENERGY AGENCYVIENNA

ISBN 92–0–114705–8ISSN 1020–6566

The explosion on 26 April 1986 at the Chernobyl nuclear power plant and the consequent reactor fire resulted in an unprecedented release of radioactive material from a nuclear reactor and adverse consequences for the public and the environment. Although the accident occurred nearly two decades ago, controversy still surrounds the real impact of the disaster. Therefore the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations, the United Nations Development Programme, the United Nations Environment Programme, the United Nations Office for the Coordination of Humanitarian Affairs, the United Nations Scientific Committee on the Effects of Atomic Radiation, the World Health Organization and the World Bank, as well as the competent authorities of Belarus, the Russian Federation and Ukraine, established the Chernobyl Forum in 2003. The mission of the Forum was to generate “authoritative consensual statements” on the environmental consequences and health effects attributable to radiation exposure arising from the accident as well as to provide advice on environmental remediation and special health care programmes, and to suggest areas in which further research is required. This report presents the findings and recommendations of the Chernobyl Forum concerning the environmental effects of the Chernobyl accident.


Environmental Consequences of the Chernobyl Accident and their Remediation: Twenty Years of Experience

RADIOLOGICALASSESSMENTR E P O R T SS E R I E S

Environmental C

onsequences of the Chernobyl A

ccident and their Rem

ediation: Twenty Years of Experience

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