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Page 1: Aerial radiological monitoring of East Japan after the ... · the Fukushima Daiichi NPP (Nuclear Power Plant), Tokyo Electric Power Company (TEPCO), occurred by the East Japan earthquake

Aerial monitoring system

Methods

Aerial radiological monitoring of East Japan after the Fukushima Daiichi NPP accident

Yukihisa SANADA a, Takeshi SUGITAa, Aatsuya KONDO a and Tatsuo TORII a Headquaters of Fukushima Partnership Operations Center of Fukushima Partnership Environmental Safety Research and Development, Japan Atomic Energy Agency, 2-2-2,Uchisaiwai-cho, Chiyoda,Tokyo,100-8577, JAPAN E-mail: [email protected]

Introduction

II. Correction factor

Comparison with the ground survey Summary

Results II. 3D map of the deposition

II. Prediction of dose rate

I. Map of dose rate and the deposition

5年後に換算1年後に換算

IV. Discrimination between radiocesium and natural radionuclides

0.001

0.01

0.1

1

10

100

0 100 200 300 400 500 600 700

Calculated (Cs134/C137=0.9)

Observed (0.0063 West Japan Average)

Observed (0.0073 Fukushima)

Cor

rect

ion

fact

or o

f hei

ght

(nor

mal

ized

of d

ose

rate

at 3

00m

)

Height(m)

Normalization

I. Procedure of data analysis

threshold

Table Aerial monitoring system

System Install Det. size(inch), quantity Energy range Channel Altimeter

A Inside 16"×4"×2", 6 detector 0.02 - 3 MeV 1,024 ch GPS

B Outside 16"×4"×4", 4 detector 0.05 - 3 MeV 256 ch Laser

C Outside 16"×4"×4", 8 detector 0.2 - 3 MeV 256 ch Radio wave

D Inside 16"×4"×4", 4 detector 0.05 - 3 MeV 256 ch GPS

10-1 100 101 10210-1

100

101

102

y = 1.01x

Dose rate by AMS(µSv/h)

Dos

e ra

te b

y N

aI s

urve

y m

eter

on

the

grou

nd (µ

Sv/

h)RS701

RS701

RS501

PDU*

* Power Distribution Unit (PDU)Input 28VDC, 115VDC

Computer+RadAssist

GPSSub-

monitor

Battery

Battery

DetectorRSX-3

DetectorRSX-3

- Count rate was obtained by helicopter with large detector - Height above the ground 150-300m - Flight space: 3km - Acquisition rate: 1 second interval

We measured the ambient dose-rate and the deposition amount of radioactive cesium by using four helicopters in the whole area of East Japan to investigate the influence of the radioactivity that released in the atmosphere due to the disaster of the Fukushima Daiichi NPP (Nuclear Power Plant), Tokyo Electric Power Company (TEPCO), occurred by the East Japan earthquake and tsunami on March 11, 2011.

Mission Goals are …. - to create the radiation map of East Japan for

grasp on the influence of a radiocesium. - to establish the method of aerial radiological

monitoring

Achievement of aerial radiation monitoring

Date Mission Note 25 Mar. 2011 MEXT Press release of plan

for aerial radiation monitoring 5 Apr. 2011 60km zone from

NPP(DOE)+60-80km zone from NPP(NUSTEC)

<1st monitoring>

17 May. 2011 80-100km zone from NPP(NUSTEC)

<2nd monitoring>

17 May. 2011 40km zone from NPP(DOE+JAEA*1)+40-80km zone from NPP(NUSTEC)

<3rd monitoring> *1:DOE system in helicopter of the Self-Defence Forces

21 Jun. 2011 Miyagi-pref., Toshigi-pref., and Ibaraki-pref. (NUSTEC+JAEA*2)

*2: DOE system in helicopter of the air-rescue

2 Aug. 2011 MEXT project <Research for diffusion condition of radionuclides using aerial radiation monitoring>

After 1 year After 5 year

101

102

103

104

105

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0.1 1 10

150m 300m 450m

Cou

nt ra

te

Dose rate at 1m on the ground( µSv/h)

y = 31032 xy = 8904 xy = 2883 x

keV900

keV450

CCSI

>

>=

( ) HFCdBGGCD m1 ××−=

( )( )Flysd HHexpHF −µ=

GC: Gross count rate (cps) BG: Cosmic-ray, Body contamination (cps) Cd: Dose conversion factor (cps/µSv/h) HF: Height correction factor µ: Attenuation factor (m-1) Hsd: Standard height (approximaetly 300m) Hfly: Flight height

Attenuation factor Dose conversion factor Example of SI distribution Comparison of contamination map by SI method

Spectrum index (SI) method was applied for discrimination between radiocesium and natural radionuclides. 1

10

100

1000

10000

100000

0 500 1000 1500 2000 2500 3000

Coun

t

Gamma energy (keV)

1

10

100

1000

10000

100000

0 500 1000 1500 2000 2500 3000

Coun

t

Gamma energy (keV)

Radiocesium

K-40

U-seriesTh-series

Radiocesium that emitted into the atmosphere was deposited along Ou Mountains, Iide Mountains, Echigo Mountains, Shimotsuke Mountains and Kanto Mountains.

Based on the created map, the prediction map was made in consideration of half-life. - Area of above 0.23 uSv/h(=1.9 mSv/y) was

limited to Fukushima, Tochigi* and Gunma* after 5 years. (* mountainous region)

AMS data was compared to ground survey data (NaI survey meter). - On the whole, it was well in agreement. - In the following cases, the data of AMS

may not match ground survey data. (1) Area of a fold of hills horizontal effects (2) Cosmic ray time, season and weather

It has been understood for the region where the dose-rate is high to extend from the NPP for northwestward, and wide to Gunma Prefecture from the vicinity of Fukushima City in the direction of the southwest. This map is utilized to determine the decontamination area and estimate the variation of contamination areas.

- The radiation map which can be used for the plan of decontamination or the determination of a refuge zone was able to be made.

- The method of aerial radiological monitoring was established. * the conversion method to a dose rate * discrimination between radiocesium and natural radionuclides

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