Fukushima derived radionuclides in the ocean

Michio Aoyama Institute of Environmental Radioactivity, Fukushima University, Japan

Talk Outline 1. Global cesium distribution and mass balance - pre Fukushima 2. Fukushima cesium - mass balance of 137Cs - surface transport and subduction to the ocean interior - comparison between model simulation and observation

Public Colloquium Fukushima and the Ocean March 14, 2014, 15:30 to 17:30

Tokyo University of Marine Science and Technology, Hakuyo Hall

Decay corrected accumulative fallout as of 1970

In NH, 765±79 PBq 1970 In the North Pacific Ocean 290±30 PBq 1970 69±7 PBq 2011 Chernobyl accident 1986 85 PBq 137Cs was released to the environment

Monthly fallout of 137Cs and 90Sr since 1957 at Tokyo/Tsukuba

Michio Aoyama, Katsumi Hirose and Yasuhito Igarashi, Re-construction and updating our understanding on the global weapons tests 137Cs fallout, Journal of Environmental Monitoring, 8, 431-438, 2006.

60 years record of 137Cs and 90Sr activity in surface water since 1953

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

100,000,000

2011/3/10 2011/6/18 2011/9/26 2012/1/4 2012/4/13 2012/7/22 2012/10/30 2013/2/7 2013/5/18 2013/8/26 2013/12/4

137 C

s act

ivity

(Bq/

m3 )

5,6 dicharge

South discharge

137Cs activity close to FNPP1 4

Reliable data of 137Cs activity close to FNPP1

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1

10

100

1000

10000

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1000000

10000000

100000000

2011/3/1 2011/6/9 2011/9/17 2011/12/26 2012/4/4 2012/7/13 2012/10/21 2013/1/29 2013/5/9 2013/8/17 2013/11/25 2014/3/5

5,6 discharge South discharge 5,6 高精度 South 高精度

A pathway of weapons tests derived 137Cs in the North Pacific Ocean,

tracer of sea water movement

Fig. S2 Possible pathway of 137Cs in the Pacific Ocean based on 3-D observations of 137Cs in 2000s (Aoyama et al., 2013)

We can expect that Fukushima origin radiocaesium should go same pathway

Pathways of Fukushima derived radionuclides to the Ocean

• Atmospheric deposition • Direct release • Groundwater discharge • River runoff

TEPCO Press release

137Cs : 1.8E+12 Bq/m3

Simulated atmospheric deposition of 137Cs (Bq m-2) (by Masingar II of MRI) (Aoyama et al., in preparation)

7

Boiling Water Reactor Systems "Nuclear Reactor Concepts" Workshop Manual, U.S. NRC

3.6±0.7 PBq to the ocea (Tsumune et al., 2013)

14–17 PBq to the atmosphere

700 PBq was in the three core 140 PBq in stagnant water (Nishihara et al.,, 2011) (Nishihara et al., 2011)

140 PBq in stagnant water

12 - 15 PBq to the ocean

137Cs mass balance

More than 99% of released radioaesium to the ocean was transported offshore, then to the ocean interior

17-30 GBq day-1

Revised estimation

R/V Mirai

NYK AQUARIUS

凌風丸

R/V Hakuho Maru

NYK Heijin

Sampling locations during the period from March 2011 to Oct. 2012

(Aoyama et al., BG 10 3067-3078, 2013)

Apr-Jun 2011

Jul-Sep 2011

Oct-Dec 2011

Jan-Mar 2012

Surface speed of contaminated water ca. 7 km day-1

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0 5 10 15 20 250

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,

KS1109-3101

RF1205-4418

134Cs / Bq m-3

Dep

th /

m Oxygen maximumSigma0=26.3

Year 2011 2012Month 10 6

Bq m-2 Bq m-2

134Csinventory 2710+-210 2350+-190

0 - 200 m 2150 520

Deeper than200 m 520 1830

Oct. 2011

Over time, Cs moves east and subducted in the ocean interior

June 2012

Bq m-3

137Cs cross section along 165 ºE in June 2012

Start of travel into ocean interior N

Possible pathway of Fukushima derived radionuclides in the North Pacific Ocean

Fig. S2 Possible pathway of 137Cs in the Pacific Ocean

We found start of travel of Fukushima derived radioactivity in the ocean interior.

Summary of budget of 137Cs for pre- and after the Fukushima accident

Main portion of Fukushima derived radioactivity already subducted into the ocean interior and is moving to southwest ward.