Survey of estimation method of washout effect of radioactive materials from soil by rainfall

Dr. Ryohji Ohba (Japan: Nuclear Safety Research Association )

Today’s reports 1. Summary of J-rapid 2011 program 2. Introduction of the new MEXT 2012-2014 project

Research Consortium

items Japan UK Project leader

Dr. M. Yagawa (President, Nuclear Safety Research Association: NSRA)

Dr. M. Hort (Met Office)

Research members

Dr. R. Ohba (NSRA) Prof. Y. Ishikawa (Kyoto Univ.) Prof. H. Yamazawa (Nagoya Univ.) et al.

Joanne Brown (HPA) Justin Smith (HPA) Julian Hunt (House of Lord) et al.

Tasks 1) Collection of Measurement data in Fukushima area

2) Analysis of radiation dose and rain radar data 3) Making of a final report

1) Joint technical meeting (1st &2nd March 2012, in HPA) 1) Information on rain deposition

and washout effect from soil

Supported organization

Japan Science and Technology Agency(JST)

Health Protection Agency（HPA) , additionally Denmark Technical University (RISO)

Example of the washout effect on radiation dose by rainfall

Relation between radiation dose and raifall amount

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Date

Radia

tion d

ose

(mic

roS

v/hr)

0

50

100

150

200

Rain

fall

am

ount(

mm

/day)

Rainfall amount

Radiation dose

Observed data in Fukushima city

Not significant effect

Significant effect

Time history of monitoring data

Monitoring post: D

0

1000

2000

3000

4000

5000

3/1 3/23/33/4 3/53/6 3/73/83/93/103/113/123/133/143/153/163/173/183/193/203/213/223/233/243/253/263/273/283/293/303/31

Radia

tion

dose

（nG

y/h)

0

20

40

60

80

100

Prec

ipita

tion（

mm

/hou

r）

Red：gamma radiation dose

Blue： Precipitaion

Monitoring post: D

0

100

200

300

400

500

9/1 9/2 9/3 9/4 9/5 9/6 9/7 9/8 9/99/109/119/129/139/149/159/169/179/189/199/209/219/229/239/249/259/269/279/289/299/30

Radia

tion

dose

（nG

y/h)

0

20

40

60

80

100

Prec

ipita

ion（

mm

/hou

r）

Red：gamma radiation dose

Blue：Precipitation

a) March/2011

b) September/2011

1st release and dry deposition

3rd release and wet deposition

Radioactive decay of I131

Official documents of Nuclear Safety Committee in Japan(2011,Aug.24)

1. To consider mainly the effect of Cs134 and Cs137 for the decontamination

2. To consider the weathering factor in addition to the decay of radioactivity

http://www.nsc.go.jp/anzen/shidai/genan2011/genan064/index.html）

Ref. (1) Komamura et al., Report of Agriculture Environment Technology Research Institute (in japanese), (2006)

(2) Golikov et al., Estimation of external gamma radiation doses to the population after Chernobyl accident, The Chernobyl Papers, Vol.1 (1993)

Ref. (1) Komamura et al. • Empirical formula from the concentration data

of Cs137 in wet and dry farm land of Japan • Total half decay period: 18.4 years (including the radioactive decay period) • Weathering half decay period : 47.2 years

Farmland No. of data (Annual ave.)

Formula Corr. Coef. Half decay period

Wet 36 5.14Exp(-0.044t)

-0.991 15.9 years

Dry 36 3.89Exp(-0.038t)

-0.977 18.4 years

http://www.nsc.go.jp/anzen/shidai/genan2011/genan064/index.html）

Ref. (2) Golikov et al

• Empirical formula from the radiation data of Cs 134 and Cs137 after Chernobyl accident

• Total half decay period of Cs134: 1.8 years • Total half decay period of Cs134: 15.2 years (including the radioactive decay time) Radioactive materials

Contribution ratio

Total half decay period (year) 10% Value Average 95% Value

Cs134 89% 1.5 1.8 2.3

Cs137 11% 10.2 15.2 19.7

http://www.nsc.go.jp/anzen/shidai/genan2011/genan064/index.html）

Official plan of decontamination (2012.Jan. 27)

Area (present

dose level)

2012 2013 2014

Dec Mar Sep Mar

Preparation to live (<20mSv/y) Limitation to live(20 to 50mSv/y)

Not to live (>50mSv/y)

10 to 20mSv/y 5 to

10mSv/y 1 to 5mSv/y

Case study to check the method and its effect

Main method of decontamination is to cut off the surface soil by appr. 5cm.

Target level: less than 10mSv/y, including the weathering factor of appr. -10%/2years

(12000ha)

(7200ha)

(9300ha)

Difficulties of decontamination •Preparation of garbage area

•Burning of tree and leaves

•Agreement of land owner

•Fund

•Man-power

•Regulatory rule of radiation

•Pollution by ground water

And so on

No available data

Additional evacuation zone

Emergency Protection Zone

Relation between radiation dose and rainfall amount(1)

150mm/day 50mm/day

Relation between radiation dose and rainfall amount(2:Fukushima city, more than 50km distance)

Relation between radiation dose and raifall amount

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0.5

1

1.5

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2.5

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2011

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1

2011

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2011

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0

2011

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2011

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2011

/8/8

2011

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2011

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2011

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6

2011

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6

2012

/1/5

Date

Radia

tion d

ose

(mic

roS

v/hr)

0

50

100

150

200

Rain

fall

am

ount(

mm

/day)

Rainfall amount

Radiation dose

Ref(1): Weathering of rdiocaesium contamination on urban streets, walls and roofs

(K.G. Andersson et al., J. of Environmental radioactivity, 62(2002)

• Observed data in Denmark after Chernobyl accident

Ref(2):Lisbeth Warming, ”Weathering and decontamination of radioactivity deposited on

concrete surfaces”,RISO-M-2473(1984)

MEXT 2012-2014 project

Advancement of Source Term Estimation model at early stage, and exposure model

at intermediate stage for severe nuclear accident

Project leader: Prof. Shinsuke Kato (Tokyo University )

Co-project leader: Dr. Ryohji Ohba (Mitsubishi Heavy Industries)

• Funded by Ministry of Education, Science, Culture, Sports and Technology (MEXT)

• Contracted by Japan Science and Technology Agency (JST)

Research Consortium Main contrcutor：Tokyo university

(1)Source Term Estimation &

(3) Long term exposure model

Sub-constructor: Mitsubishi Heavy Ind.

(2) mobile monitoring

International corporate organizations

(1) US-NRC

(2) US-NCAR

(3) US-Laurence Livermore National Lab.

(4) UK- Met office

(5) Demark Institute of Technology (RISO)

Stirring Comm.

・Governments

・Experts

Corporate organizations

・Japan Atomic Energy Agency

・Japan Agency ｆor Marine Science & Tech.

・Nagoya university

•Japan nuclear Power company

•Revision program of Regulatory rule

•Improvement of Emergency Response system

•Technical discussion by meetings

・Air concentration ・Soil contamination

Analysis of re-suspension coeff.

(3)Advancement of long term exposure model Target：to improve the ERMIN(European Model for Inhabited areas) code

Input data

・Ground Surface condition

・Soil contamination

・De-conatmination measures

Output data

・Long term exposure

（External and internal）

・Effect, cost and garbage amount

of de-contamination

Tasks of 2012

・Improve re-suspension model

・Improve Weathering model

・Installment of Japanese database

Weathering factor(washout effect et al.）

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Map of ground surface categories

Tasks of 2012: Installment of Japanese GIS database for ground surface categories into ERMIN code