Survey of estimation method of washout effect of radioactive - PowerPoint PPT Presentation

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 Dr. M. Yagawa Dr. M. Hort leader (President, Nuclear Safety (Met Office) Research Association: NSRA) Research Dr. R. Ohba (NSRA) Joanne Brown (HPA) members Prof. Y. Ishikawa (Kyoto Univ.) Justin Smith (HPA) Prof. H. Yamazawa (Nagoya Julian Hunt (House of Lord) Univ.) et al. et al. Tasks 1) Collection of Measurement 1) Joint technical meeting data in Fukushima area (1 st &2 nd March 2012, in HPA) 2) Analysis of radiation dose 1) Information on rain deposition and rain radar data and washout effect from soil 3) Making of a final report Health Protection Agency （ HPA) Supported Japan Science and Technology organization Agency(JST) , additionally Denmark Technical University (RISO)

Example of the washout effect on radiation dose by rainfall Relation between radiation dose and raifall amount 3 200 Rainfall amount Radiation dose Significant effect 2.5 Not significant 150 Radiation dose(microSv/hr) effect 2 Rainfall amount(mm/day) 1.5 100 1 50 0.5 0 0 2011/3/11 2011/4/10 2011/5/10 2011/6/9 2011/7/9 2011/8/8 2011/9/7 2011/10/7 2011/11/6 2011/12/6 2012/1/5 Date Observed data in Fukushima city

Time history of monitoring data 1 st release and dry a) March/2011 deposition Monitoring post: D 5000 100 Red：gamma radiation dose 3rd release and wet Blue： Precipitaion 4000 80 deposition Precipitation（mm/hour） Radiation dose（nGy/h) Radioactive decay 3000 60 of I131 2000 40 1000 20 0 0 3/1 3/2 3/3 3/4 3/5 3/6 3/7 3/8 3/93/10 3/11 3/12 3/13 3/14 3/15 3/16 3/17 3/18 3/19 3/20 3/21 3/22 3/23 3/24 3/25 3/26 3/27 3/28 3/29 3/30 3/31 b) September/2011 Monitoring post: D 500 100 Red：gamma radiation dose Blue：Precipitation 400 80 Radiation dose（nGy/h) Precipitaion（mm/hour） 300 60 200 40 100 20 0 0 9/1 9/2 9/3 9/4 9/5 9/6 9/7 9/8 9/99/10 9/11 9/12 9/13 9/14 9/15 9/16 9/17 9/18 9/19 9/20 9/21 9/22 9/23 9/24 9/25 9/26 9/27 9/28 9/29 9/30

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

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 Formula Corr. Coef. Half decay period (Annual ave.) Wet 36 5.14Exp(- -0.991 15.9 years 0.044t) Dry 36 3.89Exp(- -0.977 18.4 years 0.038t) 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 Contribution Total half decay period (year) materials ratio 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 2012 2013 2014 (present Dec Mar Sep Mar dose level) Preparation 10 to (12000ha) to live 5 to 20mSv/y 1 to 10mSv/y (<20mSv/y) 5mSv/y (7200ha) Limitation to live(20 to 50mSv/y) Not to live (9300ha) Case study to check the method and its effect (>50mSv/y) 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

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 Emergency Protection Zone Additional evacuation zone

Relation between radiation dose and rainfall amount(1) 50mm/day 150mm/day

Relation between radiation dose and rainfall amount(2:Fukushima city, more than 50km distance) Relation between radiation dose and raifall amount 3 200 Rainfall amount Radiation dose 2.5 150 Radiation dose(microSv/hr) 2 Rainfall amount(mm/day) 1.5 100 1 50 0.5 0 0 2011/3/11 2011/4/10 2011/5/10 2011/6/9 2011/7/9 2011/8/8 2011/9/7 2011/10/7 2011/11/6 2011/12/6 2012/1/5 Date

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 Stirring Comm. Main contrcutor ： Tokyo university ・ Governments (1)Source Term Estimation & ・ Experts (3) Long term exposure model International corporate organizations Sub-constructor: Mitsubishi Heavy (1) US-NRC Ind. (2) US-NCAR (2) mobile monitoring (3) US-Laurence Livermore National Lab. (4) UK- Met office (5) Demark Institute of Technology (RISO) Corporate organizations •Technical discussion by meetings ・ Japan Atomic Energy Agency ・ Japan Agency ｆ or Marine Science & Tech. •Revision program of Regulatory rule ・ Nagoya university •Improvement of Emergency Response system •Japan nuclear Power company

(3)Advancement of long term exposure model Target ： to improve the ERMIN(European Model for Inhabited areas) code Output data Input data ・ Long term exposure ・ Ground Surface condition （ External and internal ） ・ Soil contamination ・ Effect, cost and garbage amount ・ De-conatmination measures of de-contamination Tasks of 2012 Analysis of re-suspension coeff. ・ Improve re-suspension model ・ Air concentration ・ Soil contamination ・ Improve Weathering model ・ Installment of Japanese database 16 Weathering factor(washout effect et al. ）

Map of ground surface categories Tasks of 2012: Installment of Japanese GIS database for ground surface categories into ERMIN code 17