Dr. Ryohji Ohba (Nuclear Safety Research Association )

Transcription

1 Survey of estimation method for amount of radioactive materials emitted from nuclear power station during severe accident Dr. Ryohji Ohba (Nuclear Safety Research Association ) Funded by Ministry of Education and Science (MEXT) Contracted by Japan Science and Technology Agency (JST) Conducted by Nuclear Safety Research Association (NSRA)

2 Actual difficulties of nuclear accident Unsteady wind field Cloud shine +ground shine +Sky shine Wet & Dry depositions Multiple radioactive materials released Limited data observed Sky shine Gamma counter ray Cloud shine Insulation cover Ground shine

3 Flow Chart of Source Term Estimation (STE) Observation Simulation model Uncertainty of STE Meteorological data (Air flow) Assumed source intensity Availability and Reliability of observed data Air flow condition Concentration STE Dispersion model Turbulent diffusivity Meteorological data (Precipitation) Deposition model Deposition velocity Particle diameter Radiation dose 1)Cloud-shine 2)Ground-shine 3)Sky-shine STE Radiation model Main object of this study Content of radioactive materials Distribution of radioactive materials on the ground surface

4 Examples of STE methods applicable for nuclear accident Organization name (Code) Observed data Simulated data Release condition STE METHOD JAEA (SPEEDI) Dust sampler Radiation dose Concentration in the air Cloud, ground & sky-shines Quasisteady with time during 30 min. Comparison between simulation & observation MHI (MEASURES) Radiation dose Cloud-shine Unsteady with time Variation technique RISO (RIMPUFF) LLNL (NRAC) Radiation dose Cloud-shine? Kalman filter

5 Measurement of radiation dose excluding ground and sky shines 1. Without shield (conventional method) Gamma-ray counter 1m height 2. With shield (Improved method) 2-a) Lower shield Plumb block Gamma-ray counter 2-b) Upper shield Plumb block Gamma-ray counter 1m height 1m height 2-c) Lower shield +Check source Check source (Sc137) Gamma-ray counter 1m height in Tokai nuclear power station

6 Photos of measurement condition 2-a) Lower shield 2-c) Lower shield+check source 2-b) Upper shield

7 Observation points in Tokai nuclear power station Open space (storage yard) Inside forest (near monitoring point) Beside building (entrance space) observation in

8 Radiation dose(ngy/h) a) March/2011 Time history of monitoring data Red:gamma radiation dose Blue: Precipitaion 1 st peak and dry deposition Monitoring post: D 3rd peak and wet deposition Radioactive decay of I Precipitation(mm/hour) Radiation dose(ngy/h) /1 3/23/33/4 3/53/6 3/73/83/93/103/113/123/13/143/153/163/173/183/193/203/213/223/2 3/243/253/263/273/283/293/303/31 b) September/2011 Red:gamma radiation dose Blue:Precipitation Monitoring post: D Precipitaion(mm/hour) 0 9/1 9/2 9/3 9/4 9/5 9/6 9/7 9/8 9/99/109/119/129/139/149/159/169/179/189/199/209/219/229/239/249/259/269/279/289/2 9/30 0

9 Observed data (μsv/h) Shield condition Beside building Open space Inside forest Notes Case1 (No shield) Case2-a (Lower shield) Case2-b (Upper shield) Case2-c (+ 1Check source) Case2-c (+ 4Check sources) observation in Tokai,

10 The emergency response system of the government, named SPEEDI could not be well operated at the Fukushima accident, due to the lack of data on source intensity. 1. Most of radioactive material was released from broken space of the reactor building, not the stack, instantaneously at the time of explosion on 15 th March 2. Monitoring and network systems stopped after the earthquake, due to the shutdown of electric power Necessary research subject Technique for Identification of source intensity from 1Data of radiation dose measured by mobile gamma ray counter, including the effect of the ground shine due to radioactive materials deposited on the ground surface (real time data) 2Data of concentration measured by dust sampler ( time averaged data)

11 Draft plan of the proposal to Japan Science and Technology Agency items Japan USA Project leader Research members Dr. M. Yagawa (President, Nuclear Safety Research Association: NSRA) Prof. Shinsuke Kato (Tokyo Univ.) Prof. Hiromi Yamazawa (Nagoya Univ.) Dr. Haruyasu Nagai(JAEA) Dr. R. Ohba (NSRA) et al. Tasks 1) Analysis of data on radiation dose of gamma ray and dust sampler 3) Making of a final report Dr. Paul Bieringer (National Center for Atmospheric Research ) Dr. Steve Hanna (Harvard Univ.) Luca Delle Monache Jeff Copeland George Bieberbach Ian Sykes 1) Joint technical meeting 2) Information on source term estimation techniques Sponsor Japan Science and Technology Agency (JST) and Ministry of Education and Science DTRA

12 Information on Fukushima Accident(1) Airplane measuring data by US/DOE (color) and calculated results by Japan/SPEEDI (contour) (airplane data: converted from measured radiation data at high level to surface, green color is flight route) (source intensity of SPEEDI is estimated from dust sampling data near the power station)

13 Information on Fukushima Accident(2) Time history of radiation dose indicates the explosive Emmitt ion at 15,16,17th)

14 Information on Fukushima Accident(3) Measured data of radiation dose by car (hot spot is observed beyond 30km)

15 Information on Fukushima Accident(4) 1000 測定点 31 測定点 32 線量率 (μsv/hr) 測定点 33 測定点 36 測定点 46 測定点 61 測定点 62 測定点 79 Hot spot 1 3 月 8 3 月 18 3 月 28 4 月 7 4 月 17 4 月 27 5 月 7 5 月 17 Measured data of radiation dose near ground surface Change from effect of I131 to Cs137 5 月 27 radiation dose is influence mainly by deposition material, not cloud 測定点 81 測定点 83 半減期 (8 :I131) の減衰率 近似式 (I 年 :Cs137) Additional evacuation zone beyond 30km, more than100msv/year(11μsv/hr)