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Hirouchi, Jun; Nishizawa, Yukiyasu*; Urabe, Yoshimi*; Shimada, Kazumasa; Sanada, Yukihisa; Munakata, Masahiro
no journal, ,
After the Fukushima Dai-ichi Nuclear Power Station (NPS) accident, a series of aerial radiation monitoring (ARM) was conducted as a national project to map the ground surface distribution of radiocesium. The influence of 
-rays from natural nuclides, especially the radon progenies (Pb-214 and Bi-214) should be excluded from the ARM measurement data to accurately estimate deposition of artificial radionuclides. Therefore, the aim of this study is to develop a method for discriminating the influence of the radon progenies in air from the measurement data. The discrimination method was applied to the ARM data around Sendai NPS and we compared the dose rate at a height of 1 m above the ground measured by NaI survey meter with the ARM data. The coefficient of determination (R2) and normalized mean square error (NMSE) were improved by applying the method, showing that the validity of the method was confirmed.
Terada, Hiroaki; Nagai, Haruyasu
no journal, ,
For the assessment of the radiological doses to the public due to the atmospheric discharge of radioactive materials during the Fukushima Daiichi Nuclear Power Station accident, the spatiotemporal distribution of radioactive materials in the environment are reconstructed by atmospheric dispersion simulation with the improved WSPEEDI. In this study, the influence of chemical form of 
I (particle, inorganic and organic gas) in source term on the simulated results was analyzed to assess the uncertainty of the simulation. From the sensitivity test with the chemical form composition, surface deposition distribution of I was influenced according to the property of the chemical forms to deposition processes, whereas time-integrated air concentration was less influenced. From the comparison with the measurement, the surface deposition simulated with the source term in Katata et al. (2015) had a good reproducibility compared with those with extreme gas to particle ratios.
Mori, Airi; Takahara, Shogo; Sanada, Yukihisa; Munakata, Masahiro
no journal, ,
Inhabitants residing in part of Fukushima Prefecture are now exposed to radiation due to radioactive materials released by the Fukushima Daiichi Nuclear Power Station accident. To mitigate the radiation doses, an additional dose of 1 mSv/y was adopted as a long-term dosimetric target, and some municipalities were designated as the evacuation area. The evacuation area has been narrowing along with the decreasing of air dose rate. It was decided that evacuation orders in parts of 5 municipalities are lifted in 2016-2017. Radiation dose will be an important information for the inhabitants to make a decision on whether to return or not. Many inhabitants are concerned about radiation doses, particularly doses to their children. In this study, we developed the dose assessment model for children to estimate radiation doses to children that returned to their hometown. As a result of our calculation, it was revealed that the doses will not cause any health effect but continual efforts to achieve the dosimetric target of 1 mSv/y are necessary.
Pratama, M. A.; Takahara, Shogo; Munakata, Masahiro; Homma, Toshimitsu; Yoneda, Minoru*
no journal, ,
Kobayashi, Takuya; Kawamura, Hideyuki; Fujii, Katsuji*; Kamidaira, Yuki
no journal, ,
The Fukushima Dai-ichi Nuclear Power Station (FNPS1) accident in Japan in March 2011 led to the release of large amounts of radionuclides into the atmosphere as well as direct discharges into the ocean. Various environmental assessments have been performed by many research groups using marine dispersion simulations after the FNPS1 accident. It was recognized from these woks that the risk of radionuclide release from nuclear facilities to the environment was very high and the establishment of emergency ocean dispersion forecasting systems was necessary. Then, the Japan Atomic Energy Agency (JAEA) has developed the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) to immediately predict the radionuclide migration for a nuclear accident in ocean around Japan, by integrating previous study results. In this study, structure, performance test results, and utilization of the system are described.
Kinase, Sakae; Honda, Fumiya*
no journal, ,