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Distribution of radionuclides in surface seawater obtained by an aerial radiological survey
Authors:Yayoi Inomata  Michio Aoyama  Katsumi Hirose  Yukihisa Sanada  Tatsuo Torii  Takaki Tsubono
Affiliation:1. Asia Center for Air Pollution Research, 1182, Sowa, Nishiku, Niigata, Niigata 951-2144, Japaninomata@acap.asia;3. Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki, 305-0052, Japan;4. Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, 101-8554, Japan;5. Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda-ku, Tokyo 100-8577, Japan;6. Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan
Abstract:We investigated the distribution in seawater of anthropogenic radionuclides from the Fukushima Daiichi Nuclear Power Plant (FNPP1) as preliminary attempt using a rapid aerial radiological survey performed by the U.S. Department of Energy National Nuclear Security Administration on 18 April 2011. We found strong correlations between in-situ activities of 131I, 134Cs, and 137Cs measured in surface seawater samples and gamma-ray peak count rates determined by the aerial survey (correlation coefficients were 0.89 for 131I, 0.96 for134Cs, and 0.92 for137Cs). The offshore area of high radionuclide activity extended south and southeast from the FNPP1. The maximum activities of 131I, 134Cs, and 137Cs were 329, 650, and 599 Bq L?1, respectively. The 131I/137Cs ratio in surface water of the high-activity area ranged from 0.6 to 0.7. Considering the radioactive decay of 131I (half-life 8.02 d), we determined that the radionuclides in this area were directly released from FNPP1 to the ocean. We confirm that aerial radiological surveys can be effective for investigating the surface distribution of anthropogenic radionuclides in seawater. Our model reproduced the distribution pattern of radionuclides derived from the FNPP1, although results simulated by a regional ocean model were underestimated.
Keywords:aerial radiological survey  gamma-ray count rates  radionuclides  surface seawater  nuclear accidents  model simulation
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