Numerical reconstruction of high dose rate zones due to the Fukushima Dai-ichi Nuclear Power Plant accident

Katata, Genki; Terada, Hiroaki   ; Nagai, Haruyasu  ; Chino, Masamichi

For future planning of preventive measures against possible nuclear accident, it is important to understand how the high dose rate zones was created in the northwest area of the plant during the Fukushima Dai-ichi nuclear reactor accident. Because most of the observation equipment did not work due to the severe earthquakes, temporal information of release rates of radionuclides into the atmosphere and environmental monitoring data were limited to analyze the movements of radioactive plume in a significant release of radionuclides on 15 March, 2011. Here we reconstructed the atmospheric dispersion of radionuclides during the period from 15 to 16 March using computer-based nuclear emergency response system, WSPEEDI-II. We found that high dose rate zones were created by a significant deposition of radionuclides discharged during the afternoon on 15 March and two factors, i.e., rainfall and topography, strongly affected the distribution of surface deposition.