Development of dose evaluation method for confirmation of completion of decommissioning, 2; Evaluation method of radioactivity distribution change for safety assessment

Miwa, Kazuji ; Namekawa, Masakazu*; Shimada, Taro ; Takeda, Seiji 

In the public dose assessment in decommissioning process, remaining radionuclide in surface soil is the main source. The radionuclide in the surface soil migrates on the ground surface with a surface runoff and soil erosion caused by rain. Therefore, we have developed a dose estimation code system in considering radionuclide migration by surface runoff and soil erosion. In the radionuclide migration, the vertical radionuclide profile and the radionuclide concentration in each soil particle size are reflected. Using this dose estimation code system, Cs-137 (Cs) migration during 1 year was assessed in virtual site which has horizontal uniform Cs concentration in surface soil. Cs accumulation occurs in a depression area by radionuclide migration, and raise the air dose rate in the depression area. This result corresponds to the trend of high air dose rate in a depression area observed after Fukushima Daiichi Nuclear Plant accident.