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Oral presentation

Development of dose evaluation method for confirmation of completion of decommissioning of nuclear facilties, 2; Development of dose evauation method caused by surface soil contamination after site release

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

no journal, ,

For development of technical foundation to confirm the completion of the decommissioning of nuclear facilities, JAEA is developing the methodology to evaluate the dose in considering radionuclides migration by not only groundwater migration but also surface water migration and surface soil migration. We studied estimating methods for radionuclide migration between the surface water and surface contaminated soil, changes of radionuclide distribution, and direct outflow of radionuclides to the sea. In addition, preliminary analysis of the surface water migration and soil migration based on the topography and rainfall conditions is performed by using a general-purpose water and soil runoff evaluation code. The methodology will be applied to evaluate the dose by using the out put of the surface water migration and soil migration.

Oral presentation

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

no journal, ,

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 ( $^{137}$ Cs) migration during 1 year was assessed in virtual site which has horizontal uniform $^{137}$ Cs concentration in surface soil. $^{137}$ 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.