Biosphere modeling with climate changes for safety assessment of high-level radioactive waste geological isolation

Kato, Tomoko ; not registered; Suzuki, Yuji*; not registered ; Ishiguro, Katsuhiko; Ikeda, Takao*; Richard, L.*

In the safety assessment of a high-level radioactive waste (HLW) disposal system, it is required to estimate radiological impacts on future human beings arising from potential radionuclide releases from a deep repository into the surface environment. In order to estimate the impacts, a biosphere model is developed by reasonably assuming radionuclide migration processes in the surface environment and relevant human lifestyles. Releases from the repository might not occur for many thousands of years after disposal. Over such timescales, it is anticipated that the considerable climatic change, for example, induced by the next glaciation period expected to occur in around ten thousand years from now, will have a significant influence on the near surface environment and associated human lifestyles. In case of taking these evolution effects into account in modeling, it is reasonable to develop several alternative models on biosphere evolution systems consistent with possible future conditions affected by expected climatic changes. In this study, alternative biosphere models were developed taking effects of possible climatie change into account. In the modeling, different climatic states existing in the world from the present climate condition in Japan are utilized as an analogy. Estimation of net effects of the climatic change on biosphere system was made by comparing these alternative biosphere models with a constant biosphere model consistent with the present climatic state through flux to dose conversion factors derived from each one.