Development of a method of safety assessment for geological disposal considering long-term evolution of geological and topographical environment by uplift and erosion

This study provides a method of safety assessment for the geological disposal of HLW to evaluate the effects of uplift and erosion, which are widespread phenomena in Japan. This safety assessment method can account for different uplift and erosion rates while evaluating the repository depth and the time required for a repository to reach the weathered zone and the ground surface, and also considers the number of waste packages eroded on the basis of a landform evolution model. The landform evolution model uses altitude dispersion, which expresses the deviation of altitude from the topographical relief. The results of a trial analysis show that the maximum dose in the base case (uplift rate: 0.3 mm/y) is less than the target criterion suggested by an international organization even if the repository is close to the ground surface. Furthermore, the maximum dose can be reduced if the dispersion of the timing for the waste packages to reach the weathered zone due to heterogeneity in the altitude of the bottom of the weathered zone is considered. This method is applicable to evaluate the safety of geological disposal based on realistic uplift and erosion rates while considering the evolution of the topographical relief, and to quantify the safety margin and robustness of a geological disposal system. (author)