An Approach to establish information basis of Weathered zone for the safety assessment to HLW disposal over long-term

Shimemoto, Hidenori; Wakasugi, Keiichiro; Shibata, Masahiro ; Yamaguchi, Masaaki 

In the safety assessment of radioactive waste disposal, consideration of evolution of geological environment is requested. The disposal facility can be expected to come close to ground surface, when continuous uplift and erosion for long-term is assumed. In general, geological conditions in near-surface underground is different from those in deep-underground due to weathering. Preparing for such scenario and nuclides migration analysis, information regarding weathered zone are surveyed and arranged. As a result, 37data of depth (thickness) of weathered zone were extracted. Then the data distribution and characteristics of thick weathered case was discussed. The relation between weathered zone and landform was also discussed. Categorization into four patterns of the relation are proposed, and factors which contribute to the difference of the patterns are discussed. Regarding the geological property/condition in the weathered zone, quantitative information on hydraulic and chemical conditions is limited, to the contrary data on uniaxial strength and porosity are available. For the sake of condition setting for near-surface underground in the long-term safety assessment, continuous survey of information is important.