抄録
The geological environment has two main functions in terms of ensuring the safety of geological disposal of high-level radioactive waste. One relates to the fundamental long-term stability of the site and the other to the properties of the host rock formations and groundwaters which facilitate the emplacement of the engineered barrier system and act as a natural barrier. In this connection, the feasibility of selecting a geological environment in Japan which is appropriate for geological disposal was discussed, based on findings obtained from case studies and field measurements.
Considering long-term stability of the site, it is important to understand the effects and spatial distributions of the natural phenomena such as fault movement, volcanic activity, uplift/denudation and climatic/sea-level changes. Fault movement and volcanic activity are relatively localized phenomena, and can be avoided by considering only areas that are sufficiently remote from existing volcanoes and major active faults for these phenomena to have a negligible probability of causing significant effects. Uplift/denudation and climatic/sea-level changes are gradual phenomena and are more ubiquitous. It is, nevertheless, possible to estimate future trends by extrapolating the past changes into the future, and then to identify areas that may not be affected significantly by such phenomena.
Considering the properties of the host rocks and groundwaters, it can be understood, from the presently available data, that deep groundwater in Japan generally flows slowly and its chemistry is in a reduced state. The data also suggest that deep rock masses, where the ground temperature is acceptably low and the rock pressure is almost homogeneous, are widely located throughout Japan.
Based on the examination of the geological environment in Japan, it is possible to discuss the requirements for the geological environment to be considered and the investigations to be performed during the site selection procedure.
