The Long-Term Stability of Geological Environments in the Various Rock Types in Japan From the Perspective of Uranium Mineralization

Long-term stability of the geological environment is one of the important keys for deep geological disposal of high-level radioactive waste in the Japanese Islands due to their location in a tectonically active island-arc. Uranium occurrences in Japan have been subjected to many geological processes inherent to the island-arc setting. Geological environments associated with uranium mineralization are considered favorable for HLW disposal, because uranium mineralization is considered a natural analogue of the radionuclides in HLW. Studies on the long-term stability of the uranium mineralization in Japan can be instructive as these could provide useful information on the long-term stability of the geological environment. Information on host rock and mode of occurrence of uranium mineralization was compiled from published data. The mineralization occurs in these types of deposits, i.e., sedimentary formations, association with metallic ore mineralization of magmatic origin and stratiform manganese mineralization, pegmatite, and alluvial placer deposit. The mineralization occurs in various geological settings in Japan. This fact suggests that geological environments suitable for geological isolation are widely distributed in the Japanese Islands, despite their location in a geologically active area. This study will support building confidence in HLW disposal in the Japanese Islands.