2014 Volume 120 Issue 10 Pages 345-359
The basic concept of the geological disposal of high-level radioactive waste (HLW) in Japan relies on the construction of a multibarrier system in a stable geological environment. The requirements for the geological environment are long-term stability, favorable setting, and the presence of a natural barrier system. This study uses information on uranium deposits as an analogue for a stable and reducing environment, and for the function as a natural barrier system within geological environments throughout the Japanese islands.
Information on the distribution and mode of occurrence of uranium deposits was compiled from published data. Deposits occur in various geological settings in Japan. In the Japanese uranium deposits, uranium is mostly sorbed onto clay, limonite, chalcanthite, and secondary bismuth minerals in crystalline rock, and onto clay, limonite, carbonaceous matter, pyrite, and biotite in sedimentary rock. The occurrence of secondary minerals indicates the formation of uranium-bearing minerals in the oxidization zone.
The distribution of uranium deposits suggests that geological environments suitable for geological isolation are widely distributed in the Japanese islands, despite their location in a tectonically active area. The mode of occurrence of the uranium deposits indicates that formation of uranium-bearing minerals as well as sorption is expected in both sedimentary and crystalline rocks.
Geological environments associated with uranium deposits are considered favorable for HLW disposal, because uranium is considered to be a natural analogue of the radionuclides in HLW in terms of similarity in chemical behavior. Thus, the presence of a natural barrier would be expected in various geological environments in the Japanese islands, because mineralization and sorption act as barriers that retard the migration of radionuclides in HLW, and because the uranium deposits are located in a range of rock types.
