The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 120, Issue 10
Displaying 1-5 of 5 articles from this issue
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SPECIAL ISSUE Deep geological disposal of radioactive waste and geological sciences: Geological environment and its barrier functions
Review
  • Ferric oxyhydroxide in underground geological environments and high-level radioactive waste disposal: Analysis of influence on nuclide migration scenarios
    Hidekazu Yoshida, Koshi Yamamoto
    2014 Volume 120 Issue 10 Pages 327-343
    Published: October 15, 2014
    Released on J-STAGE: January 15, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0038
    JOURNAL FREE ACCESS
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    Ferric oxyhydroxide in subsurface geological environments may influence the long-term natural barrier function with respect to nuclide migration at potential sites of disposal of high-level radioactive wastes (HLW). Here, samples of ferric oxyhydroxide from the subsurface environment of Japan were studied in order to (1) evaluate suitable repository depths that will need to be characterized; and (2) assess how ferric oxyhydroxide will need to be treated with respect to nuclide migration at a future repository site. Analysis of the ferric oxyhydroxide provides the following insights into site characterization and the rock barrier function: (1) ferric oxyhydroxide formed along a connective fracture network that extends from the surface to deep levels, but there is a depth limit of oxidation due to geochemical buffering by redox reactions; (2) early-stage ferric oxyhydroxide remains stable even after the environment returns to reducing conditions; and (3) ferric oxyhydroxide produced in the rock matrix can contribute to retarding nuclide migration by sorbing radionuclides and clogging micropores. The results show that ferric oxyhydroxide formed in the geological environment may influence the geosphere barrier function in and around subsurface repository caverns for the disposal of HLW in Japan.
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  • Long-term stability and function as a natural barrier of various geological environments in Japan from the perspective of uranium deposits
    Eiji Sasao
    2014 Volume 120 Issue 10 Pages 345-359
    Published: October 15, 2014
    Released on J-STAGE: January 15, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0033
    JOURNAL FREE ACCESS
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    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.
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Article
  • Geochemical and Mineralogical Characterizations of Bentonite interacted with Alkaline Fluids generating in Zambales Ophiolite, Northwestern Luzons, Philippines
    Naoki Fujii, Minoru Yamakawa, Naotatsu Shikazono, Tsutomu Sato
    2014 Volume 120 Issue 10 Pages 361-375
    Published: October 15, 2014
    Released on J-STAGE: January 15, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0036
    JOURNAL FREE ACCESS
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    The Saile bentonite-zeolite mine is located in the west-central portion of Luzon Island in the northern Philippines, close to the Zambales ophiolite. The mine and surrounding area is a suitable survey site for studying a natural analogue of bentonite-cement interaction. In the area, bentonite is in contact with alkaline groundwater, a situation analogous to cement leachates. The groundwater is generated and evolves mainly by low-temperature serpentinization in the ophiolite, and it flows along faults.
    The bentonite influenced by alkaline groundwater in the survey area showed the following geochemical and mineralogical characteristics. Bentonite close to pillow basalts has high levels of Cr, Ni, and light-rare-earth elements because of increased alkaline interaction. An iron-concentration band and bentonite alteration zone containing Ca-zeolites and K-feldspar were formed at the contact interface with pillow basalts as a result of alkaline alteration. The width of the zone is 5 mm. However, bentonite is little altered at the outcrop scale because of clogging by alteration minerals.
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