Abstract
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.
