Ferric oxyhydroxide in underground geological environments and high-level radioactive waste disposal: Analysis of influence on nuclide migration scenarios

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 ( ) evaluate suitable repository depths that will need to be characterized; and ( ) 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: ( ) 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; ( ) early-stage ferric oxyhydroxide remains stable even after the environment returns to reducing conditions; and ( ) 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.

Swelling Characteristics and Permeability of Bentonite-Based Materials Immersed in Various Solutions

“…For this study, we selected four types of solutions to simulate geological disposal: Ca(OH) 2 solution (pH = 12.8) and KOH solution (pH = 13.0), based on the assumption that highly alkaline pore water is generated through the reaction of cement-based material with groundwater; FeCl 2 solution (pH = 4.9), based on the assumption that ferric iron (Fe 3+ ) is generated by the reaction between oxygen, which is carried from the ground by excavations performed in facility construction, and iron, which is in the steel support and bedrock; and MgCl 2 solution (pH 7.5), based on the assumption that metal ions are present in seawater groundwater in coastal areas. The reason for using an FeCl 2 solution despite an assumption based on ferric iron (Fe 3+ ) is as follows: According to a previous study 18) that examined the effect of iron hydroxide in a groundwater scenario in geological disposal, iron ions dissolved in groundwater as ferrous iron may be oxidized to form ferric iron after moving through cracks in the bedrock. Furthermore, the solubility of iron hydroxide (Fe(OH) 3 ) in water is extremely low.…”

Quantitative and semi–quantitative analyses using a portable energy dispersive X–ray fluorescence spectrometer: Geochemical applications in fault rocks, lake sediments, and event deposits

“…In addition, geochemical data and their statistical analyses are effective for estimating the behavior, distribution, and sources of materials regarding geological events, such as fault activities in Japan (Yoshida and Yamamoto, 2014;Niwa et al, 2015Niwa et al, , 2019. Although data accumulation is required for further research to evaluate faults and other event deposits, simple and rapid analyses using portable XRF are limited (Solum et al, 2010).…”