Migration behavior of multivalent radionuclides from fully radioactive waste glass in compacted sodium bentonite
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1265-AA06-09
Migration behavior of multivalent radionuclides from fully radioactive waste glass in compacted sodium bentonite Kenso. Fujiwara1, Kazuki. Iijima1, Seiichiro. Mitsui1, Makoto. Odakura1, Yukitoshi. Kohara2, Hiroshi. Kikuchi2 1
Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency (JAEA), 4-33 Muramatsu, Tokai, Ibaraki, 319-1194, Japan 2 Inspection and Development Company, 4-33 Muramatsu, Tokai, Ibaraki, 319-1112, Japan ABSTRACT Samples of fully radioactive glass sandwiched in bentonite for 15 years at room temperature under aerobic conditions were used to investigate the coupled processes of Eu, Pu, Am and Cm release from fully radioactive waste glass and their transport in compacted bentonite. The observed concentrations of the radionuclides in compacted sodium bentonite contacted on the glass were good agreement with their solubilities calculated from thermodynamic data. It was considered that an actinide and lanthanide leached from the glass were controlled by their solubility. The diffusion of Am in the bentonite is fitted to the experimental data based on the one-dimensional diffusion model considering several species. INTRODUCTION In a repository of high-level radioactive waste, if the radioactive waste glass is in contact with the groundwater for very long time, it is possible that the radioniclides will leach from the waste glass and migrate into through surrounding bentonite and host rock. Migration behavior of radionuclides in these processes is generally evaluated by individual models developed for each process. However, several processes are likely to progress simultaneously in the geological disposal environment. Consequently it is necessary to confirm that the entire behavior of a radionuclide is adequately modeled by combination of the individual models. The migration of radionuclides from vitrified waste is likely to be governed by leaching from glass matrix, dissolution and precipitation, diffusion in the bentonite and sorption on the minerals in bentonite. For the purpose of evaluating this migration behavior, combined leachingdiffusion experiments were carried out by sandwiching glass sample in compacted bentonite. Ashida et al. [1] reported the results of Cs in this type of experiments in compacted sodium bentonite (Kunigel V1®) in contact with fully radioactive waste glass for 15 to 300 days under aerobic conditions. As a result, Cs migration was successfully interpreted using simple one dimensional diffusion model. Mitsui et al. [2] reported the leaching behavior of waste glass based on the diffusion data of Cs for 15 to 300 days [1] and for 15 years. They demonstrated that the leaching of glass matrix in this system was explained by a general glass dissolution model taking silicon migration in compacted bentonite into account. However, migration of multivalent elements of actinide and lanthanide in fully radioactive waste glass were extremely slow because of low solubility, low effective diffusivity and high distribution coefficient. In this study,
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