Japan Geoscience Union Meeting 2022

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[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-AG Applied Geosciences

[M-AG39] Radioisotope migration: New development for dynamics study of radionuclides from 1F NPP accident

Mon. May 23, 2022 3:30 PM - 5:00 PM 202 (International Conference Hall, Makuhari Messe)

convener:Daisuke Tsumune(Central Research Institute of Electric Power Industry), convener:Yuichi Onda(Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba), convener:Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), convener:Akira Kirishima(Tohoku University), Chairperson:Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Yuichi Onda(Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba)

4:00 PM - 4:15 PM

[MAG39-09] Deep groundwater components affecting actinide migration

*Akira Kirishima1, Mariko Terasaki1, Kazuya Miyakawa2, Yoshihiro Okamoto2, Daisuke Akiyama1 (1.Tohoku University, 2.Japan Atomic Energy Agency)

Keywords:Radioactive waste, Deep groundwater, Actinides, Underground research laboratory

To better understand the migration behavior of actinides in deep groundwater (GW), the interactions between doped tracers and components of deep GWs were investigated. 10 ppb or 100 ppb of La, Sm, Ho, and U were doped as the tracers into the sedimentary rock GW samples collected from boreholes drilled at 250 m and 350 m depth in the experiment gallery of Horonobe Underground Research Laboratory in Hokkaido, Japan. Furthermore, for an investigation of effect of GW’s composition difference on the chemical speciation of actinides, the same tracers were doped into the crystalline rock groundwater samples collected from boreholes drilled at 300 m and 500 m depth gallery at the Mizunami URL in Gifu Prefecture, Japan. The groundwater sample was sequentially filtered with a 0.2 micro meter pore filter, and 10 kDa NMWL ultrafilters. Next, the filtrate solutions were analyzed with ICP-MS to determine the concentrations of the tracers retained in solution at each filtration step, while the used filters were analyzed by TOF-SIMS element mapping and XAFS to determine chemical species of the trapped tracers on each filter. The experiment results were interpreted with a help of chemical equilibrium calculations and an additional experiments using simulated GWs where the phosphate concentration was changed from the original concentration in the GWs to observe the effect of the potential key component. It was found that the solubility of the lanthanide was controlled by the phosphates in the Horonobe GW (sedimentary rock). Therefore, the solubility of MA, which have similar chemical behavior in an aqueous solution system, is also expected to be controlled by the formation of the phosphates. Besides in the Mizunami GW (crystalline rock), the result of this study indicated that a fraction of lanthanide and MA seemed to form hydroxide and/or hydroxo-carbonate. By contrast, the predicted U(VI) species were soluble carbonate complexes in both Horonobe and Mizumami GWs.