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Yuguchi, Takashi*; Sasao, Eiji; Hibara, Ryoko*; Murakami, Hiroaki; Ozaki, Yusuke
Heliyon (Internet), 10(17), p.e37417_1 - e37417_17, 2024/09
Times Cited Count：0 Percentile：0.00(Multidisciplinary Sciences)Understanding the mass transfer characteristics of matrix diffusion and sorption is important in geological disposal of high-level radioactive waste in crystalline rock. We present a comparative discussion of the effective diffusion coefficient (De), porosity, and petrological data for rock samples collected from the Toki Granite in central Japan, to evaluate the role of micropores within minerals in retardation by matrix diffusion and sorption in granitic rocks. De was derived from the through-diffusion experiments. Petrological data consist of the fracture frequency, the extent of hydrothermal alteration in the minerals, the micropore volume in the minerals, and the three-dimensional modal mineralogy for the target rock samples. The relationship between the De, porosity, and petrological data has the following implications: 1) Micropores act as storage pores that contribute to retardation; 2) Once the uranine, cations, and anion penetrate the micropores in the minerals through matrix diffusion, the cations are sorbed on the micropore surfaces; 3) Regions with a high fracture frequency are associated with not only active advection-dispersion through fractures, but also retardation due to matrix diffusion and sorption.
Yuguchi, Takashi*; Sasao, Eiji; Hibara, Ryoko*; Murakami, Hiroaki; Ozaki, Yusuke
no journal, ,
Understanding of matrix diffusion is important for geological disposal of high-level radioactive waste in terms of retardation of mass transport in deep underground. Matrix diffusion has been evaluated by effective diffusion coefficient and porosity for bulk rock, but contribution of each constituent mineral of rock to matrix diffusion was not evaluated. In the Toki granite, central Japan, micropores are found in constituent mineral of granite such as plagioclase, potassium feldspar and biotite. This study examined contribution of micropores in constituent minerals of granite to matrix diffusion and utilized effective diffusion coefficients obtained by through-diffusion experiment, porosity, petrological mode, fracture frequency, extent of hydrothermal alteration in the minerals, and volume of the micropores in the minerals. As a result of study, the following results were obtained; micropores in minerals act as "storage pore" which contributes retardation of nuclide, retardation could be caused by sorption onto minerals around micropores, and retardation could be expected even in fractured rocks, where advection is dominant. These results imply that evaluation of extent of hydrothermal alteration in the minerals is effective as an indicator of matrix diffusion.
