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Sato, Haruo; ; ; *; *; Yui, Mikazu
PNC TN8410 97-127, 57 Pages, 1997/08
Retardation of key nuclides is one of the most important mechanisms to be examined specifically and modelled for the performance assessment of geological disposal of radioactive waste. We have been studing diffusion of nuclides into the pore spaces of the rock matrix, sorption of nuclides on the rock pore surfaces and pore properties to quantify the degree of nuclide retardation in fractured crystalline rock. The work has concentrated on predominant water conducting fracture system in the host granodiorite in the Kamaishi In Situ Test Site, which consists of fracture fillings and altered granodiorite. Through-diffusion experiements to obtain effective and apparent diffusion coefficients (Da and De, respectively) for Na, Cs, HTO, Cl and Se as a function of ionic charge at 22 25C and batch sorption experiments for Cs, Sr, Se, U and Pu were conducted on fracture fillings, altered and intact granodiorite. The experiments only for Se, a redox sensitive element, were done in an N2-atmospheric glove box (O 1 ppm) to keep the chemical species. In situ groundwater (pH8.79.5) sampled from the same place as rock samples was used for the experiments. Porosity and density of cach rock sample were determined by both water saturation method and mercury porosimetry, and pore-size distribution and specific surface area of pores were measured by mercury porosimetry. The porosity is in the order; fracture fillings (5.6%) altered rock (3.2%) intact rock (2.3%). The pore-size distribution of the intact and altered granodiorite is ranging from 10 nm to 0.2 mm, and the fracture fillings have that of 50 nm to 0.2 mm, but a lot of pores were found around 100 nm and 0.2 mm in the fracture fillings. The effective diffusion coefficients for all species (Na, Cs, HTO, Cl, Se0) are in the order of fracture fillings altered rock intact rock in proportion to these porosities. Effective diffusion ...
Tachi, Yukio; Yotsuji, Kenji*; Fukatsu, Yuta; Sugiura, Yuki; Okubo, Takahiro*
no journal, ,
Understanding the radionuclide migration in clay minerals contained in the buffer material bentonite and rocks is important for the safety assessment of geological disposal of radioactive waste. The pore structures and the electrostatic interactions at the surface, formed by the clay mineral with a layered structure, are key components for developing the radionuclide migration model in clay minerals. In this study, in order to evaluate the influence of alteration from Na- to Ca-montmorillonite on radionuclide migration, the diffusion and sorption model was developed by considering the effects of both pore structures and electrostatic interactions in the compacted montmorillonite.