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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 ...
Sakata, Nagisa*; Tachi, Yukio; Iwadate, Yasuhiko*; Okubo, Takahiro*
no journal, ,
Cement-based materials will be used as a component for radioactive waste disposal facility. Understanding water paths in cement-based materials is a key to evaluate their long-term performance. It is well known that 1H transverse relaxation (T2) of water filled pores is related to their porous structure. In this study, 1H T2 distribution analyses were applied to hydration process of cement-based materials, and the relationship between porous structure and mass transport was discussed. Experimental results showed that the main path of water is the grain boundary between cement and silica sand contained in mortar. In addition, C-S-H gel layers in cement and C-S-H gel pore cannot contribute as a path of water.