Matrix diffusion of fractured crystalline rocks. Granodiorite of the Kamaishi mine

To assess the performance of the geological disposal of high-level radioactive waste, it is essential to include diffusion from fractures into the matrix in nuclide migration analysis for fractured rocks. For this, analysis much data for granitic rocks has been reported so far, but almost all data were for fresh rocks, with little data for rocks taken from fractures reported. In this study, the diffusion of nuclides into the pore spaces of a rock matrix and the pore properties were studied in a fracture in the granodiorite of the Kamaishi mine. The fracture consists of fracture filling minerals, altered granodiorite and unaltered granodiorite. Effective and apparent diffusion coefficients (De and Da, respectively) for Na+, CS+, HTO (tritiated water), Cl and SeO32 were obtained for these rocks. The porosity (φ) and pore-size distribution were also determined. Consequently, (1)De decreased with distance from the future, (2) correlativity between De and φ was found, and this tendency was consistent with those of granitic rocks reported to date, and (3) De was more dependent on the free water diffusion coefficient rather than on the ionic charge. This report introduce information obtained in laboratory tests to date on the granodiorite of the Kamaishi mine. (author)