Abstract
Diffusion of iodide anion in rock pore water and its relation to porosity and pore structure were investigated in order to evalute diffusivity of "non-sorbing" radionuclides in various rock matrix. Porosities and pore-size distributions of various rock samples (diameter: 20 or 40 mm, length: 5 mm) of siliceous sedimentary rocks, andesites, schists, limestone, sandstone hornfels, granites and tuffs were measured by the water saturation method and the mercury intrusion porosimetry. The water saturation porosity ε w of these rocks varied from 0.1 to 48% and is considered to be close to the total porosity ε tot. The mercury intrusion method is considered to measure the pores larger than 5nm and might give the porosity em close to the transport porosity ε tra.
The mercury porosimetry method provided pore-size distribution data of the rocks and they can be classified into two types: type-A has mainly larger pores from micro to nano pores and type-B has mainly pores smaller than 25 nm (nano and sub-nano pores).
Effective diffusion coefficients De of iodide anion for these water-saturated rocks were measured at room temperature using a simple diffusion cell, and their relation to the porosities ε tot. and ε tra. were studied. D e and tra. have a rough linear correlation D e=5.3×10 -10 ε tra. tra. 1.3 in a logarithmic diagram for most of the rocks. This relation is very useful to estimate effective diffusivities of ions in various rock matrix.
