Hydraulic and diffusive properties of clay-based backfill material for a low- and intermediate-level waste repository

The results of experimental studies performed to determine the radionuclide diffusion coefficients in a compacted clay and the hydraulic conductivities of clay/crushed granite mixtures with various clay contents are presented. Clay used in the experiments is a natural clay from the southeastern part of Korea, and it contains mainly calcium bentonite. The hydraulic conductivities of clay/crushed granite mixtures decreased with increasing clay content. In case of clay content of 50 wt.%, they maintain the considerably lower values even at the dry density of 1.5 Mg/m3. The diffusion coefficients for 90Sr, 137Cs, 60Co and 125I in water saturated clay at a dry density of 1.4 Mg/m3 were measured at room temperature. The average apparent diffusion coefficients obtained are 4.5 x 10-12 m2/s, 9.0 x 10-13 m2/s, 3.4 x 10-13 m2/s, and 6.7 x 10-11 m2/s for 90Sr, 137Cs, 60Co, and 125I, respectively