Swelling properties and permeability of expandable clays of potential use for nuclear waste disposal

Bentonite clay has attracted considerable attention as isolating material for safe disposal of high-level radioactive nuclear waste (HLW) on account of its low hydraulic conductivity and high swelling capacity. In the presently described study, three candidate smectitic clay materials were investigated and compared with respect to hydraulic conductivity and expandability. The clay samples were prepared from desiccated and crushed raw material placed and compacted in oedometer cells for saturation with distilled water and 3.5% CaCl2 solution in separate test series to a density at fluid saturation of 1200 ~ 1900 kg/m3. The samples were tested with respect to the hydraulic conductivity and swelling capacity. The MX-80 and Homehus clays matured as expected giving a successively monotonous increase in swelling pressure during the wetting process while GMZ clay showed two pressure peaks. The pressure development was different for low and high densities and can be explained by crystal expansion via interlamellar wetting, followed by osmotic swelling including establishment of electrical double-layers. The phenomena can alternatively be explained by the microstructural changes when clay minerals absorb solutions in the hydration phase. Differences in granule size distributions and mineral composition can explain different swelling abilities and permeabilities.<p>Validerad; 2016; Nivå 1; 20151122 (tinyan)