Temperature effect on the thermal and hydraulic conductivity of Korean bentonite buffer material

High-level radioactive waste (HLW) disposal is considered to constitute a disposal system within a deep rock mass using deep geological repository. A deep geological disposal system has an engineered barrier system (EBS) consisting of canisters, buffer material, and backfill material. Among these items, the buffer material protects a canister from groundwater inflow and prevents radionuclide outflow. It is an also very important factor for evaluating the stability of a disposal system in which heat is propagated from the canisters. The aim of this study was to evaluate the thermal and hydraulic properties of Gyeongju bentonite, a buffer material from Korea. The thermal conductivity and hydraulic conductivity of Gyeongju bentonite were measured according to different degrees of saturation and to dry density. The whole process is based on the temperature change induced in the disposal environment. The thermal conductivity increased as temperature increased, and as did the temperature effect with high initial degree of saturation. Additionally, the hydraulic conductivity also increased as temperature did, and decreased with high dry density. After the process of heating and cooling, the thermal and hydraulic conductivity of the bentonite presented irreversible changes.