Temperature dependence of apparent thermal conductivity of compacted bentonites as buffer material for high-level radioactive waste repository

Abstract Thermal conductivity of compacted bentonite is one of the parameters affecting the behaviour of high-level radioactive waste (HLW) repositories, where the bentonite will be used as a buffer. Because the heat released from the HLW will be diffused across the buffer, understanding the thermal properties of buffer materials is necessary to accurately assess the thermal performance of the HLW repository. In this study, the thermal conductivity of compacted Gaomiaozi (GMZ07) and Wyoming (MX80) bentonites was measured and investigated under different testing conditions: temperature, water content and dry density. The obtained results showed that the thermal conductivity of compacted bentonites increased with increasing temperature. The thermal conductivity increased noticeably with temperature above 60 °C, while the change in thermal conductivity with temperature was small at temperature ranging from 5 to 60 °C. The temperature effect on thermal conductivity decreased with increasing dry density, and for a dry specimen, the thermal conductivity was negligibly changed with temperature.