Abstract: One of the major functions of buffering or backfill material is to conduct and dissipate the heat generated by the high-level radioactive waste to the host rock. Sand, graphite and crushed granite rock can improve the thermal property of bentonite with relatively high thermal conductivity. In this paper, mixtures of crushed Beishan granite and GMZ01 bentonite with different dry densities and water contents were compacted, and Hot Disk TPS2500s Thermal Constants Analyzer was used to measure thermal conductivity of the mixtures. The experimental results were analyzed to observe the effects of granite content, dry density, degree of saturation on the thermal conductivity. Various theoretical models were adopted to predict the thermal conductivity of bentonite/crushed Beishan granite mixtures. It is found that the thermal conductivity of GMZ01 bentonite can be effectively improved by the addition of crushed Beishan granite. Linear correlations are observed between the thermal conductivity of bentonite/crushed Beishan granite mixtures and degree of saturation, and volumetric fraction of air, respectively. Maxwell’s equation provides the most satisfactory prediction for the thermal conductivity of bentonite/crushed Beishan granite mixtures.

Key words: HLW geological disposal, buffer/backfill material, thermal conductivity, GMZ bentonite, Beishan granite