Effect of particle size distribution on the thermal conductivity of crushed GMZ bentonite pellet mixtures

Crushed high-density bentonite pellet mixtures have been proposed to fill the construction gaps of the high-level radioactive nuclear waste repository. Compared with compacted bentonite block, the thermal conductivity of bentonite pellet mixture is relatively low, which can cause a significant increase in the peak temperature of the buffer layer. In this regard, it is crucial to investigate the thermal conductivity of bentonite pellet mixtures for the repository’s long-term safety assessment. In this study, crushed high-density GMZ bentonite pellets with six size classes were produced. The thermal conductivities of mono-size, binary-size, and multi-size class mixtures of crushed bentonite pellets were measured. The effect of particle size distributions of pellet mixtures on the thermal conductivity was analyzed. The results reveal that the thermal conductivity of a mono-size class mixture increases as the mean particle size increases. The influence of mean particle size on thermal conductivity lessens as dry density increases. The thermal conductivity of a binary-size class mixture decreases initially and subsequently increases as the mass fraction of the fine size class increases. The thermal conductivity of a multi-size class mixture firstly increases and then decreases with increasing the distribution modulus q, reaching a peak value in the range of q = 0.6 ~ 0.8.