Bentonite pellets or their mixtures with powdered bentonite are potential buffer/backfill materials for the deep geological disposal of high-level radioactive waste (HLW) and are used to backfill the joints between neighbouring bentonite blocks or the construction gaps between bentonite blocks in the buffer layer and surrounding rock. Knowledge of the thermal properties of buffer/backfill materials is essential for the thermal evaluation and design of HLW repositories. The thermal properties were measured on a mixture of GMZ07 bentonite pellets and powdered bentonite with 70% pellet content over a wide range of water contents, dry densities, and temperatures. The test results revealed that the thermal conductivity of the specimen compacted with pure bentonite powder was higher than that of the mixture. This was due to the different pore-size distributions that influenced the conductive heat transfer in the specimens. The difference in thermal conductivity between the two types of specimens made by different methods decreased with increasing dry density, which was mainly attributed to the preparation of bentonite pellets using a compaction–crushing method. In addition, the destruction of bentonite pellets increased gradually with increasing dry density. The thermal conductivity, thermal diffusivity, and volumetric heat capacity of the mixture increased with increasing temperature. For a given dry density, the size of the inter-aggregate pores and aggregates of the mixture was larger than that of compacted pure GMZ07 bentonite, resulting in a decrease in the extent or quality of connections between neighbouring aggregates and a reduction in the thermal conductivity.

膨润土颗粒或其与粉状膨润土的混合物是高放废物（HLW）深部地质处置的潜在缓冲/回填材料，用于回填相邻膨润土块之间的接缝或缓冲层中膨润土块之间的施工间隙和周围的岩石。了解缓冲/回填材料的热特性对于 HLW 储存库的热评估和设计至关重要。热性能是在 GMZ07 膨润土颗粒和粉状膨润土（颗粒含量为 70%）的混合物上在很宽的水含量、干密度和温度范围内测量的。测试结果表明，用纯膨润土粉末压实的试样的热导率高于混合物的热导率。这是由于不同的孔径分布影响了试样中的传导热传递。两种不同方法制备的试样之间的导热系数差异随着干密度的增加而减小，这主要归因于使用压实-破碎方法制备膨润土球团。此外，膨润土球团的破坏程度随着干密度的增加而逐渐增加。混合物的热导率、热扩散率和体积热容量随着温度的升高而增加。对于给定的干密度，混合物的团聚体孔隙和团聚体的尺寸大于压实的纯GMZ07膨润土，