Abstract: As an excellent backfill material of the joints and gaps in high-level radioactive waste disposal repository, granular bentonites have a great application prospect. The thermal conductivity of granular GMZ bentonite was studied compared with compacted powder bentonite, using a thermal probe method under variable parameters including temperature, dry density and water content. The test results show that at the same condition, the thermal conductivity of compacted powder bentonite is higher than that of granular bentonite. With increasing the dry density, such difference in the thermal conductivity has decreased at constant water content. Temperature effect on the thermal conductivity of granular bentonite has increased with the increasing temperature and water content, as well as decreasing dry density. One possible explanation is that the size of inter-aggregate pores of compacted powder bentonite specimens is larger than those of compacted granular bentonite specimens at the same dry density, which causes it more conducive to the heat transfer within the compacted powder bentonite specimen, consequently its thermal conductivity is larger than that of granular bentonite specimen. As the dry density increases, the inter-aggregate pores of granular bentonites decrease, which weakens the influence of the latent heat transfer of vapor and thus reduces the temperature effect.

Key words: granular bentonite, backfill material, thermal conductivity, temperature effect, latent heat transfer