Saturation of barrier materials under thermal gradient

The backfilling and sealing of deposition galleries or holes and access galleries and shafts is an important part of nuclear waste underground repository design. Any opening created during the construction of the repository is a potential preferential pathway for water, gas and radionuclides migration, and has to be effectively sealed. Bentonite or bentonite-based mixtures have been proposed as backfill and sealing materials for their low permeability, high swelling capacity and high retention capacity. This work reports the results of two laboratory tests in which two different sealing materials were subjected to conditions similar to those in a repository: a high thermal gradient and hydration with host rock water (Figure 1). The materials are contained in cylindrical cells with a plane heater at the bottom and water supply through the top surface. The temperature and relative humidity (RH) of the materials are measured online during the tests by capacitive sensors placed at different positions. The water intake and the heater power are also measured online. In addition, cell B is instrumented with a ring load cell located on the top of the cell to determine the axial pressure generated during the test. In one of them the material used is MX80 bentonite pellets (B) and in the other is a 65/35 sand/bentonite mixture (S/B). The superficial thermal conductivity of these granular materials in thei