State of a bentonite barrier after 8 years of heating and hydration in the laboratory

The conditions of the bentonite in an engineered barrier for HLW disposal have been simulated in a laboratory test. Six cylindrical blocks of bentonite compacted at a dry density of 1.64 g/cm³ were piled up in a hermetic Teflon cell. The total length of the clay column inside the cell was 60 cm. The bottom surface of the bentonite was heated at 100°C while the top surface was injected with granitic water. The duration of the test was 7.6 years. The water intake was measured during the test and, at the end, the cell was dismounted and the dry density, water content, mineralogy, geochemistry, and swelling capacity of the clay were measured in different sections along the column. At the end of the test no full water saturation was reached and water content and dry density gradients were found along the column. No mineralogical changes have been detected, although the pore water chemistry and the exchangeable complex of the smectite have changed along the bentonite. None of these changes affect drastically its swelling capacity, which remains high. The material used in this test is the FEBEX bentonite.