Behaviour of a bentonite barrier in the laboratory: experimental results up to 8 years and numerical simulation

Abstract

The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal were simulated in a series of tests performed in cylindrical cells (length 60 cm, diameter 7 cm). Inside the cells, six blocks of FEBEX bentonite compacted to dry density 1.65 g/cm3 were piled up, giving rise to a total length similar to the thickness of the clay barrier in a repository according to the Spanish concept. The bottom surface of the material was heated at 100 °C and the top surface was injected with granitic water. The duration of the tests was 6, 12, 24 and 92 months. The temperatures inside the clay and the water intake were measured during the tests and, at the end, the cells were dismounted and the dry density, water content and hydro-mechanical properties were measured at different positions. The injection of water provokes, near the hydration surface, a decrease of the dry density due to the increase of the water content and the clay swelling, while heating gives rise to an increase of the dry density and a reduction of the water content in the hottest areas.

A fully coupled thermo-hydro-mechanical (THM) formulation has been adopted as a general framework to analyse these experiments. This work presents the comparisons between the variables recorded online during the tests (water intake and temperature) and the model results. The main results of the postmortem analysis (water content and dry density) are also modelled.

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