Coupled THM analysis of a full-scale test for high-level nuclear waste and spent fuel disposal under actual repository conditions during 18 years of operation

Abstract

This study focuses on the thermo-hydro-mechanical (THM) analysis of the behaviour of a full-scale engineered barriers experiment designed to study the long-term response of a disposal concept for high-level radioactive waste (HLW) and spent fuel (SF). Crucially, the test involved two dismantling operations, a partial one after 5 years of heating and a final one, after 18·3 years of operation, allowing the direct observation of the state of the barrier at two different times. The coupled THM modelling discussed in this paper mainly focuses on the last 13 years of test operation and also on the final dismantling of the barrier system. The numerical model was unchanged from the early stages of the test, so the results presented can be considered as blind predictions. The numerical model predicted reasonably well the state of the barrier and its evolution, especially in terms of the distribution of the bentonite dry density, confirming the predictive capability of the model to capture the transient THM processes. The combination of experimental and numerical investigations, involving one of the most long-lasting full-scale in situ experiments monitoring the behaviour of the barrier components of an HLW/SF repository, has led to a better understanding of the THM behaviour of this complex system.