Thermo-Mechanical Assessment of Clay-Based Barriers for Nuclear Waste Repositories using Finite Element Analysis
Abstract
The long-term disposal of high-level nuclear waste demands engineered barrier systems capable of sustaining thermal and mechanical stability over thousands of years. This research presents a comparative thermo-mechanical finite element assessment of three candidate clay materials Callovo-Oxfordian (COx) claystone, Bentonite, and Opalinus clay used as buffer barriers in deep geological repositories. Numerical simulations were conducted in ANSYS Workbench using a transient thermal–static structural coupling scheme. The simplified repository configuration consisted of a steel canister embedded within a 0.5 m-thick cylindrical clay buffer surrounded by a fixed boundary representing the host rock. Each buffer material was evaluated under identical conditions of internal heat generation and mechanical confinement. Temperature evolution, heat flux, hoop and longitudinal stresses, and total deformation were extracted and validated against analytical formulations derived from Fourier’s law of heat conduction and Lamé’s thick-walled cylinder theory. The results demonstrated consistent temperature distributions (21 – 26 °C) across all materials, confirming correct boundary and mesh definitions, while stress and deformation responses varied significantly with stiffness and thermal conductivity. Bentonite exhibited the highest stress range (up to 25.9 MPa longitudinal, 0.18 mm deformation) owing to its low modulus, whereas Opalinus clay maintained the lowest stresses (4.1 MPa longitudinal, 0.47 MPa hoop) and minimal deformation (0.065 mm). COx clay displayed intermediate performance, balancing conductivity and mechanical resilience. These findings emphasize the important influence of coupled thermal and mechanical effects in barrier design. Opalinus clay offers superior thermo-mechanical stability, while Bentonite’s swelling potential remains advantageous for sealing functions. The validated modelling framework provides a foundation for future long-term thermo-hydro-mechanical (THM) studies and for optimizing buffer composition and thickness in nuclear waste repository design.
Keywords
Finite element analysis, Thermo-mechanical behaviour; Nuclear waste repository, Clay barrier, Opalinus clay
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