Innovative Ceramic-Based Solution for a Barrier in an EBS: Development, Mechanical Behaviour, and Ageing of a Tunnel Liner as a Test Case

The concept of a safe geological repository for managing radioactive waste relies on a multi-barrier system comprising both the host rock and various engineered barriers, these latter being referred to as the engineered barrier system (EBS). The robustness of the EBS directly depends on the materials used, which play a crucial role in ensuring its performance. These materials must exhibit exceptional durability, stability, and compatibility with the host rock and the types of waste expected in the future repository. Moreover, they must fulfil theirs functions over timescales ranging from hundreds to thousands of years, depending on the repository’s design.Among the various potential barriers considered in repository concepts, there is typically at least one component between the disposal container and the host rock—such as a buffer, liner, or casing—whose function depends on the repository design. Regardless of its role, this component will be subjected to severe in-service conditions, including mechanical stress, corrosion and leaching by groundwater, and irradiation. Consequently, the materials used for this component must withstand these harsh environments and maintain their integrity while ageing.Current reference materials for this intermediate component include metals, cement-based materials, and clay minerals. However, innovative solutions could emerge from ceramic materials, particularly ceramic matrix composites (CMCs). These composites combine the high chemical inertness of ceramics—including their advantage of not producing gas upon alteration—with enhanced mechanical properties compared to their monolithic counterparts, thanks to their fibre-reinforced structure.This study explores the use of CMCs for manufacturing an engineered barrier, specifically a micro-tunnel liner (or casing). It is part of Andra’s R&D program on the development of ceramic-based solutions as potential alternatives to conventional materials for the geological disposal of high-level waste (HLW). The proposed solution involves a liner with a specific architecture: a sandwich-like structure composed of a hollow, monolithic ceramic cylinder wrapped at the top and bottom surfaces with CMCs. Preliminary results indicate that this structure can withstand significant mechanical loads and that manufacturing defects do not compromise its integrity. A mechanical model is under development to predict the behaviour of this sandwich structure under various field conditions. In parallel, accelerated aging experiments combined with thermodynamic calculations are being conducted to assess material modifications due to groundwater exposure.Although this study focuses on the French Cigéo repository concept, the proposed innovative component could also be of interest to other stakeholders in radioactive waste management, as well as for civil engineering applications beyond liner or casing structures.