The Composite Ceramic Nuclear Liner project is part of the Cigéo project, a deep geological disposal facility for high-level and long-lived intermediate-level radioactive waste, led by Andra, the French national radioactive waste management agency. The concept of high-level radioactive waste (HLW) disposal cells involves the installation of a liner consisting of a hollow cylinder inserted into a micro-tunnel dug into the Callovo-Oxfordian clay formation. The main function of the liner is to allow the emplacement and the potential recovery of the HLW packages, all along the operating period of the facility, estimated to last around a century. The current preferred solution selected by Andra is a carbon steel liner. However, corrosion of this material under anoxic conditions generates hydrogen. Among the potential areas of development of the disposal facility, Andra studies alternative materials to metals for the liner. On top of the mechanical requirements already met by the identified metallic solution, the alternative materials must be chemically inert with respect to the vitrified waste and the geological environment. [1]
Some technological barriers associated with the use of ceramic matrix composites (CMC) for the lining of HLW cells have recently been removed; for instance, a specific multilayer structure has been developed for the component to withstand the mechanical constraints in the disposal cell. [2] This is an innovative application for materials originally developed for extreme temperature applications. The aim of the work presented here is to evaluate the aging of CMC in a severe environment, following three axes: (i) thermodynamic calculations; (ii) conception of aging devices to perform aging tests (iii) identification of the interaction mechanisms and mechanical tests on aged CMC.
With regard to the specifications related to the application, three composites that differ as much in the nature of the reinforcements as in the matrix were selected. Alumina, a common constituent into few of these composites, is chosen as the first model material for this study to establish the whole experimental and theoretical methodology. On this way, thermodynamic calculations are performed to predict the evolution of the considered systems in an aqueous solution representative of the clay host rock. The implementation of a model system will allow a simplified approach to identify the relevant trends, before enriching the model to be closer to the real physicochemical system. Finally, a comparison between the thermodynamic calculations and the real damage of the materials will be carried out in order to understand the mechanisms of deterioration and to evaluate the durability.

References
[1]        ANDRA, « Projet Cigéo ». [En ligne]. Disponible sur : https://www.andra.fr/sites/default/files/2020-04/Projet%20Cig%C3%A9o%20-%20568%20F.pdf
[2]        E. Perret, M. Box, G. Vignoles, F. Rebillat, et F. Bumbieler, « CERAMIC MATRIX COMPOSITES FOR LINER SYSTEM OF RADIOACTIVE WASTE DISPOSAL CELLS », présenté à CMC-II, Santa Fé Nouveau Mexique, nov. 2022.