Storage of High Level Radioactive Wastes. Materials, Mechanics and Corrosion

Cigéo (Centre industriel de stockage géologique) is the French project for a deep repository for radioactive waste. It will be designed to store long-lived high- and intermediate-level radioactive waste produced by all current nuclear facilities, until their decommissioning, and by the processing of spent fuel used in nuclear power plants.

Corrosion of unalloyed steels for deep geological disposal of radioactive waste has been the subject of R&D work for over 30 years. In particular, it covers different geological media (granite, clay), different concepts in terms of surrounding materials (swelling clay, clay host rock, cementitious media) and several physico-chemical conditions (temperature up to 90°C, water-saturated media, non-water-saturated media, atmospheric-type media with relative humidities ranging from dry to 100%, aerated/oxidizing to anoxic conditions, gamma radiation...) covering the range of evolution expected in a disposal situation. This work also benefits from that carried out for other applications, such as geothermal energy or the oil industry, and exploits the study of archaeological analogues, in particular to understand corrosion mechanisms over time scales of several hundred years.

Mechanical behavior was also studied experimentally and by numerical simulation. The failure modes considered were confined buckling for the liner and ductile cracking for the storage container.

Specifically for the HA (high activity) cells, Andra (Agence nationale pour la gestion des déchets radioactifs) has chosen low-carbon petroleum-grade steels (or steels with similar specifications) to guarantee low sensitivity to stress corrosion and hydrogen embrittlement, given the anisotropic mechanical loads expected in a storage situation. At this stage, these are API 5L X65 MS steel for the liner, and improved P285NH steel for the storage container.