In France, the reference concept for the geological disposal of high-level waste (HLW) consists of horizontal micro-tunnels, containing carbon steel casing and overpacks (around a stainless steel container containing vitrified waste). The overpacks and casing will be exposed to an environment that will evolve over time: from a hot and humid atmosphere containing oxygen, to an anoxic environment saturated with water at the geothermal temperature. Lots of corrosion experiments have been performed in representative environments to study steel corrosion modes (general corrosion, pitting and crevice corrosion, stress corrosion cracking, hydrogen embrittlement…) while taking into account the influence of temperature, radiation, mechanical stresses and microorganisms. Some key results have influenced the design of the HLW disposal cell, including the carbon steel grades and dimensions of the casing and overpacks, or the addition of an alkaline grout material between the casing and the host rock. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems .

This paper presents a state-of-the-art analysis of the expected degradation processes of a variety of candidate container materials for the disposal of high-level waste and/or spent nuclear fuel. The work, focusing on the most recent developments, has been performed under the auspices of the Implementing Geological Disposal Technology Platform in the context of an international conference hosted by the Nuclear Waste Management Organisation of Canada (NWMO). The scope of the analysis includes the expected corrosion and environmentally assisted cracking behaviour of copper, carbon steel and titanium in contact with relevant buffer materials (e.g. bentonite, cement) and in conditions expected in an underground disposal facility (long-term anoxic conditions). Considerations relative to the expected evolution of the environmental conditions (especially in the period following backfilling) are also presented. Beyond summarising the current state of knowledge, areas in which opportunities for international collaboration may be present are also highlighted. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Carbon steel coupons were buried in a specific low-pH cement grout designed for radioactive waste disposal and left 6 months in anoxic conditions at 80 °C. The corrosion product layers were analyzed by µ-Raman spectroscopy, XRD, and SEM. They proved to be mainly composed of iron sulfides, with magnetite as a minor phase, mixed with components of the grout. Average corrosion rates were estimated by weight loss measurements between 3 and 6 µm yr⁻¹. Corrosion profiles revealed local degradations with a depth up to 10 µm. It is assumed that the heterogeneity of the corrosion product layer, mainly composed of conductive compounds (FeS, Fe₃S₄, and Fe₃O₄), promotes the persistence of corrosion cells that may lead to locally aggravated degradations of the metal. New cement grouts, characterized by a slightly higher pH and a lower sulfide concentration, should then be designed for the considered application.