Corrosion evaluation of metallic materials for long-lived HLW/spent fuel disposal containers. Review of 15-20 years of research

Over the years many investigations have been performed to choose materials suitable for radioactive waste containers and to characterise their long-term corrosion behaviour in contact with potential disposal environments (e.g. salt, clay and granite). Carbon steels, stainless steels, nickel-based alloys, titanium-based alloys and copper have been widely investigated as potential container materials for particular host rock formations. The results obtained in salt environments indicate that the passively corroding alloy Ti99.8-Pd is the primary choice for the thin-walled corrosion-resistant concept, since its general corrosion rate is negligible and it is highly resistant to localised corrosion and stress corrosion cracking (SCC) in salt brines. Carbon steels are the prime candidate for the corrosion-allowance concept in salt environments because it is resistant to pitting corrosion and SCC, and its general corrosion rates are sufficiently low to provide corrosion allowance that is acceptable for thick-walled containers. Stainless steels, Ni-based alloys and Ti-based alloys are the most important candidate materials for thin-walled containers in clay, while carbon steel is considered the main choice for the thick-walled corrosion-allowance concept. Studies performed in granitic environments indicate that copper containers provide an excellent corrosion barrier with an estimated lifetime exceeding 100,000 years. Carbon steels are also a valid option for a thick walled container concept in granite. In this paper, some relevant corrosion data for carbon steel and stainless steel in cementitious environments are also provided because large amounts of concrete will be used as structural materials in most of the envisaged repository design concepts. This paper concludes with some recommendations for future studies. (authors)