Articles | Volume 2
Conference Abstract
06 Sep 2023
Conference Abstract |  | 06 Sep 2023

The anaerobic corrosion of the carbon steel overpack under anoxic alkaline conditions representing the Belgian supercontainer concept

Roberto Gaggiano

The Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS) is responsible for the management of all radioactive materials (currently existing and future waste) generated in Belgium. Disposal in deep stable geological formations is, at present, accepted at an international level to be the most promising option for the long-term management of high-level and/or long-lived radioactive waste. ONDRAF/NIRAS currently recommends underground disposal in a geological stable and poorly indurated clay formation as the reference management option to steer their RD&D research programmes. The supercontainer concept is currently being considered as the reference design for the final disposal of vitrified high-level radioactive waste (VHLW) and spent fuel (SF) in Belgium. It comprises a prefabricated Portland cement-based buffer that completely surrounds a carbon steel overpack. In this highly alkaline environment (pH  13.6), and under normal conditions (i.e. without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is expected to result in very low uniform corrosion rates.

The main goal of the ongoing R&D corrosion studies performed at ONDRAF/NIRAS is to provide confidence that the integrity of the carbon steel overpack will not be jeopardized at least for the duration of the thermal phase. Considering the long timescales applicable to waste disposal, determining accurate and reliable estimates of the uniform corrosion rate under anoxic conditions forms a very important part of the R&D methodology of ONDRAF/NIRAS' corrosion programme. On the other hand, the occurrence of localized forms of corrosion cannot be neglected, and therefore it is also crucial to demonstrate that no other form of corrosion apart from uniform corrosion can take place.

This paper gives an overview of the status of the research performed at ONDRAF/NIRAS with respect to the uniform corrosion, pitting corrosion and stress corrosion cracking behaviour of the carbon steel overpack of the supercontainer.

Financial support

This research has been supported by the Organisme national des déchets radioactifs et des matières fissiles enrichies.

Short summary
This paper provides an overview of the research on the uniform and localized corrosion behaviour of carbon steel overpack exposed to an artificial concrete pore water solution, representative of the Belgian supercontainer. Very low uniform corrosion rates were measured under these conditions. Moreover, the tests performed up to now have shown that localized corrosion will not represent a thread for the integrity of the overpack under the expected conditions.