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In the Belgian supercontainer concept, a carbon steel overpack will surround high-level waste and spent fuel containers and be encased in a cementitious buffer material. A programme of research has been carried out to investigate and measure the rate of anaerobic corrosion of carbon steel in an artificial alkaline porewater that simulates the aqueous phase in the cementitious buffer material and also in solid cement matrices. This paper highlights the main features of the programme and presents some recent results from the analysis of several samples, including two 20-year-old steel in cement samples, which showed that under anoxic conditions there is no localised corrosion or incorporation of iron into the surrounding cement, even in the presence of 20 000 ppm chloride in the porewater. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems. [ABSTRACT FROM AUTHOR]

In the Belgian Supercontainer concept for disposal of vitrified high level radioactive waste and spent fuel, a carbon steel overpack will surround the waste containers and be encased in a cementitious buffer material. In previous work the effects of radiation, temperature and chloride concentration on the anaerobic corrosion rate of carbon steel in an artificial alkaline porewater were measured and recently the effects of sulphur containing species, particularly sulphide and thiosulphate, on the anaerobic corrosion rate of aerobically precorroded carbon steel have been studied. Corrosion rates were measured by monitoring hydrogen evolution, by applying electrochemical methods and by gravimetric analysis. Corrosion product layers formed after several years' exposure were analysed using focused ion bombardment (FIB) and SEM/EDX analysis. This paper summarises recent results, for experiments with and without sulphur species present. No increase in the anaerobic corrosion rate of pre-corroded carbon steel in the presence of sulphide or thiosulphate was measured. [ABSTRACT FROM AUTHOR]