Effect of sulphur species on anaerobic corrosion of carbon steel in alkaline media

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.