Presence of sulphate reducing bacteria near a Boom Clay-steel interface

Within the frame of high-level waste disposal Boom Clay is currently studied as the reference host rock in Belgium. Sulphate reducing bacteria (SRB) can transform sulphate into sulphide. Sulphide can cause corrosion of for instance the carbon steel overpack surrounding the waste canister which could have a severe influence on the efficiency of the repository. Steel tubes which have been in contact with Boom Clay for 20 years were examined for traces of corrosion. Simultaneously, the clay-steel interface was investigated for the presence of SRB and different sulphur species. Culture experiments showed that the SRB concentrations in Boom Clay were highest at the clay-steel interface. The analysis of sulphur species only revealed the presence of sulphate in the clay cores with varying concentrations. Although the steel tubes showed signs of corrosion only very limited amounts of sulphur were detected. Finally, the possible influence of SRB activity, i.e. the influence of sulphide, on the supercontainer design is summarized based on discussions conducted during the SACNUC workshop (October 2008). Indeed, the supercontainer's integrity is particularly important during the thermal phase of the repository to prevent a premature release of radionuclides while the temperature of the formation is still elevated.