Sulphur chemistry of the near-field Boom Clay environment

The disposal of Belgium's High Level Nuclear Waste (HLNW) in the proposed Boom Clay repository requires careful consideration of the nature of the near-field environment, because of the presence of potentially corrosive species. The near-field environment is expected to be in contact with both carbon steel and highly alloyed iron-based alloys, such as stainless steels, although it is recognized that the canister material has yet to be specified in the Belgian programme. This chapter summarizes the chemistry of sulphur in the form of potential/pH and volt-equivalent diagrams calculated as a function of pH and temperature. It discusses little known feature of potential-pH diagrams; that of the formation of thermodynamically metastable oxide or sulphide phases on a metal surface.