Abstract
Carbon steel is being considered as a candidate canister material for high level waste disposal in underground geologic repository systems where anoxic to reducing conditions dominate after the thermal period. For example, the supercontainer concept in Belgium's proposed Boom Clay repository concept comprises a carbon steel overpack containing the waste and an outer, stainless steel liner that defines an annulus containing a cementitious material. The outer surface of the carbon steel overpack is expected to be in contact with concrete porewater with pH near 12.5 persisting for thousands of years. In this study, both literature reviews and independent experimental studies were conducted to investigate carbon steel corrosion in anoxic alkaline water and the effects of chloride, sulfide, and thiosulfate on passive dissolution. Experimental tests have confirmed low uniform corrosion rates in an alkaline anoxic environment with pH near 12 and have detected hydrogen produced from the passive dissolution process. Depassivation effects were least in chloride, greatest in sulfide, and thiosulfate was in the middle on carbon steel passivity in this anoxic alkaline environment.
