Microbial corrosion of P235GH steel under geological conditions

The role of microbial activity on the alteration of steel containers used for nuclear waste disposal is increasingly discussed. In this work we isolated and identified sulphate-reducing bacteria (SRB) in the Callovo-Oxfordian clay rock studied as a potential host rock formation for a repository for high-level and long-lived radioactive waste in France. Then, the effect of the SRB growth on the overpack steel corrosion was investigated. The corrosion rate of the steel coupons was high under biotic conditions (∼30 μm/year) in comparison to blank sterilized runs (∼14 μm/year). Culture experiments in compacted conditions with clay-stone cores and steel coupons under 120 bar, simulating deep geological conditions, gave results similar to those obtained in batch experiments (e.g. production of H2S). This indicates the plausibility of SRB growth during the construction and operational phases of the repository and their survival at least temporarily after the disposal closure if water is available, which may cause fast corrosion of the steel containers under disposal conditions.