Salinity Controls on Steel Biocorrosion relevant to the Disposal of High-level Radioactive Waste

In a geological disposal facility (GDF) for spent fuel and high-level radioactive waste, the canister serves as one of the main engineered barriers. The resistance of the canister to degradation processes such as microbially influenced corrosion (MIC) needs be characterised to support GDF environmental safety cases. Here the impacts of salinity on sulfate-reducing bacterial (SRB) activity and associated MIC were explored in 84-day batch incubations at 30 °C. A 5 % standard bentonite slurry (MX80) in a low-salinity (0.1 g l⁻¹ NaCl) artificial groundwater containing lactate added as an electron donor provided suitable conditions for the proliferation of SRB. Corrosion rates of carbon steel (080-A15) coupon surfaces in microcosms amended with lactate were > 2.5 times greater than those absent of lactate, and sterile controls. At an increased salinity of 12.4 g l⁻¹, adding lactate resulted in 2 times the corrosion depth of sterile conditions, but at 50 g l⁻¹ there was no detected microbial activity, and no pronounced increase in corrosion by adding lactate compared to sterile controls. Here, microbial activity and subsequent MIC was suppressed at high salinity (50 g l⁻¹) suggesting that groundwater composition played a controlling role in SRB biocorrosion. The relevance to geodisposal scenarios, where bentonite is used to protect and support the waste canister, is discussed.