Corrosion Behavior of Copper in Simulated Anoxic Groundwater Inoculated with Sulfate Reducing Bacteria and Methanogens

In Finland, the high level nuclear waste will be disposed in a geological repository, at the depth of 400-450 m below the sea level. The solid spent fuel rods are placed in cast iron containers, covered with 50 mm thick copper sheet, which are enclosed by a bentonite clay buffer. The surrounding rock provides the final barrier in this multi-barrier concept. Copper has been chosen for the canister material due to its good corrosion resistance in anoxic water. However, colonization and activity of microbes on the surface or in the vicinity of the canister may initiate and accelerate several corrosion mechanisms. Bentonite buffer surrounding the canister is supposed to inhibit the migration of bacteria into the vicinity of the canister. Nevertheless, due to uneven saturation and swelling of the bentonite or formation of water-bearing fractures, the groundwater and microbes may come into contact with the canister. Here biotic and abiotic mesocosms were assembled containing copper coupons and an artificial groundwater at 10 °C under argon atmosphere. Sulfate reducing bacteria and methanogens enriched from the planned disposal site were added to the biotic experiments. During the exposure of one year, several electrochemical methods were performed intermittently. Preliminary results are presented and discussed in this paper. The results can be used when evaluating risks of the microbially induced corrosion of copper canisters.