The microbial processes affecting the integrity of copper canister in geological repository of nuclear waste

The nuclear waste disposal concept in Finland is based on a multi-barrier system, where the spent nuclear fuel is disposed of in deep crystalline bedrock in copper canisters surrounded by bentonite clay buffer. The copper canisters should have lifetimes exceeding 100 000 years to prevent the release of radioactive nuclides to the environment. In anoxic water, such as the groundwater at the disposal site, the corrosion of copper should be extremely slow. However, microbial activity on the surface or in the vicinity of the copper canister can enhance corrosion in many different ways, e.g. changing the pH or redox potential, excreting of corrosive metabolites, by direct or indirect reduction or oxidation of corrosion products and formation of biofilms that create corrosive microenvironments.

In this study, microbially influenced corrosion (MIC) of copper was studied using electrochemical methods, weight loss measurements and molecular biology methods in laboratory environment. The experiment was conducted under anoxic conditions in water simulating the groundwater of disposal conditions. Inoculations of sulfate reducing bacteria (SRB) and/or acetogenic bacteria enriched from the future disposal site were added to the experiments. A sterilized abiotic environment was used as a reference environment.