Microbially induced corrosion of copper in simulated anoxic groundwater

Copper has been chosen as the outermost material used in the canister in Finnish nuclear waste disposal program. In anoxic water, the corrosion of copper should be extremely slow. However, microbial activity on the surface of the copper canister or in the vicinity of the canister can enhance corrosion in many different ways, e.g. changing the pH or redox potential, excretion of corrosivemetabolites, direct or indirect reduction or oxidation of corrosion products and formation of biofilms. In this study the later stage of the deep geological nuclear waste repository was simulated. In that stage all oxygen introduced at the construction stage has been consumed and the temperature in the repository has decreased to the level of the surrounding bedrock. It is also assumed that the copper is in direct contact with the groundwater. We studied the microbially influenced corrosion (MIC) of copper sheets in the simulation usingelectrochemical technologies, weight loss measurements and molecular biology methods in the laboratory. The chemistry of the used synthetic water was calculated to simulate the groundwater of disposal site also including the effects of bentonite, which will be used as buffer in the repository. Inoculations of sulfate reducing bacteria (SRB) and methanogens enriched from the disposal site were added to the biotic experiments. A sterilized abiotic environment was used as a reference. Preliminary results of the first year´s incubation studies are discussed in this paper