Contaminated low- and intermediate level waste is produced during the operation and decommissioning of nuclear power plants. This waste contains pipes, valves, filters, insulators etc. The metallic waste is mostly composed of carbon and stainless steel. In Finland this metallic waste is planned to be disposed in concrete boxes into bedrock silos. The effects of microbiological activity on the corrosion of decommissioning waste are still unclear and needs to be studied further. A series of semi-field exposure studies was started in October 2011 at the disposal site. Preliminary results of the first year´s on site studies are discussed in this paper. These results show that alkaline environment caused by concrete addition clearly decelerates the microbial growth and biofilm formation as well as the corrosion. Corrosion rate of carbon steel was very low after the first year of disposal simulation study. Corrosion of stainless steel was not detected at all. According to these preliminary results, concrete can be considered to inhibit microbially induced corrosion in disposal systems at least at the early stages of disposal time. The results of this study can be used when evaluating risks of the microbially induced corrosion of metallic materials in the underground repository.

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