Microbially induced corrosion (MIC) of carbon steel and stainless steels grades EN 1.4301 and EN 1.4432 in deep bedrock environment

Low and intermediate level radioactive waste (LLW and ILW) comprises of radiation-contaminated material generated during the operation, maintenance and decommissioning of nuclear power plants. The metallic waste contains, e.g., pipes, valves, filters and tools, the majority of which is made of carbon steel and various stainless steels. In Finland at Olkiluoto site, the LLW and ILW have been disposed of in a geological repository located at the depth of 60 to 95 m below surface since 1992. The groundwater in the bedrock of the disposal environment contains microbes: bacteria and archaea, which decisively influence the surface processes of the waste materials. Therefore, understanding microbially induced corrosion (MIC) in a deep bedrock environment is important for evaluating the long-term safety of LLW and ILW disposal. A laboratory system for studying the MIC of metallic decommissioning waste from nuclear power plant was designed and developed. In this work, the results from laboratory investigations concentrating on carbon steel (AISI 1005) and stainless steel grades EN 1.4301 (AISI 304) and EN 1.4432 (AISI 316L) are reported. The micro-organisms of interest here are sulphate reducing bacteria (SRB) and methanogen archaea, both frequently encountered in anoxic deep bedrock environment.