51314-4035-Microbial Diversity and Corrosion Behaviour of Carbon Steel and Stainless Steel After One Year Exposure in Alkaline Ground Water

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Product Number: 51314-4035-SG

ISBN: 4035 2014 CP

Author: Leena Carpen

Publication Date: 2014

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During the operation and decommissioning of nuclear power plants a certain amount of contaminated waste is produced. In Finland this low- and intermediate-level waste is transferred to an underground repository where it will be disposed into concrete silos. The metallic waste consists mostly of carbon steel and stainless steel. It is known that microbes can accelerate several corrosion mechanisms such as general corrosion and localised corrosion like pitting and stress corrosion cracking as well as degradation of concrete. However the effect of microbial activity on the corrosion of decommissioning waste and the release of radioactive nuclides is still unclear and needs to be studied further.A series of semi-field exposure studies was started in October 2011 at the disposal site. Carbon steel (AISI 1005) and stainless steel (EN 1.4301) samples together with crushed cement were placed in glass mesocosms (43 L) containing groundwater from the site for a total period of 3 years. In order to estimate the corrosive effects of microbial activity both biotic and abiotic (containing biocides) mesocosms were prepared. To simulate the slow motion of substances in bedrock affecting the waste disposal half of the water volume is changed every 6 months. Corrosion is evaluated by weight loss and verified by microscopy of the steel samples. The bacterial composition of the biofilm formed on the steel was studied using pyrosequencing of the bacterial 16S rRNA genes. The abundance of sulphate reducing bacteria and methanogenic archaea were determined by quantitative PCR. Biofilms were also observed using scanning electron microscopy.Preliminary results of the first year´s on site studies are discussed in this paper. The results of this study can be used when evaluating risks of the microbially induced corrosion of metallic materials in the underground repository.