Model for the Microbiological Corrosion of Copper Containers in a Deep Geologic Repository
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0RGHOIRUWKH0LFURELRORJLFDO&RUURVLRQRI&RSSHU&RQWDLQHUVLQD 'HHS*HRORJLF5HSRVLWRU\ Fraser King1, Miroslav Kolar2, Simcha Stroes-Gascoyne3, and Peter Maak4 1 Integrity Corrosion Consulting Ltd, 6732 Silverview Drive NW, Calgary, Alberta, Canada T3B 3K8 2 LS Computing, 39-5625 Silverdale Drive NW, Calgary, Alberta, Canada T3B 4N5 3 Atomic Energy of Canada Limited, Whiteshell Laboratories, Pinawa, Manitoba, Canada R0E 1L0 4 Ontario Power Generation, 700 University Avenue, Toronto, Ontario, Canada M5G 1X6 $%675$&7 A model has been developed to predict the impact of microbiological processes on the long-term corrosion behaviour of copper containers in a deep geologic repository. The model accounts for a range of aerobic and anaerobic microbial processes. Various factors expected to limit the extent of microbial activity in the repository, such as the lack of water, evolving redox conditions, and the nutrient-poor environment, are taken into account in the model. Amongst other effects, the model predicts that microbial activity will not occur close to the container in the presence of highly compacted bentonite buffer material. ,1752'8&7,21 Any assessment of the long-term safety of the deep geologic disposal of nuclear waste must include a prediction of the lifetime of the container. As with any other potential corrosion process, the impact of microbiologically influenced corrosion (MIC) on the lifetime of the container must be considered. Unlike other corrosion processes, however, relatively little attention has been paid to predictions of MIC. For copper containers, the two most likely forms of MIC are general corrosion and, possibly, stress corrosion cracking (SCC) [1,2]. General corrosion is possible if sulphide is produced by sulphate-reducing bacteria and reaches the container surface [1-3]. Although few, if any, cases of microbiologically-supported SCC of Cu alloys have been reported in the literature [1,2], microbes involved in the nitrogen cycle do produce species known to induce the SCC of copper, such as ammonia, nitrite and acetate ions [1-4]. It should be noted that these two processes would occur under completely different redox conditions, the former occurring only under anoxic conditions and the latter under oxidizing conditions in the presence of O2 and/or Cu(II). Predictions of the MIC behaviour of the container must, therefore, take into account the evolution of the environmental conditions within the repository. In general, the environmental conditions in the repository are harsh and are not expected to support extensive microbial activity [1-3,5-7]. In particular, the presence of highly compacted bentonite and the desiccation of the clay due to heat from the container are predicted to prevent microbial activity close to the container surface at any time during the evolution in the repository environment. Under these conditions, formation of a biofilm on the container surface is unlikely. In the absence of a biofilm, none of the aggressive forms of MIC reported in the literature [8] will oc
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