Microbially-induced corrosion (MIC) potential of bentonite microorganisms: implications for a deep geological repository for nuclear waste

The integrity of carbon steel canisters in deep geological repositories (DGRs) for high-level radioactive waste (HLW) may be compromised by microbiologically influenced corrosion (MIC) driven by bentonite-associated microorganisms or naturally occuring classes of subsurface microoganisms. This study investigated the MIC potential of anaerobic microbial consortia enriched from Czech bentonite (Cerny Vrch) under repository-relevant conditions. Carbon steel coupons were incubated in selective media targeting nitrate-reducing bacteria (NRB), sulfate-reducing bacteria (SRB), heterotrophs, acetogens, and methanogens, under both static and dynamic flow conditions.A two-stage (2 and 3 month long, respectively) Batch experiment was performed, with the second stage employing inocula from the first to enrich MIC-active consortia. Corrosion rates were quantified, and microbial communities were analyzed using qPCR and 16S rRNA amplicon sequencing. Highest corrosion rates were observed in Nitrate Broth (targeting NRB), R2A (heterotrophs), and Postgate (SRB) media. Organic-rich media supported greater microbial diversity and activity.To simulate worst-case scenarios (such as those that might occur in the event of barrier system failure or unexpected water ingress), dynamic flow column experiments were conducted using NRM and R2A media, alongside static controls.