Microbial responses to elevated temperature: Evaluating bentonite mineralogy and copper canister corrosion within the long-term stability of deep geological repositories of nuclear waste

• Published in: The Science of the total environment 2024-03, Vol.915, p.170149-170149, Article 170149
• Main Authors: Martinez-Moreno, Marcos F., Povedano-Priego, Cristina, Mumford, Adam D., Morales-Hidalgo, Mar, Mijnendonckx, Kristel, Jroundi, Fadwa, Ojeda, Jesus J., Merroun, Mohamed L.
• Format: Article
• Language: English
• Subjects: Compacted bentonite; Copper corrosion; High temperature; Microbial diversity; Nuclear repository; Sulfate-reducing bacteria
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.170149

Deep Geological Repositories (DGRs) consist of radioactive waste contained in corrosion-resistant canisters, surrounded by compacted bentonite clay, and buried few hundred meters in a stable geological formation. The effects of bentonite microbial communities on the long-term stability of the repository should be assessed. This study explores the impact of harsh conditions (60 °C, highly-compacted bentonite, low water activity), and acetate:lactate:sulfate addition, on the evolution of microbial communities, and their effect on the bentonite mineralogy, and corrosion of copper material under anoxic conditions. No bentonite illitization was observed in the treatments, confirming its mineralogical stability as an effective barrier for future DGR. Anoxic incubation at 60 °C reduced the microbial diversity, with Pseudomonas as the dominant genus. Culture-dependent methods showed survival and viability at 60 °C of moderate-thermophilic aerobic bacterial isolates (e.g., Aeribacillus). Despite the low presence of sulfate-reducing bacteria in the bentonite blocks, we proved their survival at 30 °C but not at 60 °C. Copper disk's surface remained visually unaltered. However, in the acetate:lactate:sulfate-treated samples, sulfide/sulfate signals were detected, along with microbial-related compounds. These findings offer new insights into the impact of high temperatures (60 °C) on the biogeochemical processes at the compacted bentonite/Cu canister interface post-repository closure. [Display omitted] •No bentonite illitization was observed over one-year anoxic incubation at 60 °C.•Sulfate-Reducing Bacteria resist tyndallization and were enhanced by nutrient addition.•Some aerobic bacteria thrive at 60 °C, while anaerobic bacteria only at 30 °C.•Microbial diversity was reduced at 60 °C being Pseudomonas the dominant genus.