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Review
. 2024 May 19;12(5):1025.
doi: 10.3390/microorganisms12051025.

Insights into the Impact of Physicochemical and Microbiological Parameters on the Safety Performance of Deep Geological Repositories

Mar Morales-Hidalgo  1 , Cristina Povedano-Priego  1 , Marcos F Martinez-Moreno  1 , Miguel A Ruiz-Fresneda  1 , Margarita Lopez-Fernandez  1 , Fadwa Jroundi  1 , Mohamed L Merroun  1
Affiliations
Review

Insights into the Impact of Physicochemical and Microbiological Parameters on the Safety Performance of Deep Geological Repositories

Mar Morales-Hidalgo et al. Microorganisms. .

Abstract

Currently, the production of radioactive waste from nuclear industries is increasing, leading to the development of reliable containment strategies. The deep geological repository (DGR) concept has emerged as a suitable storage solution, involving the underground emplacement of nuclear waste within stable geological formations. Bentonite clay, known for its exceptional properties, serves as a critical artificial barrier in the DGR system. Recent studies have suggested the stability of bentonite within DGR relevant conditions, indicating its potential to enhance the long-term safety performance of the repository. On the other hand, due to its high resistance to corrosion, copper is one of the most studied reference materials for canisters. This review provides a comprehensive perspective on the influence of nuclear waste conditions on the characteristics and properties of DGR engineered barriers. This paper outlines how evolving physico-chemical parameters (e.g., temperature, radiation) in a nuclear repository may impact these barriers over the lifespan of a repository and emphasizes the significance of understanding the impact of microbial processes, especially in the event of radionuclide leakage (e.g., U, Se) or canister corrosion. Therefore, this review aims to address the long-term safety of future DGRs, which is critical given the complexity of such future systems.

Keywords: bentonite; compaction; corrosion; deep geological repository; microorganism; nuclear waste; radiation; temperature.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
A Spanish bentonite block compacted at a dry density of 1.7 g cm−3. Heatmap of the relative abundance of the samples at genus level in triplicate (duplicates in StB.eD, B, and B.eD). Cut-off: 0.5% of r.a. Different colors show the relative abundance of each genus (the warmer the color, the greater relative abundance). Data from Martinez-Moreno et al. (2023) [68].
Figure 2
Figure 2
High-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) images of thin sections of Amycolatopsis ruanii cells treated with uranium and glycerol-2-phosphate (G2P) showing U-P deposits at cell wall level (arrow), extra- (asterisk) and intracellular (dashed arrow) uranium phosphates (A,E), and their corresponding EDX maps with the distribution of P (C,G), U (D,H), and P + U (B,F). Bar scale: 500 nm (A); 800 nm (B–D); 100 nm (E–H). Figure from Povedano-Priego et al. [90].
Figure 3
Figure 3
VP-FESEM images illustrating the Se transformation from a-Se nanospheres to t-Se nanowires, with an intermediate step of m-Se aggregates by using proteins as a template. The images correspond to samples prepared by growing Stenotrophomonas bentonitica anaerobically. Scale bars: 100 nm (A,B,E,F), 200 nm (C), and 20 nm (D). Yellow arrow in (A): a-Se nanospheres; yellow arrow in (E,F): t-Se nanowires. Figure from Ruiz-Fresneda et al. [108].
Figure 4
Figure 4
Diagrammatic representation of the evolution of the near-field environment for a repository. Modified from [110].
Figure 5
Figure 5
Schematic representation of chemical microbially induced corrosion (CMIC) of copper by sulfate-reducing bacteria (SRB).
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