Abstract
The biogeochemical gradients that will develop across the interface between a highly alkaline cementitious geological disposal facility for intermediate level radioactive waste and the geosphere are poorly understood. In addition, there is a paucity of information about the microorganisms that may populate these environments and their role in biomineralization, gas consumption and generation, metal cycling, and on radionuclide speciation and solubility. In this study, we investigated the phylogenetic diversity of indigenous microbial communities and their potential for alkaline metal reduction in samples collected from a natural analogue for cementitious radioactive waste repositories, the hyperalkaline Allas Springs (pH up to 11.9), Troodos Mountains, Cyprus. The site is situated within an ophiolitic complex of ultrabasic rocks that are undergoing active low-temperature serpentinization, which results in hyperalkaline conditions. 16S rRNA cloning and sequencing showed that phylogenetically diverse microbial communities exist in this natural high pH environment, including Hydrogenophaga species. This indicates that alkali-tolerant hydrogen-oxidizing microorganisms could potentially colonize an alkaline geological repository, which is predicted to be rich in molecular H2, as a result of processes including steel corrosion and cellulose biodegradation within the wastes. Moreover, microbial metal reduction was confirmed at alkaline pH in this study by enrichment microcosms and by pure cultures of bacterial isolates affiliated to the Paenibacillus and Alkaliphilus genera. Overall, these data show that a diverse range of microbiological processes can occur in high pH environments, consistent with those expected during the geodisposal of intermediate level waste. Many of these, including gas metabolism and metal reduction, have clear implications for the long-term geological disposal of radioactive waste.
Highlights
The United Kingdom has an extensive legacy of radioactive waste from more than 60 years of civil and military nuclear technology, and this inventory will only increase with the decommissioning of old facilities and the development of new nuclear power options
The current generic model for disposal is that intermediate level radioactive waste (ILW) will be grouted in steel containers emplaced in the geological disposal facility and eventually the waste will be sealed in the deep subsurface with a cementitious backfill (DEFRA 2008; NDA 2010a; Nirex 2003)
Very little is known about microorganisms that can potentially reduce metals and radionuclides under alkaline conditions, they may potentially control the speciation and solubility of several key radionuclides via complexation with ligands produced by microbial metabolism, by reduction or by mineralization processes
Summary
The United Kingdom has an extensive legacy of radioactive waste from more than 60 years of civil and military nuclear technology, and this inventory will only increase with the decommissioning of old facilities and the development of new nuclear power options. The current generic model for disposal is that ILW will be grouted in steel containers emplaced in the geological disposal facility and eventually the waste will be sealed in the deep subsurface with a cementitious backfill (DEFRA 2008; NDA 2010a; Nirex 2003). Very little is known about microorganisms that can potentially reduce metals and radionuclides under alkaline conditions, they may potentially control the speciation and solubility of several key radionuclides via complexation with ligands produced by microbial metabolism, by reduction or by mineralization processes. Understanding their activities will be critical in underpinning any safety case for a cementitious geodisposal facility
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
