Assessing microbial impact on trapping of radioactive contaminants from groundwaters by minerals

Informations projet

MITRad

N° de convention de subvention: 101024524

DOI

10.3030/101024524

Projet clôturé

Date de signature de la CE 23 Février 2021

Date de début 1 Mai 2021

Date de fin 31 Mai 2023

Financé au titre de

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Coût total

€ 191 852,16

Contribution de l’UE

€ 191 852,16

Coordonné par

LINNEUNIVERSITETET
Sweden

Periodic Reporting for period 1 - MITRad (Assessing microbial impact on trapping of radioactive contaminants from groundwaters by minerals)

Période du rapport: 2021-05-01 au 2023-04-30

Résumé du contexte et des objectifs généraux du projet

One of the most serious environmental concerns is the wide occurrence of radionuclides in natural and anthropogenic environments and the safe management of spent nuclear fuel (SNF) and high-level radioactive waste (HLW) generated by nuclear facilities. As of 2016 over 58,000 tons of SNF are required for disposal in repositories as soon as they become operational. The key factor for the safe operation of a geological repository is an oxygen-free environment in groundwaters to retard the degradation of SNF. Essential are the secondary minerals forming directly from the groundwater that act as scavengers for contaminants. For example, uranium (U) - the main constituent of SNF and other important radioactive elements present in SNF can be potentially trapped by secondary minerals in deep surface environments.
Natural U in deep groundwater is extensively studied in connection with the search for suitable locations for the final disposal of SNF. The U removal process in deep aquifers depends on environmental and geochemical conditions and is associated with fractionation of the U isotopes (238U and 235U), which serves as an important isotope proxy for redox specific scenarios in local to global temporal and spatial scales. The 238U/235U vary substantially in both magnitude and direction when mediated either by dissolved or solid inorganic species and/or microorganisms. Yet, multiple effects of mineral and microbial species on U retention and isotope fractionation in natural settings are poorly explored. These are crucial parameters for the long-term safety assessment safety of deep SNF repositories and require the integration of reliable geochemical models.
The main objective of the MSCA project is to increase a fundamental understanding of U removal pathways during its interaction with various minerals mediated by abiotic and microbial species in deep granitic rock-groundwater systems. The main research tasks were achieved by implementing a comprehensive experimental approach involving U speciation techniques in minerals, U isotope signatures in minerals and deep groundwaters, integration with microbiological studies, and the cross-correlation between natural and laboratory studies. This was achieved by combining the experimental approach with coherent project work packages for a multi-technique study of U in minerals collected after short- and long-term experiments from the engineered facility and from deep drilled boreholes near planned SNF repository in Sweden.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

During the project, five field campaigns were conducted for groundwater and mineral sampling, from deep boreholes located in Äspö and Forsmark, which are both engineered and natural analogues to industrial geological repositories for long-term disposal of SNF and HLW. The groundwater and mineral samplings aimed for perform laboratory incubation experiments (total 12 months) and to assess the impact of different water pre-treatment and incubation conditions on U removal rates. Several analytical techniques were utilized to reveal morphological features, U segregation, and U speciation on a micro-scale level and to link these data to isotope fractionation signatures. The studies were performed on materials selected from deep engineered and natural settings in Sweden including U-deficient and U-rich groundwaters, and laboratory experiments to estimate the dynamics and mechanism of U uptake mechanisms by carbonate minerals under different conditions.
The results of the project were reported at three international conferences: 19th Radiochemical Conference, EGU General Assembly 2022, Goldschmidt ’22 and published in one peer-reviewed article from Springer Nature Group: Communications Earth & Environment. This publication was followed by more than 80 outreach activities in social and scientific-popular resources in several countries: Sweden, Germany, Spain, United States, United Kingdom, Mexico, Argentina, Chile, and Vietnam, with nearly 60 million reaches as of May 2023. The published article summarizes project’s main findings, received a lot of recognition in all major Swedish newspapers, in the popular scientific press in the USA, and through Europas Press to major Spanish speaking newspapers. Several spin-off projects have been initiated with the industrial partner and the host institution following the success of the MSCA project. The interplay between microbiology and geochemistry has involved fruitful multidisciplinary collaborations nationally and internationally.
The project leader and network already have a good dialogue with the nuclear waste management (SKB), which assures that the results will be exploited and directly implemented in the planning of a nuclear waste repository, and thus of direct societal relevance. Still, the implications are more far-reaching and broader than for repository planning and involve groundwater quality and contaminated area remediation, which are under the responsibility of a wide number of stakeholders and authorities, from local to international levels as the following. Key stakeholders of the project are policymakers from municipal and industrial fields and academy experts involving (bio)geochemists, environmental scientists, remediation engineers, and microbiologists. The communication, guidance and supporting activities are directly arranged by several environmental agencies and research institutes.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

We demonstrated for the first time the long-term microbial effect on the uptake of U by secondary minerals that may be substantial species in deep anoxic aquifers compared to surficial settings due to different environment-specific conditions. The bacteria-driven degradation of organic constituents was shown to influence the formation of sulfidic species, facilitating reduction dissolved U with subsequent selective trapping by minerals. The isotope analyses of U in fracture water and calcite minerals provided new data on U long-term turn over and redox behaviour. In the 17-year experiment, in deep bedrock, we identified minerals that bound significant amounts of U. Our results indicate that naturally occurring bacteria may significantly affect U removal from groundwater and prevent other hazardous substances from spreading further into the environment.
The project results are useful for the remediation of contaminated groundwater, but also to improve safety assessment for the storage of SNF and HLW in deep geological repositories. The SNF is planned to be encapsulated in copper cylinders and then buried at a depth of nearly 500 m and kept in deep bedrock for at least 100,000 years, the time that the SNF must be kept separate from people so that the radioactive radiation becomes significantly less harmful. What happens if the copper capsules are damaged is of great importance. Should there be a leak from a copper capsule, it probably means that the same underground bacteria will help prevent U and other radioactive species from spreading further into the environment. Thus, the results of the project are another building block to the basis for long-term safety assessment of the nuclear waste facilities that are planned to be built in Sweden and elsewhere. Besides that, U is a radioactive element and toxic heavy metal that occurs naturally in the bedrock and is toxic both to humans and to the ecosystem. Preventing U from spreading in groundwater is a serious issue that must be solved by common research, development, and implementation efforts.

Objects and Goals of the MITRad project