Joint project: Umwandlungsmechanismen in Bentonitbarrieren - Subproject B: Einfluss von mikrobiellen Prozessen auf die Bentonitumwandlung

Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters.Für die tiefengeologische Lagerung von Wärme-entwickelnden, hoch-radioaktiven Abfällen kommen Bentonite aufgrund ihrer hohen Quellfähigkeit und ihrer geringen hydraulischen Leitfähigkeit als geo-technische Barriere in Betracht, welche sich zwischen der technischen Barriere (Behälter mit Abfall) und der geologischen Barriere (Wirtsgestein) befindet. Im Rahmen des Verbundprojektes „UMB“ (Umwandlungsmechanismen in Bentonitbarrieren) der Kooperationspartner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Fachbereich Endlagersicherheitsforschung), der Universität Greifswald (Institut für Geographie und Geologie), der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Arbeitsbereich Technische Mineralogie), der Technischen Universität München (TUM; Fachgebiet Theoretische Chemie, Quantenchemie) und dem Helmholtz-Zentrum Dresden Rossendorf (HZDR Institut für Ressourcenökologie) sollen abgesicherte, objektive Kriterien zur Auswahl geeigneter Bentonite für den Einsatz in Endlagern für wärmeentwickelnde Abfälle in Tonformationen entwickelt werden. Das HZDR analysierte hierfür die Entwicklung der mikrobiellen Diversität in den Bentoniten B36 und SD80 in Abhängigkeit von verschiedenen Parametern (Porenlösung, Temperatur, Anwesenheit von Substraten) um den möglichen Einfluss von Mikroorganismen auf die Umwandlungsprozesse im Bentonit zu erfassen. Die Bentonite wurden hierfür bei der GRS (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH) mit Opalinuston-Porenlösung bzw. verdünnter Gipshut-Lösung versetzt. Die Ansätze inkubierten in gasdichten Glasflaschen bei 25 °C, 60 °C und 90 °C für jeweils ein und zwei Jahre („Langzeit“). Des Weiteren wurden am HZDR B36 Mikrokosmen mit Opalinustonporenlösung angesetzt, welche für drei Monate bei 30 °C inkubierten („Kurzzeit“). Über die drei Monate verteilt wurden sechs Probenahmen durchgeführt, und die mikrobielle Diversität sowie ausgewählte geochemische Paramater bestimmt

Joint project: Retention of radionuclides relevant for final disposal in natural clay rock and saline systems: Subproject 2: Geochemical behavior and transport of radionuclides in saline systems in the presence of repository-relevant organics

The objective of this project was to study the influence of increased salinities on interaction processes in the system radionuclide – organics – clay – aquifer. For this purpose, complexation, redox, sorption, and diffusion studies were performed under variation of the ionic strength (up to 4 mol/kg) and the background electrolyte. The U(VI) complexation by propionate was studied in dependence on ionic strength (up to 4 mol/kg NaClO4) by TRLFS, ATR FT-IR spectroscopy, and DFT calculations. An influence of ionic strength on stability constants was detected, depending on the charge of the respective complexes. The conditional stability constants, determined for 1:1, 1:2, and 1:3 complexes at specific ionic strengths, were extrapolated to zero ionic strength. The interaction of the bacteria Sporomusa sp. MT-2.99 and Paenibacillus sp. MT-2.2 cells, isolated from Opalinus Clay, with Pu was studied. The experiments can be divided into such without an electron donor where biosorption is favored and such with addition of Na-pyruvate as an electron donor stimulating also bioreduction processes. Moreover, experiments were performed to study the interactions of the halophilic archaeon Halobacterium noricense DSM-15987 with U(VI), Eu(III), and Cm(III) in 3 M NaCl solutions. Research for improving process understanding with respect to the mobility of multivalent metals in systems containing humic matter was focused on the reversibility of elementary processes and on their interaction. Kinetic stabilization processes in the dynamics of humate complexation equilibria were quantified in isotope exchange studies. The influence of high salinity on the mobilizing potential of humic-like clay organics was systematically investigated and was described by modeling. The sorption of Tc(VII)/Tc(IV) onto the iron(II)-containing minerals magnetite and siderite was studied by means of batch sorption experiments, ATR FT-IR and X-ray absorption spectroscopy. The strong Tc retention at these minerals could be attributed to surface-mediated reduction of Tc(VII) to Tc(IV). An influence of ionic strength was not observed. The influence of ionic strength (up to 3 mol/kg) and background electrolyte (NaCl, CaCl2, MgCl2) on U(VI) sorption onto montmorillonite was studied. The U(VI) sorption is influenced by the background electrolyte, the influence of ionic strength is small. Surface complexation modeling was performed applying the 2SPNE SC/CE model. Surface complexation constants were determined for the NaCl and CaCl2 system and were extrapolated to zero ionic strength. Surface complexation in mixed electrolytes can be modeled applying surface complexation constants derived for pure electrolytes. The influence of citrate on U(VI) diffusion in Opalinus Clay was studied using Opalinus Clay pore water as background electrolyte. The diffusion parameter values obtained for the HTO through-diffusion and the U(VI) in-diffusion in the absence of citric acid were in agreement with literature data. In the presence of citric acid, U(VI) diffusion was significantly retarded, which was attributed to a change in speciation, probably U(VI) was reduced to U(IV). Larger-scale heterogeneous material effects on diffusive transport were investigated with PET. Diffusion parameters were derived by optimum fit of a FEM-model to the measurement. These parameters are in accordance with the results from 1D-through-diffusion experiments. Deviations from the simple transversal-isotropic behavior, which are identified as residuals from the model, are indications for heterogeneous transport on the mm-scale. PET measurements were also conducted in order to display the improvement of the EDZ with waterglass injections. These experiments enable to draw conclusions on the complex reactive transport process and thus an estimation of the achieved improvement of the barrier function. The image reconstruction procedure was largely improved, mainly with the aid of Monte-Carlo simulations, and now allows quantitative analysis and error estimation

Influence of riboflavin on the reduction of radionuclides by Shewanella oneidenis MR-1

Uranium (as UO22+), technetium (as TcO4−) and neptunium (as NpO2+) are highly mobile radionuclides that can be reduced enzymatically by a range of anaerobic and facultatively anaerobic microorganisms, including Shewanella oneidensis MR-1, to poorly soluble species. The redox chemistry of Pu is more complicated, but the dominant oxidation state in most environments is highly insoluble Pu(IV), which can be reduced to Pu(III) which has a potentially increased solubility which could enhance migration of Pu in the environment. Recently it was shown that flavins (riboflavin and flavin mononucleotide (FMN)) secreted by Shewanella oneidensis MR-1 can act as electron shuttles, promoting anoxic growth coupled to the accelerated reduction of poorly-crystalline Fe(III) oxides. Here, we studied the role of riboflavin in mediating the reduction of radionuclides in cultures of Shewanella oneidensis MR-1. Our results demonstrate that the addition of 10 μM riboflavin enhances the reduction rate of Tc(VII) to Tc(IV), Pu(IV) to Pu(III) and to a lesser extent, Np(V) to Np(IV), but has no significant influence on the reduction rate of U(VI) by Shewanella oneidensis MR-1. Thus riboflavin can act as an extracellular electron shuttle to enhance rates of Tc(VII), Np(V) and Pu(IV) reduction, and may therefore play a role in controlling the oxidation state of key redox active actinides and fission products in natural and engineered environments. These results also suggest that the addition of riboflavin could be used to accelerate the bioremediation of radionuclide-contaminated environments

Joint project: Umwandlungsmechanismen in Bentonitbarrieren - Subproject B: Einfluss von mikrobiellen Prozessen auf die Bentonitumwandlung

Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters.Für die tiefengeologische Lagerung von Wärme-entwickelnden, hoch-radioaktiven Abfällen kommen Bentonite aufgrund ihrer hohen Quellfähigkeit und ihrer geringen hydraulischen Leitfähigkeit als geo-technische Barriere in Betracht, welche sich zwischen der technischen Barriere (Behälter mit Abfall) und der geologischen Barriere (Wirtsgestein) befindet. Im Rahmen des Verbundprojektes „UMB“ (Umwandlungsmechanismen in Bentonitbarrieren) der Kooperationspartner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Fachbereich Endlagersicherheitsforschung), der Universität Greifswald (Institut für Geographie und Geologie), der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Arbeitsbereich Technische Mineralogie), der Technischen Universität München (TUM; Fachgebiet Theoretische Chemie, Quantenchemie) und dem Helmholtz-Zentrum Dresden Rossendorf (HZDR Institut für Ressourcenökologie) sollen abgesicherte, objektive Kriterien zur Auswahl geeigneter Bentonite für den Einsatz in Endlagern für wärmeentwickelnde Abfälle in Tonformationen entwickelt werden. Das HZDR analysierte hierfür die Entwicklung der mikrobiellen Diversität in den Bentoniten B36 und SD80 in Abhängigkeit von verschiedenen Parametern (Porenlösung, Temperatur, Anwesenheit von Substraten) um den möglichen Einfluss von Mikroorganismen auf die Umwandlungsprozesse im Bentonit zu erfassen. Die Bentonite wurden hierfür bei der GRS (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH) mit Opalinuston-Porenlösung bzw. verdünnter Gipshut-Lösung versetzt. Die Ansätze inkubierten in gasdichten Glasflaschen bei 25 °C, 60 °C und 90 °C für jeweils ein und zwei Jahre („Langzeit“). Des Weiteren wurden am HZDR B36 Mikrokosmen mit Opalinustonporenlösung angesetzt, welche für drei Monate bei 30 °C inkubierten („Kurzzeit“). Über die drei Monate verteilt wurden sechs Probenahmen durchgeführt, und die mikrobielle Diversität sowie ausgewählte geochemische Paramater bestimmt

Data publication: Microscopic and spectroscopic bioassociation study of uranium(VI) with an archaeal Halobacterium isolate

Bei diesem Datensatz handelt es sich um die Primärdaten der Untersuchung der Wechselwirkungen eines halophilen Archaeons mit Uran(VI). Dazu wurden Konzentrationsbestimmungen mittels ICP-MS durchgeführt, Lumineszenzspektren mittels zeitaufgelöster laserinduzierter Lumineszenzspektroskopie und IR Spektren aufgenommen. Darüber hinaus wurden Bilder der Zellen mit Hilfe der Fluoreszenzmikroskopie aufgenommen

Friend or Foe? Microbial impact of Calcigel bentonite on metal materials used for nuclear waste repository

Multi-barrier concept is a favorable option to store high-level nuclear waste (HLW) in a deep geological repository. Bentonites are processed clay materials that are considered as a geotechnical barrier for metal containers storing HLW. To understand the impact of indigenous microorganisms from bentonites on these metal materials, anaerobic microcosms incubating Calcigel bentonite, synthetic Opalinus clay (OPA) porewater, lactate (one of the organic acids in natural OPA porewater) or H2 gas (product from anaerobic metal corrosion) with or without cast iron metal plates were conducted for up to 9 months in triplicates for each condition and time point (sampling every 3 months). The amplicon sequencing targeting V4 region of 16S rRNA genes showed that microbial communities of raw Calcigel bentonites mainly comprised phyla Acidobacteria, Actinobacteria, Chloroflexi, Firmicutes, Proteobacteria and Methylomirabilota. In the microcosms with lactate, enrichment of Bacillaceae (Firmicutes) and uncultured MB-A2-108 (Actinobacteriota) were observed; whereas in the presence of both lactate and cast iron, genera of Firmicutes, namely Desulfotomaculum, Desulfitobacterium and Desulfallas-Sporotomaculum, were highly enriched (relative abundance ranged from 60% to 95%) associating with large decrease in sulfate and lactate concentration. These bacteria appeared to be driven by H2 gas generated from metal corrosion. Moreover, SEM-EDX analyses showed that the metal surface was corroded and covered by a carbonate passivation layer. In this layer, FeS appeared to be formed, further suggesting the influence on cast iron corrosion and formation of secondary minerals induced by sulfate-reducing bacteria.On the other hand, we supplied N2 gas mixed with H2 and CO2 (80:10:10) to stimulate growth of H2-oxidizing sulfate reducers. GC analyses showed that in the microcosms without cast iron, the content of H2 gas in the headspace decreased accompanying with decrease in sulfate concentration (measured via IC). However, in the microcosms with cast iron we noted large accumulation of H2 gas (~ 5 times more than initial value) and greater decrease in sulfate concentration. Similarly, surface corrosion was visible by SEM-EDX, and thre carbonate passivation layer with possible FeS precipitates was formed on the metal surface but in a shorter timeframe (3 months). Hence, we speculated that certain autotrophic H2-oxidizing sulfate reducers also corroded cast iron metal, and their taxonomy and mechanisms will be identified using metagenomic approaches.Altogether we concluded that microbial communities in Calcigel bentonites lead to microbially induced corrosion for cast iron under certain conditions, yet interestingly, the formation of passivation layer enhances the resistance for further metal corrosion. The actual impact of indigenous microorganisms in different bentonites, either disadvantageous or beneficial, on metal containers for HLW requires comprehensive investigations

Friend or Foe? Microbial impact of Calcigel bentonite on metal materials used for nuclear waste repository

Multi-barrier concept is a favorable option to store high-level nuclear waste (HLW) in a deep geological repository. Bentonites are processed clay materials that are considered as a geotechnical barrier for metal containers storing HLW. To understand the impact of indigenous microorganisms from bentonites on these metal materials, anaerobic microcosms incubating Calcigel bentonite, synthetic Opalinus clay (OPA) porewater, lactate (one of the organic acids in natural OPA porewater) or H2 gas (product from anaerobic metal corrosion) with or without cast iron metal plates were conducted for up to 9 months in triplicates for each condition and time point (sampling every 3 months). The amplicon sequencing targeting V4 region of 16S rRNA genes showed that microbial communities of raw Calcigel bentonites mainly comprised phyla Acidobacteria, Actinobacteria, Chloroflexi, Firmicutes, Proteobacteria and Methylomirabilota. In the microcosms with lactate, enrichment of Bacillaceae (Firmicutes) and uncultured MB-A2-108 (Actinobacteriota) were observed; whereas in the presence of both lactate and cast iron, genera of Firmicutes, namely Desulfotomaculum, Desulfitobacterium and Desulfallas-Sporotomaculum, were highly enriched (relative abundance ranged from 60% to 95%) associating with large decrease in sulfate and lactate concentration. These bacteria appeared to be driven by H2 gas generated from metal corrosion. Moreover, SEM-EDX analyses showed that the metal surface was corroded and covered by a carbonate passivation layer. In this layer, FeS appeared to be formed, further suggesting the influence on cast iron corrosion and formation of secondary minerals induced by sulfate-reducing bacteria.On the other hand, we supplied N2 gas mixed with H2 and CO2 (80:10:10) to stimulate growth of H2-oxidizing sulfate reducers. GC analyses showed that in the microcosms without cast iron, the content of H2 gas in the headspace decreased accompanying with decrease in sulfate concentration (measured via IC). However, in the microcosms with cast iron we noted large accumulation of H2 gas (~ 5 times more than initial value) and greater decrease in sulfate concentration. Similarly, surface corrosion was visible by SEM-EDX, and thre carbonate passivation layer with possible FeS precipitates was formed on the metal surface but in a shorter timeframe (3 months). Hence, we speculated that certain autotrophic H2-oxidizing sulfate reducers also corroded cast iron metal, and their taxonomy and mechanisms will be identified using metagenomic approaches.Altogether we concluded that microbial communities in Calcigel bentonites lead to microbially induced corrosion for cast iron under certain conditions, yet interestingly, the formation of passivation layer enhances the resistance for further metal corrosion. The actual impact of indigenous microorganisms in different bentonites, either disadvantageous or beneficial, on metal containers for HLW requires comprehensive investigations

Data publication: Europium(III) as luminescence probe for interactions of a sulfate-reducing microorganism with potentially toxic metals

The stored data sets represent both the raw data and the evaluated data that were used for the publication about interactions of a sulfate-reducing bacterium with europium(III)

EURAD MAGIC project – Chemo-Mechanical AGIng of Cementitious materials under coupled disturbances based on a multi-scale approach

Introduction The long-term chemo-mechanical performance of the cementitious components of a radioactive wastes repository depends notably on the cement formulation as well as on the bio/geochemistry of the disposal environment and the interactions with other near-field materials.Despite the extensive R&D studies carried out in the last decades, the alteration processes in ce-mentitious material under complex coupled perturbation phenomena are still not fully explored and understood, especially the link between the chemical and the mechanical evolution. Moreover, recent innovations in terms of material formulations (low-pH cements notably) require dedicated R&D to better understand how their long-term mechanical performance is influenced by the host rock and the near field conditions (i.e., pore saturation, chemical evolution of the barriers, microbial impact and gas formation).Summary and objectivesThe MAGIC WP within the European Joint Program on Radioactive Waste Management (EURAD) is a project that will assess the impact of several simultaneous chemical processes (hydrolysis, multi-ionic attack (i.e. sulfate and magnesium, carbonation) on the mechanical properties of cementitious materials and their evolution. The WP proposes different processes to assess the long-term perfor-mance of cement based materials, including a hydraulic transient (re-saturation period with waters from different geological media). It will leverage and build on the advances on past and current Euro-pean projects (i.e. CEBAMA, PREDIS, ACED, DONUT WPs) and explicitly exclude repeating activi-ties already conducted in these previous or ongoing projects.The use of several cement formulations will help to compare their long-term performance under the same conditions. Another important aspect to be considered is the impact of microbial activity on the evolution of the chemo-mechanical properties of cementitious materials. The integration of innovative material characterization and modelling from nano to laboratory to full scale is a key issue of the pro-ject. The final goal is to obtain an improved understanding of mechanical ageing of cementitious materials exposed to various representative chemical disturbances coming from the disposal envi-ronment including 3 main objectives:• To quantify the mechanical multi-scale evolution of cementitious materials under the chemical degradation expected in repository environments, identifying the main reactive pathways at the repos-itory scale during the re-saturation phase and at the saturated conditions. • To obtain a reference chemo-mechanical model of Portland and low-pH concretes exposed to relevant disposal environments, considering representative boundary conditions. • To estimate the extent of the impact of microbial activity on concrete properties (low-pH and Portland cement) in partially and fully saturated media.The project started in June 2021 for a duration of 3 years