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

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

The Microbiology of Nuclear Waste Disposal

DescriptionThe Microbiology of Nuclear Waste Disposal is a state-of-the-art reference featuring contributions focusing on the impact of microbes on the safe long-term disposal of nuclear waste. This book is the first to cover this important emerging topic, and is written for a wide audience encompassing regulators, implementers, academics, and other stakeholders. The book is also of interest to those working on the wider exploitation of the subsurface, such as bioremediation, carbon capture and storage, geothermal energy, and water quality.Planning for suitable facilities in the U.S., Europe, and Asia has been based mainly on knowledge from the geological and physical sciences. However, recent studies have shown that microbial life can proliferate in the inhospitable environments associated with radioactive waste disposal, and can control the long-term fate of nuclear materials. This can have beneficial and damaging impacts, which need to be quantified.Key FeaturesEncompasses expertise from both the bio and geo disciplines, aiming to foster important collaborations across this disciplinary divideIncludes reviews and research papers from leading groups in the fieldProvides helpful guidance in light of plans progressing worldwide for geological disposal facilitiesIncludes timely research for planning and safety case development<br/

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