Speciation Of Radionuclides Research Articles

Immobilization of radioactive sulphate waste simulate in polymer–cement composite based on recycled expanded polystyrene foam: evaluation of the final waste form resistance for Cs-134 and Co-60 leachability

The present study investigates to incorporate spiked sulfate solution simulate into polymer–cement composite (PCC) based on recycled expanded polystyrene foam. The main aim is to convert the waste stream into leach resistance solid forms able to slow down or even to retard the back release of hazardous radionuclides to the surrounding. Effective parameters e.g. leachant medium, temperature, radioactivity contents, leachant volumes and radionuclides speciation versus the leaching time were studied. The incremental leach rate (Rn, cm/day) and the leach index (Lx) were evaluated for the final waste form after 145 days. The experimental results revealed that the Lx for the all variances can fulfil the waste acceptance criteria for the disposal facility and are above the threshold value of 6. Moreover, leach rate percentages for Cs-134 and Co-60 were not exceeding 2%. The acquired data, based on lab leaching experiments, can recommend the developed PCC under consideration for solidification of radioactive sulphate waste stream safely.

Particulate matter from water moss of a large Siberian river: Morphometric, mineral, elemental and radionuclide composition

Particulate matter trapped by tufts of water moss Fontinalis antipyretica inhabiting fast flowing waters of the Yenisei River (Siberia, Russia) contaminated with artificial radionuclides has been studied as a potential monitor of radioactive releases to the river. Particulate matter, which was removed from wet tufts of water moss of the Yenisei by rinsing them in water, constituted at least 38% of bulk dry weight of the moss biomass sample and was similar in the contents of chemical elements, minerals, organic matter, and artificial radionuclides to bottom sediments of the Yenisei. Considerable bulk percentages of artificial radionuclides in the sample of water moss, 77% of 137Cs, 44% of 60Co, 41% of 152Eu, 55% of 154Eu, 66% of 241Am, and 34–36% of plutonium were associated with extracellular particles. The comparative study and correlation analysis suggested that 137Cs was mainly associated with mineral particles trapped by moss and that organic matter was responsible for binding plutonium in samples of water moss. Consequently, analysis of extracellular particles of water moss can provide data on contents and speciation of radionuclides transported by water current. Although a considerably high proportion of particulate matter had been washed out from tufts of water moss, some extracellular mineral particulate material and a large number of epiphytic diatoms remained attached to leaves of water moss. Our study proves that particulate matter trapped by water moss can be used as an informative monitor to trace radioactive pollutants transported by water current in running waters deficient in bottom sediments and potential biomonitors.

Unveiling fungal diversity in uranium and glycerol-2-phosphate-amended bentonite microcosms: Implications for radionuclide immobilization within the Deep Geological Repository system

Uranium (U) represents the preeminent hazardous radionuclide within the context of nuclear waste repositories. Indigenous microorganisms in bentonite can influence radionuclide speciation and migration in Deep Geological Repositories (DGRs) for nuclear waste storage. While bacterial communities in bentonite samples have been extensively studied, the impact of fungi has been somewhat overlooked. Here, we investigate the geomicrobiological processes in bentonite microcosms amended with uranyl nitrate and glycerol-2-phosphate (G2P) for six-month incubation. ITS sequencing revealed that the fungal community was mainly composed of Ascomycota (96.6 %). The presence of U in microcosms enriched specific fungal taxa, such as Penicillium and Fusarium, potentially associated with uranium immobilization mechanisms. Conversely, the amendment of U into G2P-suplemented samples exhibited minimal impact, resulting in a fungal community akin to the control group. Several fungal strains were isolated from bentonite microcosms to explore their potential in the U biomineralization, including Fusarium oxysporum, Aspergillus sp., Penicillium spp., among others. High Annular Angle Dark-Field Scanning Transmission Electron Microscopy (HAADF) analyses showed the capacity of F. oxysporum B1 to form U-phosphate mineral phases, likely mediated by phosphatase activity. Therefore, our study emphasizes the need to take into account indigenous bentonite fungi in the overall assessment of the impact of microbial processes in the immobilization of U within DGRs environments.

Binding of uranyl cations to a Zr-based metal-organic framework by density functional theory

Zr-based metal–organic frameworks (Zr-MOFs) have been widely used as ion adsorbents for the removal or extraction of toxic and/or radionuclide species from aqueous solutions. However, the mechanisms by which uranyl cations (UO22+) interact with Zr-MOFs have not been established. In this work, the nature of the bonding of uranyl cations with a Zr-MOF was determined using density functional theory for nineteen structurally distinct candidate complexes. The results showed that in all cases the binding energy was of the order of 1.5 eV, but depended on the specific bonding site. The most stable structure involved coordination of the uranyl cation and two structurally distinct oxygens in the Zr-MOF metal node. It was also found that higher degree of deprotonation in Zr-MOF correlated with higher binding energy between the Zr-MOF and uranyl cations. These insights can aid in the design of Zr-MOFs with optimized features for efficient capture of uranyl cations.

Effect of boric acid on 106Ru radionuclide speciation in aqueous solutions

Effect of boric acid on 106Ru radionuclide speciation in aqueous solutions

X-ray absorption fine structure (XAFS)-based radionuclide research at the KIT Light Source

Abstract. In the past two decades, X-ray absorption spectroscopy (XAS) and related synchrotron-based radionuclide speciation techniques have become indispensable, supporting open issues in fundamental radiochemistry and nuclear waste disposal alike. Physicochemical structure information – encoded in the element-specific X-ray absorption fine structure (XAFS) – is obtained by the precise determination of the linear mass absorption coefficient μ(E) of a specimen in an X-ray energy window ΔE encompassing an electronic bonding level of a selected atom type. The characteristic modulations of μ(E) in the vicinity of an “absorption edge” (i.e., the steeply rising absorption probability of photons tuned to the binding energy of inner shell “core” electrons) are attributed to electronic transitions into unoccupied states due to the photoelectric effect. While absorption features close to the edge (arising from excitations into molecular orbitals or empty band structure levels close to the Fermi level) are generally denoted as an X-ray absorption near-edge structure (XANES), the scattering states at higher excitation energies are causing the well-known extended X-ray absorption fine structure (EXAFS). EXAFS oscillations of the post-edge μ(E) are caused by the periodicity of the constructive and destructive interference of outbound and backscattered inbound photoelectron waves (superimposing at the absorbing atom site) when continuously increasing the excitation energy. Quantitative analysis of EXAFS data based on electron scattering theory is a well-established short-range structural probe, providing precise values of interatomic distances (between the absorber atom and its neighbors) and additional information on the type, number, and ordering of neighbor atoms within a local cluster. Recent significant advancements in the quantum theoretical description of core-excited final states have been successful in overcoming persisting ambiguities in XANES data interpretation. Meanwhile, although there are more than 50 synchrotron radiation centers operational in the world, facilities with specialized beamline infrastructure and safety protocols to allow experiments on radioactive samples with activities beyond the exemption limits are still scarce. At the KIT Light Source (at the Karlsruhe Institute of Technology, Karlsruhe, Germany), the Institute for Nuclear Waste Disposal (Institut für Nukleare Entsorgung, INE) operates two beamline end-stations dedicated to the investigation of radionuclide materials by XAFS spectroscopy and related techniques, i.e., the INE-Beamline (operational since 2005) and the ACT station of the CAT-ACT (CATalysis and ACTinide) wiggler beamline (operational since 2016). Samples with total activities amounting to 1.0×106 times the isotope specific exemption limits and 200 mg of fissile isotopes 235U and 239Pu are feasible at both beamlines. Highly versatile detection systems and sample holders – generally avoiding extensive shielding or sample handling in a glove box – have been conceived since the initial commissioning of the beamlines and have enabled unique XAFS measurements such as the first ever investigation of aqueous technetium species at the Tc L3 edge. Investigations of highly radioactive specimens (e.g., spent nuclear fuel or nuclear waste glass fragments) are feasible, regardless of the actual contact dose rate if the radiation field is limited to a few microsieverts per hour at the edge of the experimental table.

Actinide Ion (Americium-241 and Uranium-232) Interaction with Hybrid Silica-Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels.

The binding of actinide ions (Am(III) and U(VI)) in aqueous solutions by hybrid silica-hyperbranched poly(ethylene imine) nanoparticles (NPs) and xerogels (XGs) has been studied by means of batch experiments at different pH values (4, 7, and 9) under ambient atmospheric conditions. Both materials present relatively high removal efficiency at pH 4 and pH 7 (>70%) for Am(III) and U(VI). The lower removal efficiency for the nanoparticles is basically associated with the compact structure of the nanoparticles and the lower permeability and access to active amine groups compared to xerogels, and the negative charge of the radionuclide species is formed under alkaline conditions (e.g., UO2(CO3)34- and Am(CO3)2-). Generally, the adsorption process is relatively slow due to the very low radionuclide concentrations used in the study and is basically governed by the actinide diffusion from the aqueous phase to the solid surface. On the other hand, adsorption is favored with increasing temperature, assuming that the reaction is endothermic and entropy-driven, which is associated with increasing randomness at the solid-liquid interphase upon actinide adsorption. To the best of our knowledge, this is the first study on hybrid silica-hyperbranched poly(ethylene imine) nanoparticle and xerogel materials used as adsorbents for americium and uranium at ultra-trace levels. Compared to other adsorbent materials used for binding americium and uranium ions, both materials show far higher binding efficiency. Xerogels could remove both actinides even from seawater by almost 90%, whereas nanoparticles could remove uranium by 80% and americium by 70%. The above, along with their simple derivatization to increase the selectivity towards a specific radionuclide and their easy processing to be included in separation technologies, could make these materials attractive candidates for the treatment of radionuclide/actinide-contaminated water.

Identification and tracing of radionuclides in low- and medium-activity liquid radwaste sources of G.A. Siwabessy reactor

Abstract The liquid radioactive waste generated by the G.A. Siwabessy reactor (RSG-GAS) is categorized into low-activity liquid radwaste (LALR) and medium-activity liquid radwaste (MALR). The radionuclide content of both LALR and MALR can use as an indicator of the structural integrity of the reactor’s systems, structures, and components (SSC). To evaluate the degradation of the reactor SSC, the radionuclide species were identified, and their activities were measured using gamma spectroscopy. Based on the identified radionuclides, the process of their formation can be traced. The radionuclides identified in LALR were 24Na, 51Cr, 59Fe, 60Co, 65Zn, and 124Sb, while the radionuclides in MALR were 24Na, 51Cr, 58Co, 59Fe, 60Co, 65Ni, 65Zn, 89Kr, 90Kr, 109Cd, 131I, 132I, 140Ba, 137Cs, 146Ce, and several others. The radionuclides found can be classified into corrosion product activation (60Co, 65Zn, 51Cr, 59Fe, 24Na, 65Ni), topaz impurities activation (51Cr, 59Fe, 60Co, 65Zn), fission product (90Kr, 140Ba, 131I, 137Cs, etc.), and demineralized water impurities activation (51Cr, 59Fe, 65Zn, 60Co, etc.). After comparing the activity value of each radionuclide with the limit value in the safety analysis report document, we can conclude that the activity of each one is below the required level. It can infer that the structural integrity of reactor SSC is still well maintain. During routine monitoring, the radionuclide content in the primary coolant fluctuates depending on the reactor load. The concentration of radionuclides detected varies when a large or small number of research samples are loaded onto the core. Nevertheless, their activities remain within the required safety limits.

Biogeochemical interactions between aged cementitious materials and sulfate reducing microbial community with propionate as electron donor in the context of nuclear waste repository

Heterotrophic microbial sulfate reduction can occur in both natural and engineered systems. The process can influence the radionuclide speciation and mobility in deep repository of radioactive waste (DRRW). DRRW are characterised by significant masses of concrete, imposing alkaline pH in the waste cell. This paper aims to evaluate microbial sulfate reduction coupled with propionate oxidation influenced by the alkalinity of the environment: moderate alkaline pH close to 9.0 without cement paste, and moderate alkaline pH which was then moderately increased (pH 9.0 to 9.4) by the presence of pre-aged solid cement pastes via advanced and moderate ageing protocols, respectively. Regardless of the degree of ageing of the cement pastes, the sulfate reduction rate decreased by up to 84% when the pH increased from 9.0 to 9.4 in the presence of cement paste and by up to 90% in the absence of cement paste. No sulfate reduction or propionate oxidation was observed for pH > 9.5. Microbial metabolites, sulfide, CO2 and acetate, produced from the reduction of sulfate and oxidation of propionate, and the presence of the microorganisms attached to the cement pastes (composed of up to 80% of sulfate reducing bacteria) led to their biodeterioration. Sulfide enrichment, precipitation of secondary ettringite, and intensified decalcification were notably detected. Self-healing like phenomena were also observed: calcium leached from the cementitious phases reacted with carbonate produced by microorganisms to form of calcium carbonate relocated either in the micro-cracks or on the surface of the pre-aged solid cement pastes.

The theory and practice in application of methods for investigation on radionuclide speciation in soils

The paper provides a comparison of the various techniques for investigation of radionuclide speciation in soils based on fractionation of radionuclides bonded with different soil components. The dates on speciation of environmentally signifшcant technogenic and natural radionuclides in soils contaminated from testing of nuclear weapons, accidents or incidents at radiation dangerous objects, mining and mineral products processing are presented. The review looks at inf uence of natural and anthropogenic factors on the forms of the radionuclide compounds like the radionuclide and soil properties, type of radioactive fallout and the time elapsed af er fallout on soil. It has been demonstrated that experimental details of radionuclide speciation provide the basis for estimates and projections their mobility in soils, availability for plants and development of recommendations on reducing their penetration into food chains.

Radioactivity/Radionuclide (U-232 and Am-241) Removal from Waters by Polyurea-Crosslinked Alginate Aerogels in the Sub-Picomolar Concentration Range.

The removal of radionuclide/radioactivity from laboratory and environmental water samples under ambient conditions was investigated via batch-type experiments using polyurea-crosslinked calcium alginate (X-alginate) aerogels. Water samples were contaminated with traces of U-232 and Am-241. The removal efficiency of the material depends strongly on the solution pH; it is above 80% for both radionuclides in acidic solutions (pH 4), while it decreases at about 40% for Am-241 and 25% for U-232 in alkaline solutions (pH 9). This is directly associated with the presence of the radionuclide species in each case; the cationic species UO22+ and Am3+ prevail at pH 4, and the anionic species UO2(CO3)34- and Am(CO3)2- prevail at pH 9. Adsorption on X-alginate aerogels is realized by coordination of cationic species on carboxylate groups (replacing Ca2+) or other functional groups, i.e., -NH and/or -OH. In environmental water samples, i.e., ground water, wastewater and seawater, which are alkaline (pH around 8), the removal efficiency for Am-241 is significantly higher (45-60%) compared to that for U-232 (25-30%). The distribution coefficients (Kd) obtained for the sorption of Am-241 and U-232 by X-alginate aerogels are around 105 L/kg, even in environmental water samples, indicating a strong sorption affinity of the aerogel material for the radionuclides. The latter, along with their stability in aqueous environments, make X-alginate aerogels attractive candidates for the treatment of radioactive contaminated waters. To the best of our knowledge, this is the first study on the removal of americium from waters using aerogels and the first investigation of adsorption efficiency of an aerogel material at the sub-picomolar concentration range.

The Content and Speciation of Radionuclides in Water and Bottom Sediments of the Laptev Sea

In the presented work, the features of the distribution of Cs-137 and plutonium isotopes in modern sediments of various parts of the Laptev Sea, selected during the expedition studies on the RV “Academician Mstislav Keldysh” in 2017 and 2019, were studied. It was found that the activity of Cs-137 in water and sediments is within the global level, which is typical for the seas of the Arctic region. In all the collected samples the specific content of Pu-239,240 isotopes is below the level of the minimum detectable activity. According to the results of isotope analysis of Pb-210, the sedimentation rates in two columns collected in the Laptev Sea are 0.18 and 0.23 cm/year. The study by several methods of the speciation forms of Pu-239, introduced into the samples of bottom sediments under laboratory conditions, showed that the main content of Pu-239 is associated with difficult-to-dissolve organo-mineral components. 30-39% Pu-239 was found in the composition of organic easily soluble acids and humic substances, which include fulvic and humic acids of bottom sediments.

The Content and Speciation of Radionuclides in Water and Bottom Sediments of the Laptev Sea

The Content and Speciation of Radionuclides in Water and Bottom Sediments of the Laptev Sea

The Theory and Practice in the Application of Methods for Investigation on Radionuclide Speciation in Soils

The Theory and Practice in the Application of Methods for Investigation on Radionuclide Speciation in Soils

Накопление Cs–137 и Sr–90 культурой салата на почвах основных радиоактивно-загрязненных участков бывшего Семипалатинского испытательного полигона

Under conditions of a simulated pot experiment in the case of salad (Lactuca sativa), quantitative parameters of Cs-137 and Sr-90 (Tf) accumulation by plants on soils from the former Semipalatinsk Test Site territory were obtained. The variation range of Tf values derived for soil samples from different STS areas was 2 orders of magnitude for Cs-137 and 1 order of magnitude for Sr-90. Using nonparametric statistical analytical techniques, determinants of the transfer of Cs-137 and Sr-90from soil to plants for STS soils with various natures of radioactive contamination were identified. The content of biologically available species of radionuclides has a significant effect on the accumulation of Cs-137 and Sr-90by salad. Values derived for Kendall correlation coefficients showed a complete functional dependence (r=1, n=4, p<0,05) between accumulation parameters and the content of biologically available species of Cs-137 and Sr-90in soil from radioactively contaminated test site areas. The use of partial correlation coefficients allowed identification of key soil contributors to the content of available speciation and, respectively, the accumulation of Cs-137 and Sr-90by the experimental crop: for 137Cs, the common content of K (rxy-z = -0,81); for Sr-90 — the common content of Ca (r xy-z = — 0,64). Findings reveal the main mechanisms of Cs-137 and Sr-90transfer from soil to plants, which are of great practical importance in the radio ecological monitoring and planning of rehabilitation measures taken in radioactively contaminated STS areas as well as in areas impacted by nuclear fuel cycle facilities (NFC) located under similar soil and climatic conditions.

Speciation of 137Cs, 90Sr, 241Am, and 239+240Pu artificial radionuclides in soils at the Semipalatinsk test site

This paper reports the speciation of 137Cs, 241Am, 90Sr and 239+240Pu in the soil samples of the Experimental Field (EF). The EF is a testing ground of the Semipalatinsk nuclear weapons test site used for surface and atmospheric tests. The study revealed low mobility of artificial radionuclides in the EF site soils.The revealed high radionuclide concentrations in soil mainly exist in tightly bound form. On average, the content of the tightly bound form of 137Cs was revealed to be below 98%, that of 90Sr - 94%, 241Am - 89%, and 239+240Pu - 98%.The radionuclides occurrence forms were analyzed in correlation with the physicochemical parameters of soils. Reliable relationships have been established between the content of carbonates and the content of the exchangeable, acid-soluble and strongly bound 90Sr forms in soils, as well as the content of the water-soluble salts and the content of the strongly bound 239+240Pu form in the soil.Similarly, we compared the distributions of the radionuclides speciation and their stable isotopes with their analogous elements in the soil. Unlike 137Cs and 90Sr, which are in a tightly bound form in the soils of the Experimental Field site, the main content of soil “competitors” of the 137Cs radionuclide – K and Cs is observed in an exchange form, less significantly in an acid-soluble form. The alkaline earth metals (analogous elements for 90Sr) are mainly observed as a composition of the exchangeable and acid-soluble forms. The results allow to conclude that there is no equilibrium distribution of the physicochemical forms of radionuclides introduced into the soil and the natural presence forms of their stable analogs in the soil. Such equilibrium distribution can only be achieved at a complete isotopic exchange in phases and soil components, which under the conditions of the Experimental Field is not possible in the near future.It can be concluded that the behavior of the studied radionuclides in soils is stipulated by the initial form delivered by the fallouts from tests at the EF site.

Decrease of radionuclide sorption in hydrated cement systems by organic ligands: Comparative evaluation using experimental data and thermodynamic calculations for ISA/EDTA-actinide-cement systems

The sufficient retardation of radionuclide release by sorption is a central issue in assessing the safety of radioactive waste disposal systems and risks posed by contaminated sites. Various types of radioactive wastes and natural environments contain organic substances that can stabilize aqueous radionuclide complexes and therefore lead to a decrease of sorption. This effect can be quantified by sorption reduction factors (SRFs). The present study focuses on testing a methodology to quantify SRFs in the presence of organic ligands for cement systems. Three approaches for the estimation of SRFs were compared for a wide range of systems including representative organic ligands (iso-saccharinic acid: ISA and ethylenediaminetetraacetic acid: EDTA) and selected key radionuclides (trivalent-, tetravalent- and hexavalent-actinides): 1) analogy with solubility enhancement factors (SEFs) derived from published solubility data, 2) calculation based on radionuclide speciation as predicted by thermodynamic calculations, and 3) direct quantification from published experimental sorption data in ternary systems. Our approach allows to critically evaluate the dependence of SRFs in various systems on the chosen method of quantification, in accordance with the data availability for a given system. Our comparisons suggest that reliable SRFs can only be derived from sorption measurements in ternary systems, i.e, where the effect can be directly measured in the presence of solid surface, radionuclide and organic ligand. On the other hand, SRFs often need to be derived in the absence of such direct evidence, and approximations based on analogies and speciation information can be applied to estimate SRFs in such cases. However, such estimates may be subject to substantial uncertainties. This should not be seen as a fundamental hindrance to the use of approximations, but uncertainties need to be clearly acknowledged and an SRF should reflect this e.g. by providing (additional) conservative estimates.

Effect of manganese on the speciation of neptunium(V) on manganese doped magnetites

Speciation and fate of radionuclides in environment are strongly dependent on their interaction with various mineral surfaces. Presence of impurity atoms in minerals modifies these interactions. 237Np, a long-lived component of nuclear high-level waste, is highly mobile in environment as neptunyl (NpO2+) cation. Role of impurities in defining its interaction with mineral surfaces present in natural and engineered systems is yet to be completely understood. Manganese is a ubiquitous impurity present in naturally occurring iron corrosion product, magnetite. Here, a series of manganese (Mn)-doped magnetites (FM) was synthesized and the evolution of solid-sorbed speciation of Np(V) was investigated as a function of Mn doping (3–11 wt%) in near neutral pH condition. Combining Mn K-edge and Np L3-edge X-ray absorption fine structure spectra with Np M5-edge high energy-resolution X-ray absorption near-edge structure spectra, we found nanoparticulate NpIVO2 solid as the single speciation of Np sorbed on both doped and undoped magnetites. Without changing the surface speciation of Np, Mn-O sites did show preference for sorbing Np(V) vis-á-vis Fe-O sites. Mn participates through Fe(II)/Mn(III) redox couple in reducing sorbed Np(V). Its participation, however, becomes significant only when the doped-magnetite contains a critical minimum concentration (> 6 wt%) of Mn. This study highlights the significant role of impurity atom wherein it interacts with sorbing species through redox process.

Boom Clay pore water geochemistry at the Mol site: Experimental data as determined by in situ sampling of the piezometers

In many countries, geological disposal in clay is the primary option for the final disposal of high-level radioactive waste and spent fuel. In Belgium, the Boom Clay is studied as a potential host rock for the disposal of radioactive waste. In this frame, the pore water geochemistry of the Boom Clay is an essential feature for evaluating the performance and long term safety of geological disposal in a host rock because: (1) it determines the speciation and solubility of radionuclides, and (2) it is required as initial or boundary condition to evaluate the interactions with other repository components, i.e. the different waste forms and the engineered barrier system (e.g. overpack materials, backfill), as well as to evaluate the influence of the repository construction (e.g. oxidation, interaction with the liner if present). In this study, we report a unique, first of its kind data set of the in situ sampled pore waters of the Boom Clay at the Mol site, covering a depth interval of 65 m. The thorough screening of the collected data for potential geochemical perturbations and sampling artifacts led to a reference data set of 195 pore waters complemented with 39 in situ gas and pH analyses. A statistical analysis was applied to this dataset and a reference pore water composition was derived for the Boom Clay pore water at the Mol site. The reported ranges of the elemental concentrations reflect pore water natural variations at formation scale, whereas in situ sampled pCO2 and pH values are limited to the depth interval enveloped by HADES URL at 196–200 m below sea level. Thus, uncertainty remains on the variations of the pCO2 and pH at the scale of Boom Clay Formation. The reference pore water chemistry dataset will help to update current geochemical pore water chemistry model. At the same time, the presented data set can improve geochemical modelling strategies developed for low permeability sediments, like argillites and shales, where direct pore water sampling is technically difficult.

Impact of anoxic conditions, uranium(VI) and organic phosphate substrate on the biogeochemical potential of the indigenous bacterial community of bentonite

Uranium (U) is the most hazardous radionuclide in nuclear waste and its harmful effects depend on its mobility and bioavailability. Microorganisms can affect the speciation of radionuclides and their migration in Deep Geological Repositories (DGR) for high level radioactive waste (HLW) storage. Consequently, a better understanding of microbe-radionuclide interactions within a DGR concept is essential for a safe storage. With that in mind, bentonite microcosms amended with uranyl nitrate and glycerol-2-phosphate were incubated for six months under anoxic conditions. Post-incubation 16S rRNA gene sequencing revealed high microbial diversities including glycerol oxidizers such as Clostridium and Desulfovibrio and nitrate reducers (Limnobacter and Brevundimonas). In addition, uranium-reducing bacteria (Desulfovibrio and Pseudomonas) were highly enriched in glycerol-2-phosphate‑uranium amended microcosms. These bacteria may contribute to uranium immobilization through enzymatic reduction and/or biomineralization. Scanning electron microscopy of colored spots on the surface of the bentonite in the microcosms indicated the probable formation of Mn(IV) oxides likely through the activity of Mn(II)-oxidizing microbes. This could affect the biogeochemical cycle of U(VI) by concentrating and immobilizing this element in the bentonites. Finally, X-ray diffraction determined a high structural stability of bentonites. The outputs of this study help to predict the impact of microbial activity (e.g. smectite alteration, metal corrosion, and radionuclides mobilization) on the long-term performance of a DGR and to develop appropriate waste treatments, remediation, and management strategies.