This study is dedicated to the dissolution of UO2-based model compounds incorporating metallic Mo nanoparticles in 4 mol.L-1 HNO3 at 353 K (representative for PUREX process conditions) following a dynamic protocol. Compounds of structural and microstructural properties similar to spent nuclear fuel allowed us to evidence the specific impact of Mo in the metallic form on the dissolution kinetics of UO2. The dissolution of a pure metallic Mo reference sample under the same dissolution conditions was carried out to gain deeper insights into the oxidation behavior of Mo in nitric acid and to evaluate its influence on the UO2 dissolution mechanism. The evolution of the U, Mo, and nitrous acid concentrations in solution was measured and the solid residues of dissolution were characterized. The results revealed a mutual inhibitory effect between UO2 and metallic Mo during dissolution in nitric acid. No precipitates of mixed U and Mo were formed under the studied conditions. The dissolution processes of UO2 and Mo were found to be interconnected and likely compete for the same auto-catalytic nitrogen species necessary for their oxidation and solubilization in the +VI oxidation state. The results provided crucial insights into how metallic Mo reacts with nitric acid under the representative PUREX process conditions. The findings suggested that metallic Mo(0) is initially completely oxidized to an amorphous brown-red phase with an oxidation state between +IV and +VI. Further oxidation, then solubilization of this phase as Mo(VI) species appeared to be facilitated by the auto-catalytic nitrogen species.

Ce-IV(DOTA) (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) was produced both radiolytically and electrochemically in the presence of halides and azide anions. Only fluoride, the hardest Lewis base studied, ligates to both [Ce-III(DOTA)(H2O)](-) and Ce-IV(DOTA), stabilizing the high oxidation state by two orders of magnitude versus [Ce-IV/III(DOTA)](0/-) in its absence. The Ce-IV(DOTA) complexes are long-lived in the dark (decompose photochemically). The tetravalent complexes decompose mainly via kinetics which obeys a first order rate law. The first step is de-carboxylation of the DOTA ligand followed by the formation of CH2O. The kinetics of oxidation of [Ce-III(DOTA)(H2O)](-) by Cl-2(-), Br-2(-) and N-3 were studied. Cl-2(-), the strongest oxidizing agent studied, reacts mainly via H atom abstraction from the DOTA ligand. Br-2(-) at both acidic and neutral pH oxidizes [Ce-III(DOTA)(H2O)](-) with rate constants of <3 x 10(6) M(-1)s(-1), as measured by pulse radiolysis, via an inner sphere mechanism. N-3 oxidizes [Ce-III(DOTA)(H2O)](-) to its tetravalent analogue as well, as proved by UV-vis data after steady-state radiolysis. The presence of F- increased the yield of the Ce-IV(DOTA) formed. The oxidation rate by N-3 is probably lower than that measured for Br-2(-).

An original spectroelectrochemical approach was employed to probe in situ redox reactions with plutonium. Monitoring Pu electrolysis under aerated conditions revealed the formation of a transient species. Using chemometric methods, the associated spectroscopic signature was found to correspond with a dimeric peroxo-bridged Pu complex described 70 years ago, often referred to as the plutonium "brown" complex. A separate synthesis of this complex confirmed the presence of the transient species during electrolysis, challenging conventional concepts of Pu electrochemistry. The mechanistic role of the Pu "brown" complex during Pu electrolysis is also discussed.

While recent studies have provided a wealth of information about the structure of oxide nanoparticles resulting from Pu(IV) hydrolysis, little is known about their formation mechanism. This article describes the stabilization and characterization of a reaction intermediate observed during the formation of PuO2 colloidal nanoparticles in aqueous solution. The intermediate was captured by a kinetic blocking of the started hydrolysis reaction by dilution of the reacting medium into DOTA (pH 3.5), glycine (pH 2.0), or acetic acid (pH 1.1) aqueous solutions. Such an approach stopped the hydrolysis and condensation processes by complexation and allowed for stabilization of hexameric polynuclear structures of Pu(IV) that were thoroughly characterized using laboratory and synchrotron techniques (UV-vis, small angle X-ray scattering, L3-edge X-ray absorption spectroscopy, and M4-edge high energy resolution fluorescence detected-X-ray absorption near edge structure). Beyond the new insight given about the contribution of the [Pu6O4(OH)4]12+ cluster during the aqueous formation of colloidal PuO2 nanoparticles in aqueous conditions, this study confirms the added value of synchrotron radiation for the characterization of very dilute and strongly radioactive nanostructures, paving the way for further research in the domain.

Here, the uranium valence electronic structures in the perovskite-based ternary uranate systems NaUO3, KUO3 and RbUO3 are reported on the basis of high-energy resolved fluorescence-detected X-ray absorption spectroscopy experiments at the U L3 edge and relativistic quantum chemistry calculations based on density functional theory. Advanced theoretical simulations allowed us to identify the origin of spectral features and to assess the impact of structural distortion within the oxygen octahedra. The octahedral crystal-field strength extracted from both experiments and calculations is reported for all three compounds.

This work aims to investigate the behavior of Mo in UO2 +/- x for being an abundant fission product with a high fission yield and a complex speciation linked to its interaction with the fuel and other fission product elements. UO2-based model compounds containing different Mo contents (between 0 and 15 mol%) were synthesized by a wet-chemistry route using hydroxide precipitation. The recovered powders were converted to oxides, pelletized, and sintered to obtain densified pellets of UO2 incorporating Mo. PXRD analyses and Rietveld refinement calculations indicate that Mo has an almost negligible solubility in the fluorite structures of both UO2 and UO2+x samples. SEM, TEM, and EDX characterizations of the produced UO2 + Mo pellets revealed the homogeneous distribution of nanosized metallic Mo particles of spherical geometry inside and outside the UO2 grains and throughout the whole sample pellets, whatever the amount of Mo added, thus confirming that the solubility of Mo in the fluorite structure is way below 0.6 mol% Mo in accordance with the PXRD results. The microstructural properties of the UO2 + Mo pellets, including density, porosity, Mo particle size distribution, and UO2 grain size variation with Mo content, were also determined. The addition of Mo to UO2 reduced the UO2 grain size as compared to UO2 grains in pure pellets, and Mo thus plays an inhibiting role in the UO2 grain growth during sintering. The produced UO2 + Mo pellets exhibit a microstructure similar to that of the real spent nuclear fuel, except that the UO2 grains are smaller. The Mo metallic nanoparticles in these simplified UO2-based model compounds of controlled microstructure could be harnessed as surrogates of the Mo-rich epsilon-phase metallic nanoparticles in the real spent nuclear fuel for future studies.

Although hydrogen peroxide (H2O2) has been highly used in nuclear chemistry for more than 75 years, the preparation and literature description of tetravalent actinide peroxides remain surprisingly scarce. A new insight is given in this topic through the synthesis and thorough structural characterization of a new peroxo compound of Pu(IV).

The preparation of synthetic (Zr,U)SiO4 solid solution is a challenging operation, as the conventional high temperature solid state method limits the solubility of uranium (4 ± 1 mol.%). in the...

Chelation of lanthanide and actinide cations within a suitable macrocyclic ligand often results in a rigid, kinetically inert, and thermodynamically stable complex. A benchmark for such cation-ligand suitability are cyclen-derived macrocyclic ligands, frequently used as large cation hosts for various applications. Herein, a comprehensive study of the 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane ligand (DOTAM) chelates of U-IV and Ce-III and their properties in aqueous solutions is presented. By employing multiple analysis techniques, including X-ray crystallography, UV-vis absorbance, H-1 NMR, UPLC-MS, cyclic voltammetry, and differential pulse voltammetry, the study has revealed that the two aqueous complexes undergo a spontaneous, gradual, and stepwise hydrolysis of each of the coordinated amides toward carboxylates. The coordination of U-IV in the studied reaction has been shown to significantly enhance the reaction rate, leading to an acceleration of up to 6 orders of magnitude compared to the natural process of simple aqueous amides at room temperature. An attempt to describe the unusual chelated metal cation amide-activation feature, based on the relatively lower rigidity of the complex structure, is presented. Additionally, the electrochemical properties of the complex series are discussed in detail, along with the limitations of the analytical methods employed.

Actinide colloids and nanoparticles (NPs) currently constitute a topic of strong interest due to their potential role in advanced nuclear energetics and the environmental migration of radioactivity. A better understanding of the physico-chemical properties of nanoscale actinide oxides requires robust synthesis approaches. In this work, UO2+x NPs were successfully prepared by sonochemistry from U(IV) solutions previously stabilised in a hydrochloric medium (20 kHz, 65 °C, Ar/(10%)CO). Colloidal suspensions were found to be composed of crystalline and spherical NPs showing a UO2-like structure and measuring 18.0 ± 0.1 nm (SAXS, HR-TEM and PXRD techniques). In comparison with the controlled hydrolysis approach used as a reference, sonochemistry appears to be a simple and original synthesis route providing larger, better defined and more crystalline UO2+x NPs with a narrower size distribution. These well-defined NPs offer new opportunities for the preparation of reference actinide materials devoted to fundamental, technological and environmental studies.

Although ZrSiO4 is the most well-known compound in the zircon-structured family (space group I41/amd), the experimental conditions for preparing pure and well-crystallized phases that are doped with a tetravalent element via hydrothermal synthesis have never been clearly discussed in the literature. With the aim to answer this question, the experimental conditions of the preparation of ZrSiO4 and (Zr,Ce)SiO4 were investigated in order to synthesize well-crystallized and pure phases. A multiparametric study has been carried out using soft hydrothermal conditions with variables including reactant concentration, initial pH of the reactive medium, and duration of the hydrothermal treatment. Pure ZrSiO4 was obtained through hydrothermal treatment for 7 days at 250 °C, within a large acidity range (1.0 ≤ pH ≤ 9.0) and starting from CSi ≈ CZr ≥ 0.2 mol L-1. As hydrothermally prepared zircon structured phases can be both hydrated and hydroxylated, its annealed form was also studied after heating to 1000 °C. Based on these results, the synthesis of (Zr,Ce)SiO4 solid solutions was also investigated. The optimal hydrothermal conditions to acquire pure and crystallized phases were as follows: 7 days at 250 °C with initial pH = 1 and concentration of the reactants equal to 0.2 mol L-1. This led to Zr1-xCexSiO4 solid solutions with the incorporated Ce content up to 40 mol%. Samples were characterized using multiple methods, including laboratory and synchrotron PXRD, IR and Raman spectroscopies, SEM, and TGA. Moreover, it was found that these phases were thermally stable in air up to at least 1000 °C.

Due to its presence in the nuclear industry and its strong radiotoxicity, plutonium is an actinide of major interest in the event of internal contamination. To improve the understanding of its mechanisms of transport and accumulation in the body, the complexation of Pu(IV) to the most common protein calcium-binding motif found in cells, the EF-hand motif of calmodulin, was investigated. Visible and X-ray absorption spectroscopies (XAS) in solution made it possible to investigate the speciation of plutonium at physiological pH (pH 7.4) and pH 6 in two variants of the calmodulin Ca-binding site I and using Pu(IV) in different media: carbonate, chloride, or nitrate solutions. Three different species of Pu were identified in the samples, with formation of 1:1 Pu(IV):calmodulin peptide complexes, Pu(IV) reduction, and formation of peptide-mediated Pu(IV) hexanuclear cluster.

Actinide +IV complexes (AnIV = ThIV, UIV, NpIV, and PuIV) with two dipicolinic acid derivatives (DPA and Et-DPA) have been studied by 1H and 13C NMR spectroscopies and first-principles calculations. The Fermi contact and dipolar contributions to the actinide-induced shifts (AIS) are evaluated from a temperature dependence analysis, combined with ab initio results. It allows an experimental estimation of the axial anisotropy of the magnetic susceptibility Δχax and of the hyperfine coupling constants of the NMR-active nuclei. Due to the compactness of the coordination sphere, the magnetic anisotropy of the paramagnetic center is small, and this makes the contact contribution to be the dominant one, even on the remote atoms. The sign of the hyperfine coupling constants and related spin densities is alternating on the nuclei of the ligand cycle, denoting a preponderant spin polarization mechanism. This is well reproduced by unrestricted density functional theory (DFT) calculations. Those values are furthermore slightly decreasing in the actinide series, which indicates a small decrease of the covalency from UIV to PuIV.

A group of researchers from NRCN, Ben Gurion University and the CEA shows that cyclen-derived, hard-bonding ligands facilitate the formation of tetravalent cerium cations bearing oxo/hydroxo clusters in aqueous solutions. The clusters eventually decompose to form the thermodynamically favoured “in-cage” cerric macrocyclic complex. More information can be found in the Research Article by S. Pevzner, E. Maimon, Y. Ben-Eliyahu, P. Moisy, A. Bettelheim, I. Zilbermann and co-workers (DOI: 10.1002/chem.202201868).

Sonochemistry studies chemical and physical effects in liquids submitted to power ultrasound. These effects arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species. In principle, each cavitation bubble can be considered as a microreactor initiating chemical reactions at mild conditions. In addition, microjets and shock waves accompanied bubble collapse produce fragmentation, dispersion and erosion of solid surfaces or particles. Microbubbles oscillating in liquids also enable nucleation and precipitation of nanosized actinide compounds with specific morphology. This review focuses on the versatile sonochemical processes with actinide ions and particles in homogenous solutions and heterogenous systems. The redox reactions in aqueous solutions, dissolution or precipitation of refractory solids, synthesis of actinide nanoparticles, and ultrasonically driving decontamination are considered. The guideline for further research is also discussed.

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH3, CH3O2· and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with MIII(DOTA)- than the hydroxyl radicals. The various final products were identified and mechanisms for their formation are proposed. CH3O2· radicals do not react, or react too slowly to be observed, with DOTA and with MIII(DOTA)- as long as the central cation is not oxidized by the peroxyl radical. The results imply that synthesis of the MIII(DOTA)-(MIII = radioisotope) complexes in a water-organic solvent (ethanol or 2-propanol or acetonitrile) mixture is not only kinetically desired but the so formed complex also decreases the radiolytic decomposition of DOTA.

The Pourbaix diagram of an element displays its stable chemical forms with respect to the redox potential and pH of the solution, whose knowledge is fundamental for understanding and anticipating the chemistry of the element in a specified solution. Unlike most halogens, the Pourbaix diagram in the aqueous phase for astatine (At, Z = 85) is still under construction. In particular, the predominant domains of two astatine species assumed to exist under alkaline conditions, At- and AtO(OH)2-, need to be refined. Through high-performance ion-exchange chromatography, electromobility measurements, and competition experiments, the existence of At- and AtO(OH)2- has been confirmed and the associated standard potential has been determined for the first time (0.86 ± 0.05 V vs the standard hydrogen electrode). On the basis of these results, a revised version of astatine's Pourbaix diagram is proposed, covering the three oxidation states of astatine that exist in the thermodynamic stability range of water: At(-I), At(I), and At(III) (as At-, At+, AtO+, AtO(OH), and AtO(OH)2-).

The paper presents the results of a case study on evaluating performance and sustainability metrics for Russian nuclear energy deployment scenarios with thermal and sodium-cooled fast reactors in a closed nuclear fuel cycle. Ten possible scenarios are considered which differ in the shares of thermal and sodium-cooled fast reactors, including options involving the use of mixed uranium-plutonium oxide fuel in thermal reactors. The evolution of the following performance and sustainability metrics is estimated for the period from 2020 to 2100 based on the considered assumptions: annual and cumulative uranium consumption, needs for uranium enrichment capacities, fuel fabrication and reprocessing capacities, spent fuel stocks, radioactive wastes, amounts of plutonium in the nuclear fuel cycle, amounts of accumulated depleted uranium, and the levelised electricity generation cost. The results show that the sustainability of the Russian nuclear energy system can be significantly enhanced through the intensive deployment of sodium-cooled fast reactors and the transition to a closed nuclear fuel cycle. The authors have highlighted some issues for further considerations, which will lead to more rigorous conclusions regarding the preferred options for the development of the national nuclear energy system.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.