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International audience; The accurate determination of plutonium (Pu) mass fraction in nuclear materials is essential to nuclear matter accountancy and international safeguard programs. Controlled-Potential Coulometry (CPC) is one of the best available analytical methods to perform such measurements. The implementation of CPC at the Nuclear Matter Metrological Laboratory of the French Atomic Energy Commission is described as well as the evaluation of measurement uncertainty using two approaches: the guide to the expression of uncertainty in measurement, and the Monte Carlo Method. The uncertainty values determined are compared to the international target values published by the International Atomic Energy Agency.

Controlled Potential Coulometry (CPC) is generally regarded as one of the most accurate analytical methods available for the quantification of plutonium (Pu) in acidic aqueous solutions. With a growing use of mixed oxide nuclear fuel, there has been an interest in the technique’s applicability to the analysis of Pu in the presence of uranium (U). Expanding on previous studies, the work presented herein demonstrates the highly accurate CPC analysis of Pu in mixed solutions (Pu + U) containing large quantities of U (U:Pu up to 100:1) as well as establishing the role played by sulfate anions during the analyses. By combining experimental results with speciation simulations, it is shown that the introduction of U in mixed Pu + U solutions is accompanied by increases in sulfate ions in the nitric acid medium which complex unequally with the different Pu cations in solution. The anions’ stronger affinity of for Pu(IV) rather than Pu(III) causes a decrease in the formal potential of the Pu(IV)/Pu(III) redox couple, directly affecting the degree of completion of the electrochemical reactions performed during CPC. A correction factor, f , is applied to account for the degree of completion of the analysis’ electrochemical steps and compensate for the effects of complexation. Thereby, a level of accuracy comparable to that achieved during the analysis of pure Pu solutions, is attained. Ultimately, a series of recommendations are put forward such that it becomes possible to maintain CPC’s good analytical performance for the measurement of Pu content in mixed Pu + U solutions.

Since 1987, the CEA’s Committee for the establishment of analysis methods (CETAMA) has regularly implemented interlaboratory comparisons, entitled “evaluation of the quality results of analysis in the nuclear industry” (EQRAIN). Notably, the EQRAIN U and EQRAIN Pu interlaboratory comparisons assess proficiency in measuring a mass content of uranium or plutonium in reference solutions. This paper presents the results of measurement uncertainty assessments from EQRAIN U and EQRAIN Pu comparisons over 20 years of exercises (1997–2016). The mathematical approach developed in this work allowed to estimate the impact of short-term systematic and random errors to the overall uncertainty of each analytical method used in the interlaboratory comparison program. This statistical analysis shows a good consistency between measurement uncertainty values from EQRAINs and the measurement uncertainty target values established by the International Atomic Energy Agency for nuclear material balances (ITVs-2010).

International audience; Ceramic oxide green pellets for nuclear fuel or targets are manufactured by powder processes producing detrimental fines. Porous brittle microspheres offer an interesting alternative, providing that their fracture behaviour is well controlled during pressing. Here we investigate, using experimental characterization and numerical simulations, the effect of internal defects on the strength of porous microspheres. We show that although the residual porosity is the main parameter affecting their strength, the shape and location of defects also play a role. Real defects characterized by X-ray tomography are reproduced with discrete element simulations, providing new insights on their fracture behaviour. We also investigate the departure from monosized microspheres by simulating the fracture behaviour of two microspheres of different sizes, and show that it is the minimum radius that allows for a consistent strength normalization. This study offers a method for anticipating agglomerate strength that can be generalized for any ceramic systems.

The reaction between fission products Mo(VI) and Zr(IV) in hot nitric acid solution during the spent fuel dissolution process leads to the formation of hydrated zirconium molybdate precipitate. Thi...

International audience; U$_{1-x}$Am$_x$O$_{2\pm\sigma}$ mixed-oxides are considered as promising compounds for americium heterogeneous transmutation in Sodium Fast Neutron Reactor. Porous microstructure is envisaged in order to facilitate helium and fission gas release and to reduce pellet swelling during irradiation and under self-irradiation. In this study, the porosity is created by reducing (U,Am)$_3$O$_8$ microspheres into (U,Am)O$_2$ during the sintering. This reduction is accompanied by a decrease of the lattice volume that leads to the creation of open porosity. Finally, an (U0.90Am0.10)O2 porous ceramic pellet (D$\sim$89% of the theoretical density TD) with controlled porosity ($\geq$ to 8% open porosity) was obtained from mixed-oxide microspheres obtained by the Weak Acid Resin (WAR) process.

The sintering behavior of green pellets obtained from nanostructured Ce0.8Gd0.2O1.9 submillimetric microspheres is studied in the present paper. Corresponding shrinkage rate curve shows a two-step densification in dynamic conditions, with the presence of two successive extrema, at 1200 K and 1500 K. To fully understand this non-common densification behavior, an iterative study was performed. Multiple characterizations point out multiscale organization of the matter with temperature giving rise to differential sintering stages of two different particle size classes. Concerning 1200 K-first shrinkage rate maximum, it corresponds to the densification of nanometric aggregates of crystallites into submicrometric pre-sintered aggregates, resulting in a specific porous microstructure with residual open porosity. As-generated porosity combined with submicron size of pre-sintered aggregates thus prevent from a homogeneous sintering illustrated by a single maximum shrinkage rate. Finally, the second maximum shrinkage rate at 1500 K can then be associated to optimal temperature for submicrometric particles sintering. This article is protected by copyright. All rights reserved.

International audience; Nuclear metrology is an essential aspect to consider for further improvements of the initial characterization of sites under decommissioning. The H2020 Euratom project INSIDER in June 2017 aims at improving the management of contaminated materials arising from decommissioning and dismantling (D&D) operations by proposing an integrated methodology for radiological characterization. This methodology is based on advanced statistical processing and modelling, coupled with adapted or innovative measurement methods. A metrological approach supports the qualification of this integrated methodology with a concrete application to real projects representative of the use cases identified in the project. Assessment of the outcomes will be used for providing recommendations and guidance resulting in pre-standardization texts.

The use of CRMP (Calcined Resin Microsphere Pelletization) process for AmBB (Americium Bearing Blankets) fabrication is today a key research axis in americium transmutation domain, where its very high activity requires minimization of powder dissemination. In this aim, the use of oxide microspheres as compaction precursors is a promising clean alternative to powder metallurgy. Understanding the different steps of densification during CRMP pellet sintering thus appears as fundamental to obtain final materials with the specific features required for AmBB. The densification curve recorded in dynamic conditions shows different sintering steps. A first decrease of shrinkage rate happens at low temperature, around 1100 K. This phenomenon is not normally observed in the sintering of conventional powders. Chemical and microstructural studies were performed on (U,Am)O2 and also on (Ce,Gd)O2 surrogate compound to highlight the causes of this low-temperature sintering step. Multiscale reorganization finally appears as the sole explanation, through the sintering of nanometric aggregate present in the green pellet and related to the morphology of the starting microspheres employed as pelletization precursors.

International audience; Mixed uranium-americium oxides are one of the materials envisaged for Americium Bearing Blankets dedicated to transmutation in fast neutron reactors. Conversion and fabrication processes are currently developed to make those materials in the form of dense and homogeneous oxide ceramic pellets or dense granulates incorporating uranium and americium. Their development points out the need of a simplified and optimized process which could lower hazards linked to dust generation of highly contaminating and irradiating compounds and facilitate material transfer in remote handling operations. This reason motivated the development of innovative “dustless” route such as the Weak Acid Resin route (WAR) which provides the oxide precursors in the form of sub-millimeter-sized microspheres with optimal flowability and limits dust generation during conversion and fabrication steps. This study is thus devoted to the synthesis of mixed uranium-americium oxide microspheres by the WAR process and to the characterization of such precursors. This work also deals with their application to the fabrication of dense or porous pellets and with their potential use as dense spherules to make Sphere-Pac fuel.

Actinide oxide microspheres are considered as promising substituents to powder precursors for the production of ceramic pellets of nuclear fuel or targets. Porous microspheres of sub-millimetric size are synthesised using the Weak Acid Resin process. Controlling their microstructure and their mechanical properties is essential to predict the microstructure of green compacts and sintered pellets. Here, cerium and gadolinium are used to mimic actinides as metal cation. Single microspheres are crushed experimentally using a micropress in a Scanning Electron Microscope (SEM) to investigate their mechanical properties and visualise their fracture behaviour. The results are compared to numerical simulations based on the Discrete Element Method (DEM). In DEM, a microsphere is modelled as an assembly of bonded spheres representing aggregates. Bonds may fracture in tension or shear. A limited number of material parameters (aggregate elastic modulus, bond strength) are sufficient for the accurate simulation of the fracture behaviour of a microsphere.

International audience; This study presents post-analysis data processing that can be used in Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Two complementary methods were developped the optimisation of the calibration curve and the use of the Total Sum model. In order to work on a Certified Reference Material, the CETAMA EQRAIN 22 solution was used. First, the effect of the computation model used was evaluated. The Total Sum model was developped with two approaches a classical weighted mean and the excess variance weighted mean. Results show a decrease of about a factor of 4 for iron, and 2 for arsenic and palladium on uncertainties. Then, the effect of the calibration solution on both result uncertainties and method detection limits was studied . It shows that using the appropriate calibration can reduce them down by a factor of 10. Such results lead to a total gain on detection limits of about a factor of 30.

International audience; Spent fuel reprocessing and notably plutonium recycling contributes in enhancing the sustainability of nuclear energy by preserving uranium natural resources and decreasing the long term radiotoxicity of the final waste. After initial dissolution of the spent nuclear fuel in nitric acid, uranium and plutonium recovery from ultimate waste (fission products and minor actinides) is operated by a liquid liquid extraction process (PUREX process) and plutonium partitioning from uranium is run on the basis of the selective reduction of Pu and its back extraction. Therefore, the redox properties of Pu in nitric acid are of prime importance and the stabilization of Pu at its lower redox state + III is to be mastered. This study then deals with the characterization of Pu(IV)/Pu(III) redox couple in aqueous nitric acid solution. It was aimed at measuring physico-chemical features of the redox couple such as half-wave and conditional standard potentials, diffusion coefficients and charge transfer rate constant in nitric acid medium. These features have been used in modeling experimental results of preparative Pu(IV) reduction tests in nitrate medium in a laboratory parallel plate electrode cell.

In the original publication of the article, the values of u(s), u(r) and ITV for HKED were published incorrectly in Table 6.

Novel NiO/GDC (Gadolinium-doped Ceria) cermet catalysts were developed by the Weak Acid Resin (WAR) method using an ion exchange resin template. In addition, the specific surface area of these tunable materials was enhanced by NiO partial dissolution in aqueous acid solution. The whole procedure highly improved the micro-structural properties of these materials compared to previous studies. Catalysts with high metal loadings (≥10%), small Ni nanoparticles (70 m2/g) were achieved. These properties are promising for catalytic applications such as methane steam reforming for H2 production.

International audience; U3O8 is considered to be the most stable phase for uranium oxide. Its structural properties must be accurately understood to foresee and manage aspects such as its leaching behavior when spent nuclear fuel is stored in an oxidative environment. Moreover, as fuel irradiation causes the formation of fission products and activation products such as plutonium and minor actinides, it is probable that U3O8 will be mixed with other chemical elements under real conditions of oxidation. The storage issue can be extended to americium transmutation, where the irradiated compounds are mixed oxides composed of uranium and americium. This study thus focused on determining the structural properties of a solid solution containing uranium and trivalent americium (U/Am ratio = 90/10) and synthesized so as to obtain conventional U3O8 oxide. This paper presents the possibility of combining trivalent americium with uranium in a U3O8 mixed oxide for the first time, despite the high valence and atomic ratio differences, and proposes novel structural arrangements. X-ray diffraction measurements reveal americium substitution in U3O8 uranium cationic sites, leading to phase transformation into a U3O8 high-temperature structure and general lattice swelling. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure experiments highlight an excess of U+VI organized in uranyl units as the main consequence of accommodation.

U

International audience; A possible option to reduce the radiotoxicity of nuclear waste is to transmute minor actinides and notably americium into lighter short-lived elements in fast neutron reactors of fourth generation. It consists in irradiating uranium–americium mixed-oxide compounds named AmBB (Americium-Bearing Blankets) and located at the reactor core periphery. Among the processes developed to fabricate AmBB, a chemical synthesis route was investigated. Dense samples were achieved using a simplified pelletizing-sintering process from oxalate co-converted powder. This work focuses on the identification and comprehension of the steps occurring during the sintering of these co-converted (U,Am)O2 powders. To discriminate the different phenomena observed by dilatometric measurements, different experimental techniques were performed. It allowed identifying that the sintering of the finest particles occurred in the [1000–1350 K] range while the elimination of porosity and sintering of (U,Am)O2 larger grains is realized in the [1400–1900 K] range with an apparent activation energy of 430 kJ.mol−1.

International audience

International audience; This study is devoted to the synthesis and the characterization of porous metal oxide microsphere from metal loaded ion exchange resin. Their application concerns the fabrication of uranium-americium oxide pellets using the powder-free process called Calcined Resin Microsphere Pelletization (CRMP). Those mixed oxide ceramics are one of the materials envisaged for americium transmutation in sodium fast neutron reactors. The advantage of such microsphere precursor compared to classical oxide powder is the diminution of the risk of fine dissemination which can be critical for the handling of highly radioactive powders such as americium based oxides and the improvement of flowability for the filling of compaction chamber. Those millimetric oxide microspheres incorporating uranium and americium were synthesized and characterizations showed a very porous microstructure very brittle in nature which occurred to be adapted to shaping by compaction. Studies allowed to determine an optimal heat treatment with calcination temperature comprised between 700-800 A degrees C and temperature rate lower than 2 A degrees C/min. Oxide Precursors were die-pressed into pellets and then sintered under air to form regular ceramic pellets of 95% of theoretical density (TD) and of homogeneous microstructure. This study validated thus the scientific feasibility of the CRMP process to prepare bearing americium target in a powder free manner.

Mixed uranium–americium oxides are one of the materials envisaged for Americium Bearing Blankets dedicated to transmutation in fast neutron reactors. Recently, several processes have been developed in order to validate fabrication flowchart in terms of material specifications such as density and homogeneity but also to suggest simplifications for lowering industrial costs and hazards linked to dust generation of highly contaminating and irradiating compounds. This study deals with the application of an innovative route using mixed oxide microspheres obtained from metal loaded resin bead calcination, called Calcined Resin Microsphere Pelletization (CRMP). The synthesis of mixed oxide microsphere precursor of U 0.9 Am 0.1 O 2± δ is described as well as its characterisation. The use of this free-flowing precursor allows the pressing and sintering of one pellet of U 0.9 Am 0.1 O 2± δ . The ceramic obtained was characterised and results showed that its microstructure is dense and homogeneous and its density attains 95% of the theoretical density. This study validates the scientific feasibility of the CRMP process applied to the fabrication of uranium and americium-containing materials.

This study concerns the fabrication of uranium oxide pellets using the powder-free process called Calcined Resin Microsphere Pelletization (CRMP). Details are given about oxide microsphere synthesis and particularly about loading operation and heat treatments. The fabrication of ceramic pellets is also described and discussed. Results showed that this process allows the preparation of either dense or porous pellets by mixing U3O8 and UO2-like microspheres before pressing and sintering.

The coordination properties of vacant bisphosphonate derivatives of polyoxometalates, with easily tunable functions, have been explored. The preparation and crystallographic structure of their La(3+) and Zr(4+) complexes are described herein.

Hetero polyanions, namely, P2W17O61 10−, P2W18O62 6− and SiW11O39 8− were extracted by TBP/dodecane from HNO3 or HCl solution, as H10P2W17O61 in the case of P2W17O61 10−. The distribution ratio of P2W17O61 10− depended on both H+ concentration and ionic strength of aqueous solution, and free-TBP concentration in organic solution. Experimental equation was established for predicting the distribution ratio of P2W17O61 10− in nitrate system.

Mixed oxides are used as nuclear fuels and are notably envisaged for future fuel cycles including plutonium and minor actinide recycling. In this context, processes are being developed for the fabrication of uranium–americium mixed-oxide compounds for transmutation. The purpose of these processes is not only the compliance with fuel specifications in terms of density and homogeneity, but also the simplification of the process for its industrialization as well as lowering dust generation. In this paper, the use of a U0.85Am0.15O2±δ powder synthesized by oxalate co-conversion as a precursor for dense fuel fabrications is assessed. This study notably focuses on sintering, which yielded pellets up to 96% of the theoretical density, taking advantage of the high reactivity and homogeneity of the powder. As-obtained pellets were further characterized to be compared to those obtained via processes based on the UMACS (Uranium Minor Actinide Conventional Sintering) process. This comparison highlights several advantages of co-converted powder as a precursor for simplified processes that generate little dust.

International audience; In the current nano-sized material revolution, the main limitations to a large-scale deployment of nanomaterials involve health concerns related to nano-dissemination via air. Developing new chemical routes benefiting from nano-size advantages while avoiding their hazards could overcome these limitations. Addressing this need, a chemical route leading to soft nano-particle agglomerates, i.e., macroscopic precursors presenting the ability to be decomposed into nano-sized materials, was developed and applied to Ce0.8Gd0.2O2−δ. Using cerium/gadolinium-loaded ion exchange resin, the Ce0.8Gd0.2O2−δ solid solution formation as a function of temperature was studied in-situ through X-ray diffraction, X-ray absorption spectroscopy and Raman spectroscopy. Temperatures corresponding to the organic skeleton decomposition and to the mixed oxide crystallization were identified. An optimal heat treatment, leading to nanostructured soft agglomerates, was established. Microsphere processing capabilities were evaluated and particle size distribution measurements were recorded. A very low fracture strength was calculated, and a nanometric particle size distribution (170 nm) was determined.

With the aim of better understanding the process of polymerization and depolymerization of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at polyaniline-modified electrode, the electrochemical behaviour of DMcT and derivatives has first been studied on platinum by potential sweep voltammetry in acetonitrile. Reactions and redox potentials of the dithiol, thiolate, dithiolate and dimer forms of DMcT have been characterized. The reaction mechanism and kinetics of the disulphide-thiolate redox couple have been investigated; the reaction is chemically reversible but kinetically slow at ambient temperature, which is common to many organodisulphide compounds; oxidation of thiolate occurs via the formation of a thiyl radical which dimerizes in disulphide. Charge transfer is the rate determining step, whereas chemical dimerization is at equilibrium. For the dithiolate, oxidation proceeds in two steps: the dithiolate of the dimer is first formed and is further oxidized to give oligomers. This reaction, in the same manner as for oxidation of the thiolate form, is chemically reversible but kinetically hindered.

International audience; This study deals with the preliminary development of a powder-free process called calcined resin microsphere pelletization (CRMP) used for the fabrication of metallic oxide pellets. This dustless process could be used for the fabrication of mixed U1−yAmyO2±x pellets dedicated to the transmutation of Am in fast neutron reactors. In this study, porous CeO2 microspheres, used as a surrogate of AmO2, were obtained after mineralization of cerium loaded ion exchange resin beads. These millimetric oxide microspheres were die-pressed into pellets which were then sintered under air to form ceramic pellets. Their densities approached 95% of theoretical density of CeO2 and a homogeneous microstructure was obtained by using optimized microspheres. The influence of calcination parameters on the characteristics of microspheres and on the properties of sintered pellets is discussed.

International audience; This study is devoted to the characterization of ion exchange inside a microsphere of carboxylic resin. It aims at describing the kinetics of this exchange reaction which is known to be controlled by interdiffusion in the particle. The fractional attainment of equilibrium function of time depends on the concentration of the cations in the resin which can be modelized by the Nernst−Planck equation. A powerful approach for the numerical resolution of this equation is introduced in this paper. This modeling is based on the work of Helfferich but involves an implicit numerical scheme which reduces the computational cost. Knowing the diffusion coefficients of the cations in the resin and the radius of the spherical exchanger, the kinetics can be hence completely determined. When those diffusion parameters are missing, they can be deduced by fitting experimental data of fractional attainment of equilibrium. An efficient optimization tool coupled with the implicit resolution has been developed for this purpose. A monovalent/trivalent cation exchange had been experimentally characterized for a carboxylic resin. Diffusion coefficients and concentration profiles in the resin were then deduced through this new model.

International audience; Electrodeposition of CaCO3 was studied under the influence of magnesium ions present in a carbonically pure water. The investigation was performed using electrochemical, gravimetric and optical methods. The chronoamperometric measurements confirmed the inhibiting property of Mg2+ when its concentration is higher than 120 mg L−1 in a solution containing 160 mg L−1 of Ca2+. The optical technique led the nucleation-growth process to be accessed by means of an optical microscope positioned behind a transparent electrode. The increase of Mg2+ concentration changed drastically the calcite morphology. At 360 mg L−1 of Mg2+, the calcite morphology was optically amorphous but the Raman spectrum confirmed its structure. The crystal growth was recorded in situ and the image analysis software characterised the nucleation process as well as the growth rate of the crystals. It allowed the influence of the Mg2+ ions on the crystallisation process of CaCO3 to be quantified.

International audience; In this study, microbalance measurements with a GaPO4 crystal were performed to determine the dissolution rate of cerium oxide thin films at room temperature after a high temperature treatment of the hydroxide precursor Ce(OH)4 at 700 °C. The properties of the GaPO4 crystal enables gravimetric measurements to be performed after being heated at high temperatures where the classical quartz crystal microbalance irreversibly loses all its piezoelectric properties. The GaPO4 resonators were calibrated at room temperature by galvanostatic copper deposition before and after a high-temperature treatment, and the sensitivity coefficients KS were found to be identical, which proved the high potential of GaPO4 at high temperatures. However the accuracy of the gravimetric measurements is lower after a high temperature treatment. The rate determining step of the cerium oxide dissolution seems to be the reduction reaction of Ce(IV) to Ce(III), which is carried out by the hydrogen peroxide present in the dissolution medium.

The conversion of minor actinides to fuel starting materials for transmutation in a cl osed nuclear cycle is a big challenge for the next decades and the development of Gen(IV) nuclear systems. Conversion routes are numerous, but one needs to prove that they can be adapted to handle minor actinides. One of them is called the resin process and is particularly attractive because it stands for a "dustless" process as it produces microspheres of oxide or carbide after thermal treatment of the loaded resin. The study presented herein focuses on the experiments and tests which enable us to optimize the fixation of minor actinides onto ionic exchange resin and their carbonization into oxide type materials.

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Summary form only given. The interest of sulfur and sulfur compounds for battery electrodes have been demonstrated since several years (L.C. Jonghe et al.). The interest of polyaniline was also demonstrated, in terms of stability, and feasability. But the results was not enough in terms of charge capacity. The association of polyaniline with some sulfur compounds was already investigated (K. Naoi et al.). The aim of this contribution is to present an opinion on the question of battery electrodes using polyaniline associated with sulfur compounds. It is based on the electrochemical behaviour of polyaniline films in different media and in presence of sulfur compounds and on the growing of polyaniline films with sulfur compounds. The sulfur species were: sulfur, carbone disulfide, aminoethanethiol, 1,2-ethanedithiol, 2-aminothiophenol, 3 aminothiophenol and 2,5-dimercapto-1,3,4-thiadiazole. Generally, sulfur compounds have strong interactions with metallic electrodes which give passive films. With polyaniline it is also true, because of interactions between nitrogen and sulfur. Still now, the electrocatalysis of redox systems of sulfur compounds or the increase of the charge capacity of polyaniline seems not really significative.