Chemical and structural investigations on uranium oxide-based microparticles as reference materials for analytical measurements

The analysis of individual micrometre- and submicrometre-sized particles collected by IAEA’s safeguards inspectors on swipe samples during in-field verification activities requires the implementation of a sustainable quality control system such as suitable microparticulate reference materials. To this end, pure and neodymium-doped uranium oxide-based microparticles utilising an aerosol-based particle production process were prepared. SEM/EDX measurements confirmed the monodispersity of the produced microspheres as well as the incorporation of 15 mol% Nd into the compound particles. The timeline of structural investigations mirror the ongoing alteration of particles being stored under laboratory atmosphere. While results from in-SEM Raman (CEA, DAM) on microparticles after two years storage time point to the formation of U3O8 and a minor fraction of schoepite phase (hydrated UO3), in U L3-edge XAFS after four months storage time and U M4-edge HR-XANES after ten months storage time spectra (INE-Beamline and ACT station @ KIT synchrotron radiation source) mainly U(IV) and U(V), respectively, was observed. These results provide new insight into ageing mechanism of the microparticles after preparation. From these results important conclusions with respect to storage conditions and shelf life of the reference particles can be drawn. The first batch of pure U-oxide microparticles produced in Juelich was successfully certified regarding the isotopic composition and the U amount per particle and applied in an international laboratory exercise NUSIMEP-9

Comparing results of X-ray diffraction, \ub5-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, \ub5-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO 2 in two materials, and as a mixture of UO 2 , U 3 O 8 and an intermediate species U 3 O 7 in the third material

Détection d’indices chimiques et radioactifs dans l’environnement - Recherche d’ultra-traces d’actinides dans des échantillons de l’environnement

Le CEA a été amené à réaliser des analyses d’ultra-traces d’uranium et de plutonium dans le cadre de ses programmes de surveillance de l’environnement dédiés à ses centres et de sa mission de détection de la prolifération nucléaire. Le procédé de ces analyses combine une purification chimique poussée et des mesures isotopiques effectuées à l’aide de spectromètres de masse très performants

Study of the chemical changes of μm-sized particles of uranium tetrafluoride (UF4_4) in environmental conditions by means of micro-Raman spectrometry

International audienceThe purpose of this work is to determine how long UF$_4$ in micro-particles can be detected after release in the environment, what the degradation products are and what are the parameters which mostly lead to degradation of UF$_4$. For this, Raman spectra of UF$_4$ μm-sized particles (typical diameters ∼5 μm) stored in various conditions (humid or dry air/argon, without or with UV light, 20 °C, 40 °C, 80 °C) were monitored by micro-Raman spectrometry over three months. The characteristic spectral signature of UF$_4$ followed here is the very intense and broad fluorescence peak which covers the 700—1100 cm-1 region when a visible laser at 514 nm is used. This study shows that persistence of the UF$_4$ signature in μm-sized particles released in the environment is strongly dependent on ambient conditions: typically a few days when submitted to both humid air or argon atmosphere and only intense UV light, a few weeks when exposed to a humid air or argon atmosphere in the dark, till at least several months and most probably several years, when kept in a dry atmosphere. Reaction of UF4 with water vapor ultimately leads to the formation uranyl hydroxide (schoepite) whereas exposure to both water vapor and UV light produces mainly uranyl peroxide (studtite)

A simple and fast method for measurement of elemental impurities in powdered U-oxide materials by means of ns-UV laser ablation coupled to a sector-field ICP-MS

International audienceThe determination of elemental impurities in uranium ore concentrates (UOCs) is of great importance in the fields of nuclear forensics and nuclear safeguards and more generally for the nuclear industry. To avoid the use of chemical reagents, prevent waste generation, and reduce the duration of the analysis, a simple method based on sample preparation involving the conversion of UOCs into glass beads by alkaline fusion followed by direct measurement by laser ablation—sector-field ICP-MS (LA-ICP-MS) is proposed. External calibration was performed with a mix of UOCs and geological standard reference materials. Accurate results were obtained for most of the 48 elements of interest in six UOC materials. The lowest detection limits are in the ng g−1 range. With this method, concentrations of a wide range of elements can be determined within 24 h

240^{240}Pu/239^{239}Pu isotopic ratio measurements in micrometric Pu and MOX particles using Secondary Ion Mass Spectrometry

International audienceEvery accident affecting industrial or nuclear facilities emits micrometric fragments of material into the environment whose elemental and isotopic compositions are characteristic of the process or event. Particle analysis, mainly implemented in the framework of the Non Proliferation Treaty to detect clandestine nuclear activities, provides a powerful tool to identify the origin of the nuclear particulate matter and to assess the environmental impact of nuclear accidents. Initially, particle-scale isotopic analyses aimed at the determination of the U isotopic composition. Now, focus is increasingly given on Pu isotopic measurements to address its origin and potential use. Such measurements are more challenging because of isobaric interferences, including those induced by hydride ions, like $^{239}$PuH+ on $^{240}$Pu+ and $^{238}$UH+ on $^{239}$Pu+ in Mixed Oxide (MOX). Such ions are generated during ionization processes by Secondary Ion Mass Spectrometry. Based on a parametric study aiming at the measurement of uranium oxide, uranium carbide and uranium single and double hydride rates, we determined that Pu and U should be detected as elementary ions to limit the impact of such interferences, although mono-oxide ions are more abundant. Thus, we developed an analytical methodology to obtain accurate$^{240}$Pu/$^{239}$Pu atomic ratios both for weapon grade Pu and MOX materials. Hydride rate is first measured in U oxide particles and then applied to correct $^{240}$Pu+ and $^{239}$Pu+ signals. The relative difference of corrected $^{240}$Pu/$^{239}$Pu isotopic ratios with expected values is reduced by a factor of 4 when measuring weapon grade Pu particles and by a factor of 10-100 when measuring MOX particles containing 1 to 10 wt% of Pu. We also proposed a method to determine the Relative Sensitivity Factor (RSF) based on the decay of Pu in order to quantify the Pu content in MOX samples. The estimated lowest measurable $^{239}$Pu/$^{238}$U atomic ratio in MOX particles is ∼1.6 × 10$^{-3}

Synthesis of uranium oxide microspheres under hydrothermal conditions as a reference material for nuclear safeguards

International audienc

Synthesis of uranium oxide microspheres under hydrothermal conditions as a reference material for nuclear safeguards

International audienc

Synthesis of mixed uranium/thorium oxide microspheres under hydrothermal conditions as a reference material for nuclear safeguards

National audienc

Comparison of the fluctuations of the signals measured by ICP-MS after laser ablation of powdered geological materials prepared by four methods

International audienceSample preparation is a crucial point for quantitative multi-elemental analses by LA-ICP-MS of powdered geological materials. Four different methods are compared in this study with respect to signal stability and intensity as follows: the preparation of glass beads (GlassB) by alkaline fusion method and three grinding and pelletizing methods relying on the use of an organic binder (VanBind, vanillic acid), an adhesive binder (MixGlue, methyl methacrylate) and a sol–gel process for glass formation (SolGel, chemical reaction of tetraethoxysilane), respectively. Sixty elements were analyzed by means of a ns-UV (213 nm) laser ablation system coupled to a single collector sector field ICP-MS with a low or medium mass resolution. Signal stability was found to strongly depend on the sample homogeneity provided by the preparation method. These methods were applied to three geological standard materials (CRM). The following criteria were used to evaluate and compare the methods: (1) proportion of the measurement cycles which are above a given signal intensity threshold (defined here as signal average ± 3 times the standard deviation), (2) signal stability of the analyzed nuclides (internal precision estimated by the relative standard deviations on raw count rates), (3) signal stability of the internal standards added to the samples, (4) external precision estimated by the relative standard deviation over five preparations for each geological CRM. For the majority of the analyzed elements, signals measured for samples prepared with the four methods are reproducible. Specific contamination in one or several elements (Cr, Fe, Co, Ni, Cu, Mo, W, Au and Bi) was observed depending on the sample preparation method. In addition, compared to grinding made with PTFE material, grinding performed with tungsten carbide material was found to produce better homogeneity, especially for the sol–gel and mixing with glue protocols, although some metallic contamination (W and Co) was observed. Thanks to the suppression of grain effects by alkaline melting, the glass bead method systematically provided signal stability and percentage of “over the threshold” close to those of the NIST glasses. This may be explained by the preparation of more homogeneous samples by alkaline melting. Finally, the described methods were found to be reproducible for the majority of the analyzed elements