A modelling exercise on the importance of ternary alkaline earth carbonate species of uranium(VI) in the inorganic speciation of natural waters

International audiencePredictive modelling of uranium speciation in natural waters can be achieved using equilibrium thermodynamic data and adequate speciation software. The reliability of such calculations is highly dependent on the equilibrium reactions that are considered as entry data, and the values chosen for the equilibrium constants. The working group " Speciation " of the CETAMA (Analytical methods establishment committee of the French Atomic Energy commission, CEA) has organized a modelling exercise, including four participants, in order to compare modellers' selections of data and test thermodynamic data bases regarding the calculation of U(VI) inorganic speciation. Six different compositions of model waters were chosen so that to check the importance of ternary alkaline earth carbonate species of U(VI) on the aqueous speciation, and the possible uranium solid phases as solubility-limiting phases. The comparison of the results from the participants suggests i) that it would be highly valuable for end-users to review thermodynamic constants of ternary carbonate species of U(VI) in a consistent way and implement them in available speciation data bases, and ii) stresses the necessary care when using data bases to avoid biases and possible erroneous calculations

Sustainable Solvent Extraction Process for Fe Analysis in Radioactive Samples Based on Microfluidic Tools

International audienceThe decommissioning and dismantling of nuclear plants, and the subsequent management of the wastes require a large number of radiochemical analyses in the timeline of the operations. Validated analytical methods for radionuclides measurements are employed to ensure reliable sample characterizations. The radioactivity of the samples, which induces handling and shipment constraints, and the use of harmful chemical reactants in some analytical procedures, are among the motivations to use miniaturized techniques that would considerably lower the amounts of samples and chemicals. Moreover the decrease of the analytical time is a major concern considering the increasing demand for radiochemical analyses. The purpose of this work is to develop a microsystem-based protocol for the recovery of 55Fe from samples. Analytical solvent extraction protocols adapted to co-flow glass microsystems, were developed and tested on iron extraction into ethyl acetate. A first extraction protocol consists of the partitioning of the Fe(cupferrate)3 chelate, from the aqueous phase to the organic phase. A second extraction protocol is based on the reactive transfer of iron using the cupferron in the organic phase. The two protocols were tested on a single Y-junction and a double stage Y-junction glass microsystems. After optimization of the liquid flow rates, the iron extraction was achieved within about 2 s or less. While the best extraction yield of (60.3 ± 4.9) % was obtained with the former protocol in the double stage Y-junction, higher values of (83.1 ± 5.2) % and (81.7 ± 2.0) % were obtained with the single and double stage microsystems, respectively, with the second protocol. These last results compare well with the yield of (93.0 ± 2.3) % measured in batch, and could even be optimized by using slightly longer microchannels. Such microsystem-based extractions will be further applied to the analysis of 55Fe by liquid scintillation

Complexes aqueux de lanthanides (III) et actinides (III) avec les ions carbonate et sulfate. Etude thermodynamique par spectrofluorimétrie laser résolue en temps et spectrométrie de masse à ionisation électrospray

La prévision de l'impact sur l'environnement d'un éventuel stockage géologique de déchets radioactifs, s'appuie sur la modélisation thermodynamique du comportement de radionucléides dans des eaux souterraines. Dans ce cadre, l'analogie entre lanthanides et actinides(III) est bien confirmée par analyse critique de la littérature et comparaison aux résultats expérimentaux obtenus. Le complexe limite, Eu(CO3)33 , est identifié par mesures de solubilité en solutions de Na2CO3. Puis les constantes de formation des complexes Eu(CO3)i3 2i (i = 1-3) et Eu(SO4)i3 2i (i = 1-2) sont mesurées par SLRT. L'étude de la formation de LaSO4+ en solution par ESI-MS montre un bon accord avec la spéciation attendue. L'enthalpie et l'entropie de la réaction Cm(CO3)2 +CO32 =Cm(CO3)33 sont déduites de mesures de la constante d'équilibre par SLRT entre 10 et 70C. L'effet de la force ionique est calculée par la formule TIS.The prediction of the environmental impact of a possible geological disposal of radioactive wastes is supported by the thermodynamic modelling of the radionuclides behaviour in the groundwater. In this framework, the analogy between lanthanides and actinides(III) is confirmed by a critical analysis of the literature and the comparison with experimental results obtained here. The limiting complex, Eu(CO3)33 , is identified by solubility measurements in Na2CO3 solutions. Then the formation constants of the complexes Eu(CO3)i3 2i (i = 1-3) and Eu(SO4)i3 2i (i = 1-2) are measured by TRLFS. The formation of aqueous LaSO4+ is studied by ESI-MS and is in good agreement with the expected speciation. The enthalpy and entropy of the reaction Cm(CO3)2 +CO32 =Cm(CO3)33 are deduced from TRLFS measurements of the equilibrium constant between 10 and 70C. The ionic strength effect is calculated using the SIT formula.EVRY-BU (912282101) / SudocSudocFranceF

Spectroluminescence measurements of the stability constants of CanUO2(CO3)3(4−2n)− complexes in NaClO4 medium and the investigation of interaction effects

International audienc

Investigation of the luminescence of [UO₂X₄]^2- (X=Cl, Br) complexes in organic phase using time-resolved laser-induced fluorescence spectroscopy and quantum chemical simulations

International audienceThe luminescence properties of the [UO2Cl4]2- complex in an organic phase, especially the influence of large organic counter cations, have been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and ab initio modeling. The experimental spectrum was assigned by vibronic Franck-Condon calculations on quantum chemical methods on the basis of a combination of relativistic density functional approaches. The shape of the luminescence spectrum of the uranyl tetrachloride complex is determined by symmetrical vibrations and geometrical change upon emission. The possible change in the luminescence properties depending on the first and second uranyl coordination spheres was predicted theoretically for the [UO2Br4]2- and [R4N]2[UO2Cl4] ([R4N] = [Bu4N], [A336]) systems. The computations reveal that for U(VI), the second coordination sphere has little influence on the spectrum shape, making speciation of uranyl complexes with identical first coordination-sphere ligands tedious to discriminate. The computed structural changes agreed well with experimental trends; theoretical spectra and peak attributions are in a good accordance with TRLFS and magnetic circular dichroism (MCD) data respectively

Exploring excited state potential energy profile and luminescence properties of uranyl complexes by TRLFS and ab initio methods

International audienc

A combined ab initio and time-resolved laser-induced fluorescence study of uranium-ligand interactions

International audienc

Les microsystèmes au service de la chimie analytique verte pour le nucléaire

International audienceMiniaturization of analytical devices provides new perspectives for safety improvement, optimisation, anddiversification of processes (reduction of matter shipment, reduction of stored materials, energy savings,reaction conditions that are inaccessible with macroscopic reactors…). This reduced scale satisfies most ofthe criteria of green analytical chemistry as well as the principle of minimization of hazards associated toradioactive samples, thanks to a major reduction of sample quantities, reactants, wastes, and analysis time,and to automation. An increasing number of specific microsystems or “labs-on-a-chip” have been developedwith this ambition, particularly for radionuclides purification and separation steps, and for their analysesin complex and hard-to-handle samples. This article illustrates the development of analytical microsystemsfor isotopic, elemental and speciation analysis as met in nuclear-related activities, and underlines the mainchallenges to take up.La miniaturisation des dispositifs analytiques offre, pour le domaine nucléaire, des perspectives nouvellespour la sécurisation, l’optimisation et la diversification des procédés (réduction des transports de matière,réduction des quantités stockées, énergétique, conditions réactionnelles inaccessibles aux réacteursmacroscopiques…). Cette échelle réduite satisfait la plupart des critères de la chimie analytique verte, ainsique le principe de minimisation des risques et nuisances associés aux échantillons radioactifs, par uneréduction très importante des quantités d’échantillons, des réactifs, des déchets générés par les installations,du temps d’analyse et par l’automatisation. Un nombre croissant de développements de microsystèmesou « laboratoires sur puce » spécifiques sont réalisés dans ce sens, en particulier pour les étapes depurification et séparation de radionucléides, et pour leurs mesures dans des échantillons complexes etdifficiles à manipuler. Cet article propose d’illustrer le développement de microsystèmes analytiquesappliqués à des problématiques d’analyse isotopique, élémentaire et de spéciation rencontrées dans lenucléaire, et de souligner les principaux défis qui restent à relever

Exploring excited state potential energy profile and luminescence properties of uranyl complexes by combination of TRLFS and ab initioab\ initio methods

International audienc

Thermodynamic data provided through the FUNMIG project: Analyses and prospective

International audienceIn this paper some of the needs for good quality thermodynamic data in radioactive waste management are highlighted. A presentation of the thermodynamic data produced within the 6th EC framework programme integrated project FUNMIG (Fundamental processes of radionuclide migration) and how these have helped in filling relevant thermodynamic data gaps is given. The manuscript does not intend to be a complete review of thermodynamic data, but a short overview of the aqueous complexation of Am(III), lanthanides (III), U(VI), and Th(IV) by sulfates, silicates, carbonates and phosphates. The work presented is based on the latest developments published in the literature and specifically addressed within the IP FUNMIG