Homogenous recycling of transuranium elements from irradiated fast reactor fuel by the EURO-GANEX solvent extraction process

The EURO-GANEX process was developed forco-separating transuranium elements from irradiatednuclear fuels. A hot flow-sheet trial was performed in acounter-current centrifugal contactor setup, using a genuinehigh active feed solution. Irradiated mixed (carbide,nitride) U80Pu20 fast reactor fuel containing 20 % Pu wasthermally treated to oxidise it to the oxide form which wasthen dissolved in HNO3. From this solution uranium wasseparated to >99.9 % in a primary solvent extraction cycleusing 1.0 mol/L DEHiBA (N,N-di(2-ethylhexyl)isobutyramidein TPH (hydrogenated tetrapropene) as the organicphase. The raffinate solution from this process, containing10 g/L Pu, was further processed in a second cycle of solventextraction. In this EURO-GANEX flow-sheet, TRU andfission product lanthanides were firstly co-extracted intoa solvent composed of 0.2 mol/L TODGA (N,N,N′,N′-tetran-octyl diglycolamide) and 0.5 mol/L DMDOHEMA (N,N′-dimethyl-N,N′-dioctyl-2-(2-hexyloxy-ethyl) malonamide)dissolved in Exxsol D80, separating them from most otherfission and corrosion products. Subsequently, the TRUwere selectively stripped from the collected loaded solventusing a solution containing 0.055 mol/L SO3-Ph-BTP(2,6-bis(5,6-di(3-sulphophenyl)-1,2,4-triazin-3-yl)pyridinetetrasodium salt) and 1 mol/L AHA (acetohydroxamicacid) in 0.5 mol/L HNO3; lanthanides were finally strippedusing 0.01 mol/L HNO3. Approximately 99.9 % of the TRUand less than 0.1 % of the lanthanides were found in theproduct solution, which also contained the major fractionsof Zr and Mo

An overview of solvent extraction processes developed in Europe for advanced nuclear fuel recycling, Part 2 — homogeneous recycling

The hydrometallurgical separation concepts for the recycling of irradiated nuclear fuels developed in Europe are presented and discussed. Whilst Part 1 of the review focused on concepts for heterogeneous recycling of minor actinides, this article focuses on group recycling of transuranic actinides, which would support homogeneous recycling scenarios. Most of these concepts were developed within European collaborative projects and involve solvent extraction processes separating all the actinides (U-Cm) in two cycles. The first cycle uses a monoamide extractant to recover uranium leaving all the transuranic actinides in the aqueous raffinate with the fission products. The second cycle aims for a group recovery of the transuranium elements and several strategies have been proposed for this stage. In this review article, the various solvent extraction processes are summarised and the key features of the process schemes are compared

Etude thermodynamique de la complexation des ions actinide(III) et lanthanide(III) par des ligands polyazotés en milieu homogène

Les recherches menées au cours de cette thèse s'inscrivent dans une démarche de compréhension des mécanismes intervenant lors de la complexation des ions f trivalents en milieu homogène par un ligand polyazoté tridente, l'Adptz. L 'approche thermodynamique des interactions a été utilisée afin d'évaluer, d'un point de vue énergétique, l'influence des diverses contributions sur la réaction et d'acquérir une base de données thermodynamiques la plus complète possible sur cette réaction. Dans un premier temps, l'influence de la nature du cation sur les valeurs des grandeurs thermodynamiques a été considérée. Les paramètres thermodynamiques (enthalpie libre, enthalpie et entropie) des complexes 1/1 formés ont été déterminées par la méthode de van't Hoff et/ou par microcalorimétrie dans le solvant mixte méthanol/eau (en proportions volumiques 75/25%) pour tous les ions lanthanide(III), pour l'yttrium(III) et pour trois cations actinide(III) : le plutonium, l'américium et le curium. La comparaison des valeurs pour les deux familles d'éléments f met en évidence l'augmentation de la stabilité des complexes d'un rapport 20 en faveur des actinides. Ce gain de stabilité s'explique par une réaction plus exothermique, et a été associé, dans l'interprétation des données à un effet covalent plus marqué lors de la formation de la liaison actinide(III)-azote. L'influence du changement de composition du solvant d'étude sur la thermodynamique de complexation a ensuite été abordée dans le cas de la réaction entre l'europium(III) et l'Adptz. Lorsque la fraction de méthanol augmente dans le mélange, le complexe formé devient plus stable grâce à une augmentation du terme entropique, mettant en valeur l'importance des phénomènes de réorganisation du solvant au cours de la complexation sur le bilan énergétique de la réaction dans ces systèmes.The aim of the researches carried out during this thesis was to better understand the chemical mechanisms of the complexation of trivalent f-elements by Adptz, a tridentate N-donor ligand, in homogeneous conditions. A thermodynamic approach was retained in order to estimate, from an energetical point of view, the influence of the different contributions to the reaction, and to acquire a complete set of thermodynamic data on this reaction. First, the influence of the nature of the cation on the thermodynamics was considered. The thermodynamic parameters (free energy, enthalpy and entropy) of the 1/1 complexes were systematically determined by van't Hoff method and/or microcalorimetry in a mixed solvent methanol/water (in volumic proportions 75/25%) for every lanthanide(III) ion, yttrium(III) and for three actinide(III) cations: plutonium, americium and curium. The comparison of the values obtained between the two series of f-element highlights the increase of stability of the complexes by a factor of 20 in favour of the actinide cations. This gap is explained by a more exothermic reaction and is associated, in the data interpretation, to a higher covalency of the actinide(III)-nitrogen bond. Then, the influence of the change of solvent composition on the thermodynamic of complexation was studied for the reaction between europium(III) and Adptz. The stability of the complex formed increases with the percentage of methanol in the mixed solvent, owing to an increase of the entropic contribution. The solvent reorganization upon complexation seems to be the prominent process from the energetical point of view.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

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Optimization of new extractant molecules for U(VI)/Pu(IV) separation

International audienceThe standard industrial solvent extraction process PUREX involves tri-n-butyl phosphate (TBP) as extractant to separate uranium(VI) and plutonium(IV) from fission products. TBP extractant has been used for decades but has some limitations such as its non-incinerable nature and the formation of some troublesome degradation products by radiolysis. The partition between uranium and plutonium requires the reduction of Pu(IV) to Pu(III) by introduction of reducing and stabilizing agents such as uranium(IV) and hydrazinium nitrate. New monoamide extractants showing higher selectivity are studied in order to separate U(VI) from Pu(IV) in one single cycle without reducing plutonium. This new extraction system would allow the reprocessing of MOX fuels with a higher Pu content. Amongst potential candidates, unsymmetrical N-methyl-N-alkyl monoamides are so far the most promising molecules to achieve U(VI) and Pu(IV) separation without redox chemistry. The effect of structural modifications (alkyl chains length and ramifications) on extraction performances (U and Pu distribution ratios, U/Pu selectivity) and physico-chemical properties (viscosity and loading capacity) was evaluated. In particular, the length of alkyl chains (total number of carbon atoms on the molecule) was adjusted to give enough lipophilicity preventing from third phase formations, but in the same time maintain a reasonable viscosity (compatible with a good hydrodynamic behavior)

Kinetics extraction of uranium(vi) and plutonium(iv)by n,n-dialkylamides using different experimental techniques

International audienceMass transfer coefficients of uranium(VI) and plutonium(IV) between nitric acid and a monoamide-based solvent upon extraction were determined to support the development of a liquid-liquid extraction process for the multirecycling of plutonium from the future spent nuclear fuels. The kinetics data were obtained by using three different techniques the single drop technique, the Nitsch cell and the rotating membrane cell (RMC). Beyond the comparison of the influence on the kinetics of the different technics, the main objective of this study was to determine whether the transfer is controlled by diffusion or chemistry. The results obtained by the single drop technique showed that U(VI) and Pu(IV) mass transfer constants are quite similar for the extraction step. The global results point out that the resistance to the transfer is essentially located in the organic phase and the diffusion process would mainly control the kinetics

New Bitopic Ligands for the Group Actinide Separation by Solvent Extraction

The synthesis and evaluation of solvent extraction performance of N,N,N',N'-tetraalkyl-6,6''-(2,2':6',2''-terpyridine)diamides and N,N'-diethyl-N,N'-diphenyl-6,6''-(2,2':6',2''-terpyridine)diamide are reported here. These new bitopic ligands were found to extract actinides in different oxidation states (U(VI), Np(V and VI), Pu(IV), Am(III), and Cm(III)) from 3 M nitric acid. The presence of three soft nitrogen donors led to the selective extraction of actinides(III) over lanthanides(III) (Ce, Eu) and the presence of two amide functional groups grafted to the terpyridine unit allowed the extraction to occur from a highly acidic medium by minimizing the basicity of the ligand. Ligands bearing long alkyl chains (C4 and C8) or phenyl groups showed increased performances in a polar diluent like nitrobenzene

Experimental and modeling study of fission products and minor actinides extraction with N,N-dialkylamides

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