Identification des contributions enthalpiques a l'origine de la sélectivité en extraction liquide/liquide

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Effect of the Structure of Amido-polynitrogen Molecules on the Complexation of Actinides

AbstractThe complexation and solvent extraction of Eu(III) and actinides in different oxidation states (Am(III), Pu(IV), Np(V)) by bitopic molecules with a dipyridyl-phenanthroline cycle as nitrogen unit and one or two amido functions are described. The complexation has been studied in methanol-water solution with hydrophilic molecules to enhance knowledge about this new family of ligands and to identify the most interesting structural effect. Some extraction tests have been performed with lipophilic molecules of the family to check the possible utility of the new class of ligands under representative fuel reprocessing conditions. These first studies have demonstrated that the presence of a preorganized N-donors unit like dipyridyl-phenanthroline improves the ligand's affinity for actinides and its An/Ln selectivity

Modeling and Flowsheet Design of an Am Separation Process Using TODGA and H₄TPAEN

Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H4TPAEN was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H4TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed: • An increase in the concentration of TPAEN as much as the solubility limit allows. • An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase. A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments. A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project

Modeling and Flowsheet Design of an Am Separation Process Using TODGA and H₄TPAEN

Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H4TPAEN was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H4TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed: • An increase in the concentration of TPAEN as much as the solubility limit allows. • An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase. A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments. A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project

Effects of Gamma Irradiation on the Extraction Properties of Innovative Stripping Solvents for i-SANEX/GANEX Processes

Recovery of trivalent minor actinides or of the transuranium elements from highly active raffinate could be industrially achieved by innovative Selective ActiNide EXtraction (i-SANEX) and Grouped ActiNide EXtraction (GANEX) processes, respectively. All chemicals involved in the partitioning of actinides must be resistant to acidic and radioactive environments since hydrolysis and radiolysis can have a huge impact on process safety and performance. In this work, the hydrolytic and radiolytic stabilities of two innovative hydrophilic complexing agents, 2,6-bis[1-(propan-1-ol)-triazolyl]pyridine and 2,6-bis[1-(propan-1,2-diol-triazolyl)]pyridine, have been investigated as they proved to be endowed with high actinide selectivity. In order to simulate the damage experienced under process conditions, the stripping solutions were aged in HNO3 for several weeks and γ-irradiated up to 200 kGy with 60Co sources. Batch liquid-liquid extraction tests were performed on fresh, aged, and irradiated stripping solutions in order to verify whether aging and γ-irradiation affect system performance. Furthermore, nuclear magnetic resonance (NMR) analyses were carried out to ascertain the radiation-induced ligand degradation and subsequent byproduct formation. The stripping solutions manifested exceptional performance and radiochemical stability, even under harsh process conditions, to demonstrate their industrial applicability to i-SANEX and GANEX processes

Redox behavior of gas phase Pu(IV)-monodentate ligand complexes: an investigation by electrospray ionization mass spectrometry

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an(iii) and ln(iii) complexation with tpaen selectivity quantification for an americium(iii) separation process.

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Modelling of Am stripping step with TODGA - TPAEN

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Thermodynamic approach of uranium(VI) extraction by N,N-(2-ethylhexyl)isobutyramide

International audienceThe study of extraction of U(VI) from LiNO3 media by N, N-(2-ethylhexyl)isobutyramide (DEHiBA) in dodecane has been performed at 25.00 degrees C using isothermal titration microcalorimetry. The raw heat measured is a sum of contributions. To obtain the net extraction enthalpy variation, different heats have to be evaluated as the dilution of amide into dodecane phase which has been measured and subtracted. The microcalorimetric extraction results are then compared to data obtained by Van't Hoff classical method. The extraction enthalpies obtained by both methods are similar. This first study allowed to define the experimental calorimetric conditions and will be followed by determination with other actinides and amides. (C) 2012 Elsevier B. V... Selection and/or peer-review under responsibility of the Chairman of the ATALANTE 2012 Program Committe

Determination of the structure in organic solution combining experimental characterization and molecular dynamic simulation

International audienceIn the frame of the nuclear fuel recycling, various solvent extraction processes have been developed using mono-or di-amide extractants in an aliphatic diluent. In order to better understand the extraction mechanisms involved in such extraction processes, a detailed description of the organic phases is essential. The properties of the solvent extraction system have traditionally been understood from concepts rooted in coordination chemistry. However, since the researches done by Osseo-Assare in the beginning of the 90s, it is now well established that, due to the extractants amphiphilic properties, the organic phases involved in such processes (especially at high solute concentrations) are not molecular solutions of extractants but, rather, structured solutions with an organization at the supramolecular scale. The speciation in organic phase after solvent extraction remains therefore challenging since both level of description have to be assessed concomitantly. To overcome this issue, a new approach, combining experimental studies with molecular dynamic (MD) simulations has been developed. The solutions were first prepared at the laboratory and characterized in order to obtain: (i) the phases composition (quantitative analysis of all the organic phase constituents) that allowed us to build virtual solution "boxes" for the MD simulations with precisely the same composition than the experimental ones, and (ii) the structural data related to this experimental phases (manly: densities and Small and Wide Angle X-Ray Scattering-SWAXS). Molecular dynamic simulations were then performed and the structural data were computed from the simulation trajectories. As soon as these computed data match the experimental ones (Figure 1), the simulated solution is assumed to be representative of the experimental one. The MD simulation can then be accurately analyzed to describe the structure of the solution at both the molecular and the supramolecular levels