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

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Extraction of RF equivalent circuit and semiconductor parameters of SOS MOSFETs from S-Parameter measurements

This paper describes the use of on-wafer measured microwave scattering parameters (S-parameters) for the extraction of RF equivalent circuit elements and semiconductor parameters of an SOS MOSFET. © Copyright 2011 IEEE – All Rights Reserve

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

Use of bifunctional compounds N, P for extracting uranium from aqueous solutions of nitric acid

International audienceA new series of N, P bifunctional ligands was found to give excellent extraction properties for uranium from a nitric media [1]. Two of them, which only differ by the presence of an alkyl chain between their reactive sites, gave interesting performance in terms of extraction and selectivity towards zirconium. We could observe that the separation factor U/Zr increased from 21.7 for the unbranched molecule to 220 for the branched one. Based on the know-how of the LTSM group in the field of bifunctional ligands synthesis and study and of the CEA / DMRC teams in the data acquisition on major actinides [2], [3], the objective of this study was to explore the capacity of these new molecular architectures for uranium and zirconium extraction, and to understand their extraction mechanisms.The extraction of cations, acid and water by the new bifunctional ligands were characterized by ICP-AES, coulometry and potentiometry. The molecular structures of the complexes were probed with different techniques such as infrared spectrometry and EXAFS. The organization of the ligands in supramolecular aggregates was assessed by X-ray and neutron scattering measurements, and related to their extraction properties.It is indeed now well established that the mechanisms underlying the liquid-liquid extraction processes are based not only on the chelating properties of the extracting molecules [4], but also on their capacity to form supramolecular aggregates because of their amphiphilic nature. This study concentrates therefore on both molecular and supramolecular mechanisms to understand and master both chelation and self-assembly properties of these molecules in order to optimize extraction processes.Thanks to the applied techniques, the influence of this alkyl chain on the selectivity has been put in regards with the complexation of the ligands with the uranium and zirconium and also, with the supramolecular organization in the organic phase

Use of bifunctional compounds N, P for uranium purification from aqueous solutions of nitric acid

International audienceThe refining plants of natural uranium concentrates rely on a solvent extraction process to produce uranium at the so-called "nuclear" purity. Extraction of uranium (from yellow cake) is performed thanks to an organic phase containing a specific extractant, further washed to recover pure uranium in a new aqueous phase. The conventional extractant is tri-n-butyl phosphate (or TBP). However, even though the TBP works pretty well at industrial scale, it is still of research interest to find optimized and highly efficient systems. Research has therefore been undertaken to find alternatives to TBP.It turns out that most of the tested extractants have a moderate affinity for uranium (VI) with little or no selectivity for this element toward the other metallic species. A new series of N, P bifunctional ligands showed excellent properties in a nitric medium in terms of affinity for uranium extraction. Based on the know-how of the LTSM team in the field of bifunctional ligands synthesis and study and of the CEA / DMRC teams in the data acquisition on major actinides , the objective of this study is to explore and study the capacity of new molecular architectures for uranium extraction, and to understand their extraction mechanisms. It is now established that the mechanisms underlying the liquid-liquid extraction processes are based not only on the complexing properties of the extracting molecules, but also on their capacity to form supramolecular aggregates because of their amphiphilic nature. This study concentrates therefore on both molecular and supramolecular mechanisms to understand and master both chelation and self-assembly properties of these molecules in order to optimize extraction processes.The molecular structures of the complexes are probed using different techniques such as infrared spectrometry. The extraction of cations, acid and water by the new bifunctional ligands are characterized by ICP, coulometry and potentiometry. The organization of the ligands in supramolecular aggregates is characterized by X-ray and neutrons scattering measurements. Critical aggregation concentrations are measured in detail by surface tensiometry to relate them to aggregation energies. All these molecular and supramolecular aspects of the system are related to its extraction properties

Perrhenate and pertechnetate complexation by an azacryptand in nitric acid medium

Technetium is present as the pertechnetate anion in spent nuclear fuel solutions, and its extraction by several extractant systems is a major problem for the liquid-liquid extraction processes used to separate uranium and plutonium. To prevent technetium extraction into the organic phase, a complexing agent may be added to the aqueous nitric acid phase to selectively bind the pertechnetate anion. In the present study, liquid-liquid extraction experiments reveal that technetium distribution ratios are considerably lowered with addition of an azacryptand, which is a good receptor for pertechnetate anion recognition. This ligand is able to overcome the Hofmeister bias and selectively bind techetium in nitric acid solution. Coordination studies using infrared and Raman spectoscopies and DFT calculations show the formation of an inclusion complex with hydrogen bonds stabilizing the oxo-anion within the cavity. For the first time, the cage molecules are studied for an extraction process

Bifunctional Amidophosphonate Molecules for Uranium Extraction in Nitrate Acidic Media

International audienceBifunctional amidophosphonate derivatives, already known as efficient ligands in uranium extraction from phosphoric media, have been evaluated and compared to the conventional trin-butyl phosphate (TBP) for uranium extraction from nitric medium. The efficiency of U extraction and its selectivity towards competing elements such as Th, Zr, Mo, Fe and V was evaluated with various ligand structures. It was found that extractant molecules containing a monosaponified phosphonate moiety instead of phosphonate moieties are less effective and selective. Furthermore, it was observed that alkylation of the methylene bridge linking the two functional groups prevent the formation of precipitates during the uranium loading. Effects of acidity as well as ligand concentration were also investigated to estimate the loading capacity of the molecules. More detailed stoichiometry and transfer energy were further determined by the slope analysis method and a thermodynamic study. The possible uranium recovery from the organic phase has finally been demonstrated thanks to stripping steps at low nitric acid concentration