Modelisation moleculaire des phases organiques apres extraction de plutonium

International audienceDans le cadre des etudes menees sur les systemes de 4eme generation, des procedes hydrometallurgiques de separation sont en cours de developpement au CEA. La comprehension et l'amelioration des processus d'extraction selective peuvent etre realisees grace a l'etude plus fondamentale de la chimie de coordination des actinides, en phase aqueuse et organique. Plusieurs etudes experimentales ont ete realisees ces dernieres annees sur les ions An4+ dans le milieu aqueux et organique [1], cependant, elles restent toujours difficiles a interpreter. Les simulations a l'echelle moleculaire peuvent aider a mieux comprendre la coordination, la dynamique et la mobilite de ces elements en phase organique (ou/et aqueuse). Compte tenu de la taille du systeme, les simulations de dynamique moleculaire classique semblent etre l'outil le plus pertinent pour traiter le systeme complet sur des temps de simulation relativement longs. La dynamique moleculaire permet de simuler le comportement d'un systeme au cours du temps pour des conditions de pression et de temperature donnees et de prendre en compte explicitement les effets de solvatation.Cependant, ces simulations s'appuient sur l'utilisation d'un champ de force pour decrire les interactions entre tous les constituants des phases de solvant (cf.fig.1). Alors que le developpement de champs de force pour le Pu(IV) en phase aqueuse a deja ete initie [2] , en particulier pour simuler l'interaction entre l'ion et l'eau, il reste un important travail de developpement pour caracteriser les modifications de proprietes de la phase organique en presence du complexe metallique

Force Field Parameterization of Actinyl Molecular Cations Using the 12-6-4 Model

International audiencen this work, a set of 12-6-4 force fields (FFs) parameters were developed for the actinyl molecular cations, AnO2n+ (n = 1, 2), from uranium to plutonium for classical molecular dynamics (MD) for four water models: TIP3P, SPC/E, OPC3, and TIP4Pew. Such a non-bonded potential model taking into account the induced dipole between the metallic center and the surrounding molecules has shown better performances for various cations than the classic 12-6 non-bonded potentials. The parametrization method proposed elsewhere for metallic cations has been extended to these molecular cations. In contrast to the actinyl 12-6 FFs from the literature, the new models reproduce correctly both solvation and thermodynamic properties, thanks to the inclusion of the induced dipole term (C4). The transferability of such force fields was assessed by performing MD simulations of carbonato actinyl species, which are highly implicated in actinide migration or actinide extraction from seawater. A highly satisfying agreement was found when comparing the EXAFS signals computed from our MD simulation to the experimental ones. The set of FFs developed here opens new possibilities for the study of actinide chemistry

Structural and thermodynamics properties of pure phase alkanes, monoamides and alkane/monoamide mixtures with an ab initio based force-field model

15 pages, 11 figuresInternational audienceA polarizable force-field (FF) model for short- and long-alkane chains and amide derivatives was constructed based solely on accurate quantum chemical (QC) calculations. First, the FF model accuracy was accessed by performing molecular dynamics (MD) simulations to calculate liquid-phase thermodynamic and structural properties for alkanes, for which experimental data are available. Second, The FF was then used to perform molecular dynamics simulations to calculate thermodynamic, structural and excess properties of monoamide/dodecane mixtures, namely DEHiBA/dodecane and DEHBA/dodecane. Aggregation phenomena appear for both types of mixtures and monoamide pure phases. A detailed structural analysis revealed, at small monoamide mole fraction the formation of dimers, while trimerization at larger monoamide concentrations and in their pure phases. Analysis of the relative orientation of the dimers have also been performed and showed a small difference for both phases

Insights from quantum chemical calculations into into inner and outer-sphare complexation of plutonium(IV) by monoamide and carbamide extractants

International audienceIn the context of nuclear fuel reprocessing, the recovery and purification of major actinides is achieved using a hydrometallurgical process known as PUREX (Plutonium Uranium Recovering by Extraction). Based on Liquid-Liquid extraction technics, this process requires a specific molecule to extract Pu and U, the Tri-n-butyl phosphate TBP. Monoamides are regarded as alternative family of extraction molecules to TBP, as they are well known for their strong extraction ability of Pu(IV) and U(VI) elements. In addition to this, they show some interesting features, such as the complete incinerability of the solvent degradation products, and a strong dependence of the extraction properties (distribution coefficient and selectivity) on the chemical conditions [1-3]. The strong influence of the structure of amide derivatives on their extraction properties has been demonstrated in several studies in the literature. In this study, we propose to investigate and rationalize the influence of the nature and length of the monoamide alkyl chains on Pu(IV) extraction/complexation, using the Density Functional Theory (DFT) method in the scalar relativistic framework. We will discuss the geometries of the inner/outer-sphere complexes and the interaction energies of [Pu(NO3)4] and [Pu(NO3)6]2- with different monoamide and carbamide ligands have been calculated. Our investigation focuses on discriminating the influence of the bulkiness of the alkyl group, and that of the solvent polarity on the stability of inner and outer-sphere complexes. This study suggests key possibilities to tune the substituent effect by changing the polarity of the solution [4]. References[1]G. Milanole et al. WO/2018/138441 (2018).[2]C. Berger et al., Solvent Extr. Ion Exch., 37 , 111-125 (2019).[3]E. Acher et al., Inorg. Chem., 55, 5558-5569 (2016). [4]A. Failali et al., Phys. Chem. Chem. Phys., 23, 2229-2237 (2021).<br

Theoretical study of Plutonium complexes with monoamides

International audienc