Facing the challenge of predicting the standard formation enthalpies of n-butyl-phosphate species with ab initio methods

Tributyl-phosphate (TBP), a ligand used in the PUREX liquid-liquid separation process of spent nuclear fuel, can form explosive mixture in contact with nitric acid, that might lead to violent explosive thermal runaway. In the context of safety of a nuclear reprocessing plant facility, it is crucial to predict the stability of TBP at elevated temperatures. So far, only the enthalpies of formation of TBP is available in the literature with a rather large uncertainties, while those of its degradation products, di-(HDBP) and mono-(H$_2$MBP}) are unknown. In this goal, we have used state-of-the art quantum chemical methods to compute the formation enthalpies and entropies of TBP and its degradation products di-(HDBP), mono-(H$_2$MBP) in gas and liquid phases. Comparisons of levels of quantum chemical theory revealed that there are significant effects of correlation on their electronic structures, pushing for the need of not only high level of electronic correlation treatment, namely local coupled cluster with single and double excitation operators and perturbative treatment of triple excitations [LCCSD(T)], but also extrapolations to the complete basis to produce reliable and accurate thermodynamics data. Solvation enthalpies were computed with the conductor like screening model for real solvents [COSMO-RS], for which we observe errors not exceeding 22 kJ mol$^{-1}$. We thus propose with final uncertainty of about 20 kJ mol$^{-1}$ standard enthalpies of formation of TBP, HDBP, and H$_2$MBP which amounts to -1281.7$\pm$24.4, -1229.4$\pm$19.6 and -1176.7$\pm$14.8 kJ mol$^{-1}$, respectively, in the gas phase. In the liquid phase, the predicted values are -1367.3$\pm$24.4, -1348.7$\pm$19.6 and -1323.8$\pm$14.8 kJ mol$^{-1}$, to which we may add about -22 kJ mol$^{-1}$ error from the COSMO-RS solvent model. From these data, we predict the complete hydrolysis of TBP to be nearly thermoneutral

Etude théorique de matériaux pour la spintronique

Ce mémoire présente les travaux réalisés durant ces trois années de thèse. Ils se sont orientés autour de l'étude des propriétés électroniques et magnétiques des matériaux pour la spintronique. Ce domaine d'avenir doit encore trouver les matériaux adaptés qui permettraient de réaliser les concepts liés à la spintronique. Nos résultats sont les suivants. Nous avons proposé un nouveau modèle qui décrit l'arrangement magnétique dans les couches minces ferromagnétiques possédant une anisotropie uniaxiale. Le modèle apporte une meilleure description des largeurs de domaine en fonction de l'épaisseur ainsi qu'une bonne estimation de l'épaisseur critique à partir de laquelle les domaines de Weiss ne sont plus stables. L'ensemble d'équations en unité réduite découlant du modèle apporte quant à lui un outil supplémentaire aux expérimentateurs. L'étude ab-Initio fait sur les semi-Conducteurs magnétiques dilués à mis en évidence l'importance de la corrélation forte et de l'effet Jahn-Teller dans les matériaux tel que le (Ga,Mn)N et le (Zn,Cr)S. Ces calculs confirment l'ensemble des données expérimentales existantes sur le (Ga,Mn)N. La modélisation analytique apporte un complément aux calculs ab-Initio en faisant le lien entre les paramètres expérimentaux et la théorie de Vallin, très largement utilisée pour interpréter les mesures optiques du (Zn,Cr)S. Nos calculs ab-Initio ont montré que le métacinabre est un isolant topologique robuste, qui se distingue par la présence d'un cône de Dirac extrêmement anisotrope. Les effets de passivation à l'hydrogène influencent les états de surface des isolants topologiques de la série HgX (X : S, Se, Te).This thesis contains the scientific work of three years. The main topic can be defined as follows : study of electronic and magnetic properties of materials for spintronics. That technology of the future has still to find the necessary materials to realize new concepts. Our results are the following : We propose a new model to describe the magnetic configuration in thin ferromagnetic film with uniaxial anisotropy. It gives a better description of domain widths in function of film thickness and permits to obtain a good evaluation of the critical thickness where domains of Weiss type are no longer stable. The set of equations in reduced units is a useful tool to analyze experimental data. The ab-Initio study of diluted magnetic semiconductors has demonstrated the combined effect of strong correlations and Jahn-Teller distortion in (Ga,Mn)N and (Zn,Cr)S. The calculations confirm the experimental results of (Ga,Mn)N. We develop an analytical model that is complementary to the ab-Initio calculations and permits to create a link between several experimental parameters, the ab-Initio calculations and the former theory of Vallin. It has been used to interpret the optical measurements of (Zn,Cr)S. Our ab-Initio studies show that metacinnabar is a strong topological insulator with one peculiarity, it has a highly anisotropic Dirac cone. The passivation with hydrogen atoms influences the surface states of the topological insulator in the series HgX (X : S, Se, Te). When the dangling bonds are saturated by hydrogen, the trivial surface states disappear

Etude théorique de matériaux pour la spintronique

Ce mémoire présente les travaux réalisés durant ces trois années de thèse. Ils se sont orientés autour de l'étude des propriétés électroniques et magnétiques des matériaux pour la spintronique. Ce domaine d'avenir doit encore trouver les matériaux adaptés qui permettraient de réaliser les concepts liés à la spintronique. Nos résultats sont les suivants. Nous avons proposé un nouveau modèle qui décrit l'arrangement magnétique dans les couches minces ferromagnétiques possédant une anisotropie uniaxiale. Le modèle apporte une meilleure description des largeurs de domaine en fonction de l'épaisseur ainsi qu'une bonne estimation de l'épaisseur critique à partir de laquelle les domaines de Weiss ne sont plus stables. L'ensemble d'équations en unité réduite découlant du modèle apporte quant à lui un outil supplémentaire aux expérimentateurs. L'étude ab-initio fait sur les semi-conducteurs magnétiques dilués à mis en évidence l'importance de la corrélation forte et de l'effet Jahn-Teller dans les matériaux tel que le (Ga,Mn)N et le (Zn,Cr)S. Ces calculs confirment l'ensemble des données expérimentales existantes sur le (Ga,Mn)N. La modélisation analytique apporte un complément aux calculs ab-initio en faisant le lien entre les paramètres expérimentaux et la théorie de Vallin, très largement utilisée pour interpréter les mesures optiques du (Zn,Cr)S. Nos calculs ab-initio ont montré que le métacinabre est un isolant topologique robuste, qui se distingue par la présence d'un cône de Dirac extrêmement anisotrope. Les effets de passivation à l'hydrogène influencent les états de surface des isolants topologiques de la série HgX (X : S, Se, Te).This thesis contains the scientific work of three years. The main topic can be defined as follows : study of electronic and magnetic properties of materials for spintronics. That technology of the future has still to find the necessary materials to realize new concepts. Our results are the following : We propose a new model to describe the magnetic configuration in thin ferromagnetic film with uniaxial anisotropy. It gives a better description of domain widths in function of film thickness and permits to obtain a good evaluation of the critical thickness where domains of Weiss type are no longer stable. The set of equations in reduced units is a useful tool to analyze experimental data. The ab-initio study of diluted magnetic semiconductors has demonstrated the combined effect of strong correlations and Jahn-Teller distortion in (Ga,Mn)N and (Zn,Cr)S. The calculations confirm the experimental results of (Ga,Mn)N. We develop an analytical model that is complementary to the ab-initio calculations and permits to create a link between several experimental parameters, the ab-initio calculations and the former theory of Vallin. It has been used to interpret the optical measurements of (Zn,Cr)S. Our ab-initio studies show that metacinnabar is a strong topological insulator with one peculiarity, it has a highly anisotropic Dirac cone. The passivation with hydrogen atoms influences the surface states of the topological insulator in the series HgX (X : S, Se, Te). When the dangling bonds are saturated by hydrogen, the trivial surface states disappear.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Les moissons de lumière : une traversée du Haut-Atlas marocain / François Virot ; photogr. de l'auteur...

Contient une table des matièresAvec mode text

Solubility and diffusivity of hydrogen and its isotopes in the BeO system

International audienceThis work revisits hydrogen insertion in the wurtzite beryllium oxide in order to fill the gap in scientific knowledge regarding the diffusion coefficients of the different chemical states of hydrogen (neutral, charged, or molecular). Both first-principle and macroscopic models were used to this end. In the former, two exchange-correlation functionals (PBE and SCAN) were used to compute the properties of interest and accuracy was then discussed. Regarding the behavior of interstitial insertion of hydrogen, this work is slightly different from previous works; hydrogen was mainly found in the form of charged H− or H+ ions, depending on experimental conditions. In regard to diffusivity properties, a complex migration pathway was found for hydrogen cation. Finally, the present study succeeded in producing a reliable set of diffusion coefficients for neutral, charged, and molecular hydrogen

ALAMBIC, a simulation tool to assess the red-oils hazards in reprocessing facilities

International audienceIn the French nuclear industry, the reprocessing of spent nuclear fuel is based on the PUREX aqueous process (“Plutonium Uranium Refining by EXtraction”). The main involved compounds are an organic mixture of hydrocarbon diluted tri-n-butyl phosphate (TBP) as well as a nitric acid solution used to dissolve the spent fuel. Even if the neat TBP is thermally stable, an extended contact with an acid solution (nitric acid and extractable heavy metal nitrates) forms a mixture called red-oils due to reaction at elevated temperature between involved species. These complex reactions and the formation of unstable by-products can lead to a thermal runaway in the plants’ evaporators potentially followed by an explosion, a containment failure and a radioactive release into the environment [1]. In the past, these phenomena have been responsible of several significant accidents such as, two accidents in the United States at Savannah River plant (1953 and 1975) and more recently one accident in Russia at Tomsk (1993). This raises the question of exothermicity of reactions involving extractant TBP, its diluent (hydrogenated tetra-propylene, HTP) and their by-products and calls for a better knowledge of underlying thermochemical phenomena. In the context of safety reviews regarding the French reprocessing plants at La Hague, one of the important risks concerning the evaporators is the explosion risk due to the red-oils compounds formation. Therefore, in order to simulate the behaviour of reactant solutions in evaporators during an accidental transient due to a thermal runaway, a simulation tool, ALAMBIC, is being developed at IRSN to support, in the next future, safety analyses. Its aim will be to simulate the thermal degradation of TBP in contact with nitric acid/uranyl nitrate solution and thus investigate the conditions leading to violent thermal runaways. This tool is built from modules of the ASTEC software package (Accident Source Term Evaluation Code) [2], one able to simulate the thermal-hydraulic behaviour coupled with another one to calculate the chemical evolution. For the latter, several key data are mandatory as the thermodynamic properties of species in aqueous and organic liquids or the kinetics rate laws of TBP and by-products degradations. Before addressing the chemical kinetics, a study based on quantum chemical methods has been started to fill the lack of knowledge regarding the standard heat of formation of n-butyl phosphate species [3]. Similarly, efforts have been recently continued towards the uranyl nitrate complex because the potential by-products are not as evident as TBP-nitric acid system. We will first introduce the safety controls useful for safety reviews applied to evaporators in reprocessing facilities. Then, a highlight will be made on the recent theoretical results obtained about the reaction pathways of uranyl nitrate complexes. Finally the state of progress of ALAMBIC simulation tool will be presented.References1. V.N. Usachev et al., Radiochemistry 45, 1 (2003).2. L. Chailan et al., Overview of ASTEC code and models for Evaluation of Severe Accidents in Water CooledReactors, IAEA Technical Meeting, Vienna (Austria), October, 9-12, 20173. M. Saab et al., J. Chem. Phys. 146, 244312 (2017

MEMS with an embedded fluidic microchannel for sensitive weighing of liquid samples

International audienceThis paper reports hollow MEMS plate oscillators for the characterization of liquid samples, with a one-fold improvement in both Q-factor and Allan deviation compared to previous alike structures, and fluidic constriction larger than 1μm. These new characteristics make the devices amenable for the first time to liquid weighing with a 100 Hz.(g.L-1)-1 sensitivity and a few g.L-1 detection floor

ALAMBIC, a simulation tool to assess the red-oils hazards in reprocessing facilities

International audienceIn the French nuclear industry, the reprocessing of spent nuclear fuel is based on the PUREX aqueous process (“Plutonium Uranium Refining by EXtraction”). The main involved compounds are an organic mixture of hydrocarbon diluted tri-n-butyl phosphate (TBP) as well as a nitric acid solution used to dissolve the spent fuel. Even if the neat TBP is thermally stable, an extended contact with an acid solution (nitric acid and extractable heavy metal nitrates) forms a mixture called red-oils due to reaction at elevated temperature between involved species. These complex reactions and the formation of unstable by-products can lead to a thermal runaway in the plants’ evaporators potentially followed by an explosion, a containment failure and a radioactive release into the environment [1]. In the past, these phenomena have been responsible of several significant accidents such as, two accidents in the United States at Savannah River plant (1953 and 1975) and more recently one accident in Russia at Tomsk (1993). This raises the question of exothermicity of reactions involving extractant TBP, its diluent (hydrogenated tetra-propylene, HTP) and their by-products and calls for a better knowledge of underlying thermochemical phenomena. In the context of safety reviews regarding the French reprocessing plants at La Hague, one of the important risks concerning the evaporators is the explosion risk due to the red-oils compounds formation. Therefore, in order to simulate the behaviour of reactant solutions in evaporators during an accidental transient due to a thermal runaway, a simulation tool, ALAMBIC, is being developed at IRSN to support, in the next future, safety analyses. Its aim will be to simulate the thermal degradation of TBP in contact with nitric acid/uranyl nitrate solution and thus investigate the conditions leading to violent thermal runaways. This tool is built from modules of the ASTEC software package (Accident Source Term Evaluation Code) [2], one able to simulate the thermal-hydraulic behaviour coupled with another one to calculate the chemical evolution. For the latter, several key data are mandatory as the thermodynamic properties of species in aqueous and organic liquids or the kinetics rate laws of TBP and by-products degradations. Before addressing the chemical kinetics, a study based on quantum chemical methods has been started to fill the lack of knowledge regarding the standard heat of formation of n-butyl phosphate species [3]. Similarly, efforts have been recently continued towards the uranyl nitrate complex because the potential by-products are not as evident as TBP-nitric acid system. We will first introduce the safety controls useful for safety reviews applied to evaporators in reprocessing facilities. Then, a highlight will be made on the recent theoretical results obtained about the reaction pathways of uranyl nitrate complexes. Finally the state of progress of ALAMBIC simulation tool will be presented.References1. V.N. Usachev et al., Radiochemistry 45, 1 (2003).2. L. Chailan et al., Overview of ASTEC code and models for Evaluation of Severe Accidents in Water CooledReactors, IAEA Technical Meeting, Vienna (Austria), October, 9-12, 20173. M. Saab et al., J. Chem. Phys. 146, 244312 (2017

Quantum chemical prediction of standard formation enthalpies of uranyl nitrates and its degradation products

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Méthodes multi-références relativistes pour analyser les propriétés des systèmes fortement corrélés: oxydes de plutonium

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