Le dioxyde d’uranium UO2 est le combustible standard dans les réacteurs nucléaires à eau pressurisée (REP). Durant le fonctionnement du réacteur les pastilles combustibles subissent des contraintes thermiques et mécaniques. Pour cette raison il est très important de bien connaître les propriétés de ce système à la fois dans les conditions de fonctionnement normales et accidentelles (300 à 2000K). Lors des réactions de fission de l’uranium, des gaz rares comme le xénon sont produits à l’intérieur du combustible. En raison de leur faible solubilité, ces gaz vont former des bulles intra- et inter- granulaires dans l’UO2. La présence de ces bulles dans le combustible a un impact sur les propriétés macroscopiques de ce dernier. A l'échelle nanométrique, les bulles intragranulaires prennent la forme d’un octaèdre facetté, essentiellement suivant les directions (111) et (100). Devant la complexité de l’étude de la stabilité de cet octaèdre, nous avons décomposé le problème afin de pouvoir l’étudier de façon plus systématique et de découpler les différents effets. Dans un premier temps, nous avons déterminé la stabilité des surfaces planes (111) et (100) de l’UO2 et les modifications de microstructure engendrées par leur relaxation. Dans un deuxième temps, nous avons caractérisé les isothermes d’adsorption du xénon sur ces surfaces relaxées, en les comparant à ceux de l’incorporation dans une boîte vide pour identifier les effets de surface. Une attention particulière a été portée sur la microstructure du xénon dans ces systèmes. Finalement, nous avons effectué une analyse des propriétés mécaniques (profils de pression et de contrainte au voisinage des surfaces). / Uranium dioxide UO2 is the standard fuel in nuclear pressurized water reactors (PWR). During the operation of the reactor the fuel pellets undergo thermal and mechanical stresses. For this reason it is very important to understand these thermomechanical properties of this system both in normal operation conditions and accidental situations (300 to 2000K). During fission reactions of uranium, rare gases such as xenon are produced within the fuel. Due to their low solubility, these gases will either be released or form intra- and inter-granular bubbles inside the UO2. The presence of these bubbles in the fuel has an impact on the thermomechanical properties of the latter. We focus in this thesis on the study of intragranularbubbles and their impact on the thermomechanical properties of UO2 , through modeling at the atomic scale. At this scale, intragranular bubbles take the shape of an octahedron, presenting mainly (111) and (100) facets. Given the complexity of the study of the stability of this octahedron, we have simplified the problem in order to study it in a more systematic way and to decouple the various effects. First, the stability of (100) and (111) extended surfaces of UO2 and microscructural modifications generated by their relaxation were studied. In a second step, we dermined adsorption isotherms of xenon on these relaxed surfaces, and compared them to the incorporation ones inside an empty box in order to isolate surface effects. A specific attention has been given to the microstructure of xenon in these systems. Finally, an analysis of the mechanical properties (pressure and stress profiles near by the surface).

La Multifragmentation du système nucléaire formé dans les collisions centrales Xe+Sn entre 32 et 50 MeV/A est étudiée avec le multidétecteur INDRA. Une analyse tensorielle permet la sélection des collisions centrales. Une proportion importante de la charge (environ 85 %) est émise isotropiquement, ce qui indique qu'un degré d'équilibration élevé est atteint. Les partitions de charges sont caractéristiques d'un régime de production multiple de fragments. La forme des distributions en énergie cinétique des fragments, ainsi que celle des fonctions de corrélation en vitesse réduite indiquent que la fragmentation est simultanée et se produit à une densité plus faible que la densité de saturation. La comparaison des données expérimentales avec les prédictions du modèle de multifragmentation statistique de Copenhague (SMM), permet de montrer que les partitions de charges sont compatibles avec l'hypothèse d'un équilibre thermodynamique, alors que les variables cinématiques sont plus contraignantes et difficiles à reproduire conjointement. Les fonctions de corrélations entre fragments permettent de contraindre le volume de freeze-out et d'estimer la part de l'énergie emmagasinée sous forme collective radiale. A 50 MeV/A, le volume de freeze-out est estimé à 2 .7 fois le volume correspondant à la densité de saturation. Il diminue avec l'énergie incidente et peut atteindre des valeurs de l'ordre de 2 fois le volume de saturation à 32 MeV/A. L'énergie collective varie de 0 à 1.3 MeV/A quand l'énergie incidente augmente. Elle n'est pas purement thermique et est probablement due à une phase de compression développée lors des premiers instants de la collision.

Ce mémoire de thèse sera consacré à l'étude de quelques aspects phénoménologiques de la supersymétrie avec, comme principaux sujets, d'une part, la physique du MSSM dans le cas où les superparticules scalaires sont lourdes et les implications possibles auprès de collisionneurs à haute énergie tels que le LHC et, d'autre part, les caractéristiques des particules de matière noire et leurs détermination auprès des collisionneurs et dans des expériences d'astroparticules.

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); 21 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56768" Urban, Jeffry Todd. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 12/21/2004. Report is also available in paper and microfiche from NTIS.

Ce travail se place dans le cadre des réacteurs nucléaires de 4ème génération tels que les réacteurs à neutrons rapides et caloporteur gaz (RNR-G), pour lesquels des matériaux réfractaires comme le nitrure de titane (TiN) enroberont le combustible afin de permettre la rétention des produits de fission. Cette étude a porté sur le comportement thermique intragranulaire du xénon dans des échantillons de TiN obtenus par frittage à chaud sous charge. Le rôle de la microstructure sur le comportement thermique du xénon a été étudié. Plusieurs lots ont ainsi été synthétisés sous différentes conditions de température et de composition de la poudre initiale. Le xénon a été introduit par implantation ionique. Les échantillons ont ensuite subi des traitements thermiques entre 1300°C et 1600°C, soient les températures accidentelles envisagées. Un transport majoritaire du xénon vers la surface a été mis en évidence. Ce dernier est ralenti lorsque la température de frittage augmente. Des différences de comportement ont été observées selon les poudres mises en oeuvre dans la synthèse et selon l'orientation cristalline du grain considéré. Le relâchement du xénon a également été corrélé à l’oxydation de TiN. Des bulles de Xe dès 0,38 % atomique ont été observées. Leur taille est proportionnelle à la concentration en Xe et augmente avec la température de recuit, d’où une certaine mobilité du Xe au sein de TiN. Plusieurs mécanismes pouvant expliquer cette mobilité sont proposés. En complément, des calculs ab initio ont confirmé le caractère fortement insoluble du Xe dans TiN et révélé que les bilacunes sont les plus favorables à l'incorporation du xénon au sein de ce matériau. / This work concerns the generation IV future nuclear reactors such as gas-cooled fast reactor (GFR) for which refractory materials as titanium nitride (TiN) are needed to surround fuel and act as a fission product diffusion barrier. This study is about Xe thermal behavior in sintered titanium nitride. Microstructure effects on Xe behavior have been studied. In this purpose, several syntheses have been performed using differents sintering temperatures and initial powder compositions. Xenon species have been introduced into samples by ionic implantation. Then, samples were annealed in temperature range from 1300°C to 1600°C, these temperatures being the accidental awaited temperature. A transport of xenon towards sample surface has been observed. Transport rate seems to be slow down when increasing sintering temperature. The composition of initial powder and the crystallographic orientation of each considered grain also influence xenon thermal behavior. Xenon release has been correlated with material oxidation during annealing. Xenon bubbles were observed. Their size is proportional with xenon concentration and increases with annealing temperature. Several mechanisms which could explain Xe intragranular mobility in TiN are proposed. In addition with experiments, very low Xe solubility in TiN has been confirmed by ab initio calculations. So, bivacancies were found to be the most favoured Xe incorporation sites in this material.

Les réacteurs GEN IV (GFR) nécessitent l’emploi de matériaux d’enrobage ayant une bonne transparence aux neutrons, une conductivité thermique élevée et agissant comme barrière de diffusion pour les produits de fission. Le but de cette étude est de déterminer le rôle de la température et de l’irradiation sur le comportement du xénon implanté dans l’oxycarbure de zirconium (ZrCxOy). A cet effet, des poudres de deux stoechiométries ZrC0,95O0,05 et ZrC0,8O0,2 ont été synthétisées puis frittées par frittage flash, ou sous charge. Pour étudier le rôle de la fluence d’implantation sur la migration thermique du xénon dans le ZrC0.95O0.05, des ions 136Xe2+ ont été implantés à une énergie de 800 keV à trois fluences : 1015, 1016 et 1017 at/cm². Les échantillons ont ensuite été recuits sous vide secondaire dans une gamme de températures de 1500 à 1800°C. Les profils de distribution du xénon ont été mesurés par RBS ou par SIMS. Des analyses par MET, MEB, NBS et PAS-DBS ont été réalisées à chaque étape. Cette étude a montré qu’à 1015 et 1016 at/cm2 le xénon est piégé dans des bulles nanométriques dans les murs de dislocations. A 1017 at/cm2, la coalescence des bulles de plus grandes tailles conduit au relâchement du xénon aux joints de grains. Pour les échantillons de ZrC0,8O0,2, les recuits conduisent à une oxydation de surface corrélée à un important relâchement du xénon. Parallèlement, des expériences d’irradiation ont été effectuées sur la plateforme JANNUS et auprès du Tandem afin de déterminer le rôle respectif des dégâts balistiques et électroniques sur la migration du xénon. Nous avons observé que ces conditions d’irradiation n’entrainaient pas de migration du xénon / Refractory ceramics are considered for the GEN IV reactors (GFR). Transition metal carbides, like ZrC, are candidates as components for fuel elements owing to their good thermal stability and their neutronic performance. An extensive study was carried out to elucidate the role of temperature on the diffusion of xenon, an abundant and volatile radionuclide, in zirconium oxycarbide. For that purpose, dense zirconium carbide samples ZrC0.8O0.2 and ZrC0.95O0.05 were synthesized using Spark Plasma Sintering and Hot Pressing. 136Xe2+ ions were implanted at three fluencies: 1015, 1016 and 1017 at/cm2, at an energy of 800 keV. Thermal annealing were carried out under vacuum in a temperature range of 1500°C to 1800°C. The Xe distribution profiles were measured either by Rutherford Backscattering Spectrometry or by Secondary Ion Mass Spectrometry before and after the different treatments. Our results show that the ZrC0.8O0.2 stoichiometry is not stable at high temperature and for the ZrC0.95O0.05 stoichiometry, the Xe migration behaviour depends on the implantation fluence. The role of the implantation defects, their evolution during annealing and the trapping of Xe into bubbles was evidenced using Positron Annihilation Lifetime Spectroscopy and Transmission Electron Microscopy. In order to simulate the effects due to neutron irradiation, irradiation experiments were carried out at the JANNUS irradiation platform at CEA Saclay and the Alto Tandem accelerator at Orsay taking into account the respective roles of the ballistic and electronic processes. We observed that no xenon migration occurred after irradiation

Les cryptophanes sont des récepteurs moléculaires qui présentent des propriétés de complexation intéressantes vis-à-vis de nombreux substrats. Ces quinze dernières années, les cryptophanes ont fait l’objet de beaucoup d’études portant sur leur utilisation pour l’obtention de biosondes pour l’IRM du xénon hyperpolarisé. De très nombreux progrès ont été réalisés, et des études in vivo semblent à présent envisageables, à condition de parvenir à synthétiser les biosondes en larges quantités. Plus récemment, un champ d’application parallèle s’est développé. Celui-ci porte sur la complexation des cations métalliques monovalents en solution aqueuse au sein de cryptophanes polyphénoliques. Ceci laisse envisager des applications pour la dépollution des eaux contaminées par des cations Cs+ ou Tl+. Cependant, ici encore, l’un des enjeux majeurs est la synthèse de larges quantités de cryptophanes présentant les caractéristiques recherchées. Les travaux réalisés au cours de cette thèse traitent de la conception et de la synthèse de nouvelles plateformes moléculaires pour l’obtention de biosondes au xénon hyperpolarisé et pour la complexation des cations métalliques monovalents Cs+ et Tl+. Les voies de synthèse mises au point permettent l’obtention de quantités appréciables d’un ensemble de nouvelles plateformes hydrosolubles pour chacune de ces applications. Les propriétés d’encapsulation de ces molécules hôtes envers leur substrat de prédilection ont été étudiées par RMN des noyaux encapsulés, par dichroïsme circulaire ou encore par titrage calorimétrique. Dans chaque cas, les nouvelles plateformes remplissent les caractéristiques recherchées et ouvrent la voie aux applications visées. / Cryptophanes are molecular receptors known for their complexation properties of various substrates. Over the last fifteen years, cryptophanes were the subject of numerous studies for they can be used to obtain biosensors for xenon MRI. This field has experienced significant growth and advances to the point were in vivo applications are now envisioned, provided that large amounts of biosensors can be synthesized. More recently, polyphenolic cryptophanes have been studied for their ability to encapsulate monovalent metallic cations like Cs+ and Tl+ in aqueous solution. This could lead to applications for depollution of contaminated water sources but would require, once again, the synthesis of large amounts of cryptophanes.The work carried out during this thesis focus on the conception and the synthesis of new molecular platforms that could either be used to obtain new hyperpolarized xenon biosensors or to encapsulate monovalent metallic cations as Cs+ and Tl+. Synthetic routes have been developed to produce good amounts of a variety of new hydrosoluble molecular platforms designed for each application. The encapsulation properties of these new host molecules were studied through NMR of the encapsulated nucleus, circular dichroism or isothermal calorimetry. In each case, the new platforms meet the expected requirements thus opening the door for the envisioned applications.

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.

This Thesis extends the chemistry of group VII transition metal oxide fluorides, namely ReO3F and MnO3F. The fundamental chemistry of ReO3F has been significantly extended with the development of its high-yield and high-purity synthesis. This has been achieved by solvolysis of Re2O7 in anhydrous HF (aHF) followed by reaction of the water formed with dissolved F2 at room temperature. The improved synthesis has allowed the Lewis acid and fluoride-ion donor-acceptor properties of ReO3F to be further investigated. The Lewis acid-base complex, (HF)2ReO3F·HF, was obtained by dissolution of ReO3F in aHF at room temperature and was characterized by vibrational spectroscopy with aid of quantum-chemical calculations and single-crystal X-ray diffraction at −173 °C. The HF molecules are F-coordinated to rhenium, representing the only known example of an HF complex with rhenium. The study of the fluoride-ion acceptor properties of ReO3F resulted in the syntheses and characterization of the [{ReO3(μ-F)}3(μ3-O)]2−, [ReO3F3]2−, and [ReO3F2]− anions. The [{ReO3(μ-F)}3(μ3-O)]2− anion was obtained as the [N(CH3)4]+ salt by the reaction of stoichiometric amounts of ReO3F and [N(CH3)4]F in CH3CN solvent. The anion was structurally characterized in CH3CN solution by 1D and 2D 19F NMR spectroscopy and in the solid state by Raman spectroscopy and a single-crystal X-ray structure determination of [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN. The structure of the [{ReO3(μ-F)}3(μ3-O)]2– anion consists of three ReO3F units linked to each other through dicoordinate bridging fluorine atoms (F) and a central tricoordinate bridging oxygen atom (O3). Calculated vibrational frequencies and Raman intensities of the [{MO3(μ-F)}3(μ3-O)]2− (C3v) and [{MO3(μ-F)}3(μ3-F)]− (C3v) anions (M = Re, Tc) have been used to assign the Raman spectrum of [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN. The fac-[ReO3F3]2− and [ReO3F2]− anions have been synthesized by the reactions of ReO3F with CsF and KF in aHF, and by reaction of ReO3F with NOF. Additionally, the [ReO3F2]− anion has been synthesized by the reaction of ReO3F with [NH4]F in aHF. Both anions were characterized by Raman spectroscopy in the solid state and single-crystal X-ray diffraction. The calculated vibrational frequencies of the fac-[ReO3F3]2− (C3v) and [(µ-F)4(ReO3F)4]4− (C4v) anions were used to assign the Raman spectra of fac-[ReO3F3]2− and [ReO3F2]−, respectively. The rhenium atoms in the open-chain, fluorine-bridged [ReO3F2]− anion and the monomeric fac-[ReO3F3]2− anion are six-coordinate with a facial arrangement of the oxygen ligands. The fluoride-ion donor properties were established by the reactions of ReO3F with excess AsF5 and SbF5/SO2ClF. Both reactions resulted in the formation of white friable solids, µ-O(ReO2F)(AsF5)∙2AsF5 and [ReO3][Sb3F16]. The [ReO3][Sb3F16] salt is stable at room temperature and decomposes to [ReO2F2][SbF5], when maintained at 45 oC under dynamic vacuum. The µ-O(ReO2F)(AsF5)∙2AsF5, however, slowly decomposes at 0 oC to ReO3F and AsF5. Both products were characterized by Raman spectroscopy in the solid state with aid of quantum-chemical calculations. The vibrational analyses revealed that the geometry of [ReO3][Sb3F16] is consistent with a trigonal pyramidal arrangement of oxygen atoms around rhenium, whereas in µ-O(ReO2F)(AsF5)∙2AsF5, ReO3F interacts with one of the AsF5 molecules through an O-bridge, which represents the first example of such type of bonding. The reactions of µ-O(ReO2F)(AsF5)∙2AsF5 and [ReO3][Sb3F16] with CH3CN resulted in the formation of the white salts, [O3Re(NCCH3)3][PnF6] (Pn = As, Sb), which were characterized by Raman spectroscopy. The reactivity of ReO3F has been extended to the synthesis of a new Re(VII) oxide fluoride, (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2}, which was synthesized by the reaction of 1:3 molar ratio of ReO3F and ReO2F3. The compound, (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2}, a rare example of an O-bridged rhenium oxide fluoride, has been characterized by single-crystal X-ray diffraction and solid-state Raman spectroscopy. The vibrational assignments of (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2} were confirmed by 18O-enrichment and quantum-chemical calculations. The improved synthesis of ReO3F has also led to the synthesis and characterization of the novel [XeOXeOXe]2+ cation as its [μ-F(ReO2F3)2]− salt by the low-temperature reaction of ReO3F and XeF2 in aHF. The [XeOXeOXe]2+ cation provides an unprecedented example of a xenon(II) oxide and a noble-gas oxocation as well as a rare example of a noble-gas dication. The crystal structure of [XeOXeOXe][µ-F(ReO2F3)2]2 consists of a planar, zigzag-shaped [XeOXeOXe]2+ cation (C2h symmetry) that is fluorine bridged through its terminal xenon atoms to two [µ-F(ReO2F3)2]– anions. The Raman spectra of the natural abundance and 18O-enriched [XeOXeOXe]2+ salts are consistent with a centrosymmetric (C2h) cation geometry. Quantum-chemical calculations were used to aid in the vibrational assignments of [Xe16/18OXe16/18OXe][µ-F(Re16/18O2F3)2]2 and to assess the bonding in [XeOXeOXe]2+ by NBO, QTAIM, ELF, and MEPS analyses. Ion pair interactions occur through Re–Fμ---Xe bridges, which are predominantly electrostatic in nature and result from polarization of the Fμ-atom electron densities by the exposed core charges of the terminal xenon atoms. Each xenon(II) atom is surrounded by a torus of xenon valence electron density comprised of the three valence electron lone pairs. The positive regions of the terminal xenon atoms and associated fluorine bridge bonds correspond to the positive σ-holes and donor interactions that are associated with “halogen bonding”. The reactions of MnO3F with noble-gas fluorides, KrF2 and XeF6, have been studied as the possible synthetic routes to MnOF5 and MnO2F3. The reaction of MnO3F with KrF2 yielded a red solid, which was isolated as a crystalline solid at room temperature and its crystal structure was assigned to manganese(V) fluoride, MnF5. The crystal structure of polymeric MnF5 consists of MnF6-octahedra which are trans-coordinated through fluorine bridges. The geometrical parameters of MnF5 could not be reliably determined due to unresolved twinning issues. The reaction of MnO3F with KrF2 in the presence of K[HF2] yielded a red-orange solid mixture of K[MnF6] (soluble in HF) and MnF3 (insoluble in HF). The HF solution of the solid mixture was characterized by 19F NMR spectroscopy and the resonance observed in the 19F NMR spectrum was preliminary assigned to [MnF6] by comparison with the chemical shift observed in the 19F NMR spectrum of MnO3F. Additionally, MnO3F was characterized by 19F−55Mn COSY NMR and 55Mn NMR spectroscopies, the latter provided the first 1J(19F−55Mn) coupling constant. The K[MnF6] salt was also characterized by single-crystal X-ray diffraction. The resulting octahedral geometry is imposed by symmetry, therefore, the anticipated Jahn-Teller distortion, which would result in D4h symmetry for the [MnF6] anion, could not be observed. The reaction of MnO3F with XeF6 resulted in the isolation of [Xe2F11]2[MnF6] and [XeF5]2[MnF6]. Both salts were characterized by low-temperature single-crystal X-ray diffraction. The [Xe2F11]2[MnF6] salt was additionally characterized by low-temperature Raman spectroscopy with the aid of quantum-chemical calculations, whereas the assignment of the known Raman spectrum of [XeF5]2[MnF6] has been improved in the present work. / Thesis / Doctor of Philosophy (PhD)