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Дисертації з теми "Dioxyde d'uranium – Synthèse (chimie)":
Vigier, Jean-François. "Synthèse d’oxydes d’actinides en milieu chlorure fondu : études structurales et mécanismes réactionnels." Electronic Thesis or Diss., Lille 1, 2012. http://www.theses.fr/2012LIL10051.
The study developed in this thesis concerns actinide oxides synthesis for nuclear fuel refabrication, and more specifically, the actinide (III) precipitation in molten salt LiCl-CaCl2 (30-70%mol) salt at 700°C using wet argon sparging. First, this conversion method is described for neodymium (III) and cerium (III) coconversion. The conversion rates are around 99.9%, and the obtained powders contain mixed oxychloride Ce1-xNdxOCl as main component, with a small amount of mixed oxide Ce1-xNdxO2-0.5x for the high cerium ratio. A second oxychloride CeIV(Nd0.7Ce0.3)IIIO3Cl is obtained in specific conditions and in very low quantity. The structure of this oxychloride is described in this study. The partially oxidative property of the conversion method induces the oxidation of a part of cerium (III) to oxidation state (IV). In the case of uranium (III) conversion by wet argon sparging, all the uranium is oxidized and give the oxide UO2 as single compound. The conversion rate for this element is over 99.9% in the molten chloride, but significant amount of uranium is lost by volatilization during the conversion. Finally, the U(III) and Pu(III) coconversion study shows the highest precipitation sensitivity of uranium (III) in comparison with plutonium (III), responsible of a successive conversion of the two elements, giving an oxide mixture of UO2 et PuO2 with quantitative conversion rate. Surprisingly, the conversion of Pu(III) in the same conditions led to a mixture of PuO2 and PuOCl, characteristic of a partial oxidation from Pu (III) to Pu (IV), in contrast with coconversion of U(III)-Pu(III)
Vigier, Jean-François. "Synthèse d’oxydes d’actinides en milieu chlorure fondu : études structurales et mécanismes réactionnels." Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10051/document.
The study developed in this thesis concerns actinide oxides synthesis for nuclear fuel refabrication, and more specifically, the actinide (III) precipitation in molten salt LiCl-CaCl2 (30-70%mol) salt at 700°C using wet argon sparging. First, this conversion method is described for neodymium (III) and cerium (III) coconversion. The conversion rates are around 99.9%, and the obtained powders contain mixed oxychloride Ce1-xNdxOCl as main component, with a small amount of mixed oxide Ce1-xNdxO2-0.5x for the high cerium ratio. A second oxychloride CeIV(Nd0.7Ce0.3)IIIO3Cl is obtained in specific conditions and in very low quantity. The structure of this oxychloride is described in this study. The partially oxidative property of the conversion method induces the oxidation of a part of cerium (III) to oxidation state (IV). In the case of uranium (III) conversion by wet argon sparging, all the uranium is oxidized and give the oxide UO2 as single compound. The conversion rate for this element is over 99.9% in the molten chloride, but significant amount of uranium is lost by volatilization during the conversion. Finally, the U(III) and Pu(III) coconversion study shows the highest precipitation sensitivity of uranium (III) in comparison with plutonium (III), responsible of a successive conversion of the two elements, giving an oxide mixture of UO2 et PuO2 with quantitative conversion rate. Surprisingly, the conversion of Pu(III) in the same conditions led to a mixture of PuO2 and PuOCl, characteristic of a partial oxidation from Pu (III) to Pu (IV), in contrast with coconversion of U(III)-Pu(III)
Jouffret, Laurent. "Synthèse hydrothermale d’uranyle-vanadates et d’uranyle-phosphates : influence des amines et dimensionnalité des arrangements inorganiques." Electronic Thesis or Diss., Lille 1, 2009. http://www.theses.fr/2009LIL10065.
Solid state chemistry of hybrid organic-inorganic compounds containing uranium has been enriched recently by a multiplication of papers dealing with two and three dimensional inorganic materials. This work deals with hydrothermal synthesis of compounds in the uranyl-phosphate-amine and uranyl-vanadate-amine systems. Determination of their structure was done by X-ray diffraction on single crystals. Their thermal stability was also studied. According to the pH of the initial solutions, and nature of the amine used, different families of compounds appear. With a basic pH, the obtained compounds are two dimensional with the layers corresponding to those found in naturally occurring phases, such as carnotite type layer for the uranyl-vanadate system and autunite for the uranyl-phosphate system. With an acidic pH, compounds with three dimensional frameworks are stabilized by the presence of the amines. The frameworks result from uranophane type uranyl-vanadate or uranyl-phosphate layers connected by uranyl pillars. They display different U/V or U/P ratios depending on the geometric isomer of the uranophane layer. Identification of new geometric isomers has led to a simple classification of the isomers which helps to their comparison and to the understanding of their formation. Finally, using ethylene diamine in the uranyl-phosphate system reduces in situ uranium (VI) into uranium (IV) and forms a uranium (IV) phosphate in which the uranium-phosphate layers alternate with diprotonated ethylene diamine layers
Jouffret, Laurent. "Synthèse hydrothermale d’uranyle-vanadates et d’uranyle-phosphates : influence des amines et dimensionnalité des arrangements inorganiques." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10065/document.
Solid state chemistry of hybrid organic-inorganic compounds containing uranium has been enriched recently by a multiplication of papers dealing with two and three dimensional inorganic materials. This work deals with hydrothermal synthesis of compounds in the uranyl-phosphate-amine and uranyl-vanadate-amine systems. Determination of their structure was done by X-ray diffraction on single crystals. Their thermal stability was also studied. According to the pH of the initial solutions, and nature of the amine used, different families of compounds appear. With a basic pH, the obtained compounds are two dimensional with the layers corresponding to those found in naturally occurring phases, such as carnotite type layer for the uranyl-vanadate system and autunite for the uranyl-phosphate system. With an acidic pH, compounds with three dimensional frameworks are stabilized by the presence of the amines. The frameworks result from uranophane type uranyl-vanadate or uranyl-phosphate layers connected by uranyl pillars. They display different U/V or U/P ratios depending on the geometric isomer of the uranophane layer. Identification of new geometric isomers has led to a simple classification of the isomers which helps to their comparison and to the understanding of their formation. Finally, using ethylene diamine in the uranyl-phosphate system reduces in situ uranium (VI) into uranium (IV) and forms a uranium (IV) phosphate in which the uranium-phosphate layers alternate with diprotonated ethylene diamine layers
Pipon, Yves Moncoffre Nathalie Toulhoat Nelly. "Diffusion thermique et sous irradiation du chlore dans le dioxyde d'uranium." [s.l.] : [s.n.], 2006. http://tel.archives-ouvertes.fr/docs/00/13/97/07/PDF/These_Yves.pdf.
Baurens, Bertrand. "Couplages thermo-chimie mécaniques dans le dioxyde d'uranium : application à l' intéraction pastille-gaine." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4047/document.
Nuclear fuels under power transient undergo high thermal and mechanical stresses, as well as deep chemical modifications. Stresses on the cladding at the inter-pellet plane due to the pellet thermal expansion, associated to the corrosive fission product release, can lead to clad failures, resulting from a stress corrosion cracking mechanism. The thermal, mechanical and chemical properties of the UO2 irradiated fuel are closely dependent and play a major role on the behavior of the material during a power transient. The aim of this work is to model at the pellet scale the chemical, thermal and mechanical coupled changes of the UO2 fuel during a power transient scenario and to evaluate the consequences on the fuel behavior. The final objective is to obtain an evaluation of the iodine release source term to be used in I-SCC modelling codes dedicated to Pellet-Clad-Interaction studies
Pipon, Yves. "Diffusion thermique et sous irradiation du chlore dans le dioxyde d'uranium." Phd thesis, Université Claude Bernard - Lyon I, 2006. http://tel.archives-ouvertes.fr/tel-00139707.
- l'influence de la température a été étudiée en effectuant des recuits thermiques dans une gamme de température comprise entre 900 et 1300°C ; nous avons montré que le chlore implanté était mobile dès 1000°C et déterminé une énergie d'activation de 4,3 eV ;
- l'influence de l'irradiation par des produits de fission a été étudiée en irradiant les échantillons avec des ions 127I (énergie de 63,5 MeV). Nous avons pu déterminer que la diffusion du chlore implanté sous irradiation et dans la gamme de température 30 – 250°C n'était pas purement athermique. Nous avons calculé un coefficient de diffusion sous irradiation D250 °C de l'ordre de 10^(-14) cm^2s^(-1).
Nous avons montré l'importance des défauts d'implantation et d'irradiation qui constituent notamment des chemins préférentiels pour un transport rapide du chlore. Les calculs ab-initio effectués en complément de l'étude expérimentale montrent que le site préférentiel du chlore est un site substitutionnel. Cela nous permet de penser que le mécanisme de diffusion du chlore est un mécanisme atomique de type Frank-Turnbull ou bien un mécanisme de diffusion par paires « lacune / chlore ».
Hingant, Nina. "Synthèse, frittage et dissolution de solutions solides d'oxydes mixtes de thorium et d'uranium(IV) : influence de la méthode de préparation du précurseur." Paris 11, 2008. http://www.theses.fr/2008PA112225.
Mixed actinide dioxides are currently considered as potential fuels for the third and fourth generations of nuclear reactors. In this context, thorium-uranium (IV) dioxide solid solutions were studied as model compounds to underline the influence of the method of preparation on their physico-chemical properties. Two methods of synthesis, both based on the initial precipitation of oxalate precursors have been developed. The first consisted in the direct precipitation ("open" system) while the second involved hydrothermal conditions ("closed" system). The second method led to a significant improvement in the crystallization of the samples especially in the field of the increase of the grain size. In these conditions, the formation of a complete solid solution Th1 xUx(C2O4)2 ?€? 2H2O was prepared between both end-members. Its crystal structure was also resolved. Whatever the initial method considered, these compounds led to the final dioxides after heating above 400°C. The various steps associated to this transformation, involving the dehydration of precursors then the decomposition of oxalate groups have been clarified. Moreover, the use of wet chemistry methods allowed to reduce the sintering temperature of the final thorium-uranium (IV) dioxide solid solutions. Whatever the method of preparation considered, dense samples (95% to 97% of the calculated value) were obtained after only 3 hours of heating at 1500°C. Additionally, the use of hydrothermal conditions significantly increased the grain size, leading to the reduction of the occurrence of the grain boundaries and of the global residual porosity. The significant improvement in the homogeneity of cations distribution in the samples was also highlighted. Finally, the chemical durability of thorium-uranium (IV) dioxide solid solutions was evaluated through the development of leaching tests in nitric acid. The optimized homogeneity especially in terms of the cations distribution, allowed to limit the influence of the composition, probably because of the absence of UO2 aggregates in the samples while the decrease of the number of grain boundaries led to dissolution rates one order of magnitude lower than that determined for samples prepared in "open" conditions. Finally, the precipitation of thorium in secondary neoformed phases (such as ThO2, xH2O or Th(OH)4) when the saturation conditions were reached in the leachate was also underlined
Belhabib, Tayeb. "Comportement thermique des défauts lacunaires induits par l'hélium et les gaz de fission dans le dioxyde d'uranium." Phd thesis, Université d'Orléans, 2012. http://tel.archives-ouvertes.fr/tel-00831705.
Gilardi, Thierry. "Etude par analyse thermique à vitesse de transformation contrôlée des mécanismes d'oxydation et de réduction des oxydes d'urnium." Aix-Marseille 1, 1993. http://www.theses.fr/1993AIX11054.