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Le combustible nucléaire usé, constitué d’uranium, de plutonium et de produits de fission (palladium, technétium, molybdène etc.), est traité industriellement en France par le procédé PUREX. Ce procédé hydrométallurgique permet d’extraire l’uranium et le plutonium à l’aide d’une phase organique composée de tri-n-butylphosphate (TBP) dilué dans un mélange d’hydrocarbures aliphatiques (TPH). Au cours des différents cycles d’extraction, la phase organique est soumise à des phénomènes d’hydrolyse acide et de radiolyse conduisant à la formation de produits de dégradation. Afin d’assurer le recyclage du solvant organique et le bon fonctionnement du procédé industriel, un traitement approprié permet d’éliminer ces produits. Néanmoins, après plusieurs décennies de fonctionnement des usines, des encrassements de certains équipements ont été observés. Ces solides contiennent les éléments palladium, carbone, oxygène et azote. Industriellement, une solution curative a été mise en œuvre pour éliminer ces crasses. Il convient toutefois de comprendre les phénomènes qui ont conduit à leur formation. Ce travail de doctorat a pour objectif d’étudier le comportement physico-chimique du palladium dans les cycles d’extraction et les mécanismes conduisant à la formation de solides. Pour cela, un système biphasique, constitué d’une phase organique de TBP dilué dans le TPH et d’une phase aqueuse d’acide nitrique contenant du nitrate de palladium(II), a été irradié par une source externe de rayonnement gamma afin de simuler le vieillissement du solvant d’extraction. Des précipités non radioactifs contenant du palladium et représentatifs des encrassements industriels ont été obtenus. Des analyses multi-techniques de ces précipités ont montré que les solides sont constitués d’un mélange complexe de cyanure de palladium(II), de carboxylate de palladium(II) et de divers produits organiques (di-n-butylphosphate (HDBP), composés à fonctions amines et hydrazine). Les produits menant à la précipitation du palladium proviennent de la dégradation du TBP et de celle du TPH et sont présents en phase aqueuse et en phase organique.Certains produits de dégradation formés lors de l’irradiation semblent favoriser l’extraction du palladium. Pour comprendre le rôle des produits de dégradation sur l’extraction du palladium, le solvant d’extraction utilisé dans le procédé PUREX a été dopé en composés organiques. Les composés testés sont des composés commerciaux représentatifs de produits de dégradation identifiés un solvant dégradé. De plus, les espèces testées sont des composés susceptibles d’interagir avec le palladium(II) (cétone, acide carboxylique, alcool, aldéhyde et alcène). Parmi ces composés, seul le 5-dodécène conduit à une augmentation significative de l’extraction du palladium(II) par rapport à une phase organique non dopée et à la formation d’un précipité noir constitué de palladium métal. Les analyses réalisées sur la phase organique dopée en 5-dodécène ont mis en évidence la formation d’un complexe ternaire dans lequel le palladium serait entouré de molécules de TBP, de 5-dodécène et d’ions nitrate. Par ailleurs, une fraction du palladium(II) extrait dans la phase organique oxyde le 5-dodécène en cétone et est réduit en palladium métal (précipité noir). Des voies de formation des différents composés constituant les crasses ont été proposées. Les alcènes, les cétones et l’acide nitreux apparaissent comme des précurseurs dans la formation de cyanure de palladium(II). Un carboxylate de palladium(II) serait formé par réaction de palladium(II) avec l’acide carboxylique correspondant. Les amines primaires pourraient se former par hydrogénation des nitroalcanes catalysé par la présence de palladium métal tandis que l’hydrazine pourrait se former par radiolyse des amines primaires. / The spent nuclear fuel composed of uranium, plutonium and fission products (such as palladium, technetium, molybdenum, etc.) is industrially processed in France by the PUREX process. This hydrometallurgical process allows separating uranium and plutonium by using an organic phase composed of tri-n-butyl phosphate (TBP) diluted in a mixture of aliphatic hydrocarbons (TPH = tetra propylene hydrogen). During the various extraction cycles, the organic phase is subjected to acid hydrolysis and radiolysis phenomena leading to the formation of degradation products. To ensure the recycling of the organic solvent and a normal operation of the industrial process, an appropriate treatment eliminates these degradation products. Nevertheless, after several decades of industrial operation of the factories, precipitates have been observed in some equipments. These solids contain palladium, carbon, oxygen and nitrogen atoms. Industrially, a curative solution has been found and allows eliminating these cruds containing in particular palladium. However, it is important to understand the formation of palladium precipitates in the liquid-liquid extraction cycles. This thesis aims to study the behavior of palladium in the extraction cycles and the mechanisms leading to the formation of solids.For this purpose, a biphasic system containing an organic phase of TBP diluted in TPH and a aqueous phase of nitric acid containing palladium(II) nitrate has been irradiated by an external source (gamma-irradiation). This irradiation allows simulating the aging of the extraction solvent. Nonradioactive precipitates which are representative of the industrial crud were obtained. A multi-technical analysis of these inactive precipitates has shown that the solids are composed of a complex mixture: (i) palladium cyanide(II), (ii) palladium(II) carboxylate and (iii) various organic products (di-n-butyl phosphate (HDBP)), compounds with amine functions and hydrazine. Moreover, we demonstrate that the degradation products leading to the precipitation of palladium come from either TBP or TPH and are present in the aqueous phase and in the organic phase.Some degradation products formed during irradiation seem to favor the extraction of palladium(II). To understand the role of degradation products on palladium extraction, the extraction solvent used in the PUREX process was doped with organic compounds. The compounds tested are commercial compounds representative of degradation products identified a degraded solvent. In addition, the compounds tested are species which can react with palladium(II) (ketone, carboxylic acid, alcohol, aldehyde and alkene). Among these compounds, only 5-dodecene leads to a significant increase in the extraction of palladium(II) in comparison with an undoped organic phase and the formation of a black precipitate composed of palladium metal. The analyses carried out on the 5-dodecene-doped organic phase revealed the formation of a ternary complex in which the palladium would be surrounded by TBP molécules, 5-dodecene and nitrate ions. In addition, a fraction of the palladium(II) extracted in the organic phase oxidizes the 5-dodecene to ketone and is reduced to palladium metal (black precipitate).Formation pathways of the various compounds present in the nonradioactive solids have been proposed. Alkenes, ketones and nitrous acid appear as precursors in the formation of palladium cyanide(II). A palladium(II) carboxylate would be formed by reaction of palladium(II) with the corresponding carboxylic acid. Primary amines could be formed by hydrogenation of nitroalkanes catalyzed by the presence of palladium metal while hydrazine could be formed by radiolysis of primary amines.Key word: palladium, radiolysis, PUREX process, degradation products, precipitates

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RMN de Exchange em estado sólido é uma importante técnica utilizada na caracterização de processos dinâmicos em ciência dos materiais. Entretanto, a utilização desta técnica no estudo de materiais complexos tem sido limitada. Neste trabalho, serão propostas novas metodologias de RMN de Exchange em estado sólido, que permitem analisar eficientemente movimentos moleculares na escala de tempo de milisegundos. A técnica denominada Pure Exchange Solid-State NMR (PUREX), provê a supressão dos segmentos rígidos dos espectros de exchange, tomando possível observar os segmentos com mobilidade na escala de ms seletivamente. A técnica Centerband-Only Detection of Exchange (CODEX), permite a observação e caracterização de reorientações moleculares lentas com a maior sensibilidade e resolução disponíveis em RMN de estado sólido, através de espectros obtidos sob rotação da amostra em tomo do ângulo mágico (MAS). Utilizando essas técnicas as funções e tempos de correlação e a geometria de movimentos moleculares lentos podem ser determinadas diretamente, sem a necessidade da utilização de modelos que relacionem as grandezas medidas e as características do movimento molecular. A utilização dos métodos apresentados, permite a identificação e caracterização da dinâmica lenta em materiais complexos, tais como polímeros amorfos, semicristalinos e proteínas. Com objetivo inicial de demonstrar as técnicas, elas foram aplicadas para confirmar detalhes da dinâmica molecular em amostras modelo. Através destas técnicas foi possível confirmar a escala de tempo e os ângulos de reorientação envolvidos na dinâmica molecular de cristais orgânicos, Dimetil Sulfona (DMS), e também para revisitar processos de relaxação local em alguns polímeros, polimetacritato de metila (PMMA) e isotatico polipropileno (iPP). As metodologias foram também aplicadas no estudo da transição vítrea em polímeros semicristalinos, isotatico poli(1-buteno) (iPB 1) e sindiotático polipropileno, os quais não tinham sido ainda estudados por técnicas de RMN de Exchange, já que neste caso a maioria dos segmentos moleculares (porção cristalina do polímero) é rígida durante a transição vítrea. Utilizando os métodos CODEX e PUREX os movimentos lentos que ocorrem na região amorfa destes polímeros em temperaturas próximas as suas temperaturas de transição vítrea foram caracterizados. Um estudo dos movimentos lentos que ocorrem em tomo das temperaturas de transição vítrea nas cadeias poliméricas de dois tipos de nanocompostos híbridos siloxano/(polietileno glicol) (ormolitas) também é apresentado. Heterogeneidades nos movimentos das cadeias poliméricas associados com a interação PEG/siloxano foram diretamente observadas através de experimentos PUREX 1D de Exchange 2D. Evidenciais da presença de movimentos de grande e pequena amplitude foram observados para os dois tipos de híbridos. Os resultados revelam que a restrição do movimento das cadeias poliméricas pelas estruturas de siloxano depende tanto do comprimento da cadeia como da natureza das interações entre as fases orgânica e inorgânica do nanocomposto. Finalmente os resultados referentes a caracterização da dinâmica molecular rápida e lenta e sua relação com as propriedades estruturais de um hidrogel protéico são apresentados. Utilizando uma versão modificada da técnica CODEX, juntamente com experimentos de polarização direta, polarização cruzada e RMN de correlação 2D, foi possível não somente confirmar a estrutura e o modelo de formação propostos para o gel, mas também determinar a geometria e a escala de tempo dos movimentos lentos que ocorrem na região de hélice do hidrogel protéico em grandes detalhes. A demonstração teórica e experimental das técnicas e suas aplicações no estudo dessas importantes classes de materiais serão apresentadas. / Solid-State Exchange NMR is an important method to characterize details of dynamic process in materials science. However, the application of these techniques to study complex materials has been limited. In this work new solid-state Exchange NMR techniques, which allows efficient analysis of molecular motions in the millisecond time scale, are presented. The Pure Exchange Solid-State NMR (PUREX) method provides the suppression of the rigid segments in standard exchange spectrum, making possible to observe the slow moving moieties selectively. The Centerband-Only Detection of Exchange (CODEX) technique allows observing and characterizing slow segmental reorientations with the highest available NMR sensitivity and site resolution, in a magic angle spinning (MAS) NMR spectrum. Correlation functions, correlation times and information about the motional amplitude and geometry can be direct1y obtained using the techniques, without any model assumption. These methods allowed identifying and characterizing slow dynamics in complex materials such as, semicrystalline and amorphous polymers and proteins. To demonstrated the proposed techniques they have been applied to confirm some kwon aspect of the slow dynamics of model samples. Using the methods it was possible o confirm the time scale and the reorientation angles involved in the molecular dynamics of organic crystals, Dimethyl Sulfone (DMS), and also to revisit some relaxation process in standard polymers, such as the beta relaxation of poly(methyl metacrylate) (PMMA) and the alfa relaxation in isotactic polypropylene (iPP). The time scale and the geometry of the molecular motions responsible by these relaxation process obtained using the PUREX and CODEX techniques are in excellent agreement with the data taken from the literature, confirming the reliability of the proposed methods. Moreover, the techniques were also applied to study the slow molecular motions involved in the glass transition of semicrystalline polymers, such as isotactic poly (l-butene) form I (iPB1) and syndiotactic Polypropylene (sPP). The glass transition of these polymers had not been studied using Exchange NMR methods because most of the molecular segments (crystalline portion of the polymers) are rigid during the glass transition. Using the PUREX and CODEX methods the slow molecular reorientations within the amorphous region of the polymers were characterized for temperatures near its glass transition. A study of the slow motions occurring around the glass transition temperature in the polymer chains of two types of siloxane/(polyethylene glycol) nanocomposites (ormolites) is also presented. Motional heterogeneities associated with PEG/ siloxane interactions were directly observed in the 13C 1D PUREX and 2D exchange data. Evidences of both small and large angle amplitude motions were direct1y observed for both types of hybrids. The results revealed that the hindrance to the slow molecular motions of the polymer chains due to the siloxane structures depends on the chain length and the nature of the interaction between the organic and inorganic phases. Finally the results concerning the characterization of the fast and slow dynamics and its relationship with the structural properties of a protein hidrogel are presented. Using a modified version of the CODEX technique, together with standard direct polarization, cross polarization and 2D NMR correlation experiments, it was possible not only to confirm the proposed structure and the gel formation model, but also to characterize the geometry and the time scale of the slow motions in the helical domains of the protein hidrogel in great detail. The theoretical and experimental demonstration of all proposed methods and also its applications in these important classes of material will be present.