Au cours de ces dernières décennies, des études ont étés menées pour identifier plusieurs traceurs des matériaux du cycle du combustible nucléaire, dans le cadre de la lutte contre la prolifération nucléaire. Ces matériaux sont généralement collectés lors d’inspections dans des installations nucléaires, ou saisis lors de contrôles de trafics illicites. Les informations fournies par ces traceurs sont parcellaires et ne permettent pas de déterminer avec exactitude la provenance et l’historique industriel de ces matériaux.Le but de ce travail de thèse est de démontrer le potentiel de l’utilisation des isotopes du molybdène pour le traçage des matériaux du cycle du combustible nucléaire. Le choix s’est porté sur le molybdène car en raison de la similarité de leurs propriétés chimiques, le molybdène et l’uranium sont étroitement associés dans les minerais d’uranium et tout au long de la chaîne de purification de l’uranium. L’étude s’est focalisée sur une partie de l’amont du cycle du combustible, depuis l’extraction des minerais d’uranium jusqu’à la production des concentrés miniers d’uranium : divers procédés physiques et chimiques sont appliqués, à la fois pour purifier l’uranium et abaisser la concentration en molybdène.Au cours de cette étude, une nouvelle méthode de séparation du molybdène a été développée pour caractériser sa composition isotopique dans des minerais, minéraux et concentrés miniers d’uranium. La variabilité des compositions isotopiques du molybdène dans un gisement d’uranium est principalement due aux mécanismes d’adsorption et/ou de précipitation du molybdène. Les gisements magmatiques et sédimentaires ont des compositions isotopiques différentes, ce qui permet ainsi leurs distinctions. Les concentrés miniers d’uranium produits à partir de ces deux types de gisements ont des compositions isotopiques similaires aux minerais. Ces résultats soulignent ainsi le potentiel des isotopes du molybdène comme traceur des origines des concentrés miniers d’uranium. Cependant, un fractionnement des isotopes du molybdène a été établi lors de la production des concentrés miniers d’uranium pour deux usines au Niger. Les procédés de purification de l’uranium tels que la lixiviation, l’extraction par solvant et la précipitation ont été reproduits en laboratoire sur des échantillons réels pour expliquer le fractionnement isotopique du molybdène lors de la production des concentrés miniers. Au cours de ces procédés, le fractionnement peut être positif (lixiviation), négatif (extraction par solvant, précipitation à l’eau oxygénée) ou nul (précipitation à l’ammoniaque). Dans le cas des échantillons du Niger, la somme de ces procédés est négative, dans le sens des données expérimentales que nous avons obtenues, démontrant ainsi également le potentiel de l’utilisation des isotopes du molybdène comme traceur des procédés de transformations des matériaux du cycle du combustible nucléaire. / Nuclear forensics aims at determining the age, provenance as well as industrial or storage history of uranium ores and uranium ore concentrates that are part of the nuclear fuel cycle. Several potential tracers have already been identified for this purpose. However, these tracers are not providing always unambiguous information. This study is focused on establishing Mo isotopes as a new tracer of uranium ore provenance and of ore processing for its application in nuclear forensics. Molybdenum and uranium share a number of common geochemical properties. In the nuclear fuel cycle, molybdenum is an impurity that is difficult to separate during uranium extraction and purification processes, while its concentration is required to be lower than some specification limits. We focused this study on the first part of the nuclear fuel cycle, from the uranium ores extraction to the production of uranium ore concentrates.We developed an enhanced separation method for Mo from a uranium-rich matrix (uranium ores, uranium minerals, uranium ore concentrates) in order to analyze the mass fractionation induced by processes typical of the nuclear fuel cycle. Molybdenum isotopic compositions in uranium ores depend of adsorption and precipitation processes. The δ98Mo values of sedimentary uranium ores is shifted to negative values relative to magmatic ores. This provides a means of distinguishing these types of uranium ores. Uranium ores concentrates produced from both uranium ore natures (magmatic and sedimentary) have Mo isotope compositions similar to the uranium ores. These results suggest that molybdenum isotopes have a strong potential of as a tracer for identifying the origin of the uranium ore concentrates. However, Mo isotopes fractionations were established during the production of uranium ore concentrates in the both Niger mills. We reproduced in laboratory the lixiviation, solvent extraction and precipitation processes to explain these observations. The Mo isotopes fractionation is positive for the lixiviation process, negative for the solvent extraction and precipitation with hydrogen peroxide, and null for ammonia precipitation. In the case of the Niger samples, the sum of these processes is negative and agrees with our experimental data. Mo isotopes have a strong potential as a tracer for identifying the origin and transformation of uranium in the nuclear fuel cycle, in the framework of nuclear forensics.

A S-metilcisteína (SMC) e o peptídeo γ-glutamil-S-metilcisteína (γ-Glu-SMC), presentes em algumas leguminosas comestíveis, principalmente no feijão comum (Phaseolus vulgaris L.), apresentam efeitos biológicos controversos após a sua ingestão por animais de laboratório e humanos. O presente trabalho teve por finalidade investigar a absorção intestinal da SMC e da γ-Glu-SMC, empregando ensaios com segmentos intestinais isolados de rato, comparando-se a assimilação destes com a de aminoácidos protéicos. Os segmentos de duodeno e jejuno foram evertidos e incubados em solução nutritiva contendo isoladamente os aminoácidos (SMC, Phe e Met) ou o peptídeo em estudo, . acompanhando-se a taxa de absorção de cada um, em intervalos regulares entre 10 e 60 min. A taxa de absorção foi determinada por cromatografia de troca iônica em autoanalisador de aminoácidos. A SMC apresentou valores superiores aos aminoácidos Met e Phe. As mesmas amostras foram analisadas também por cromatografia líquida de alta eficiência em fase reversa após derivatização com o-oftalaldeído (Gustine, 1985). Os resultados por esta metodologia não foram conclusivos pois ocorreu perda de eficiência da coluna cromatográfica, provavelmente devido à adsorção irreversível de subprodutos resultantes da reação de derivatização. Sugere-se que sejam estudadas modificações no protocolo analítico. Em relação à absorção do peptídeo-Glu-SMC, comprovou-se a sua hidrólise pelo aparecimento de pequenas quantidades de SMC livre no lado seroso dos segmentos intestinais, supondo-se que esta hidrólise tenha ocorrido pela enzima γ-glutamiltranspeptidase (γ-GT). A reduzida quantidade de SMC livre encontrada poderia ser atribuída a uma eventual perda de atividade desta enzima durante o preparo e manuseio do segmento intestinal. Contudo, em ensaios adicionais, não foi observada perda de atividade desta enzima durante a incubação dos segmentos intestinais em solução nutritiva por 40 minutos. A atividade da enzima γ-GT foi aproximadamente três vezes superior no duodeno do que no jejuno, sendo de relevância em estudos de absorção intestinal. Mais estudos são necessários para um melhor entendimento do processo absortivo do peptídeo. / The biological effects of S-methyl-cysteine (SMC) and the peptide γ-glutamyl-cysteine (γ-Glu-SMC), distributed in some edible legume seeds, mainly in common bean (Phaseolus vulgaris L.), are controversial when these compounds are ingested by laboratory animals and humans. In the present study it was investigated the rate of intestinal absorption of SMC and γ-Glu-SMC employing isolated segments of rat intestines and analyzing comparatively the absorption of protein amino acids. The everted segments of duodenum and jejunum were incubated in a nutritive solution and the aminoacids SMC, Phe and Met and the peptide γ-Glu-SMC were added individually in order to measure their absorption rates in intervals of 10 min until reaching 60 minutes of incubation. The absorption rate of each compound was measured by ion exchange chromatography (amino acid analyzer). The absorption rates observed for SMC were higher than those observed for Met and Phe. The same samples were also analyzed by reversed phase-HPLC after derivatization with o-phthalaldehyde (Gustine,.1985). Results did not succeed because the chromatographic column lost efficiency probably due to adsorption of byproducts of the derivatization reaction. We suggest that modifications on the analytical protocol should be developed. Results showed that the peptide γ-Glu-SMC seem to be hydrolyzed supported by the appearance of small amounts of free SMC on the serosal side of the intestines. The hydrolysis was probably catalyzed by the enzyme γ-glutamyltranspeptidase (γ-GT). The appearance of only small amounts of free SMC could be explained by an eventual loss of the activity of γ-GT during preparation and incubation of the intestinal segments. However, in additional assays, the enzyme did not show any loss of activity during incubation of the segments for 40 min. We observed also that the activity of the enzyme γ-GT was 3 times higher in duodenum than in jejunum. This observation could be relevant for absorption studies employing intestinal segments. Further studies are necessary for a better understanding of the absorption process of the peptide γ-Glu-SMC.