Tesi sul tema "Radioactif element"

De nombreuses applications industrielles de génie civil, de génie pétrolier et de génie minier nécessitent la résolution de problèmes mettant en jeu des couplages entre les comportements thermique, hydraulique et mécanique des géomatériaux. La démarche adoptée dans cette étude consiste à examiner divers modèles de comportement, en suivant une progression depuis les modèles les plus simples jusqu'a des modèles plus complexes. Des comparaisons sont effectuées sur des problèmes à géométrie simple (problèmes faisant intervenir une seule variable d'espace). On présente dans une première partie une méthode de résolution directe de problèmes de dégagement de chaleur en thermo-poro-élasticité linéaire, en milieux infinis ou semi-infinis. Des solutions et des applications sont présentées sur différents problèmes liés au projet de stockage de déchets radioactifs. Ces études permettent de dégager les paramètres déterminant l'importance des couplages thermo-hydro-mécaniques, par exemple le rapport entre les diffusivités hydraulique et thermique. L'étude du comportement irréversible des milieux poreux saturés nécessite une approche numérique. On a développé le code de calcul aux éléments finis thyme adapté à l’étude des problèmes de couplages thermo-hydromécaniques sur des structures à géométrie simple. Ce code est utilisé pour étudier le comportement différé de cavités souterraines excavées dans les argiles profondes. On commence par étudier les effets différés liés à la diffusion de la masse fluide, puis, dans le cas d'une argile raide les effets différés liés également à la viscosité. On étudie enfin le problème de l'empilement de conteneurs de déchets enfouis dans l'argile de boom.

Une prédiction fiable du comportement a long terme des barrières de confinement en béton nécessite d'avoir bien identifie les divers mécanismes de détérioration et de les avoir convenablement modélisés. L'originalité de cette étude est de coupler le comportement mécanique avec une dégradation d'origine chimique (dissolution des hydrates cimentaires due a un ruissellement d'eau pure). Afin d'évaluer ce couplage, un modèle a été développé et implanté dans un code de calculs par éléments finis. Le module d'élasticité évolue comme une fonction d'une variable de vieillissement dépendant de la teneur locale en calcium. Le comportement mécanique non-linéaire du béton est modélisé selon la théorie de l'endommagement. Parallèlement, deux procédures expérimentales ont été développées. La procédure bipède a été développée afin d'étudier les mécanismes de développement de la fissuration et des propriétés de permutation sous chargement mécanique de traction. La procédure lift a été développée pour la réalisation accélérée d'échantillons cimentaires dégradés chimiquement dans le but d'évaluer le couplage mécanique-chimie. Des essais de micro dureté ont été réalisés pour identifier la fonction de vieillissement chimico-mécanique. Plusieurs simulations numériques ont été réalisées. La présence d'une fissure modifie localement la pénétration de la dégradation. L'ouverture de la fissuration constitue un paramètre dominant le couplage diffusion-chimie-mécanique. A l'issue de ces simulations, plusieurs applications industrielles sont directement envisageables. Les limitations et les extensions futures du modèle ont aussi été discutées

Afin d'établir des voies possibles d'utilisation de métaux nobles récupérées du combustible nucléaire tels que le 107Pd, la présente thèse vise à étudier l'effet du rayonnement dans trois applications différentes : la catalyse hétérogène, avec - comme réaction modèle - l'hydrogénation du cinnamaldéhyde (CNA) ; la photocatalyse, avec - comme réaction modèle - la décoloration de l'orange de méthyle (MO) et la régénération des catalyseurs, désactivés lors de la synthèse de l'hydroxyméthyl furfural. Des protocoles ont été élaborés pour répondre aux exigences de sécurité nucléaire : applicable en boîte à gant et sorbonne, selon le cas.Le rayonnement β émis par le 107Pd n'a montré aucun effet lors de l'hydrogénation du CNA, indépendamment des conditions de réaction. En revanche, la décoloration a été initié par la présence de la radiation β sur le catalyseur en substituant de la lumière visible. Une diminution de l'absorbance (au point isosbéstique) a été observée. Ce dernier corrélait avec la quantité de catalyseur radioactif, mettant en évidence l'activation par le rayonnement β. Enfin, la régénération du catalyseur à base de Pd a donné des résultats prometteurs après l'irradiation γ, montrant notamment une augmentation de la performance catalytique après irradiation du catalyseur désactivé. Par ailleurs, le catalyseur à base de Ru, bien que généralement peu performant, a montré une activité plus élevée que l'activité du catalyseur frais après irradiation par rayonnement 
This thesis aimed to identify applications of noble metals recovered from spent nuclear fuels such as 107Pd. To study the effect of the radiation three different applications were selected: heterogeneous catalysis, with the hydrogenation of cinnamaldehyde (CNA) as model reaction; photocatalysis, with the decolourisation of methyl orange (MO) as model reaction; and the regeneration of catalysts, deactivated with the synthesis of hydroxymethyl furfural. Protocols were developed for the synthesis of the catalysts and the performance testing in restricted nuclear environment, namely in glove box and for the implementation of the reactions in glove box and extractor column as appropriate.Regarding the results it was found that β-radiation did not show any effect on the hydrogenation of CNA independent of the applied reaction conditions. On the other hand, the decolourisation of MO was successfully activated by the β-radiation of the catalyst. A decrease in absorbance (at the isosbestic point) was observed and was correlated to the amount of the catalyst employed, evidencing the effect of the irradiation doses. Finally, the regeneration of the Pd-based catalyst showed promising results after γ-irradiation, notably with a partial recovery of the initial catalytic performance after -irradiation. Meanwhile, the Ru-based catalyst, although generally not performing well, showed increased activity compared to the fresh catalyst upon -irradiation

La production d'énergie nucléaire nécessite des systèmes avancés pour améliorer les procédures de stockage et de confinement des déchets radioactifs. Par ailleurs, la capture d'éléments radioactifs mobiles dans les effluents des centrales nucléaires demande une amélioration de la capacité et de la sélectivité. L'iode 129-I est un des produits les plus critiques à confiner et il est produit pendant les procédés de recyclage des déchets nucléaires. Dans ce travail de thèse, la classe de matériaux moléculaires, dénommée structures de type Hofmann, a été étudiée en tant que matériaux massifs et nanoparticules supportées pour la capture sélective de l'iode moléculaire. En premier lieu, les matériaux M'(L)[M''(CN)4] ont été précipités sous la forme de poudres microcristallines. L'insertion d'iode dans le réseau des matériaux massifs a été effectuée par différents protocoles: 1) adsorption d'iode dans des solutions de cyclohexane à température ambiante; 2) adsorption d'iode en phase gazeuse à 80 °C; 3) adsorption de vapeurs d'iode en phase gazeuse à 80 °C et en présence de vapeurs d'eau. Les différents protocoles pour l'insertion d'iode n'ont pas influencé la nature de l'iode confiné. Pour la capture en solution, les structures NiII(pz)[NiII(CN)4], NiII(pz)[PdII(CN)4] et CoII(pz)[NiII(CN)4] ont montré une capacité d'une molécule d'iode par unité de maille. L'iode confiné est physisorbé en tant qu'iode moléculaire en interaction avec le réseau. Les modélisations GCMC ont confirmé la capacité maximale et ils ont indiqué que l'iode interagit avec la pyrazine et avec les cyanures. Sur la base des données expérimentales, la modulation des métaux dans le réseau a montré une légère différence dans la force d'interaction entre l'iode et le réseau et une adaptation de la maille spécifique pour chaque composition. Une complète régénération du réseau a été possible, puisque l'iode était complètement désorbé avant la décomposition du réseau. Pour le réseau NiII(pz)[PtII(CN)4], on a observé un mécanisme différent de capture puisque ce réseau contenant Pt a réagi avec l'iode en donnant le complexe de coordination NiII(pz)[PtII/IV(CN)4].I-. La formation de ce type de complexe était déjà observée dans la littérature par Ohtani et al. lesquels avaient préparé le complexe via une synthèse in-situ. Ensuite, le changement du ligand organique pyrazine avec d'autres ligands plus longs, c'est-à-dire la 4,4'-bipyridine (bpy) ou 4,4'-azopyridine (azpy), pour avoir des cages plus grandes a montré une diminution de la capacité maximale de capture d'iode. Les données expérimentales ont suggéré que pour un confinement d'iode optimisé, le réseau doit disposer de cages avec une dimension très proche de la molécule d'iode (0.5 nm). Après l'étude des matériaux massifs, nous avons considéré la préparation de nanoparticules supportées de NiII(pz)[NiII(CN)4] pour la capture d'iode. Nous avons obtenu les nanoparticules via un procédé étape par étape, par imprégnation d'une série de silices mésoporeuses greffées avec un ligand diamine, puis avec les précurseurs de NiII(pz)[NiII(CN)4]. Nous avons utilisé en tant que supports, une silice SBA-15 modifiée et des billes de verre poreux pour obtenir respectivement les nanocomposites Sil@NP and Glass@NP. Par microscopie électronique à transmission, nous avons détecté pour Sil@NP des nanoparticules de diamètre moyen 2.8 nm. L'adsorption d'iode dans les nanoparticules a été confirmée par spectroscopie FT-IR. Les traitements thermiques ont indiqué que la portion d'iode dans les nanoparticules pouvait être désorbé dans l'intervalle 150-250 °C. Nous avons pu estimer que la capacité de capture des nanoparticles était très proche de la capacité du massif NiII(pz)[NiII(CN)4]@I2
Nuclear power industry still demands further research to improve the methods for the storage and the confinement of the hazardous radioactive wastes coming from the fission of radionuclide 235U. The volatile radioactive 129I (half-life time 15x107 years) is one of the most critical products coming from the reprocessing plants in the fuel-closed cycles. In the present thesis the family of coordination solid networks, known as Hofmann-type structures, was studied in the form as both bulk and supported nanoparticles for the selective entrapment of the molecular iodine. This set of investigated materials exhibited a general formula M'(L)[M''(CN)4] where M' = NiII or CoII; L = pyrazine, 4,4'-bipyridine, 4,4'-azopyridine; M'' = NiII, PdII or PtII. Initially, the material NiII(pz)[NiII(CN)4] and its analogue structures were precipitated as microcrystalline bulky compounds and fully characterized. The insertion of the iodine in the bulky host structures was performed with different methods: 1) adsorption of iodine in solutions of cyclohexane at room temperature; 2) adsorption of iodine vapours at 80 °C; 3) adsorption of iodine vapours at 80 °C in presence of water steam (for few selected materials). The different methods did not affect the nature of the confined iodine. For the entrapment in solution, results indicated that the Hofmann-type structures NiII(pz)[NiII(CN)4], NiII(pz)[PdII(CN)4] and CoII(pz)[NiII(CN)4] could host one I2 molecule per unit cell. The iodine resulted physisorbed as molecular iodine in interaction with the host structure. GCMC simulations confirmed the maximal capacities and indicated that iodine could interact with both the pyrazine and the coordinated cyanides. Experimentally, however, the modulation of the metals showed a slightly different strength of interaction I2-lattice bringing to a different lattice adaptation. The materials also could be fully regenerated since the complete desorption of iodine occurred before the decomposition of the host structure. Reiterated adsorption-desorption steps (3 cycles) on the networks NiII(pz)[NiII(CN)4] and NiII(pz)[PdII(CN)4] indicated an excellent structural resistance to cycling and a maintained high capacity. A different mechanism of confinement was detected for the structure NiII(pz)[PtII(CN)4] which reacted with iodine giving complex NiII(pz)[PtII/IV(CN)4].I-. Finally, the modulation of the organic ligand L indicated that the replacement of the ligand pyrazine with longer ligands, to obtain larger pores, had a detrimental effect on the maximal iodine loading due to a weaker confinement. After the study of the bulk materials, we considered the preparation of supported nanoparticles of NiII(pz)[NiII(CN)4] for the entrapment of iodine. The nanoparticles were obtained by a step-by-step method, impregnating a set of diammine-grafted mesoporous silicas with the precursors of NiII(pz)[NiII(CN)4]. We detected nanoparticles with mean size 2.8 nm by transmission electronic microscopy. The insertion of iodine in the nanoparticles was confirmed by FT-IR. Thermal treatments indicated that the portion of iodine inside the nanoparticles could be reversibly desorbed in the range 150-250 °C and reintroduced in a cyclic process. It was estimated that the amount of physisorbed iodine in the NPs, with respect to the amount of deposited NPs matched with the maximal capacity NiII(pz)[NiII(CN)4]@I2

Ce travail porte sur la modélisation du comportement du béton en dynamique rapide et son application au calcul des structures et ouvrages en béton, béton armé et béton de fibres. Il présente, d’une part, le développement d’une loi de comportement adaptée au matériau béton en dynamique, et d’autre part, le développement des algorithmes nécessaires à sa mise en œuvre dans un code de calculs par éléments finis. Enfin, une partie importante de ce travail concerne l’application de ce modèle à un problème industriel concret : l’étude prédictive de la réponse de conteneurs en béton de fibres, utilisée pour le stockage des déchets radioactifs, suite à l’impact résultant d’une chute libre de 5 mètres. La modélisation des différents aspects du comportement du béton en dynamique (augmentation de résistance et de module d’élasticité avec la vitesse de chargement) est effectuée au niveau macroscopique en s’appuyant sur les résultats expérimentaux permettant d’identifier les paramètres importants dans le comportement du matériau à haute vitesse. Principalement, l’importance de l’eau dans les pores du béton sur ses propriétés mécaniques en dynamique conduit à introduire, dans une modélisation élasto-plastique du béton, une variable supplémentaire, prenant en compte ce paramètre au niveau macroscopique. Le développement de ce modèle couplé amène à définir une loi de comportement visco-élasto-plastique dans laquelle un concept nouveau, l’écrouissage visqueux, qui traduit l’évolution du seuil de plasticité avec la variable de déformation visco-élastique, est introduit pour modéliser au niveau macroscopique l’augmentation de résistance du béton avec la vitesse de chargement. Cette loi de comportement est alors implantée dans un code de calculs par éléments finis. L’intégration des contraintes visco-élasto-plastiques du modèle conduit au développement de deux algorithmes permettant une actualisation implicite ou explicite des variables du modèle. Le modèle est alors appliqué à la simulation de la réponse de structures simples soumises à des chargement dynamiques : éprouvettes en traction et compression simples, prismes en flexion simple et dalles armées testées au tube à choc. La comparaison avec les résultats expérimentaux permet de vérifier la précision du modèle et de définir ses limites. Enfin, afin de traiter le problème industriel à l’origine de cette thèse, la loi de comportement visco-élasto-plastique est appliquée à un béton de fibres à ultra haute résistance, le Béton de Poudres Réactives (BPR). Les paramètres du modèle sont estimés d’après des résultats d’essais de traction directe à différentes vitesses de chargement. Des simulations de chutes de conteneurs en BPR de différentes hauteurs sont alors présentées. La bonne corrélation entre les résultats numériques et expérimentaux, notamment en ce qui concerne l’évaluation de la hauteur de chute « critique », de l’orientation et de la position des fissures, du mode de ruine, montre l’intérêt du modèle pour les ingénieurs, notamment lors des études de pré-dimensionnement
This work is concerned with the modelling of concrete behaviour in high rate dynamics and its application to the finite element calculation of concrete, reinforced concrete and fiber-reinforced concrete structures. It consists, on the one hand, in the development of a suitable onstitutive law for concrete in dynamics and, on the other hand, in the development of algorithms for its integration in a finite element code. Finally, a major part of this work is dedicated to the treatment of an industrial application : the estimation of the response of fiber-reinforced concrete containers for radioactive waste when subjected to a 5 meter high drop test. Modelling of the main aspects of concrete behaviour in high rate dynamics (characterized by the increase of strenght and elastic modulus with the loading rate) is treated at the macroscopic level and is based on experimental results that clearly identify the important parameters in the behaviour of concrete at high loading rates. Mainly, the importance of the presence of water in the pores of concrete on its mechanical properties in dynamics, leads to the introduction of an additional variable in an elasto-plastic model for concrete, in order to account for this parameter at the macroscopic level. The development of this coupled model leads to a visco-elasto-plastic constitutive law in which a new concept, visvous hardening, which expresses the evolution of the plastic yield limit with a visco-elastic variable, is introduced to account at the macroscopic level for the strength enhancement observed in dynamics for concrete. This constitutive law is then implemented in a finite element program. The integration of the visco-elasto-plastic stresses leads to the development of two return mapping algorithms characterized by an implicit or explicit updating of the variables of the model. The model is then applied to the modelling of the response of simple structures subjected to dynamic loading : specimens tested in direct tension and compression, small beams tested in bending and reinforced slabs tested with a shock tube. The accuracy of the model and its limits are then evaluated through the comparison between experimental and numerical results. Finally, in order to treat the industrial problem at the origin of this thesis, the visco-elasto-plastic constitutive law is applied to an ultra high strength fiber reinforced concrete : the Reactive Powder Concrete (RPC). The parameters of the model are obtained through direct tensile tests results at various loading rates. Modelling of drop tests of the RPC containers from various heights are then presented. The good correlation between experimental and numerical results, in terms of the evaluation of the critical height, the orientation and the position of the cracks, demonstrate the suitability of the model for engineering purposes, speially for initial design studies

Philosophiae Doctor - PhD
Mine water poses a serious environmental challenge and contains elements such as Fe, Al, and Mn in potentially toxic concentrations. The major anion in mine water is sulphate. The complexity and diversity of mine water composition makes its treatment very expensive, and there is no “one-fits-all” treatment option available for mine water. Active treatment of mine water produces water with good quality but the processes are not sustainable because of the costs. Previous studies have shown that acid mine drainage can be treated with coal FA to produce better quality water. The use of coal FA, a waste material from coal fired power station and mine water would go a long way in achievement of sustainable treatment of mine water as per previous studies. In this study mine water and coal FA were characterized to determine their physiochemical properties. This study linked the modelling results obtained by using the Geochemist’s workbench (GWB) software to the results obtained during the actual treatment of Matla mine water and Rand Uranium mine water using coal FA and lime. The chemistry involved when Matla mine water and Rand Uranium mine water were treated with flocculants was also investigated. Lastly the chemistry and kinetics involved was investigated when mine water was treated with various ameliorants such as Matla coal FA, lime and/or Al(OH)3 using jet loop mixing or overhead stirring. Mine water from Matla coal mine had a pH of 8 and therefore was classified as neutral mine drainage (NMD). Rand Uranium mine water had a pH of less than 3 and therefore was classified as acid mine drainage (AMD). The concentration of sulphate, Na, Ca, Mg, B, Hg, Se and Cd ions in Matla mine water was 1475, 956, 70, 40, 15, 2.43, 1.12 and 0.005 mg/L respectively. The concentration of sulphate, Fe, Ca, Mn, Mg, Al, B, Cr, Pb, U, Cd, Se and As ions in Rand Uranium mine water was 4126, 896, 376, 282, 155, 27, 5.43, 3.15, 0.51, 0.29, 0.007, 0.06 and 0.006 mg/L respectively . These concentrations were above the target water quality range (TWQR) for potable water set by the Department of Water Affairs (DWA) and World Health Organization (WHO). The gross alpha radioactivity was 6.01 Bq/L and gross beta radioactivity was 6.05 Bq/L in Rand Uranium mine water.

V-Th-Pb fractionation trends, and the associated variations in Pb-isotopes, provide important constraints on the nature, and age, of a wide range of geological processes. This thesis presents three detailed case studies from a carbonatite intrusive complex, lower crustal granulite xenoliths, and young volcanic rocks which represent a range of processes that fractionate V, Th and Pb. New major, trace element and Sr, Nd and Pb isotope results are presented for carbonatites and pyroxenites from the 130 Ma old Jacupiranga complex in southern Brazil. The data preclude simple models in which the Sr-Nd and Sr-Pb isotope arrays are the result of crustal contamination processes, or liquid immiscibility between the carbonatites and magmas similar to those from which the pyroxenites crystallised. The initial Sr, Nd and Pb isotope ratios in the Jacupiranga complex are similar to those in the Parana high-Ti basalts and to the oceanic basalts of the Walvis Ridge and Tristan da Cunha, and were apparently inherited from the mantle source regions associated with incipient magmatism of the Tristan da Cunha hotspot and the opening of the South Atlantic. Most carbonatites have high V/Pb and low Rb/Sr ratios and infiltration and/ or metasomatism by such melts is one process that may be responsible for the negative correlation of U/Pb and Rb/Sr inferred for the source of certain oceanic basalts such as Tristan da Cunha. Correlations between trace and major elements in mostly mafic granulite xenoliths from southern Africa probably result from magmatic processes such as fractional crystallisation and crystal accumulation. From Pb and Nd isotope systematics it can be inferred that the northern Lesotho xenoliths are Proterozoic in age, whereas Cape province xenoliths appear to have been fonned in the Archaean and to have had their Nd isotopes reset in the Proterozoic. Most Pb isotope ratios from the granulites xenoliths are unradiogenic relative to the Geochron, which indicates relatively low V /Pb ratios in the later parts of their histories. The correlation between Pb isotope ratios and K₂O/A1₂O₃ in the granulites from Markt is considered to reflect magmatic control of the V /Pb fractionation. The Archaean, and some of the younger mantle derived rocks on the Kaapvaal craton, plot on similar Pb isotope trends. It is argued that segments of the crust and uppennost mantle beneath southern Africa stabilised together in the Archaean, and that both were remobilised in subsequent magmatic and orogenic events. Volcanic rocks in the Northland-Auckland peninsula, New Zealand, range from silica-undersaturated basanites to tholeiites and andesites. Although all the volcanic fields are in intraplate settings, two types of mantle source enrichment can be recognised. One is subduction-related and characterised by high Sr and low Nd isotope ratios and negative Nb anomalies. The other type has geochemical features characteristic of intraplate enriched mantle sources with Sr and Nd isotope ratios and Nb/Ba, Ba/La, similar to HIMV OIB, which has been attributed to the deep recycling of oceanic crust. The differences in Pb isotopes between the two mantle sources, i.e. higher /lB/4 and 7/4, but lower ²⁰⁶Pb/²⁰⁴Pb in the subduction-related material than in the inferred HIMU source, indicate that V/Pb in shallow recycled crustal material tend to be lower than in the deeper recycled material. These case studies confirm that (i) metasomatism by small degree melts can have significant effects on mantle trace element characteristics, (ii) the lower crust is a relatively low 11 environment and crystal accumulation may be an important mechanism in the fractionation of Th and U from Pb, cUld (iii) incorporation of recycled crustal material at different levels can result in different V-Th-Pb fractionation and so, with time, different Pb isotope ratios.

O problema de rejeitos radioativos é uma preocupação de âmbito mundial, uma vez que não há, ainda, um local definido para a construção de um repositório para rejeitos radioativos de alto nível. Uma das etapas preliminares para a escolha do local mais apropriado é o estudo geológico associado a estudos experimentais de adsorção das espécies químicas envolvidas nos processo. Neste trabalho foi utilizado uma amostra de rocha basáltica, da região sul da Formação Serra Geral, coletada em Frederico Westphalen (RS), que servirá como candidata à rocha hospedeira para locação de rejeitos radioativos. Foram realizados dois experimentos, a saber: "Batch Test" e percolação, ambos sob pressão atmosférica, à temperatura ambiente de 25°C, com a finalidade de estudar a capacidade de sorção dos elementos terras raras - ETR. Os ETR são utilizados neste trabalho em função de sua analogia com os actinídeos, visando a investigar o comportamento geoquímico e a especiações dos mesmos em águas naturais, buscando a possibilidade de armazenamento geológico de rejeitos radioativos, uma vez que a adsorção dos ETR depende de variáveis do ambiente como pH, força iônica, temperatura e presença de ligantes, como carbonatos e constituintes de superfícies dos minerais. Foi realizado experimento de percolação dos ETR, a 100ppb, no basalto (com granulometria 80 mesh) em soluções com força iônica I= 0,025 M e I=0,5 M de NaCl. O pH foi controlado em uma faixa de 5,6 a 7,6 com adição de HNO3. As concentrações foram analisadas por ICP-MS. O "Batch Test" é uma eficiente forma de se obter isotermas de sorção/dessorção, além de valores da razão entre as distribuições sólido/solução e estimar a solubilidade. O experimento de percolação, foi realizado sob pH controlado em torno de 6, e permitiu verificar a "preferência" dos ETR pesados em relação aos ETR leves.
The problem of radioactive wastes is a concern of world-wide scope, a time that does not still have a defined local for the construction of a repository for radioactive wastes of high level. One of the preliminary stages for the choice of the place more appropriate is the geologic study associated to the experimental studies of adsorprtion of the involved chemical species in the process. In this work, a sample of basaltic rock was used, of the South Region of the Formation Serra Geral, collected in Frederico Westphalen Town (RS), that it will be probably a candidate to the rock hostess for location of radioactive wastes. Two experiments have been carried out through, namely: "Test Batch" and Percolating, both under atmospheric pressure, at the ambient temperature of 25°C, with the purpose to study the capacity of sorption of the rare earth elements - REE. The REE are used in this work in function of its analogy with the actinídes, aiming at to investigate the chemistry behavior and the speciations of the same in natural waters, searching the possibility of geologic storage of radioactive wastes, a time that the adsorption of the REE depends on variables of the environment as pH, ionic strengh, temperature and presence of ligants, as carbonates and constituent of surfaces of minerals. Experiment of percolating of the REE was carried through, 100ppb, in the basalt (with 80 mesh) in solutions with ionic strengh I= 0,025 M and I=0,5 M of NaCl. pH was controlled in a range of 5,6 the 7,6 with HNO3 addition. The concentrations were analyzed by ICP-MS. The "Batch Test" is an efficient form of studing sorption/dessorption isotherms, beyond values of the reason between the distributions solid/solution and estimation of the solubility. The percolating experiment, was carried through under pH controlled around 6, and allowed to verify the behaviour of heavy REE in comparison with the light REE.

Le traitement des déchets radioactifs issus de la production d’énergie nucléaire constitue un des problèmes industriels les plus importants. Ce travail se situe en amont de ces applications et vise à acquérir des données fondamentales pour la séparation des radionucléides à vie longue des déchets radioactifs liquides en utilisant trois familles de nouveaux composés macrocycliques polyfonctionnels basés sur des calix[n]arènes : des dérivés substitués par des oxydes de phosphine, soit au bord large, soit au bord étroit, et des dérivés substitués au bord large par des groupements diphosphonates. Deux approches ont été utilisées pour évaluer les interactions entre les ions La3+, Eu3+, Yb3+, Am3+, Th4+, Pu4+, UO22+ et TcO4- et les nouveaux ligands : (i) l’extraction des sels métalliques, de solutions aqueuses d’acide nitrique vers des solutions organiques (m-nitrobenzotrifluorure, dichlorométhane); (ii) la complexation dans le méthanol et l’acétonitrile en utilisant la spectrophotométrie d’absorption dans l’UV et la microcalorimétrie isotherme de titrage. Cette dernière technique s’est révélée particulièrement utile pour la détermination des stœchiométries des complexes et a permis leur caractérisation thermodynamique complète (DG, DH et DS). Les résultats ont montré la grande affinité de ces composés envers les cations Eu3+, Am3+ et UO22+. L’influence de l’acidité de la phase aqueuse sur les coefficients de distribution et l’influence de caractéristiques structurales des ligands (nature des groupes fonctionnels et des substituants, degré de condensation) sur les paramètres thermodynamiques de complexation ont été examinées. La remarquable solubilité dans l’eau des dérivés substitués au bord large par des oxydes de phosphine a permis le développement d’une nouvelle méthode de séparation des actinides par extraction micellaire, qui a été testée sur des déchets réels
The treatment of radioactive wastes issuing from nuclear power is one of the most important industrial problems. This work aims at acquiring basis data for the separation of long-lived radionuclides by using three families of new polyfunctional macrocyclic compounds based on calix[n]arenes: derivatives substituted with phosphine oxides either at the wide or the narrow rims, and derivatives substituted at the wide rim with diphosphonate groups. Two approaches were used to evaluate the interactions between La3+, Eu3+, Yb3+, Am3+, Th4+, Pu4+, UO22+ and TcO4- ions and the new ligands: (i) extraction of the metal salts, from aqueous solutions of nitric acid into an organic solution (m-nitrobenzotrifluorure, dichloromethane); (ii) complexation in methanol and acetonitrile using UV absorption spectrophotometry and isothermal titration microcalorimetry. The latter technique revealed to be particularly useful for the determination of the complex stoichiometry and allowed their full thermodynamic characterization (DG, DH and DS). The results show the high affinity of these compounds for Eu3+, Am3+ and UO22+ cations. The influence of the acidity of the aqueous phase on the distribution coefficients and the influence of some structural features of the ligands (nature of the functional groups and substituents, condensation degree) on the thermodynamic parameters have been examined. The remarkable water solubility of the wide rim phosphine oxide calix[4]arenes allowed the development of a new actinide separation method based on micellar extraction, which was tested on real wastes

A contaminação do ambiente é crescente no mundo, com grandes extensões de áreas afetadas por metais pesados em concentrações que podem representar perigo ambiental. Em face ao aumento da atividade industrial e à agricultura altamente tecnificada, é fundamental o monitoramento dos níveis de metais pesados nos solos, já que as plantas se comportam como mecanismo de transferência de contaminantes do solo para níveis mais altos da cadeia trófica. A ingestão de vegetais contendo elevadas concentrações de metais pesados é uma das principais vias de acesso desses elementos ao corpo humano. No corpo humano, os metais pesados depositam-se no tecido ósseo e gorduroso, ocupando o lugar de minerais nobres. Lentamente liberados no organismo, podem provocar uma série de doenças. O projeto foi dividido em três etapas, cada qual com um objetivo específico: 1º) determinar as concentrações de cádmio, níquel, chumbo, cobalto e cromo em vegetais frequentemente consumidos no Estado de São Paulo, e compará-las com os limites estabelecidos na legislação brasileira; calcular a ingestão diária de metais pesados para estimar o risco à saúde humana; identificar as culturas que apresentam maior potencial de translocação de cádmio para a cadeia alimentar 2º) avaliar os teores de cádmio em hortaliças e nos solos dos campos de produção 3º) avaliar a disponibilidade de cádmio do solo para as plantas com maior potencial de acúmulo do mesmo, com auxilio de extratores químicos e pela técnica de traçador radioativo (109Cd). As amostras vegetais foram coletadas na Companhia de Entrepostos e Armazéns Gerais de São Paulo e a concentração de metais pesados foi determinada por espectrometria de absorção atômica. Todos os vegetais analisados apresentaram concentrações de Cd e Ni abaixo do limite tolerável estabelecido pela legislação brasileira. No entanto, para Pb e Cr, 44% das amostras excederam o limite permitido. Não há nenhuma recomendação estabelecida de limite máximo de tolerância para Co no Brasil. Quanto ao hábito de consumo da população do Estado de São Paulo, a ingestão diária de metais pesados está abaixo da máxima permitida, consequentemente o consumo desses alimentos pode ser considerado seguro e sem riscos à saúde humana. As hortaliças folhosas foram as que mais acumularam Cd. Algumas regiões do Estado de São Paulo apresentaram teores totais de Cd no solo acima do valor de intervenção estabelecido pela CETESB. Entretanto, os vegetais cultivados nesses locais apresentaram teores de Cd inferiores ao limite máximo de tolerância, estabelecido pela ANVISA. É importante, ao estudar a contaminação de áreas agrícolas por metais pesados, observar, além do teor total, outros parâmetros, como a sua disponibilidade para plantas. No experimento em casa de vegetação, as correlações entre o Cd disponível do solo e o Cd acumulado pelas plantas foram significativas somente para a rúcula. O extrator mais eficiente em determinar a fitodisponibilidade de Cd, analisado por meio do Valor L e Razão L, foi o extrator Ácidos Orgânicos
The environmental contamination is increasing worldwide, with large areas affected by heavy metals at concentrations which may pose environmental hazard. Due to industrial activity and highly technical agriculture, it is important to monitor heavy metals levels in soils, since vegetables behave as transfer mechanism of contaminants from soils to higher levels of the food chain. Ingestion of vegetables containing high concentrations of heavy metals is one of the main ways in which these elements enter the human body. Once in human body, heavy metals are deposited in the bone and fat tissues, overlapping noble minerals. Slowly released into the body, heavy metals may cause an array of diseases. The project was divided into three stages, each one with a specific objective: 1st) to determine the concentrations of cadmium, nickel, lead, cobalt and chromium in the most frequently consumed foodstuff in the São Paulo State, Brazil and to compare the heavy metal contents with the permissible limits established by the Brazilian legislation; to calculate intake of heavy metals in human diets for estimating the risk to human health; and to identify crops with the greatest potential for translocation of cadmium into food chain 2nd) to evaluate the cadmium content in leafy vegetables and soils at crop fields 3th) evaluate the phytoavailability of cadmium for leafy vegetables with aid of chemical extractants and radioactive tracer technique (109Cd). The vegetable samples were collected at São Paulo General Warehousing and Centers Company, and heavy metal content was determined by atomic absorption spectrophotometry. All vegetables sampled presented average concentrations of Cd and Ni lower than the permissible limits established by the Brazilian legislation. Exception for Pb and Cr in that 44% of the samples exceeded the maximum permitted limits. The Brazilian legislation has not established a permissible limit for Co contents. Regarding the consumption habit of the population in the São Paulo State, the daily ingestion of heavy metals is below the oral dose of reference, therefore, the consumption of these vegetables can be considered safe and without risk to human health. Leafy vegetables were those most accumulated Cd. Some regions of São Paulo State showed total contents of Cd in soil higher than intervention value established by CETESB. However, the vegetables grown in these areas showed Cd concentrations lower than Brazilian limit established by ANVISA. It is important, when studying environmental contamination by heavy metals, to observe, beside their total content, other parameters, like soil availability. In the greenhouse experiment, the correlation between soil available Cd and plants accumulated Cd were significant only for rocket. The most efficient chemical extractant in determining Cd phytoavailability, analyzed by L Value and L Ratio, were Organic Acids

Rare Physics event is playing a crucial role, not only in Fundamental Interaction Physics, but also in Astroparticle Physics and in Cosmology. These signals, if detected, would give an importatnt evidence of new Physics. The CUORE experiment (Cryogenic Underground Observatory for Rare Events) is a proposed tightly packed array of 988 TeO2 bolometers, each being a cube 125 cm3 on a side with a mass of 750 g. The array consists of 19 vertical towers, arranged in a compact cylindrical structure. Each tower will consist of 13 layers of 4 crystals. The design of the detector is optimized for ultralow-background searches. Neutrinoless double-beta decay (ββ0ν) is the main goal of CUORE. What is new is the fact that positive observation of neutrino oscillations gives new motivation for more sensitive searches. Neutrino oscillation experiments can only provide data on the mass differences of the neutrino mass-eigenstates. The absolute scale can only be obtained from direct mass measurements (β-decay end point measurements), or in the case of Majorana neutrinos, more sensitively by neutrinoless double-beta decay observation. ββ0ν is not the only exotic process which can be observed in the CUORE experiment. Other rare events, from cold dark matter, to rare nuclear decays and electron decay can in principle be studied with the CUORE experimental facility. I will discuss the last process in the 6th chapter. The topic which joins the exotic and rare processes discussed is the unwanted radioactive background which is inevitably present in the experimental measurements. CUORICINO, almost a single CUORE tower, was constructed as a smaller scale ex- periment and operated from december 2003 to June 2008. Besides being a sensitive experiment on 130Te double beta decay, CUORICINO is a conclusive test of CUORE. CUORICINO provided important results concerning both the technical performances of the bolometric tower (CUORE will be made of 19 such towers), the background level .In particular, one of the information gained is that the most probable candidates for the continuum background observed in the spectra, are the surface α contaminations of the copper mounting frame. Rare Physics event is playing a crucial role, not only in Fundamental Interaction Physics, but also in Astroparticle Physics and in Cosmology. These signals, if detected, would give an importatnt evidence of new Physics. The CUORE experiment (Cryogenic Underground Observatory for Rare Events) is a proposed tightly packed array of 988 TeO2 bolometers, each being a cube 125 cm3 on a side with a mass of 750 g. The array consists of 19 vertical towers, arranged in a compact cylindrical structure. Each tower will consist of 13 layers of 4 crystals. The design of the detector is optimized for ultralow-background searches. Neutrinoless double-beta decay (ββ0ν) is the main goal of CUORE. What is new is the fact that positive observation of neutrino oscillations gives new motivation for more sensitive searches. Neutrino oscillation experiments can only provide data on the mass differences of the neutrino mass-eigenstates. The absolute scale can only be obtained from direct mass measurements (β-decay end point measurements), or in the case of Majorana neutrinos, more sensitively by neutrinoless double-beta decay observation. ββ0ν is not the only exotic process which can be observed in the CUORE experiment. Other rare events, from cold dark matter, to rare nuclear decays and electron decay can in principle be studied with the CUORE experimental facility. I will discuss the last process in the 6th chapter. The topic which joins the exotic and rare processes discussed is the unwanted radioactive background which is inevitably present in the experimental measurements. CUORICINO, almost a single CUORE tower, was constructed as a smaller scale ex- periment and operated from december 2003 to June 2008. Besides being a sensitive experiment on 130Te double beta decay, CUORICINO is a conclusive test of CUORE. CUORICINO provided important results concerning both the technical performances of the bolometric tower (CUORE will be made of 19 such towers), the background level .In particular, one of the information gained is that the most probable candidates for the continuum background observed in the spectra, are the surface α contaminations of the copper mounting frame. Silicon Barrier Detectors (SBD) are a powerful instrument to study charged particle radiation (like α particles). During my PHD one of the activity I focused on was the optimization of the SBD used in the radioactivity laboratoty of the the University of Milano Bicocca A complete procedure for the calibration of these detectors was set- tled. In fact, one of the main problem to face with, (due also to the extremely low activity measured), is the discrimination of their intrinsic background level from that of the sample measured. The SBD are always operated in Ultra Low Background vacuum chambers. In the context of the discrimination of the background, evaluation of the muon and shower contribution to the acquired spectra were performed. The latter were done through a coincidence measurement between the SBD and a scintillator. The result of the measurements and of their ananlysis showed that the major contribution to the spurious counts comes from the showers. A dedicated acquisition was done for the detectors, with a module which lets to have event’s temporal imformation. To give limits on the surface activities of the samples the use of Monte Carlo (MC) simulation is mandatory in order to have an estimation of the efficiency of energy detection. The use of the MC simulation was optimized: different depht and profiles of contamination were studied and tested. This optimization allows to give limits on surface 232Th, 238U and 210Pb-Po activities which depend on the depht of contamination. The drastic reduction of the sensitivity achieved (from 10−5 to 10−7 and 10−8 Bq · cm2 fo the cleanest material measured) is due to the described optimiza- tion. Last, but non least, the SBD measurements played a crucial role in the material selection, depending on the radiopurity required, for the CUORE experiment. Concering the ββ0ν, a crucial role, in the theoretical interpretation of the experimental result, is played by the Nuclear Matrix Element (NME) used to transalte the observed rate (in the energy region where the signal is expected) in a sensitivity on the effective neutrino mass |mν|. I performed a study in order to compare and understand the different nuclear models used nowadays, and the respective Phase Space Factors (PSF) used. This study allows to compare, in a quantitative way, the different experiments on neutrinoless double beta decay. A database was realized in which all the inputs are collected, comments and references on NME and PSF are illustrated and the kind of short range correlation is used in the calculation of the matrix element. The database, with the information collected and properly organized, allows to evaluate the sensitivity on |mν| of all the experiments now at work, depending on the nuclear model used. The difficulties encountered in the comprehension of the nuclear models and in the PSF used are due to three main reasons. • the PSF shoul be in principle standard and unambiguous, not depending on the nuclear model, but just on the initial and final states JP . This is not what the study showed: the PSF, in the different formulation, show discrepancies of a factor 5 or 6. • the nuclear models assume different approaches to the process and should lead to different results. Two models, i.e., the Shell Model and the IBM (Interactive Boson Model) have a similar approach, but they differ in handling the states which are ’far from closed shells’, so in the handling of the nuclear deformations. The QRPA, (in the version pnQRPA an rQRPA, Quasi Random Phase Approximation), have a different approach to the previous models, because it introduces the concept of quasiparticle, which are states built with a ’mixing’ of creation and annihilation operators (a theory very similar to BCS for the superconductivity) and it leads to a correlation between particles and holes and not just between particles (gph and not only gpp pairing). • the SRC (shot range correlation) used should be univocal, but this is not the case. The theoreticians don’t give a clear choice of the proper SRC to be used. Finally I performed a study on the electron decay, in the channel e− ← γ + ν, using CUORICINO data. Moreover I performed a calculation of the cross section for the process, assuming a massless neutrino in the first step and a massive neutrino in the second step. The study of the channel implies to evaluate the signature of the decay, which depends on the material and atomic shell from which the electron disappears. In fact the visible energy changes if the decay happens in the active volume of the detector or in the surroinding materials: Ev = (mec2−Eb) 2 + EX = (mec2+Eb) 2 where me is the electron mass, Eb is the binding energy, EX is the X-ray energy following the decay. The last term is included only if the decay happens inside the active volume of the detectors. Thus, there are several signatures which can be discriminated from the background only if the detector resolution is excellent. Moreover the doppler broadening of the lines, due to the orbital motion of the electron in the shell, must be considered. I thus studied the different signatures in several materials, (potential emitters). In the analysis I included the efficiences for the signatures, using Monte Carlo simulations, expressely conformed to experimental set-up and charachteristics (such as real thresholds, active channels). The correction to the efficiencies, i.e. the loss of ’good events’, due to the analysis cuts, was evaluated. All the analysis done led to a promising result for this decay, in competition with the current limits given from other collaborations. The cross section calculation allowed to give an estimation of the CNC parameter, using as inputs the available experimental data.

Dans le cadre du projet Cigéo d’enfouissement de déchets radioactifs en couche géologique profonde, l’Andra souhaite optimiser le nombre d’Extensomètres à Corde Vibrante (ECV) à mettre en place pour suivre la convergence de sections de tunnel (alvéoles) se trouvant à 490 m de profondeur. La réponse à cette problématique est posée en quatre chapitres avec (1) un état de l’art sur les méthodes de détection de dommages, d’optimisations et les modèles inverses, (2) la mise en place d’un modèle numérique, (3) la méthodologie d’optimisation permettant d’estimer la contrainte horizontale ou la déformée d’une section d’alvéole et enfin (4) les résultats de l’optimisation. Le modèle numérique permet de créer une Base De Données (BDD) des déformations potentielles et ce en fonction des paramètres qui sont issus de mesures in situ. Les incertitudes sur la rigidité du sol encaissant, la variation d’épaisseur du revêtement ainsi que la position et l’erreur intrinsèque aux capteurs sont considérées. La méthodologie d’optimisation par algorithme génétique consiste à déterminer le nombre et le placement optimaux des capteurs permettant soit d’estimer la contrainte horizontale ayant engendrée les déformations mesurées par les capteurs, soit de construire une déformée probable de l’alvéole à partir des déformations mesurées. La première méthode permet de connaître l’emplacement optimal des ECV pour détecter les déformations liées à des contraintes probables. Elle est basée sur un modèle inverse. La seconde méthode consiste à s’assurer de la réversibilité du stockage (déformée de l’alvéole permettant le retrait des colis). Elle construit une spline passant par les valeurs de déformée aux emplacements des ECV. Pour l’estimation de la contrainte horizontale, les zones de placement de capteurs les plus propices se trouvent à proximité des reins. Pour l’estimation de la déformée, les capteurs ont tendance à s’équirépartir sur le pourtour de la section. Devant la possibilité de placer les capteurs suivant différentes orientations, l’influence de cette orientation donne une préférence aux ECV orthoradiaux, tandis que les ECV radiaux n’apportent pas d’informations complémentaires
In the Cigéo project for deep geological of radioactive waste, Andra wants to optimize the number of Vibrating Wire Extensometers (VWE) to follow the convergence tunnel (cells) cross-section built at 490 m depth. The answer to this problem is given in four chapters with (1) a state of the art on methods of damage detection, optimizations and inverse models, (2) the implementation of the numerical model, (3) the optimization methodology to estimate the horizontal stress or the deformed cell cross-section and finally (4) the results of the optimization. The numerical model allows creating a DataBase (DB) of potential strain according to the input parameters measured in situ. Uncertainties of the stiffness of the soil, the thickness variation of the coating and locations and intrinsic error of each sensor are considered. The genetic algorithm optimization methodology consists in determining the optimal number and location of the sensors allowing either to estimate the horizontal stress having generated strains measured by sensors, or build a probable deformation of the cell cross-section from the measured strains. The first method makes it possible to know the optimal location of VWE to detect strains linked to probable stresses. It is based on an inverse model. The second method is to ensure the reversibility of the storage (cell deformed allowing the withdrawal packages). It constructs a spline passing through the deformed values at the VWE locations. To estimate the horizontal stress, the best sensors placements are close to the kidneys. For the deformed estimation, sensors tend to be distributed on the cross-section periphery. Given the possibility of placing sensors in different orientations, the influence of this orientation gives preference to orthoradial VWEs while radial VWEs do not provide additional information

The major concern of this work is the development of hierarchically porous structured zeolite composites for ion-exchange applications by deposition of a thin layer of zeolite on inexpensive porous supports which offers better efficiency in separation processes. The merits of utilization of zeolite composites in industrial applications are generally reducing mass transfer resistance and pressure drop. In addition to this they have advantages in the removal of metal ions from wastewater such as increasing the metals uptake and minimizing the volume of waste disposed especially after vitrification. This thesis presents results from a combination of experimental work and simulation study of experimental data to give isotherm and kinetic models. The experimental work shed light on the preparation of zeolite composites using zeolite X (Si/Al ~ 1.35) and clinoptilolite (Si/Al ~ 4.3), studying the performance of these composites on the removal of the Sr2+ and Mn2+ ions and then stabilization of waste materials resulting from the ion-exchange process. Clinoptilolite was hydrothermally synthesized to show the effect of non-framework cations on the removal process. The porous supports were diatomite which is naturally occurring silica and carbon which is obtained from Iraqi date stones by a thermal treatment conducted at 900°C. Coating the support surface with zeolites crystals was conducted in two different ways. The layer by layer approach, which has not previously been used, was used to prepare monolithic carbon clinoptilolite composite using a combination of sucrose/citric acid and zeolite. The other approach was modifying the support surface by ultrasonication in the presence of nanoparticles suspension prepared using ball mill to create nucleation sites and enhance the crystal attachment during hydrothermal treatment. Characterisation was implemented in each case using XRD, SEM, EDAX, TGA and BET method. Ion-exchange experimental results showed higher ion-exchange capacity obtained when the composites were used in comparison to pure zeolites, when a comparison is based on actual weight of zeolite used for removal of Sr2+ and Mn2+ ions. A study of encapsulation of ions showed that it is feasible to solidify the waste materials by vitrification and/or geopolymerization to eliminate leaching of ions to the environment. The simulation studies showed that the ion-exchange kinetic followed the pseudo second order kinetic model. This fitting indicates that the rate of ion-exchange process is controlled by a chemical reaction related to valence forces. The overall ion-exchange process is controlled by a combination of ion-exchange reaction, film diffusion and intra-particle diffusion. Moreover, the thermodynamic studies which were conducted under different temperatures revealed that the ion-exchange of Sr2+ and Mn2+ ions is practicable, spontaneous and endothermic.

Methods for the determination of the actinide elements in water, biological, soil and sediment samples have been developed using on-line solid phase extraction and high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Initial applications utilised a commercially available resin, namely TRU-Spec resin, for efficient removal of the matrix prior to elution of uranium and thorium analytes. Comparative analyses of reference materials and natural water samples from Plymouth and Dartmoor demonstrated significant improvement in precision and speed of analysis by using TRU-Spec coupled to ICP-MS compared with alpha spectrometry. Further applications of the TRU-Spec resin for the determination of the transuranic actinide elements neptunium, plutonium and americium, resulted in the successful determination of 239Pu and 237Np in biological reference materials. Detection limits were 700, 850, and 600 attograms (ag) for 237Np, 233Pu, and 241Am, respectively, for a 0.5 ml sample injection, and better than 200 ag/g with 50 ml pre-concentration when sector field (SF) ICP-MS was used. A method for the selective sequential elution of uranium and plutonium was also developed to facilitate the determination of 239Pu without interference due to the 238U1H+ polyatomic ion, caused by high concentrations of 238U in sediment samples. Investigations were performed into the use of a polymeric substrate, which was dynamically coated with chelating dyes such as xylenol orange and 4-(2-pyridylazo) resorcinol, and a silica substrate coated with permanently bonded iminodiacetic acid. The latter was used for the successful determination of uranium and thorium in certified reference material waters. However, the column was found to have a high affinity for iron, making it unsuitable for the determination of the actinides in soil and sediment samples. Subsequently, a polystyrene substrate which was dynamically coated with dipicolinic acid was used for HPLC coupled with SF-ICP-MS. Using this column it was possible to separate the various actinides from each other and from the matrix. In particular, it was possible to separate plutonium and uranium to facilitate interference-free determination of the former. The column also exhibited some selectivity for different oxidation states of Np, Pu and U. Two oxidation states each for plutonium and neptunium were found, tentatively identified as Np(V) and Pu(III) eluting at the solvent front, and Np(IV) and Pu(IV) eluting much later. Detection limits were 12, 8, and 4 fg for 237Np, 239Pu, and 241Am, respectively, for a 0.5 ml injection, and the system was successfully used for the determination of 239Pu in water, biological and soil reference materials.

The aim of this study was to test whether one could use the same methods as used for sampling heavy metals and apply them to radioactive elements. Furthermore a sampling protocol was developed, the first of its kind, for the sampling of radioactive elements in fractured rock aquifers. This was achieved by initially examining local as well as international manuals and methods. The aforementioned was done in conjunction with a literature review of the movement of radioactive elements in these fractured rock aquifers. Beaufort West was utilised as a study area and the geology, hydrogeology and topography was outlined. Background radioactivity was generally acceptable except for two samples which were anomalously high. Taking cognisance of the methods used, as well as those previously applied in the area and abroad, a sampling protocol for radioactive elements in fractured rock aquifers was developed and attached as an appendix. In conclusion it was suggested that multiple methods be tested on one well in order to check whether similar results would occur. This would thus determine the best applicable methods. Also it was proposed that a new method, called DGT sampling, be applied in order to gain a time weighted average of the heavy metals and radioactive elements in groundwater. It could also be clearly seen, by comparing historical data and the current data, that the methods used for sampling heavy metal can be applied to radioactivity.

Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Production of graphite dust inside the Pebble Bed Modular Reactor (PBMR) influences the reactor operation negatively. Graphite is used as a moderator in the reactor core and the formation and transportation of graphite dust away from the reactor core decreases the amount of moderator which in turn has a negative impact on the reactor operation. High levels of radioactive dust may also contaminate reactor components which may pose a health risk to maintenance personnel. In this study a pressure vessel was designed and used to measure the wear of a graphite pebble in helium at elevated temperatures. By means of a multi-linear regression analysis a proper mathematical function was established in order to relate graphite wear to certain tribological parameters. These parameters were identified through a literature study. Discrete Element Modelling (DEM) was used to simulate the gravitational flow of graphite pebbles through the reactor core. The experimentally determined mathematical function was incorporated into the DEM simulation to estimate the annual mass of graphite dust to be produced by the PBMR pebble bed as a result of pebble-pebble interaction and pebble-wall interaction during refuelling.
AFRIKAANSE OPSOMMING: Die vorming van grafiet stof binne die korrelbed-modulêre reaktor (PBMR) beïnvloed die werking daarvan negatief. Grafiet word gebruik as 'n moderator in die reaktor kern en die vorming en vervoer van grafietstof weg van die reaktor kern lei tot 'n afname in die hoeveelheid moderator en dit het 'n negatiewe impak op die werking van die reaktor. Hoë vlakke van radioaktiewe grafietstof kontamineer ook reaktorkomponente wat 'n gesondheidsrisiko vir onderhoudspersoneel inhou. In hierdie studie was 'n drukvat ontwerp en gebruik om die slytasie van 'n grafietkorrel in helium by verhoogde temperature te meet. 'n Multi-lineêre regressie analise is dan gebruik om 'n wiskundige funksie daar te stel wat die verband tussen grafietslytasie en die eksperimentele parameters vas stel. Hierdie parameters was met behulp van 'n literatuurstudie geïdentifiseer. Diskrete Element Modellering (DEM) was gebruik om die gravitasionele vloei van grafietkorrels in die reaktor te modelleer. Die eksperimenteel bepaalde wiskundige funksie word in die DEM simulasie ge-inkorporeer om 'n skatting te maak van die jaarlikse massa grafietstof wat gevorm sal word in die PBMR korrelbed as 'n gevolg van korrel-korrel interaksie en korrel-wand interaksie gedurende hersirkulasie.

In 1902 Friedrich Giesel has discovered after co-precipitation with lanthanum from samples obtained by chemical treatment of uranium minerals a new radioactive element. Because of its emanating properties he named it emanium, which we now know as actinium. In 1899 André-Louis Debierne found a radioactive substance with chemical properties of titanium, and after further investigations in 1900 of thorium. Because of its high activity he explained it as a new element and named it actinium. It mainly consisted of 230Th. In 1904 he explained that his actinium was identical with the emanium found by Giesel. He had taken over the discovery of Giesel and had rejected his own one, because he had been afraid that his discovered substance which he could not separate from thorium would not be accepted as a new chemical element. In 1909 Boltwood looked for the long-lived precursor of radium. He isolated according to the procedure of Debierne the thorium fraction from the pitchblende and after some time he found in it radium but not in emanium produced according the procedure of Giesel. Boltwood named the mother-element of radium ionium, which was first accepted as a new radioactive element and later identified as thorium isotope 230Th. Although Debierne has discovered and later rejected this substance for a long time he was accepted as discoverer of actinium.
Entdeckung des Actiniums und des Thoriumisotopes 230Th Im Jahr 1902 entdeckte Friedrich Giesel nach Mitfällung von Lanthan aus Proben der chemischen Behandlung von Uranmineralen ein neues radioaktives Element, das er wegen seiner starken Bildung von Emanation Emanium nannte und mit dem jetzt als Actinium bezeichneten Element identisch ist.1899 fand André-Louis Debierne in Pechblende eine dem Titan chemisch ähnliche radioaktive Substanz, der er 1900 eine größere Ähnlichkeit mit dem Thorium zuschrieb. Wegen seiner hohen Radioaktivität erklärte er sie für ein neues Element und nannte es Actinium. Es bestand hauptsächlich aus 230Th. 1904 erklärte er, dass sein Actinium mit dem von Giesel entdeckten dem Lanthan ähnlichen Emanium identisch sei. Er übernahm Giesels Entdeckung und verwarf seine eigene, weil er fürchtete, dass seine entdeckte Substanz, die er nicht vom Thorium trennen konnte, nicht als neues chemisches Element anerkannt werden würde. Als Bertran Boltwood1909 nach den langlebigen Vorgängerelement von Radium suchte, trennte er nach der Vorschrift von Debierne die Thoriumfraktion aus der Pechblende ab und stellte fest, dass sich daraus mit der Zeit Radium gebildet hatte, wogegen sich aus dem nach der Vorschrift von Giesel abgetrennten Emanium kein Radium gebildet hatte. Boltwod nannte das Vorgängerelement von Radium Ionium, das zuerst als neues radioaktives Element anerkannt und entspäter als Thoriumisotop 230Th identifiziert wurde. Trotzdem Debierne nicht Actinium sondern diese Substanz entdeckt und später verworfen hatte, war er lange Zeit als Entdecker des Actiniums anerkannt.

The Joint Research Center, the European Commission’s science and knowledge service, started the European Atlas of Natural Radiation project with the objective of gathering all the data related to natural radioactivity from the European countries. The estimate of the terrestrial natural radioactivity is one of the priority of the project and it includes the realisation of concentration maps of the radioactive elements naturally occurring in the environment, that are the elements of the U and Th families together with 40K. The aim of this work is to study the methodology to develop the first complete K2O, U and Th concentration maps of the bedrock in Italy through the creation of geological units identified on a pre-compiled basis and the collection of geochemical data from scientific literature. The geological units were determined based on litho-, chrono- and tectono-stratigraphic features of the bedrock. The dataset was created using global open-access database and peer-reviewed articles; the data, more than 15000 in total, was checked for outliers and representativeness and then studied with statistical analysis, in order to evaluate the methodology and to assign an average K2O, U and Th concentration to the geological units. The results confirm that the methodology is reliable and allows to create K2O, U and Th concentration maps at 1:1M scale. The main sources of errors come from the high lithological variability of the units, which implies a high variability in the distribution of the concentration values, and from the heterogeneity of the data coverage. Focusing on these problems, it’s still possible to improve the methodology, especially by increasing the amount of available geochemical data and, subsequently, by realising more accurate maps on a smaller scale.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

First-principles calculations such as density functional theory (DFT) employ numerical approaches to solve the Schrodinger equation of a system. Standard functionals employed to determine the cohesive system energy, specifically the local density and generalized gradient approximations (LDA and GGA), underestimate the correlation of 5f electrons to their ions in AO₂ systems (A=U/Pu/Np). The standard correction, the "Hubbard +U," causes the multidimensional energy surface to develop a large number of local minima which do not correspond to the ground state (global minimum). Because all useful energy values derived from DFT calculations depend on small differences between relatively large cohesive energies, comparing systems wherein one or more of the samples are not in the ground state has the potential to introduce large errors. This work presents an analysis of the fundamental issues of metastable states in both pure and binary AO₂ systems, investigates novel methods of handling them, and describes why current literature approaches which appear to work well for the pure compounds are not well-suited for systems containing multiple actinide species.

Le travail est axé sur l'accumulation d'éléments chimiques essentiels et non essentiels avec une attention particulière pour les parties des consommées, en lien avec la qualité sanitaire des produits alimentaires. Le travail de thèse est divisé en deux grandes parties. La première porte sur une expérimentation en plein champ où des plantes de blettes et de tomates ont été cultivées du stade plantules jusqu'à la maturité pendant 5 mois avec des pratiques agricoles conventionnelles ou biologiques. Les plantes ont été récoltées à 6 stades différents de croissance et nous avons déterminé la concentration des organes végétaux pour 27 éléments chimiques. L'objectif était d'étudier la répartition des éléments entre les organes en fonction de l'âge de la plante et des pratiques culturales.La seconde partie de la thèse a été consacrée à la compréhension et à la modélisation de la répartition du cadmium (Cd) chez le tournesol aux stades reproducteurs. Des plantes ont été cultivées du stade plantule jusqu'à la maturité, en solution nutritive avec une faible concentration en Cd cohérente avec les expositions aux champs. Durant la phase reproductive, cinq échantillonnages ont été effectués pour comprendre la répartition du Cd entre les organes ainsi que l'origine du Cd des graines (prélèvement racinaire versus remobilisation à partir d'autres organes). Au stade du bouton floral et pendant le remplissage des graines, le devenir du Cd récemment absorbé par les racines a été suivi et modélisé par traçage isotopique avec du 111Cd. Les rôles de la transpiration et de l'allométrie entre organes ont été plus particulièrement examinés
This work is focuded on the accumulation of essential and non-essential elements, paying a special attention to the dible part of the plants, in terms of food safety and human health. The thesis work has been divided in two main parts. The first one is related to a field expeiment performed in open-air plots, where Swiss chards and tomato plants were grown from seedlings to maturity in a natural soil during five months, using organic or conventional agricultural practices. Plants were harvested at six different growth satges and the total concentrations of 27 elements were measured in all plants organs. The objective was to study the partitioning of elements between the plant organs, depending on the plant age on the cultivation practice. The second part of the thesis is devoted to the understanding and modelling of the partitioning of cadmium (Cd) in sunflowers at the reproductive stages. Sunflowers wre grown in nutrient solution at low Cd availability consistent with thaht found in the field, from germination toi maturity. During the reproductive period, five samplings were carried out to investigate the partitioning of the total Cd between plant organs and the origin of the Cd allocated to seeds (root uptake vs; remobilization from other plant organs). At the flower bud and grain filling stages, the partitioning of the Cd recently taken up between the different plant organs was followed and modelled by exposing several plants for the three days to a 111Cd enriched nutrient solution. The roles of the transpiration and of the plant allometry were specially investigated

Ce travail de thèse s'inscrit dans le cadre de recherches sur le retraitement futur du combustible nucléaire usé et notamment sur la gestion poussée des radionucléides à vie longue tels que les actinides mineurs. Il concerne la fabrication de pastilles céramiques de Couvertures Chargées en Actinides Mineurs (CCAM) dédiées à la transmutation pour les réacteurs à neutrons rapides. Les pastilles céramiques utilisées dans le milieu nucléaire sont classiquement fabriquées en utilisant les procédés issus de la métallurgie des poudres. En raison de la pulvérulence des précurseurs poudres utilisés et de la forte radioactivité des actinides mineurs et notamment de l’américium, un procédé « sans poudre » innovant a été proposé. Ce procédé prévoit la fabrication de pastilles céramiques en utilisant des précurseurs oxydes non plus sous forme de poudre mais sous forme de microsphères (Calcined Resin Microspheres Pelletization, CRMP). Le principe de ce procédé consiste à compacter sous forme de pastilles des microsphères d’oxyde puis à fritter le comprimé obtenu.La première partie de cette étude concerne la synthèse et la caractérisation de précurseurs oxyde sous la forme de microsphères sub-millimétriques d’oxyde de lanthanides (simulants les actinides) par le procédé aux résines. Différents lots de microsphères ont pu être synthétisés afin de mieux appréhender l’influence de certains paramètres de synthèse, tel que la température de calcination, le tri en taille de la résine ou encore la teneur en lanthanides dans le cas des oxydes mixtes ont été investigués dans le but de déterminer leur impact sur les propriétés microstructurales et mécaniques de microsphères d’oxyde.L'étude aborde dans un deuxième temps la mise en forme des microsphères d’oxyde à travers une approche à la fois expérimentale et numérique. L’approche numérique utilise la méthode éléments discrets (Discrete Element Method, DEM), bien adaptée pour ces milieux granulaires. Les microsphères d’oxyde, prises individuellement, sont caractérisées mécaniquement notamment à travers la mesure de leur résistance à l'écrasement. Une mise en relation des conditions de synthèse et des tenues mécaniques des microsphères a été entreprise afin de comprendre l'impact de ces paramètres de synthèse sur le comportement mécanique du matériau. La compaction en matrice de lots de ces microsphères sous forme de pastille a été étudiée. En particulier, la compressibilité d'un certain nombre de microsphères a été analysée expérimentalement puis simulée par la DEM en mesurant la densification de la pastille en cru en fonction de la contrainte axiale appliquée et en décrivant l’évolution de sa microstructure
One option envisioned for the future management of high level nuclear waste is the transmutation of minor actinides into short-lived fission products in sodium fast reactor. This route requires the development of pellet fabrication processes to prepare Minor Actinide Bearing Blanket (MABB) for the transmutation of americium.Currently, those ceramic pellets are produced by powder metallurgy processes involving numerous grinding and milling steps that generate very fine and highly contaminating and irradiating particles. A viable option for reducing the amount of those fine particles would be to develop a dustless process by working on much coarser particles. In this context, this study is concerned with the pelletization of porous and spherical lanthanides oxide precursors (surrogates of actinides). The present work uses both experimental data and numerical simulations to optimize the pelletization step. The final aim is to obtain, after sintering, homogeneous, dense and undistorted ceramic pellets.Firstly, this study concerns the synthesis and characterisation of these oxide microspheres precursors by the Weak Acid Resin process, which consists in loading beads of ion exchange resin with lanthanides cations and mineralizing the metal loaded resin leads into sub-millimetric-sized oxide microspheres. Comprehensive characterisations of the microstructure and mechanical properties of oxide microspheres have been carried out to better understand their behaviour into the matrix when producing pellets.Secondly, the mechanical properties of a single microsphere were investigated in order to better understand its behaviour during compaction steps. They were also analysed using multi-scale simulations based on the Discrete Element Method (DEM), which is well suited for such particulate materials. In a second approach, compaction studies were carried out in a three parts die to characterize the mechanical behaviour under pressure of a large number of oxide precursors. The behaviour of several microspheres in the matrix was finally simulated using DEM in order to describe interactions between microspheres and to have a better understanding of their evolution during pressing

Cette thèse s’inscrit dans l’étude du comportement à long terme des verres nucléaires en conditions de stockage. Son objectif est de déterminer, de comprendre et de comparer les effets de certains éléments chimiques présents dans la composition du verre et/ou dans le milieu de stockage (Zn, Mg, Ni, Co, Fe, Ca, Gd, Ce, K, Cs, Cr et Ag) sur les différents processus mis en jeux lors de l’altération aqueuse des verres nucléaires. Dans ce cadre, une attention particulière a été portée sur le caractère cumulatif ou compétitif des effets de ces éléments chimiques. Pour cela, un verre simple à 6 oxydes (ISG) a été altéré pendant plus de 500 jours dans une solution contenant un ou plusieurs des éléments chimiques d’intérêt. Les éléments Zn, Mg, Ni, Co et Fe augmentent l’altération du verre en formant des phases secondaires de même structure (smectites tricotaédriques) et de même stœchiométrie (à l’élément près). Leur précipitation consomme des éléments chimiques du milieu (Si, Al) et induit une diminution de pH. Ce processus se maintient jusqu’à l’atteinte d’un pH limite propre à chaque phase secondaire, au-dessous duquel leur précipitation est inhibée. Par la suite, ces éléments peuvent s’intégrer dans le gel d’altération en remplacement du Ca rendu plus soluble par la baisse du pH. Tant qu’ils forment des phases secondaires, les effets de ces éléments sont cumulatifs. Les terres rares Gd et Ce augmentent aussi l’altération du verre en formant des phases secondaires mais leurs effets sont plus faibles car elles sont moins silicatées. Ces éléments, ne s’intègrent pas dans le gel. Le Cr précipite avec le Ca pour former une phase qui appauvrit le gel en Ca, entraine une diminution du pH et augmente l’altération du verre.Les éléments K, Cs et Ca limitent l’altération du verre en s’intégrant dans le gel et en ralentissant les phénomènes de transport en son sein. Cette intégration est compétitive : l’ordre d’intégration (quantité et efficacité sur la limitation de l’altération) est le suivant Ca >> Cs > K. L’élément Ag précipitant sous forme d’AgCl, n’a pas d’effet sur l’altération du verre : cette phase ne modifie ni le milieu, ni le développement de la pellicule d’altération.Ainsi, l’augmentation de l’altération pourrait être proportionnelle à la quantité d’éléments favorisant la précipitation de phases secondaires, mais la diminution de pH qui l’accompagne limite ce processus. Les effets des éléments qui diminuent l’altération du verre en s’incorporant dans le gel, sont limités en quantité par la composition du gel et sa capacité à les recevoir, et en qualité par la nature même des éléments
This work takes place in the context of the long-term behavior of nuclear glasses under repository conditions. The main objective is to identify, understand and compare the effects of some chemical elements present in the glass composition and/or in the repository media (Zn, Mg, Ni, Co, Fe, Ca, Gd, Ce, K, Cs, Cr and Ag) on the processes involved in glass alteration by water. The cumulative or competitive nature of the effects of these chemical elements was determined. To reach this goal, a 6 oxides simple glass (ISG) has been altered for more than 500 days in a solution containing one or more of the chemical elements of interest.The results indicated that Zn, Mg, Ni, Co and Fe elements increase glass alteration forming secondary phases with the same structure and stoichiometry (trioctahedral smectites). To form, these silicates consume chemical elements (Si, Al) from the environment and induce a pH decrease until a limiting value of pH. Beyond this pH the precipitation of secondary phases is inhibited and these chemical elements can be integrated into the gel, replacing Ca whose solubility increases at lower pH. As long as they form secondary phases, the effects of these elements are cumulative. Rare earths Gd and Ce also increase glass alteration forming secondary phases but their effects are lower as they contain less silicon. These elements are not integrated in the gel. Chromium increases glass alteration by precipitating with Ca and leading to a less protective gel, depleted in Ca. Silver precipitates as AgCl and has no effect on the alteration of the glass.The chemical elements K, Cs and Ca limit glass alteration by integrating into the gel and slowing down the transport phenomena therein. This integration is competitive: the order of integration (quantity and effectiveness glass alteration limitation) is the following Ca >> Cs > K. Thus, the increase of glass alteration may be proportional to the quantity of elements promoting the precipitation of secondary phases, but the pH decrease limits the process. The effects of the elements that reduce glass alteration by incorporating into the gel, are quantitatively limited by the gel composition and its ability to incorporate them, and qualitatively by the nature of the elements

Le but de cette thèse était de mieux contraindre les flux continent-océan à l’aide de traceurs géochimiques, les terres rares (REE) et la composition isotopique du néodyme (Nd-IC), en se focalisant sur les mers de Corail et des Salomon, région de l'Océan Pacifique Sud-Ouest (OPS) où circulent les eaux alimentant le Pacifique Equatorial et qui est le siège d'importantes modifications hydrologiques et géochimiques des masses d'eau.Un nouveau protocole analytique des terres rares dissoutes (dREE)a été développé. Ce système ‘seaSLOW’ permet la préconcentration simultanée de 8 échantillons d'eau de mer, réduisant considérablement le temps d'analyse, avec un excellent blanc de chimie -moins de 0,5% du signal de dREE-, des limites de détection ~1/40 de la concentration moyenne d'eau de mer et des rendements > 90%. Mais surtout, le seaSLOW est peu coûteux, facile à fabriquer, ce qui le rend accessible pour d'autres utilisateurs, en particulier des pays en développement.Les profils verticaux de dREE ont été réalisés pour 143 échantillons prélevés en mers de Corail et des Salomon (campagne PANDORA; été 2012). Les concentrations de dREE - à l'exception du Ce insoluble – montrent des profils de type nutriment soit de faibles valeur en surface et plus riches en profondeur (ex: les concentrations de Nd varient de ~ 5 à 25 pmol / kg entre surface et fond) Des enrichissements locaux en dREE sont observés le long des côtes et dans les trois détroits, sorties de la mer Salomon. Des modèles en boite révèlent un enrichissement net significatif de REE dans la thermocline inférieure (soit: 145 ± 46 tNd / an). L'empreinte basaltique a été mise en évidence par des anomalies positives Eu et Ce, en particulier dans la couche de surface. La très bonne corrélation entre les Terres Rares lourdes et le silicium dissous est confirmée. Ces résultats sont publiés dans Pham et al (2019).Le Nd-IC dissous a également été mesuré sur les mêmes échantillons. Les distributions des deux paramètres Nd (concentration Nd et Nd-IC) entre la mer de Corail, l'entrée et la sortie de la mer Salomon ont été établies sous forme de profils verticaux et de cartes représentant les couches transportant les différentes masses d'eau. Les profils verticaux montrent tous plus de Nd-IC radiogénique dans la couche de surface (jusqu'à ε_Nd = +3), des valeurs minimales de εNd à des profondeurs intermédiaires (~ 1100m) avant d'augmenter à nouveau en profondeur. À l'échelle régionale, des signaux de Nd-IC très positifs sont observés aux sorties nord de la mer Salomon, reflétant probablement la libération de matières radiogèniques dans les masses d'eau au cours de leur parcours à travers la mer Salomon. L'occurrence de processus d'échange aux frontières (BE) a été suggérée à de nombreux endroits, soit à l'échelle locale (ex: les eaux de surface traversant Indispensable Strait) ou à l'échelle régionale (ex: les eaux profondes à travers la mer Salomon). La quantification du BE via des modèles en boîtes a pu être réalisée pour la partie inférieure de la thermocline inférieure (LLTW) et la couche supérieure des couches d'eau profonde (UCDW). À titre d'illustration, l'apport externe de Nd nécessaire pour équilibrer à la fois les variations de Nd-IC et les concentrations de Nd de la couche profonde supérieure (UCDW) entre l'entrée sud et les sorties nord de la Mer des Salomon est de 105 ± 50 TNd / an. L'application des deux paramètres Nd a permis de mieux identifier les sources de matière et de réduire les incertitudes affectant les processus. Les études futures de ces distributions de paramètres sur les particules en suspension collectées aux mêmes stations permettront d'obtenir une image complète des processus régissant les échanges entre particules et dissous
The aim of this thesis was to better constrain the land-ocean fluxes using geochemical tracers, Rare Earth Element (REE) and Neodymium Isotopic Composition (Nd-IC). The studied area was the Coral and Solomon Seas, a part of the Southwest Pacific Ocean (SPO) where the waters feeding the Equatorial Pacific Ocean are circulating which confers an important role in the climate regulation to this area. The SPO is also a place where important hydrological and chemical modifications of the water masses occur. A new dREE analytical protocol was developed to replace the one used for years in my research team. This “seaSLOW” manifold allows the simultaneous treatment of 8 seawater samples, dramatically reducing the analytical time, with a low matrix blank signal - less than 0.5% for dREE signal. Affordable detection limits (equal ~1/40 of the average seawater concentration) and high quantitative recoveries (>90%) were obtained during the blank and performance tests, respectively. The strong points of seaSLOW are that it is low-cost (equal one fifteenth of the commercial product seaFAST) and easy to fabricate, making it accessible for other users, including developing countries.Vertical profiles of dissolved REE (dREE) concentrations for 143 samples collected in the Coral and Solomon Seas as part of the PANDORA cruise in summer 2012 were analyzed. dREE concentration –except the insoluble Ce– indicates the nutrient like profiles, i.e. low values at the surface increasing at depth (e.g. Nd concentrations range from ~5 pmol/kg at the surface to ~ 25 pmol/kg in the deepest layers). Local dREE enrichments are observed along the coast and in the three northern exiting straits of the Solomon Sea (a.k.a: Indispensable, Solomon and Vitiaz Straits). dREE variations in the different water layers were quantified using box models, pointing out a net enrichment of 145 ± 46 tNd/year in the lower thermocline. The basaltic material imprint was brought to light by positive Eu and Ce anomalies, especially in surface layer. The better correlation between heavy REE (HREE) and Si cycle than that observed for the LREE in the oceanic water was also confirmed. These results are published in Chemical Geology (Pham et al, 2019).Dissolved Nd-IC were also measured on the same samples. The distributions of both Nd parameters (Nd concentration and Nd-IC) between the the Coral Sea, the entrance and the exit of the Solomon Sea were established as vertical profiles and as maps representing the layers transporting the different water bodies. All the vertical profiles show similar patterns with more radiogenic Nd-IC in the surface layer (up to ε_Nd = +3), minimal ε_Nd values at Intermediate depths (~1100m) before increasing again toward the bottom. On a regional scale, higher Nd-IC signals are observed at the northern exits than at the southern entrance of the Solomon Sea, likely reflecting the release of radiogenic material to the water masses during their pathways across the Solomon Sea. The occurrence of boundary exchange (BE) processes were suggested at many place within the sea, either at a local scale (e.g: surface water passing through Indispensable strait) or at the regional scale (e.g: deep water across the Solomon Sea). Quantification of BE via box models was conducted for the lower part of the Lower thermocline (LLTW) and the upper layer of the deep water layers (UCDW). As an illustration, the external input of Nd required to balance both the Nd-IC and Nd concentrations of the upper deep layer (UCDW) between the southern entrance and the northern exits is of 105±50 TNd/y. Applying Nd both parameters helped to better identify the sources of material and to reduce the uncertainties affecting the processes. Future studies of these parameter distributions on the suspended particles collected at the same stations will help to get a full picture of the processes governing the dissolved-particulate exchanges

Dans le cadre de la gestion des déchets radioactifs dits de moyenne activité à vie longue et de haute activité, la France a fait le choix du stockage géologique profond dans une formation rocheuse située à l’est du bassin parisien, dans une zone tectoniquement stable. Cette formation d’argilites du Callovo-Oxfordien a été choisie pour ses propriétés de rétention des radionucléides puisqu’elle est très peu perméable. Un laboratoire de recherche souterrain a été construit à environ 500 mètres de profondeur afin d’étudier in-situ les propriétés de la roche. Il a été montré que l’argilite du Callovo-Oxfordien présente une anisotropie liée à sa formation géologique. L’objectif principal de cette thèse est de pouvoir reproduire le comportement mécanique anisotrope à l’aide d’un modèle de comportement élasto-plastique. Le modèle de comportement thermo-élasto-viscoplastique et isotrope nommé LKR est la résultante de tout le savoir-faire et l’expertise d’EDF en ce qui concerne le dimensionnement d’ouvrages souterrains. On cherche donc à appliquer une méthode de prise en compte de l’anisotropie structurelle caractérisant plusieurs types de géomatériaux dont l’argilite du Callovo-Oxfordien à ce modèle de comportement. Afin d’atteindre cet objectif, deux méthodes de prise en compte de l’anisotropie développées dans la littérature scientifique sont appliquées à un modèle de Drucker-Prager à écrouissage linéaire négatif et sont comparées. La première méthode consiste à introduire un tenseur de microstructure ou de fabrique permettant de définir les orientations préférentielles du matériau. La seconde méthode est l’approche par plan de faiblesse qui consiste à décrire le comportement anisotrope du matériau via deux mécanismes distincts, l’un décrivant le comportement de la matrice rocheuse isotrope et l’autre décrivant les plans de faiblesse. C’est par ce deuxième mécanisme que l’anisotropie est introduite. Ces deux applications ont été faites dans le logiciel libre de simulation en mécanique, Code Aster, développé par EDF et ont permis d’appréhender les difficultés numériques de chacune de ces méthodes, et de choisir l’approche la plus pertinente pour l’extension du modèle LKR. Ainsi, c’est la méthode avec le tenseur de fabrique qui est, dans notre cas, la plus adaptée. Elle a donc été appliquée au modèle LKR. Cette nouvelle extension au modèle permet de prendre en compte la dépendance à l’orientation du matériau des résistances en compression. Dans ces travaux, on se place dans le cadre de la mécanique des milieux continus. L’anisotropie est introduite seulement dans le mécanisme élasto-plastique du modèle de comportement LKR
Within the framework of radioactive waste management, for long-lived and high-level radioactive waste, France has chosen deep geological storage. This storage will be located in a rock formation, in the east of the basin Parisian, in a tectonically stable area. This Callovo-Oxfordian claystone formation was chosen for its radionuclides retention properties since it is not very permeable. An underground research laboratory was built 500 meters deep to study the properties of the rock in-situ. The Callovo-Oxfordian claystone has been shown to exhibit anisotropy related to its geological formation. The main objective of this PhD thesis is to reproduce anisotropic mechanical behaviour using an elasto-plastic constitutive model. The thermo-elasto-viscoplastic and isotropic behaviour model named LKR is the result of all EDF’s knowledge and expertise in the design of underground structures. Therefore, we seek to apply a method of taking into account structural or inherent anisotropy characterizing several types of geomaterials including Callovo-Oxfordian claystone to this LKR constitutive model. In order to achieve this objective, two methods of taking anisotropy into account and developed in the scientific literature are applied to a Drucker-Prager model with linear softening and then are compared to each other. The first method consists of introducing a microstructure or fabric tensor to define the preferential orientations of the material. The second method is the weakness plane approach which consists of describing the anisotropic behaviour of the material through two distinct mechanisms, one describing the behaviour of the isotropic rock matrix and the other describing the weakness planes. It is through this second mechanism that anisotropy is introduced. These two applications were made using the free mechanical simulation software, Code Aster, developed by EDF. This allowed to understand the numerical difficulties of each of these methods, and to choose the most relevant approach for the extension of the LKR model. Thus, it is the method with the fabric tensor which is, in our case, the most suitable. It was therefore applied to the LKR model. This new extension to the model enables the material orientation dependency of the compression strengths to be taken into account. In this work, the mechanics of continuous media are considered. Anisotropy is introduced only into the elasto-plastic mechanism of the LKR behaviour model

L’exploitation minière de l’uranium et les processus de traitement du minerai sont à l’origine d’un marquage potentiel de l’environnement par les descendants des chaînes de désintégration U-Th et des éléments traces métalliques (ETM) associés. Ces contaminants s’accumulent ensuite préférentiellement dans des zones de sédimentation continentales (étangs ou lacs) ou des zones humides (tourbières, berges de rivière) situées à l’aval hydraulique des mines. Les zones humides en particulier sont des milieux sensibles aux changements globaux et à la pression anthropique, situés en général en tête de bassin versant. Cela pose donc un risque en cas relargage des contaminants depuis ces milieux. L’objectif de cette étude est de mettre en place une méthodologie aisément reproductible, y compris aux sites miniers orphelins, et permettant l’identification et la caractérisation des contaminations et la compréhension des mécanismes d’accumulation et des risques de relargage. Cette étude a été réalisée dans l’environnement de l’ancienne mine de Bertholène (Aveyron, 12, France). Les zones d’accumulations préférentielles ont été identifiées par spectrométrie gamma in situ mobile et fixe. Des échantillons de sols, sédiments, végétaux, eaux et tourbes ont été prélevés autour du site, afin (a) de caractériser l’activité des différents descendants des chaînes de l’U et du Th et les contaminations en ETM associées à différentes échelles d’observation, (b) de comprendre les mécanismes d’accumulation et de relargage potentiel et (c) de tracer les sources des contaminants. Les résultats obtenus montrent que l’essentiel de la contamination est localisée dans une zone inondable de l’environnement proximal aval de la mine. Les activités en uranium élevées (U-238 > 20000 Bq.kg-1) et le fort enrichissement des radionucléides du début de chaîne par rapport à la fin de chaîne de l’U-238 traduisent un apport préférentiel d’U-238 et de Th-230, par rapport au Ra-226, lors d’inondations. Les contaminations en ETM associées sont relativement faibles, excepté en Mn, en Ba et en S. Les accumulations en radionucléides et en ETM sont expliquées à la fois par les caractéristiques géochimiques du minerai d’uranium et par les processus de traitement du minerai et des eaux d’exhaure. Les lessivages chimiques réalisés révèlent que les fractions acido-solubles et oxydes amorphes des sols constituent des pièges prépondérants des contaminants et que des variations du pH ou du potentiel d’oxydoréduction pourraient générer des relargages important d’uranium et de radium dans l’environnement. Finalement les déséquilibres radiologiques et les isotopes du plomb sont des traceurs fiables de la contamination associée à l’exploitation d’une mine d’uranium
Uranium mining and uranium ore processing increase the environmental activity of U and Th decay products and trace elements, in particular in case of releases to the adjacent rivers. Contaminants accumulate then preferentially in sedimentation areas (such as ponds or lakes) or in wetlands (peatlands, marshes or riverbanks) located downstream to the mine. Wetlands – generally located at the head of watershed – are particularly sensitive to environmental changes and anthropogenic pressure. This poses a risk of release of contaminants from these accumulation areas. The objective of the present study is to propose an easily reproducible methodology – in particular for the orphan mining sites – to identify and characterize accumulation areas. This study also aims to improve our understanding of the mechanisms of accumulation and release, in these areas. This study was performed around the former mining site of Bertholène (France). Standing and mobile in situ gamma spectrometry is used to accurately locate the accumulation areas. Soils, sediments, vegetation, water and peat are also sampled upstream and downstream of the mine, in order to (a) characterize the activities and the disequilibria of the U-Th decay chains and the associated trace elements according to the scale of observation, (b) understand the mechanisms of accumulation and release and (c) identify the potential sources using geochemical proxies and isotopic analyses. The results obtained show that radionuclides are mainly accumulated in a flooding area located downstream the mine. Strong U-238 activities (> 20000 Bq.kg-1) and strong Ra-226/U-238 and Th-230/Ra-226 activity ratios are recorded, involving preferential inputs of U-238 and Th-230 during flooding events. Trace element contamination is low, except for Mn, Ba and S. Such contaminations are potentially explained by the geochemical composition of the uranium ore and by the past and current processes of ore and water mine. Sequential extractions highlight the importance of the acido-soluble and the amorphous oxides in the trapping of contaminants. Thus, pH or Eh potential changes could induce major releases of uranium to the environment. The large differences in Pb isotope composition between natural soils and uranium ores, as well the activity ratios of the U-238 and decay chain products, make these indicators helpful to identify the soils and the sediments impacted by uranium mining

La Nouvelle-Calédonie, île située au Sud-Ouest de l’Océan Pacifique et actuel 6e producteur mondial de nickel, est confrontée à une pollution sédimentaire sans précédent de ses cours d’eau. En effet, l’exploitation minière débutée dès les années 1880 a fortement amplifié les processus d’érosion des sols et de transport sédimentaire. Une hyper-sédimentation des hydro-systèmes calédoniens a notamment été constatée suite au déploiement de l’activité minière sur l’archipel. Bien que ce phénomène constitue un facteur aggravant les problèmes d’inondation caractéristiques de ces régions tropicales, les contributions sédimentaires générées par l’exploitation minière restent encore inconnues à ce jour et sont pourtant importantes pour guider la mise en œuvre de mesures visant à réduire ces apports sédimentaires.À cette fin, une étude de traçage sédimentaire qualifiée de fingerprinting a été menée sur un bassin « pilote » : le bassin versant de Thio (397 km²), considéré comme le « berceau » de l’activité minière en Nouvelle-Calédonie. Différents marqueurs tels que les radionucléides, la géochimie élémentaire ou la « couleur » ont été testés pour quantifier les contributions des sources minières aux apports sédimentaires générés par deux crues cycloniques récentes (dépression tropicale en 2015, cyclone Cook en 2017). Une carotte sédimentaire a également été prélevée dans la plaine inondable de la rivière Thio afin de reconstruire l’évolution temporelle des contributions des sources minières. Les résultats de cette étude montrent que les contributions des sources minières dominent, avec une contribution moyenne comprise entre 65-68% pour la crue de 2015 et entre 83-88% pour celle de 2017. L’impact de la variabilité spatiale des précipitations a notamment été mis en évidence pour expliquer les variations des contributions de ces sources. Les variations temporelles des contributions des sources minières déduites de l’analyse de la carotte sédimentaire ont, quant à elles, pu être associées aux différentes périodes historiques de l’exploitation minière sur le bassin versant de Thio (pré-mécanisation, mécanisation, post-mécanisation de l’activité minière). Les contributions des sources minières restent, là encore, dominantes avec une contribution moyenne le long du profil sédimentaire de 74%. La méthode de traçage validée a ensuite été testée sur quatre autres bassins versants de Nouvelle-Calédonie afin d’évaluer la transposabilité de cette approche
New Caledonia, an island located in the south-western Pacific Ocean and currently the world's sixth largest producer of nickel, is facing unprecedented sedimentary pollution of its river systems. Indeed, nickel mining that started in the 1880s accelerated soil erosion and sediment transport processes. Hyper-sedimentation of the Caledonian hydro-systems has been observed after the deployment of mining activities on the archipelago. Although this phenomenon exacerbates the flooding problems experienced in these tropical regions, the sediment contributions generated by nickel mining remain unknown and are nevertheless required to guide the implementation of control measures to reduce these sediment inputs.To this end, a sediment fingerprinting study was carried out in a "pilot" catchment: the Thio River catchment (397 km²), considered as one of the first areas exploited for nickel mining in New Caledonia. Different tracers such as radionuclides, elemental geochemistry or "colour" properties were tested to trace and quantify the mining source contributions to the sediment inputs generated during two recent cyclonic flood events (tropical depression in 2015, cyclone Cook in 2017). A sediment core was also collected in the floodplain of the Thio River catchment to reconstruct the temporal evolution of these mining source contributions. The results of this study show that mining sources dominated sediment inputs with an average contribution ranging from 65-68% for the 2015 flood event to 83-88% for the 2017 flood event. The impact of the spatial variability of precipitation was highlighted to explain the variations in the contributions of these sources across the catchment. The temporal variations in the contributions of the mining sources deduced from the analysis of the sediment core were interpreted at the light of the mining history in the Thio River catchment (pre-mechanization, mechanization, post-mechanization of mining activity). The contributions of mining sources were again dominant with an average contribution along the sedimentary profile of 74 %. Once validated, this tracing method has been tested in four other catchments of New Caledonia in order to evaluate the validity of the approach in other contexts

Dans le cadre de la gestion des déchets radioactifs dits de moyenne activité à vie longue et de haute activité, la France a fait le choix du stockage géologique profond dans une formation rocheuse située à l’est du bassin parisien, dans une zone tectoniquement stable. Cette formation d’argilites du Callovo-Oxfordien a été choisie pour ses propriétés de rétention des radionucléides puisqu’elle est très peu perméable. Un laboratoire de recherche souterrain a été construit à environ 500 mètres de profondeur afin d’étudier in-situ les propriétés de la roche. Il a été montré que l’argilite du Callovo-Oxfordien présente une anisotropie liée à sa formation géologique. L’objectif principal de cette thèse est de pouvoir reproduire le comportement mécanique anisotrope à l’aide d’un modèle de comportement élasto-plastique. Le modèle de comportement thermo-élasto-viscoplastique et isotrope nommé LKR est la résultante de tout le savoir-faire et l’expertise d’EDF en ce qui concerne le dimensionnement d’ouvrages souterrains. On cherche donc à appliquer une méthode de prise en compte de l’anisotropie structurelle caractérisant plusieurs types de géomatériaux dont l’argilite du Callovo-Oxfordien à ce modèle de comportement. Afin d’atteindre cet objectif, deux méthodes de prise en compte de l’anisotropie développées dans la littérature scientifique sont appliquées à un modèle de Drucker-Prager à écrouissage linéaire négatif et sont comparées. La première méthode consiste à introduire un tenseur de microstructure ou de fabrique permettant de définir les orientations préférentielles du matériau. La seconde méthode est l’approche par plan de faiblesse qui consiste à décrire le comportement anisotrope du matériau via deux mécanismes distincts, l’un décrivant le comportement de la matrice rocheuse isotrope et l’autre décrivant les plans de faiblesse. C’est par ce deuxième mécanisme que l’anisotropie est introduite. Ces deux applications ont été faites dans le logiciel libre de simulation en mécanique, Code Aster, développé par EDF et ont permis d’appréhender les difficultés numériques de chacune de ces méthodes, et de choisir l’approche la plus pertinente pour l’extension du modèle LKR. Ainsi, c’est la méthode avec le tenseur de fabrique qui est, dans notre cas, la plus adaptée. Elle a donc été appliquée au modèle LKR. Cette nouvelle extension au modèle permet de prendre en compte la dépendance à l’orientation du matériau des résistances en compression. Dans ces travaux, on se place dans le cadre de la mécanique des milieux continus. L’anisotropie est introduite seulement dans le mécanisme élasto-plastique du modèle de comportement LKR
Within the framework of radioactive waste management, for long-lived and high-level radioactive waste, France has chosen deep geological storage. This storage will be located in a rock formation, in the east of the basin Parisian, in a tectonically stable area. This Callovo-Oxfordian claystone formation was chosen for its radionuclides retention properties since it is not very permeable. An underground research laboratory was built 500 meters deep to study the properties of the rock in-situ. The Callovo-Oxfordian claystone has been shown to exhibit anisotropy related to its geological formation. The main objective of this PhD thesis is to reproduce anisotropic mechanical behaviour using an elasto-plastic constitutive model. The thermo-elasto-viscoplastic and isotropic behaviour model named LKR is the result of all EDF’s knowledge and expertise in the design of underground structures. Therefore, we seek to apply a method of taking into account structural or inherent anisotropy characterizing several types of geomaterials including Callovo-Oxfordian claystone to this LKR constitutive model. In order to achieve this objective, two methods of taking anisotropy into account and developed in the scientific literature are applied to a Drucker-Prager model with linear softening and then are compared to each other. The first method consists of introducing a microstructure or fabric tensor to define the preferential orientations of the material. The second method is the weakness plane approach which consists of describing the anisotropic behaviour of the material through two distinct mechanisms, one describing the behaviour of the isotropic rock matrix and the other describing the weakness planes. It is through this second mechanism that anisotropy is introduced. These two applications were made using the free mechanical simulation software, Code Aster, developed by EDF. This allowed to understand the numerical difficulties of each of these methods, and to choose the most relevant approach for the extension of the LKR model. Thus, it is the method with the fabric tensor which is, in our case, the most suitable. It was therefore applied to the LKR model. This new extension to the model enables the material orientation dependency of the compression strengths to be taken into account. In this work, the mechanics of continuous media are considered. Anisotropy is introduced only into the elasto-plastic mechanism of the LKR behaviour model

Les propriétés des argilites du Callovo-Oxfordien les désignent comme une barrière naturelle sûre pour le stockage de déchets radioactifs. Afin d’optimiser la prédiction de leur comportement, leur réponse à diverses sollicitations à court et long termes est étudiée. Notamment, lors de la phase d’exploitation, l’air ventilé dans les galeries n’est pas à l’équilibre hydrique avec la roche et peut perturber ses propriétés hydromécaniques (HM). Il semble alors essentiel de caractériser la réponse HM de la roche à des sollicitations hydriques.La démarche adoptée consiste à proposer un modèle physique adéquat, sur la base d’essais au laboratoire. L’essai de séchage est retenu puisqu’il permet d’étudier la réponse des échantillons en conditions non-saturées. A partir des résultats HM, un modèle élastique 2D isotrope est proposé, puis est élevé à la 3D avec un module de Young isotrope transverse. Ensuite, les données expérimentales servent à estimer certains paramètres poroélastiques et de transfert du modèle. Cette étape est accomplie par procédure inverse (minimisation de l’erreur mesures-calculs). Enfin, une modélisation 2D du comportement in situ est proposée, et compare les prédictions de modèles plastique isotrope et élastique isotrope transverse.Les simulations d’essais au laboratoire reproduisent assez bien les données expérimentales. Pour la modélisation in situ, une bonne corrélation est obtenue entre les prédictions et les mesures, et ce sans ajustement préalable des paramètres. Toutefois, le modèle souligne une influence limitée de la plasticité à l’échelle du laboratoire, alors que les phénomènes dissipatifs sont marqués in situ. Les modélisations 3D au laboratoire ne donnent pas de résultats plus fins qu’en 2D, mais reproduisent plus de données expérimentales (variations de masse, déformations axiales et latérales). De plus, injecter plusieurs types de données dans la formulation inverse permet d’améliorer la précision de l’algorithme. Par ailleurs, une meilleure stabilité de l’algorithme est obtenue en adoptant une convergence en deux étapes (simplex, puis méthode de type gradient). Les estimations numériques des paramètres corroborent les mesures expérimentales obtenues par ailleurs
The Callovo-Oxfordian claystones’ properties make them reliable as a geological barrier for the confinement of radioactive wastes. In order to optimally predict their behavior, how they respond to various short and long terms loadings has to be studied. Particularly during the exploitation phase, air is continuously ventilated throughout the galleries. The climatic properties of this air are not balanced with those of the rock, and may perturb its hydromechanical (HM) attributes. Thus, assessing the HM response of the rock under hydric loading seems to be a priority.This dissertation begins with laboratory tests to propose an appropriate physical model. Drying tests were studied as they focus on the HM response of samples undergoing hydric loadings. A first 2D isotropic model is proposed, and then enhanced to 3D by considering a transversely isotropic Young modulus. Secondly, experimental results provide relevant data to estimate poroelastic and transport parameters involved in the model. Estimation is achieved according to an inverse procedure, which minimizes the error between measurements and model predictions. Finally, a real-size test is simulated using 2D models: an isotropic plastic one and a transversely isotropic elastic one.Model predictions reproduce well the laboratory tests data. When simulating the in situ behavior, a rather good agreement is obtained between the numerical and experimental results (although using the parameters estimated at the laboratory scale). However, the model highlights a limited influence of plasticity in the laboratory tests, while dissipative phenomena obviously occur in situ. 3D laboratory simulations do not improve the precision of 2D results, but reproduce more experimental data (mass variations, axial and lateral strains). Moreover, the inversion process is more efficient when ran over various kinds of data. Furthermore, stability of the algorithm is improved when adopting a two-phase convergence (simplex, followed by a gradient-like method). Numerical estimates of the parameters are in agreement with the direct experimental measurements obtained through other tests

Aquifers in the arid alluvial basins of the southwestern U.S. are recharged predominantly by infiltration from streams within the basins and by water entering along the margins of the basins from surrounding mountains (mountain -front recharge). The Tucson Basin of Southeastern Arizona is such a basin. The Santa Catalina Mountains form the northern boundary of this basin and receive more than twice as much precipitation (about 70 cm/yr) as the basin does (about 30 cm/yr). In this study environmental isotopes were employed to investigate the migration of precipitation basinward through joints and fractures. Water samples were obtained from springs in the Santa Catalina Mountains. Stable isotopes and thermonuclear bomb-produced tritium enabled qualitative characterizations of flow paths and flow velocities. Stable isotopic measurements fail to display a direct altitude effect. Tritium values indicate that although a few springs discharge pre-bomb water, most springs discharge waters from the 1960's or later.

{u2075}{u00B3}Mn-{u2075}{u00B3}Cr short-lived nuclide dating of certain meteoritic materials can be achieved in situ using Secondary Ion Mass Spectrometry (SIMS) as an alternative to bulk methods. This thesis reports on the Mn-Cr systematics of olivine from two differentiated meteorite classes: angrites and pallasites. Much of the previously published SIMS Mn-Cr data relies on reference materials that are not compositionally matched to unknowns, particularly with respect to olivine (e.g. Mg-rich San Carlos olivine is used alongside Fe-rich meteoritic olivine). Previous studies may suffer from systematic biases due to the differing sensitivities of SIMS to Mn and Cr. To assess olivine Mn-Cr relative sensitivity factors (RSFs), synthetic olivines with varying Mg-Fe-Ca components were produced using gas-mixing furnaces and piston-press apparatus, and analysed by SIMS and LaserAblation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS). RSF is correlated with Fe-content of olivine; San Carlos olivine is therefore an inappropriate standard for most SIMS Mn-Cr work. For angrites, a mixing model was used to account for RSF, using three of the synthetic olivines. Two quenched angrites (D'Orbigny and Sahara 99555) and two plutonic angrites (NWA 4590 and 4801) were analysed with Sensitive High-mass Resolution Ion Micro-Probe (SHRIMP) Reverse Geometry (-RG) and SHRIMP-II. The initial {u2075}{u00B3}Mn/{u2075}{u2075}Mn for D'Orbigny and Sahara 99555 was found to be 3.52 ({u00B1}0.16) x 10-6 and 3.57 ({u00B1}0.22) x 10-6 , which is in agreement with some previous work but not with the SIMS study of Sugiura et al. (2005). NWA 4590 and 4801 were found to have initial {u2075}{u00B3}Mn/{u2075}{u2075}Mn of 1.00 ({u00B1}0.27) x 10-6 and 0.52 ({u00B1}1.2) x 10-6 respectively; less precise than but in agreement with previous work. To check if the difference between this study and Sugiura et al. (2005) represents inter-laboratory bias or meteorite heterogeneity, the same piece of D'Orbigny as analysed in that study was reanalysed using SHRIMP-RG; initial {u2075}{u00B3}Mn/{u2075}{u2075}Mn of 3.61 ({u00B1}0.39) x 10-6 was found, still in disagreement with Sugiura et al. (2005). The source of bias remains elusive; it is not due to differing RSF since both studies found similar values for this variable. For pallasite olivine, trace-elemental maps were made using LA-ICPMS to provide context for Mn-Cr measurements. Two contrasting pallasites were selected: Brahin, which has fragmental olivine, and Brenham, which has rounded olivine. Both olivine types are normally zoned for divalent elements Ni and Co, but non-divalent elements AI, Cr, Ti are heterogeneously distributed, often with no relationship to grain morphology. In Brenham, these complex elemental structures are superimposed on normal zoning. Preservation of these structures probably hinges on slow diffusion of AI, which other non-divalent elements associate with to maintain charge-balance. SIMS measurements indicate initial {u2075}{u00B3}Mn/{u2075}{u2075}Mn of -2.25 ({u00B1}4.9) x 10-6 and 2.55 ({u00B1}0.62) x 10-5 for Brahin and Brenham respectively; the latter is an unreasonably high value and is unlikely to reflect Mn-Cr chronology. This apparent value could reflect loss of {u2075}{u2075}Mn after decay of {u2075}{u00B3}Mn, although the geochemical behaviour of Mn is unfavourable for such a model. Instead, excess {u2075}{u00B3}Cr* derived from Mn-rich phosphates originally present in the metallic groundmass could have been introduced into olivine rims during the grain growth and annealing process which formed rounded olivine.

School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa, 2018
In an uncertain future with regards to coal utilisation due to environmental regulations, coal mining, and particularly the future of coal mining located in the Waterberg Coalfield of the Ellisras Basin in South Africa, needs to be aware of all the risks and possible pitfalls that could hamper its further development. The radioactive elements, U and Th, which are typically associated with sedimentary environments where coal is formed, if found in elevated quantities, would be one of the risks that needs to be quantified. Based on the impact elevated U levels has had on the development of the Springbok Flats Basin, this study was instigated to evaluate if there was a similar risk to the coal resources and reserves in the Waterberg Coalfield, which lies 150 km to the northwest of the Springbok Flats Basin. Due to limitations related to access to samples it was not possible to sample the entire Karoo Supergroup sequence within the Waterberg Coalfield. However, a database of downhole wireline geophysical logs was compiled and used as a first order study to identify the most suitable horizons for sampling for geochemical analysis. A total of 34 exploration holes and 7,451 blast holes were used to compile the geophysical database. Trends related to gamma anomalies were determined where gamma values, here measured in American Petroleum Institute (API) values, are greater than 300. These were associated with the Eendragtpan (Beaufort) and Swartrant (Vryheid) Formations. The 54 anomalies (where API values greater than 300) within the Eendragtpan (Beaufort) Formation did not appear to follow any apparent trend. The 118 anomalies within the Swartrant (Vryheid) Formation conformed to two trends – the first was associated with a gradual increase in gamma values towards the base of the interburden between the coal zones 3 and 4A, Grootegeluk Bench 8. The second trend identified was that the anomalies were not associated with the coal seams, but instead with the interburden. The largest anomalies occurred in the interburden between the coal zones 2 and 3, at Grootegeluk Bench 10. Geochemical analysis of the Bench 10 interburden yielded only two anomalous U and Th values (compared to U and Th values reported by Swaine (1994)), with the mean values for U and Th being 2.89 ppm and 2.47 ppm respectively. Various classifications and analysis were applied to the geochemical results to help ascertain if there was any correlations or trends within the results; 1) Th/U ratios indicate that Bench 10 was deposited under reducing conditions; and 2) the samples with anomalous U and Th values also report elevated values for Y, Zr, Nb and Ag, and are depleted in Na and Al. The overall conclusion of the study was that while there was some U and Th, as would be expected in such an environment, there was not significant quantities found for exploitation purposes and it is unlikely that the radioactive elements will pose a health risk within the region. As such there is little cause for concern regarding the mining of coal within the Waterberg Coalfield, in particular pertaining to U or Th.
XL2019

High-level radioactive waste (HLW) poses threat to the biosphere. Geological disposal is accepted as a safe way for HLW disposal. Waste canisters made of Sintered Silicon Carbide (SSiC) are proposed and geomechanical safety aspects relating to such SSiC canisters are investigated. First part of the thesis reviews the state-of-the-art and demands for HLW disposal. The reason for considering Silicon Carbide (SiC) as canister material is explained. Especially in terms of corrosion and lifetime, ceramics and especially SiC is superior to metals or concrete. The only concern is its brittle behavior. The second part of the thesis presents results on static and dynamic mechanical properties of SiC in general and in particular for SSiC based on literature review and own lab tests. Although strength values for SiC and especially SSiC are very high, the extreme brittle behavior has to be considered in case of impact or point-like loading. The third and most extensive part of the thesis part contains numerical simulations, which consider most critical potential loading situations during transport and installation of the canisters underground. Both, pure elastic continuum and DEM based models are used considering the following loading situations (critical scenarios): Freefall of canister during transport or installation (FF), Impact by falling rock block at disposal site (RF), Point loading due to accidental insertion of small stone below the canister (PL), Anisotropic earth pressure loading after disposal (EP). Coating to protect the canisters against damage is investigated and preliminary parameters in terms of stiffness and thickness are recommended.

Concentration ratios are used to determine the transfer of nuclides from soil to biota to fauna. Some nuclides have limited associated data though, this has not prevented predictions from being performed at sites without associated data. These ratios are site specific and are not fully applicable when applied to other locations. A recent literature review for a waste repository performance assessment determined that a significant portion of the environmental data was based on recursively published material. To address this deficiency neutron activation analysis (NAA) was used to determine concentration ratios of certain biota. Three sites, two riparian and one shrub steppe, were sampled in the eastern Washington Columbia basin, near the Hanford site. Two hundred and fifty eight samples of opportunity were collected. This included 15 soil samples, 10 water and sediment samples, 40 different species of biota, and 2 terrestrial animal species and 3 aquatic animal species. These samples were prepared for NAA by drying, weighing, and in certain cases ashing to improve detection efficiency. After activation, the samples were placed in a HPGe detector to perform spectral analysis. The concentration results of 26 elements of interest are presented, along with newly established concentration ratios for all of the species sampled.
Graduation date: 2013

Although products of coal combustion (PCCs) such as coal ash are currently exempted from classification as a hazardous waste in the United States under the 1976 Resource Conservation and Recovery Act (RCRA), the U.S. Environmental Protection Agency (EPA) is now revising a proposed rule to modify disposal practices for these materials in order to prevent contamination of ground- and surface water sources by leached trace elements. This paper analyzes several aspects of EPA’s scientific reasoning for instating the rule, with the intent of answering the following questions: 1) Are EPA’s cited values for PCC production and disposal accurate estimates of annual totals?; 2) In what ways can EPA’s leaching risk modeling assessment be improved?; 3) What is the total quantity of trace elements contained within all PCCs disposed annually?; and 4) What would be the potential costs and feasibility of reclassifying PCCs not under RCRA, but under existing NRC regulations as low-level radioactive waste (LLRW)? Among the results of my calculations, I found that although EPA estimates for annual PCC disposal are 20% larger than industry statistics, these latter values appear to be closer to reality. Second, EPA appears to have significantly underestimated historical PCC disposal: my projections indicate that EPA’s maximum estimate for the quantity of fly ash landfilled within the past 90 years was likely met by production in the last 30 years alone, if not less. Finally, my analysis indicates that while PCCs may potentially meet the criteria for reclassification as low-level radioactive waste by NRC, the cost of such regulation would be many times that of the EPA June proposed disposal rule ($220-302 billion for PCCs disposed in 2008 alone, versus $1.47 billion per year for the Subtitle C option and $236-587 million for Subtitle D regulatory options).
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