The accumulation of spent nuclear fuel may be hindering the expansion of nuclear electricity production. However, the reprocessing and recycling of spent fuel may reduce its volume and environmental burden. Although fast spectrum reactors are the preferred modality for transuranic element transmutation, such fast spectrum systems are in very short supply. It is therefore legitimate to investigate the recycling potential of thermal spectrum systems, which constitute the overwhelming majority of nuclear power plants worldwide. To do so efficiently, several new fuel assembly designs are proposed in this Thesis: these include (1) Mixed Oxide Fuel (MOX), (2) MOX fuel with Americium coating, (3) Inert-Matrix Fuel (IMF) with UOX as inner zone, and (4) IMF with MOX as inner zone. All these designs are investigated in a multi-recycling strategy, whereby the spent fuel from a given generation is re-used for the next generation. The accumulation of spent nuclear fuel may be hindering the expansion of nuclear electricity production. However, the reprocessing and recycling of spent fuel may reduce its volume and environmental burden. Although fast spectrum reactors are the preferred modality for transuranic element transmutation, such fast spectrum systems are in very short supply. It is therefore legitimate to investigate the recycling potential of thermal spectrum systems, which constitute the overwhelming majority of nuclear power plants worldwide. To do so efficiently, several new fuel assembly designs are proposed in this Thesis: these include (1) Mixed Oxide Fuel (MOX), (2) MOX fuel with Americium coating, (3) Inert-Matrix Fuel (IMF) with UOX as inner zone, and (4) IMF with MOX as inner zone. All these designs are investigated in a multi-recycling strategy, whereby the spent fuel from a given generation is re-used for the next generation.

The closure of the nuclear fuel cycle is a topic of interest in the sustainability context of nuclear energy. The implication of such closure includes considerations of nuclear waste management. This originates from the fact that a closed fuel cycle requires recycling of useful materials from spent nuclear fuel and discarding of non-usable streams of the spent fuel, which are predominantly the fission products. The fission products represent the near-term concerns associated with final geological repositories for the waste stream. Long-lived fission products also contribute to the long-term concerns associated with such repository. In addition, an ultimately closed nuclear fuel cycle in which all actinides from spent nuclear fuels are incinerated will result in fission products being the only source of radiotoxicity. Hence, it is desired to develop a transmutation strategy that will achieve reduction in the inventory and radiological parameters of significant fission products within a reasonably short time. In this dissertation, a transmutation strategy involving the use of the VHTR is developed. A set of specialized metrics is developed and applied to evaluate performance characteristics. The transmutation strategy considers six major fission products: 90Sr, 93Zr, 99Tc, 129I, 135Cs and 137Cs. In this approach, the unique core features of VHTRs operating in equilibrium fuel cycle mode of 405 effective full power days are used for transmutation of the selected fission products. A 30 year irradiation period with 10 post-irradiation cooling is assumed. The strategy assumes no separation of each nuclide from its corresponding material stream in the VHTR fuel cycle. The optimum locations in the VHTR core cavity leading to maximized transmutation of each selected nuclides are determined. The fission product transmutation scenarios are simulated with MCNP and ORIGEN-S. The results indicate that the developed fission product transmutation strategy offers an excellent potential approach for the reduction of inventories and radiological parameters, particularly for long-lived fission products (93Zr, 99Tc, 129I and 135Cs). It has been determined that the in-core transmutation of relatively short-lived fission products (90Sr and 137Cs) has minimal advantage over a decay-only scenario for these nuclides. It is concluded that the developed strategy is a viable option for the reduction of radiotoxicity contributions of the selected fission products prior to their final disposal in a geological repository. Even in the cases where the transmutation advantage is minimal, it is deemed that the improvement gained, coupled with the virtual storage provided for the fission products during the irradiation period, makes the developed fission product transmutation strategy advantageous in the spent fuel management scenarios. Combined with the in-core incineration options for TRU, the developed transmutation strategy leads to potential achievability of engineering time scales in the comprehensive nuclear waste management.

Minimization of HLW inventories and U consumption are key elements guaranteeing nuclear energy expansion. The integration of complex nuclear systems into a viable cycle yet constitutes a challenging multi-parametric optimization problem. The reactors and fuel cycle performance parameters may be strongly dependent on minor variations in the system's input data. Proven discrepancies in nuclear data evaluations could affect the validity of the system optimization metrics. This study first analyzes various advanced AP1000-VHTR fuel cycle scenarios by assessing their TRU destruction and their U consumption minimization capabilities, and by computing reactor performance parameters such as the time evolution of the effective multiplication factor keff, the reactors' energy spectrum or the isotopic composition/activity at EOL. The performance metrics dependence to prompt neutron fission spectrum discrepancies is then quantified to assess the viability of one strategy. Fission spectrum evaluations are indeed intensively used in reactors' calculations. Discrepancies higher than 10% have been computed among nuclear data libraries for energies above 8MeV for 235U. TRU arising from a 3wt% 235U-enriched UO2-fueled AP1000 were incinerated in a VHTR. Fuels consisting of 20%, 40% and 100% of TRU completed by UO2 were examined. MCNPX results indicate that up to 88.9% of the TRU initially present in a VHTR fueled with 20% of TRU and 80% of ThO2 were transmuted. Additionally, the use of WgPu instead of RgPu should reduce the daily consumption of 235U by 1.3 and augment core lifetime. To estimate the system metrics dependence to fission spectrum discrepancies and validate optimization studies outputs, the VTHR 235U fission spectrum distribution was altered successively in three manners. keff is at worst lowered by 1.7% of the reference value and the energy spectrum by 5% between 50meV and 2MeV when a significantly distorted fission spectrum tail is used. 233U, 236Pu and 237Pu inventories and activities are multiplied by 263, 523 and 34 but are still negligible compared to 239Pu mass or the total activity. The AP1000-VHTR system is in conclusion not dependent on the selected fission spectrum variations. TRU elimination optimization studies in AP1000-VHTR systems will be facilitated by freeing performance metrics dependency from 1 input parameter.

Les réacteurs hybrides, bases sur le couplage entre un accélérateur de particules et un coeur sous-critique via une cible<br />de spallation, présentent des possibilités de réduction de la radiotoxicité des déchets de haute activité et a vie<br />longue promis au stockage. Les différents concepts proposes ces dernières années dans la communauté scientifique montrent<br />la nécessite de réaliser un démonstrateur.<br />Ce travail de thèse a porte sur l'optimisation par simulation Monte Carlo a l'aide du code MCNPX, de la neutronique d'un tel<br />système dans le but de réaliser un réacteur pilote.<br />Tout d'abord, nous avons indique les principales caractéristiques neutroniques d'un réacteur hybride avant de présenter le<br />concept de démonstrateur refroidi au gaz base sur le remontage effectue par la société Framatome ANP. Nous avons<br />caractérise puis optimise la neutronique a travers la géométrie et les matériaux utilises pour ce démonstrateur.<br />Dans le cadre de l'incinération des actinides mineurs, nous avons calcule l'évolution des combustibles envisageables suivant<br />les phases de démonstration prévues. Les grandeurs liées a l'incinération des actinides mineurs sont rapportées. En vue<br />de la transmutation du 99Tc et de l'129I, nous avons calcule les temps caractéristiques et les taux de transmutation<br />a l'équilibre.<br />D'autre part, nous avons analyse le passage du démonstrateur vers un réacteur incinérateur de puissance a partir de<br />critères physiques tels que les facteurs de forme et les niveaux de flux. A partir de cette analyse, des solutions innovantes sont<br />proposées pour améliorer les facteurs de forme d'un incinérateur de puissance.<br />Enfin, dans des perspectives a plus long terme, l'utilisation des réacteurs hybrides dans le cadre de la génération<br />d'233U pour accélérer le démarrage d'une filière de réacteurs a sels fondus basée sur le cycle<br />232Th/233U a été explorée et s'avère particulièrement efficace.

Experiments were performed at the Nuclear Engineering Teaching Laboratory (NETL) in 2005 and 2006 in which a 20 MeV linear electron accelerator operating as a photoneutron source was coupled to the TRIGA (Training, Research, Isotope production, General Atomics) Mark II research reactor at the University of Texas at Austin (UT) to simulate the operation and characteristics of a full-scale accelerator driven subcritical system (ADSS). The experimental program provided a relatively low-cost substitute for the higher power and complexity of internationally proposed systems utilizing proton accelerators and spallation neutron sources for an advanced ADSS that may be used for the burning of high-level radioactive waste. Various instrumentation methods that permitted ADSS neutron flux monitoring in high gamma radiation fields were successfully explored and the data was used to evaluate the Stochastic Pulsed Feynman method for reactivity monitoring. / text

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O objetivo da presente pesquisa foi desenvolver um conceito que desse conta do fenÃmeno de agrupamentos genÃricos designado aqui de constelaÃÃo de gÃneros. Para o alcance deste objetivo, a investigaÃÃo se inscreve na base epistemolÃgica das formulaÃÃes teÃrico-filosÃficas de Bakhtin, relativas aos usos da linguagem. A Tese foi organizada em duas grandes partes. Na primeira, apresento a elaboraÃÃo de um percurso teÃrico-metodolÃgico que permitiu elaborar um constructo de constelaÃÃo de gÃneros a partir da eleiÃÃo de pelo menos uma caracterÃstica marcante da esfera de comunicaÃÃo em que se ambienta o agrupamento constelar, do processo formativo de seus gÃneros e das funÃÃes sociais que eles realizam. Na segunda parte, ilustro a elaboraÃÃo do constructo com a anÃlise de sete tipos de chats, elegendo a hipertextualidade, a transmutaÃÃo e o propÃsito comunicativo dos bate-papos virtuais como as categorias operantes para caracterizaÃÃo do agrupamento constelar desses gÃneros. Para a construÃÃo dos dados, foi realizada uma pesquisa de carÃter etnogrÃfico na Internet durante trÃs anos. A partir de um exercÃcio intenso de observaÃÃo participante, em diversas salas de chat, e de pequenas entrevistas realizadas por e-mail com alguns chatters, a triangulaÃÃo dos dados e a sua posterior anÃlise apontam para os seguintes resultados: a constelaÃÃo dos chats assume uma natureza hipertextual, pois tal caracterÃstica aproxima os gÃneros quanto a este aspecto; os chats sÃo gÃneros que compartilham o mesmo fenÃmeno formativo, uma vez que todos transmutam e reinterpretam gÃneros orais de variadas esferas de comunicaÃÃo; finalmente, esses gÃneros se tornam distintos entre si graÃas à teia de propÃsitos comunicativos que eles formam dentro da constelaÃÃo para atender Ãs mais diversas funÃÃes sociais. / O objetivo da presente pesquisa foi desenvolver um conceito que desse conta do fenÃmeno de agrupamentos genÃricos designado aqui de constelaÃÃo de gÃneros. Para o alcance deste objetivo, a investigaÃÃo se inscreve na base epistemolÃgica das formulaÃÃes teÃrico-filosÃficas de Bakhtin, relativas aos usos da linguagem. A Tese foi organizada em duas grandes partes. Na primeira, apresento a elaboraÃÃo de um percurso teÃrico-metodolÃgico que permitiu elaborar um constructo de constelaÃÃo de gÃneros a partir da eleiÃÃo de pelo menos uma caracterÃstica marcante da esfera de comunicaÃÃo em que se ambienta o agrupamento constelar, do processo formativo de seus gÃneros e das funÃÃes sociais que eles realizam. Na segunda parte, ilustro a elaboraÃÃo do constructo com a anÃlise de sete tipos de chats, elegendo a hipertextualidade, a transmutaÃÃo e o propÃsito comunicativo dos bate-papos virtuais como as categorias operantes para caracterizaÃÃo do agrupamento constelar desses gÃneros. Para a construÃÃo dos dados, foi realizada uma pesquisa de carÃter etnogrÃfico na Internet durante trÃs anos. A partir de um exercÃcio intenso de observaÃÃo participante, em diversas salas de chat, e de pequenas entrevistas realizadas por e-mail com alguns chatters, a triangulaÃÃo dos dados e a sua posterior anÃlise apontam para os seguintes resultados: a constelaÃÃo dos chats assume uma natureza hipertextual, pois tal caracterÃstica aproxima os gÃneros quanto a este aspecto; os chats sÃo gÃneros que compartilham o mesmo fenÃmeno formativo, uma vez que todos transmutam e reinterpretam gÃneros orais de variadas esferas de comunicaÃÃo; finalmente, esses gÃneros se tornam distintos entre si graÃas à teia de propÃsitos comunicativos que eles formam dentro da constelaÃÃo para atender Ãs mais diversas funÃÃes sociais. / In the present research my objective was to create a concept to the phenomenon of the constellation of genres. Thus, to define that category, about which I developed my Thesis, the theoretical and philosophical formularizations of Bakhtin relative to the uses of the language were my support. The text which relates this research is organized in two great parts. In the first one, I present my theoretical and methodological construction for the study of the constellations of genres, bringing as proposal the choice of the strongest characteristic of the communication sphere where the grouping of genres is, the observation of the formative process of those genres and the identification of the social functions that they realize. In the second part, I present the chats like an example of constellation of genres and I illustrate my theoretical and methodological construction through of seven different types of chats, focusing the hypertextuality, the transmutation of genres and the communicative purpose as the operational categories to the analysis. In this research, I tried give an ethnographic character through an intense exercise of participant observation, accessing many chat rooms in the Internet during three years. For obtaining the data, besides the participant observation, I did small interviews with some chatters by e-mail. After the triangulation of the data and its posterior analysis, I arrived to the following results: the constellation of chats assumes a hypertextual nature because such characteristic is what brings chats closer as for the aspect of their communication sphere; chats are genres that share the same formative phenomenon, in other words, everyone of them is formed by the transmutation and the reinterpretation of oral genres from various communication spheres; finally, chats become distinct of each one because they build a web of communicative purposes inside of the constellation in order to serve to several social functions. / In the present research my objective was to create a concept to the phenomenon of the constellation of genres. Thus, to define that category, about which I developed my Thesis, the theoretical and philosophical formularizations of Bakhtin relative to the uses of the language were my support. The text which relates this research is organized in two great parts. In the first one, I present my theoretical and methodological construction for the study of the constellations of genres, bringing as proposal the choice of the strongest characteristic of the communication sphere where the grouping of genres is, the observation of the formative process of those genres and the identification of the social functions that they realize. In the second part, I present the chats like an example of constellation of genres and I illustrate my theoretical and methodological construction through of seven different types of chats, focusing the hypertextuality, the transmutation of genres and the communicative purpose as the operational categories to the analysis. In this research, I tried give an ethnographic character through an intense exercise of participant observation, accessing many chat rooms in the Internet during three years. For obtaining the data, besides the participant observation, I did small interviews with some chatters by e-mail. After the triangulation of the data and its posterior analysis, I arrived to the following results: the constellation of chats assumes a hypertextual nature because such characteristic is what brings chats closer as for the aspect of their communication sphere; chats are genres that share the same formative phenomenon, in other words, everyone of them is formed by the transmutation and the reinterpretation of oral genres from various communication spheres; finally, chats become distinct of each one because they build a web of communicative purposes inside of the constellation in order to serve to several social functions.

Initially, we use the quadratic transmutation maps to compose a new probability model: the transmuted log-logistic distribution. Transmutation maps are a convenient way of constructing new distributions, in particular survival ones. It comprises the functional composition of the cumulative distribution function of one distribution with the inverse cumulative distribution (quantil) function of another. Its comprehensive description of properties, such as moments, quantiles, order statistics etc., along with its survival study and the classical and Bayesian estimation methods, are also part of this work. Focusing on analysis of survival, the study included two practical situations commonly found: the presence of regression variables, through the transmuted log-logistic regression model, and the presence of right censorship. In a second moment, searching for a more flexible model than the transmuted, we present its generalization, the transmuted distributions of cubic rank. Using the methodology presented in this first generalization, two models were considered to compose the new cubic transmuted distributions: the log-logistic and Weibull models. Faced with problems presented in the transmutated class of quadratic and cubic orders (such as the restricted parametric space of the transmutation parameter &lambda;), we propose in this work, a new family of distribution. This family, which we call e-transmuted or e-extended, is as simple as the transmuted model, because it includes a single parameter to the base model, but more flexible than the class of transmuted models, once the transmuted is a particular case of the proposed family. In addition, the nem family presents important properties such as, orthogonality between the baseline model parameters and the e-transmutation parameter, along with unrestricted parametric space for the &omega; e-transmutation parameter, which is dened on the real line. Simulation studies and real data applications were performed for all proposed models and generalizations. / Inicialmente, usamos os mapas de transmutação quadráticos para compor um novo modelo de probabilidade: a distribuição log-logística transmutada. Mapas de transmutação são uma forma conveniente de construção de novas distribuições, em especial de sobrevivência/confiabilidade, e compreendem a composição funcional da função de distribuição acumulada e da função de distribuição acumulada inversa (quantil) de um outro modelo. Uma descrição detalhada de suas propriedades, tais como, momentos, quantis, estatística de ordem, dentre outras estatísticas, juntamente com o estudo de sobrevivência e métodos de estimação clássico e Bayesiano, também fazem parte deste trabalho. Focando em análise sobrevivência, incluímos no estudo duas situações práticas comumente encontradas: a presença de variáveis regressoras, através do modelo de regressão transmutado log-logístico, e a presença de censura à direita. Em um segundo momento, buscando um modelo mais flexível que o transmutado, apresentamos uma generalização para esta classe de modelos, as distribuições transmutadas de rank cúbico. Usando a metodologia apresentada nesta primeira generalização, dois modelos foram considerados para compor as novas distribuições transmutadas cúbica: os modelos log-logístico e Weibull. Diante de problemas apresentados na classe transmutada de ordens quadrática e cúbica (tal como o espaço paramétrico restrito do parâmetro de transmutação &lambda;), propomos neste trabalho, uma nova família de distribuição. Esta família, a qual chamamos e-transmutada ou e-extendida, é tão simples quanto o modelo transmutado, por incluir um único parâmetro ao modelo base, porém mais flexível do que a classe de modelos transmutados, sendo esta classe um caso particular da família proposta. Além disso, apresenta propriedades importantes, como ortogonalidade entre os parâmetros do modelo base e o parâmetro de e-transmutação, e espaço paramétrico não restrito para o parâmetro de etransmutação &omega;, que é definido em toda reta real. Estudos de simulação e aplicações a dados reais foram realizados para todos os modelos e generalizações propostas.

Jusqu’à présent, les travaux sur la réception de la théorie darwinienne en France ont surtout porté sur le monde savant. Ils ont conclu à un échec de sa diffusion. En élargissant cette étude à la société dans son ensemble, on découvre qu’il s’agit, en réalité, d’un succès. Le rôle du débat public dans l’introduction du darwinisme en France fait l’objet d’une première partie. Les thèses darwiniennes suscitent d’autant plus la curiosité d’un large public, à Paris et en province, qu’elles paraissent suggérer des réponses à des questions qui sont dans l’air du temps. Une deuxième partie analyse les enjeux soulevés par le darwinisme dans la société, qui expliquent pour une bonne part son audience. Au-delà des réflexions sur l’évolution suscitées par Darwin dans la plupart des pays, le contexte politique et social entraîne des interprétations et des peurs spécifiquement françaises. Une troisième partie étudie les réticences du monde savant. Malgré l’engouement public pour le darwinisme, la science officielle reste à l’écart du débat. Finalement, il a fallu qu’un vaste débat public s’instaure et que le darwinisme devienne l’enjeu d’affrontements politiques pour que Darwin soit reconnu par les institutions académiques parisiennes. / Most works on the reception of Darwin’s theory in France have heretofore chiefly focused on the scientific community. They conclude that the theory failed to spread to the whole country. By widening the scope of this analysis to French society as a whole, we realise that, in fact, Darwin’s theory had successfully circulated in most social circles. In the first part of this study, we will analyse how the public debate contributed to introducing Darwinism in France. Darwinian theories were all the more appealing to the wider public, both in Paris and in the rest of the country, as they seemed to suggest answers to topical concerns. Then, we will study the issues raised by Darwinism in French society, and how these issues can account for Darwinism’s wide audience. In addition to the reflexions on evolution triggered by Darwin’s theory in most countries, the social and political context paved the way for specifically French interpretations and fears. The third part of this work deals with the scientific reluctance to adopt Darwin’s theory. We can therefore conclude that it is precisely the fact that Darwinism triggered a vast public debate, and became a central political issue, that allowed this theory to be acknowledged by Parisian academic institutions.

This thesis deals with the idea of using accelerator driven systems for thorium transmutation into the fissile material, which can be utilized in the accelerator driven systems and in thermal nuclear reactors. Thorium occurs on Earth only in fertile isotope Th-232. It can be converted to fissile U-233 by neutron capture and subsequent beta decay. The experimental part handles the data measured by the irradiation of four thorium samples by the secondary neutrons in the QUINTA spallation target, which was irradiated with 660~MeV protons. Reaction rates for the fission and spallation products were estimated using gamma spectroscopy and activation techniques. Furthermore, Pa-233 production rates were also determined in all experimental samples. Pa-233 and fission production rates were calculated in all experimental samples using the MCNPX transport code and evaluated nuclear data for high-energy reactions. The experimental results are of a great importance for the future investigation of thorium in the accelerator driven system concept, validation of Monte-Carlo based calculation codes and validation of high-energy nuclear models.

The Master Thesis deals with the use of thorium nuclear fuel in accelerator driven systems. Basic principle of ADS, present situation and future possibilities are described in this work. The main goal of the work is determination of neutron flux in spallation target QUINTA. In December 2013, an experiment was performed at Joint Institute for Nuclear Research, Dubna. Samples of cobalt, situated at different positions in QUINTA target, were irradiated in secondary neutron field generated by deuteron beam of energies 2 AGeV and 4 AGeV and beam of C-12 with energy 2 AGeV. The samples were measured with the use of germanium semiconductor detectors and analysed using gamma-ray spectrometry. Reaction rates of Co-59 products were determined. Neutron flux was determined in setup QUINTA on the base of experimental reaction rates. Experimental reaction rates were compared with calcula1tion of MCNPX code.