Les estuaires, de par leur position stratégique à l'interface entre les eaux continentales et les eaux marines jouent un rôle écologique de première importance et sont le siège de nombreuses activités humaines. L’estuaire de Seine est caractéristique des grands estuaires anthropisés. Le management à long terme de ces écosystèmes soumis à des pressions croissantes réside notamment en une meilleure connaissance de la dynamique spatiale et temporelle des réseaux trophiques estuariens. Le phytoplancton et le microphytobenthos sont les principaux contributeurs de la production primaire (PP) dans ces écosystèmes et sont à la base des réseaux trophiques. Ces compartiments sont souvent réduits à la teneur en chlorophylle du milieu et leur productivité n’a jamais été mesurée à l’échelle de l’estuaire de Seine. L’objectif de ces travaux a été d’estimer la PP de ces compartiments le long du gradient halin. Afin d’accéder à des mesures à une haute résolution spatiale, des mesures de fluorescence modulée (PAM) à haute fréquence ont été couplées à des mesures d’incorporation de carbone (13C) à basse fréquence. Les mesures de production primaire ont été mises en perspective avec la dynamique des paramètres physico-chimiques du milieu et la structure communautés phytoplanctoniques déterminés par différentes techniques (microscopie, cytométrie, biologie moléculaire). La dynamique du carbone excrété sous forme de TEP (Transparent Exopolymeric Particules) et EPS (Exopolymeric substances) a également été étudiée pour chacun des compartiments. Au-delà des méthodologies innovantes mises en place qui montre l’intérêt des mesures à haute fréquence dans ces écosystèmes très dynamiques, ce travail apporte une nouvelle vision de la dynamique du phytoplancton et de la richesse spécifique du microbiome estuarien et apporte une estimation fiable de la production primaire. / The estuaries play an important ecological role and are the site of many human activities because of their strategic position at the interface between continental and marine waters. Seine estuary is characteristic of large anthropized estuaries. Long-term management requires better knowledge of the spatial and temporal dynamics of the estuarine food webs. Phytoplankton and microphytobenthos are the main contributor of primary production (PP) in these ecosystems and are at the basis of trophic food webs. These compartments are often reduced to the chlorophyll concentration and their productivity has never been measured along the Seine estuary. The objective of this study was to estimate the PP of these compartments along the salinity gradient. In order to access to measurements at high spatial resolution, high-frequency measurements of modulated fluorescence (PAM) were coupled to low-frequency carbon (13C) incorporation measurements. The primary production measurements have been put into perspective with the dynamics of the physical and chemical parameters and the structure of phytoplankton communities determined by different techniques (microscopy, cytometry, molecular biology). The dynamics of carbon excreted as TEP (Transparent Exopolymeric Particles) and EPS (Exopolymeric substances) were also studied for each compartment. Beyond the innovative methodologies which demonstrate the interest of high-frequency measurements in these highly dynamic ecosystems, this work provides a new insight into the phytoplankton dynamics and the specific richness of the estuarine microbiome and provides a reliable estimate of primary production.

As pesquisas que abordam a temática de planejamento tributário, nas últimas décadas, têm identificado que o tamanho das organizações é um fator determinante à adoção de práticas de planejamento tributário. No entanto, existe certa controvérsia, nessa questão, uma vez que as pesquisas têm encontrado relações tanto positivas quanto negativas entre o tamanho das organizações e o nível de planejamento tributário praticado. Os autores justificam essa relação partindo do pressuposto do custo reputacional, em que empresas maiores possuem maior monitoramento por parte da autoridade tributária e dos demais stakeholders. Outros argumentam que as empresas maiores possuem mais recursos e mais influência política para reduzirem suas cargas tributárias. Porém, ambas análises consideram uma relação linear entre o tamanho das empresas e o nível e planejamento tributário, ignorando particularidades econômicas, financeiras e operacionais das empresas. Tal assunção, considerando todas as empresas numa única amostra, pode-se levar a conclusões controversas, ao considerar que todas as empresas possuem as mesmas estruturas e estratégias ao longo do tempo. Desse modo, essa pesquisa tem por objetivo identificar se o estágio de ciclo de vida organizacional impacta o nível de planejamento tributário. Assim, entende-se que a Teoria do Ciclo de Vida Organizacional distingue as empresas pelas suas estruturas e estratégias adotadas, a exemplo do modelo proposto por Dickinson (2011) o qual classifica os estágios de ciclo de vida a partir da necessidade e disponibilidade de recursos, por meio dos sinais dos fluxos de caixa (operacional, de investimento e de financiamento). Assim, espera-se compreender melhor a relação entre o nível de planejamento tributário e as decisões de endividamento, de intensidade de capital, de investimento em capital de giro e a interação dos mecanismos de governança corporativa nos diferentes estágios de ciclo de vida. Para a realização das análises empíricas foram empregados testes de Kruskal Wallis, regressões de dados em painel e regressões quantílicas com dados anuais das empresas brasileiras de capital aberto que compuseram o índice IBrX 100 da BM&FBOVESPA, no período de 2008 a 2015. Os resultados apontam que as empresas em estágios inicias e avançados de ciclo de vida organizacional possuem maiores níveis de planejamento tributário do que as empresas em estágio de maturidade. Considerando as métricas de planejamento tributário ETR Corrente, BTD e DVA, por ciclo de vida, nos testes de Kruskal Wallis, obteve-se que as empresas em estágios iniciais possuem níveis maiores de planejamento tributários do que as empresas da maturidade. Já nos estágios Avançados, constatou-se que as métricas ETR Corrente, Cash ETR e DVA também apresentam níveis maiores de planejamento tributário do que as empresas maduras. As análises por meio de regressões quantílicas reafirmam esses resultados, para as métricas de BTD e de ETR Corrente. Esses achados remetem à conclusão de que empresas em estágios iniciais possuem menores custos reputacionais devido a maior propensão ao risco, em virtude da sua participação de mercado ainda não estar consolidada. Já as empresas em estágios avançados, dadas as baixas oportunidades de investimento, adotam estratégias menos defensivas, uma vez que nesses estágios não dispõem de condições financeiras e econômicas favoráveis para captar recursos, pois os ativos já estão depreciados e não servem como garantia real. Portanto, as adoções de planejamento tributário nas empresas analisadas indicam que há uma relação entre as particularidades econômicas e financeiras das empresas, classificadas pelos estágios de ciclo de vida, com as estratégias tributárias adotadas para a obtenção de economia fiscal. / Research addressing the issue of tax planning in recent decades, have identified that the size of the organizations is a determining factor for the adoption of tax planning practices. However, there is some controversy in this matter, since research has found both positive and negative relationship between the size of organizations and tax planning practiced. The authors explain this relationship assuming the reputational cost, where larger firms have greater monitoring by the tax authority and other stakeholders. Others argue that larger companies have more resources and more political influence to reduce their tax burdens. However, both research suggests a linear relationship between the size of companies and the level and tax planning, ignoring economic, financial and operational peculiarities of the company. Such an assumption, considering all companies in a single sample, can lead to controversial conclusions, considering that all companies have the same structures and strategies over time. Thus, this research aims to identify the organizational life cycle stage impacts the level of tax planning. Thus, it is understood that the Organizational Life Cycle Theory recognizes companies for their structures and strategies adopted, such as the model proposed by Dickinson (2011) which classifies the stages of life cycle from the need and availability of resources through the signs of the cash flows (operating, investing and financing). Therefore, we hope to better understand the relationship between the level of tax planning and borrowing decisions, capital intensity, investment in working capital and the interaction of corporate governance mechanisms in different stages of life cycle. To carry out the empirical analysis were used Kruskal Wallis test, regressions in data panel and quantile regressions using annual data of Brazilian public companies that composed the IBrX 100 from BM&FBOVESPA, in the period 2008 to 2015. The results show that companies in initial and advanced stages of organizational life cycle have higher tax planning levels than companies in the maturity stage. Considering the tax planning metrics ETR, BTD and DVA by life cycle, in the Kruskal Wallis test was found that the companies in early stages have higher levels of tax planning than the mature companies. Already in the Advanced stages, it was found that the metrics ETR Current, Cash ETR and DVA also have higher levels of tax planning than mature companies. Analyses by quantile regressions reaffirm these results to the metrics of BTD and ETR current. These findings refer to the conclusion that companies in early stages have lower costs reputational due to higher propensity for risk, by virtue of its market share has not yet been consolidated. The companies in advanced stages, given the low investment opportunities, adopt less defensive strategies, since these stages do not have the financial and economic conditions favorable to raise funds because the assets are already depreciated and do not serve as collateral. Therefore, the adoption of tax planning in the analyzed companies indicate that there is a relationship between economic and financial characteristics of companies, classified by the stages of life cycle, with tax strategies adopted to achieve tax savings.

As pesquisas que abordam a temática de planejamento tributário, nas últimas décadas, têm identificado que o tamanho das organizações é um fator determinante à adoção de práticas de planejamento tributário. No entanto, existe certa controvérsia, nessa questão, uma vez que as pesquisas têm encontrado relações tanto positivas quanto negativas entre o tamanho das organizações e o nível de planejamento tributário praticado. Os autores justificam essa relação partindo do pressuposto do custo reputacional, em que empresas maiores possuem maior monitoramento por parte da autoridade tributária e dos demais stakeholders. Outros argumentam que as empresas maiores possuem mais recursos e mais influência política para reduzirem suas cargas tributárias. Porém, ambas análises consideram uma relação linear entre o tamanho das empresas e o nível e planejamento tributário, ignorando particularidades econômicas, financeiras e operacionais das empresas. Tal assunção, considerando todas as empresas numa única amostra, pode-se levar a conclusões controversas, ao considerar que todas as empresas possuem as mesmas estruturas e estratégias ao longo do tempo. Desse modo, essa pesquisa tem por objetivo identificar se o estágio de ciclo de vida organizacional impacta o nível de planejamento tributário. Assim, entende-se que a Teoria do Ciclo de Vida Organizacional distingue as empresas pelas suas estruturas e estratégias adotadas, a exemplo do modelo proposto por Dickinson (2011) o qual classifica os estágios de ciclo de vida a partir da necessidade e disponibilidade de recursos, por meio dos sinais dos fluxos de caixa (operacional, de investimento e de financiamento). Assim, espera-se compreender melhor a relação entre o nível de planejamento tributário e as decisões de endividamento, de intensidade de capital, de investimento em capital de giro e a interação dos mecanismos de governança corporativa nos diferentes estágios de ciclo de vida. Para a realização das análises empíricas foram empregados testes de Kruskal Wallis, regressões de dados em painel e regressões quantílicas com dados anuais das empresas brasileiras de capital aberto que compuseram o índice IBrX 100 da BM&FBOVESPA, no período de 2008 a 2015. Os resultados apontam que as empresas em estágios inicias e avançados de ciclo de vida organizacional possuem maiores níveis de planejamento tributário do que as empresas em estágio de maturidade. Considerando as métricas de planejamento tributário ETR Corrente, BTD e DVA, por ciclo de vida, nos testes de Kruskal Wallis, obteve-se que as empresas em estágios iniciais possuem níveis maiores de planejamento tributários do que as empresas da maturidade. Já nos estágios Avançados, constatou-se que as métricas ETR Corrente, Cash ETR e DVA também apresentam níveis maiores de planejamento tributário do que as empresas maduras. As análises por meio de regressões quantílicas reafirmam esses resultados, para as métricas de BTD e de ETR Corrente. Esses achados remetem à conclusão de que empresas em estágios iniciais possuem menores custos reputacionais devido a maior propensão ao risco, em virtude da sua participação de mercado ainda não estar consolidada. Já as empresas em estágios avançados, dadas as baixas oportunidades de investimento, adotam estratégias menos defensivas, uma vez que nesses estágios não dispõem de condições financeiras e econômicas favoráveis para captar recursos, pois os ativos já estão depreciados e não servem como garantia real. Portanto, as adoções de planejamento tributário nas empresas analisadas indicam que há uma relação entre as particularidades econômicas e financeiras das empresas, classificadas pelos estágios de ciclo de vida, com as estratégias tributárias adotadas para a obtenção de economia fiscal. / Research addressing the issue of tax planning in recent decades, have identified that the size of the organizations is a determining factor for the adoption of tax planning practices. However, there is some controversy in this matter, since research has found both positive and negative relationship between the size of organizations and tax planning practiced. The authors explain this relationship assuming the reputational cost, where larger firms have greater monitoring by the tax authority and other stakeholders. Others argue that larger companies have more resources and more political influence to reduce their tax burdens. However, both research suggests a linear relationship between the size of companies and the level and tax planning, ignoring economic, financial and operational peculiarities of the company. Such an assumption, considering all companies in a single sample, can lead to controversial conclusions, considering that all companies have the same structures and strategies over time. Thus, this research aims to identify the organizational life cycle stage impacts the level of tax planning. Thus, it is understood that the Organizational Life Cycle Theory recognizes companies for their structures and strategies adopted, such as the model proposed by Dickinson (2011) which classifies the stages of life cycle from the need and availability of resources through the signs of the cash flows (operating, investing and financing). Therefore, we hope to better understand the relationship between the level of tax planning and borrowing decisions, capital intensity, investment in working capital and the interaction of corporate governance mechanisms in different stages of life cycle. To carry out the empirical analysis were used Kruskal Wallis test, regressions in data panel and quantile regressions using annual data of Brazilian public companies that composed the IBrX 100 from BM&FBOVESPA, in the period 2008 to 2015. The results show that companies in initial and advanced stages of organizational life cycle have higher tax planning levels than companies in the maturity stage. Considering the tax planning metrics ETR, BTD and DVA by life cycle, in the Kruskal Wallis test was found that the companies in early stages have higher levels of tax planning than the mature companies. Already in the Advanced stages, it was found that the metrics ETR Current, Cash ETR and DVA also have higher levels of tax planning than mature companies. Analyses by quantile regressions reaffirm these results to the metrics of BTD and ETR current. These findings refer to the conclusion that companies in early stages have lower costs reputational due to higher propensity for risk, by virtue of its market share has not yet been consolidated. The companies in advanced stages, given the low investment opportunities, adopt less defensive strategies, since these stages do not have the financial and economic conditions favorable to raise funds because the assets are already depreciated and do not serve as collateral. Therefore, the adoption of tax planning in the analyzed companies indicate that there is a relationship between economic and financial characteristics of companies, classified by the stages of life cycle, with tax strategies adopted to achieve tax savings.

SAMMANFATTNING   Titel: Hållbarhetsprestationer och bolagsskatt: Komplement eller substitut? - En kvantitativ studie om publika europeiska bolag   Nivå: C-uppsats i ämnet företagsekonomi   Författare: Nicklas Johansson   Handledare: Jan Svanberg   Datum: 2017 - Januari   Syfte: Företagens sociala ansvar (CSR) är en viktig fråga för många av företagets intressenter, inte minst samhället. Hur företag betraktar bolagsskatt som en del av detta ansvar är därmed en betydelsefull fråga då statens skatteintäkter bidrar till välfärden i samhället. Syftet med denna studie är att undersöka sambandet mellan CSR och europeiska bolags effektiva skattesats, dels utifrån total CSR-prestation samt utifrån dimensioner av CSR.   Metod: Studien utgår från en positivistisk forskningsfilosofi och en deduktiv ansats. Studien har vidare en kvantitativ strategi och en longitudinell design för att samla in sekundärdata från Thomson Reuters databas Datastream för åren 2011-2016. Urvalet består av 465 publika europeiska företag för vilka data analyserats med multipla regressionsanalyser i statistikprogrammet IBM SPSS.   Resultat & slutsats: Studiens resultat indikerar ett negativt samband mellan total CSR-prestation och bolagsskatt, men att detta samband drivs av att CSR-aktiviteter inom miljödimensionen har en starkare negativ inverkan än den positiva inverkan som CSR-aktiviteter inom den sociala dimensionen bidrar med. Slutsatsen därav är att CSR och bolagsskatt både kan utgöra substitut och komplement till varandra. CSR-aktiviteter inom miljödimensionen används som substitut till bolagsskatt medan bolagsskatt betraktas som ett komplement till CSR inom den sociala dimensionen.   Förslag till fortsatt forskning: Då sambanden visat sig skilja sig åt mellan olika dimensioner bör framtida forskning inte utgå från ett samlat mått på CSR utan gå in mer i detalj på de kategorier och indikatorer som bygger upp dimensionerna. Det kan också finnas skillnader mellan industrier och land, varför det vore intressant med studier som undersöker sambandet inom respektive industritillhörighet och land i Europa.   Uppsatsens bidrag: Studien bidrar till att fylla forskningsgapet som existerat för europeiska bolag om sambandet mellan CSR och bolagsskatt samt till att undersöka sambandet på dimensionsnivå av CSR. Studien bidrar också till teorin om CSR och bolagsskatt som substitut, komplement eller oberoende aktiviteter. Slutligen kan studien öka förståelsen för hur bolags CSR- och skattebeteende hänger ihop hos myndigheter och organisationer som arbetar med lagstiftning och upprättandet av riktlinjer för hållbarhetsredovisning.   Nyckelord: CSR, ETR, ESG, socialt ansvar, hållbarhetsarbete, bolagsskatt, skattebetalningar, miljödimension, social dimension och företagsstyrningsdimension. / ABSTRACT   Title: Sustainability performance and corporate tax: Complement or substitute? - A quantitative study of public European companies   Level: Final assignment for Bachelor Degree in Business Administration   Author: Nicklas Johansson   Supervisor: Jan Svanberg   Date: 2017 - January   Aim: Corporate Social Responsibility (CSR) is an important issue for many of the company's stakeholders, not least society. How companies regard corporate tax as part of this responsibility is therefore an important issue as the state's tax revenues contribute to the welfare of society. The purpose of this study is to investigate the relationship between CSR and European companies' effective tax rate, partly based on total CSR performance as well as dimensions of CSR.   Method: The study is based on a positivistic research philosophy and a deductive approach. The study also has a quantitative strategy and a longitudinal design for collecting secondary data from the Thomson Reuters database Datastream for the years 2011-2016. The sample consists of 465 public European companies for which data were analyzed by multiple regression analyzes in the IBM SPSS statistics program.   Result & conclusions: The study's results indicate a negative relationship between total CSR performance and corporate tax, but this connection is driven by the stronger impact of CSR activities in the environmental dimension relative to the positive impact of CSR activities in the social dimension. The conclusion is that CSR and corporate tax can both be substitutes and complementary to each other. CSR activities within the environmental dimension are used as substitutes for corporate tax while corporate tax is considered as a complement to CSR in the social dimension.   Suggestions for future research: When the relationships were found to differ between different dimensions, future research should not be based on a single measure of CSR, but go into more detail on the categories and indicators that build the dimensions. There may also be differences between industries and countries, so it would be interesting with studies that examine the relationship within each industry and country in Europe.   Contribution of the thesis: The study contributes to filling the gap of research that exists for European companies on the relationship between CSR and corporate taxation and to investigate the relationship at the dimensional level of CSR. The study also contributes to the theory of CSR and corporate taxation as substitutes, complements or independent activities. Finally, the study can increase understanding of how companies' CSR and tax behavior relate to government agencies and organizations involved in legislation and the establishment of guidelines for sustainability reporting.   Keywords: ETR, Corporate Tax, Tax Payments, CSR, ESG, Social Responsibility, Sustainability, Environmental Dimension, Social Dimension and Corporate Governance Dimension.

La caractérisation de matériaux diffusants, tels les pigments, par leur indice optique complexe demeure actuellement un véritable challenge. Cet indice est la caractéristique intrinsèque au matériau, et est de ce fait, indispensable pour la simulation d'effets colorés et peut, dans le champ de la conservation-restauration, permettre la mise en place d'une méthode d'identification non-ambigüe des matériaux composant les œuvres d'art. L'objectif de cette recherche est d'élaborer une méthodologie permettant de déterminer l'indice optique complexe de ce type de matériaux. Elle constitue l'étape primordiale à l'élaboration d'une base de données d'indices optiques des pigments. Dans un premier temps, une étude théorique des phénomènes conjoint de diffusion et d'absorption résultant de l'interaction d'une onde électromagnétique avec un diffuseur, ou un ensemble de diffuseurs homogènes et sphériques, est développée. Elle consiste à définir l'influence des paramètres intrinsèques (des matériaux) et morphologiques (d'un milieu) sur les résultats obtenus lors de la résolution de l'équation du transfert radiatif (ETR) traité par la méthode 4-flux et de la théorie de Mie dans le sens direct. Dans un second temps, nous aborderons le problème inverse. À savoir, dans notre cas, remonter à l'indice complexe de particules diffusantes à partir des propriétés optiques de la couche. Nous illustrerons cette approche par l'étude d'un pigment rouge, le cinabre. Le modèle de calcul développé prend en compte les flux diffus et les flux spéculaires, mesurés sur les échantillons par spectrophotométrie couplée à une sphère d'intégration dans le domaine du visible

La complexité et le besoin en bande passante des architectures de communication avioniquene cessent de croitre avec le nombre des calculateurs et l’expansion des données échangées. Latechnologie AFDX a été introduite pour offrir des communications haut débit (100Mbps) pourles avions de nouvelle génération. Cependant, ce réseau commuté est déployé de manièreentièrement redondante, ce qui conduit à des quantités importantes de câbles, augmentant lepoids et les coûts d’intégration. Pour faire face à ces problèmes, on propose dans cette thèsel’intégration d’un réseau Ethernet en anneau comme une solution principale pour diminuerle poids et la complexité liés au câblage. Dans ce contexte, notre objectif est de concevoir etvalider un nouveau réseau de communication avionique, AeroRing, basé sur de l’EthernetGigabit avec une topologie anneau. / The inherent complexity and bandwidth requirement of avionics communication architecturesare increasing due to the growing number of interconnected end-systems and theexpansion of exchanged data. The Avionics Full Duplex Switched Ethernet (AFDX) has beenintroduced to provide high-speed communication (100Mbps) for new generation aircraft.However, this switched network is deployed in a fully redundant way, which leads to significantquantities of wires, and thus increases weight and integration costs. To cope with thesearising issues, integrating ring-based Ethernet network in avionics context is proposed in thisthesis as a main solution to decrease the wiring-related weight and complexity. In this context,our main objective is to design and validate a new avionic communication network, calledAeroRing, based on a Gigabit Ethernet technology and supporting a Full Duplex ring topology.To achieve this aim, first, a benchmarking of the most relevant Real-Time Ethernet (RTE)solutions supporting ring topologies vs avionics requirements has been conducted, and weparticularly assess the main Performance Indicators (PIs), specified in IEC 61784-2. Thisbenchmarking reveals that each existing RTE solution satisfies some requirements better thanothers, but there is no best solution in terms of all the requirements.

Pesticide use in rice farming is a common practice in the Mekong Delta and poses ecological risks to aquatic organisms, the environment, and human health. This study focused on the ecological risk assessment of pesticide use in rice farming using the PRIMET model as a decision support tool to evaluate the risks of pesticide exposure, ecotoxicity, and risk characterization, as well as employing the species sensitivity distribution (SSD) assessment model to calculate the potentially affected fraction (PAF) of species based on the computed predicted environmental concentrations (PECs) from PRIMET. The study involved collating and analyzing data on pesticide inventories and the application of 138 farmers, which formed the basis for pesticide use, farming practices,environmental variables, and ecological indicators from two provinces in the Mekong Delta: Dong Thap and Hau Giang. This study showed that pesticide use was high with a wide range of pesticide types. The ecotoxicity assessment indicated that some pesticides pose a potential acute and chronic risk to non-target organisms. The active ingredient identified as posing acute toxicity risk with an ETR >100 is the insecticide indoxacarb, which belongs to the chemical class of oxadiazine of which Arthropods were seen to be highly sensitive to when exposed making them more at risk even at very low concentrations. In contrast, fish generally exhibit moderate tolerance and are sensitive to certain chemicals. The risk characterization revealed that the ecological risks of pesticide use were higher in Dong Thap than in Hau Giang due to differences in ecological conditions, pesticide practices, and farming systems. Overall, this study highlights the need for improved pesticide management practices in rice farming in the Mekong Delta region to reduce ecological risks and protect the environment and human health. The practical and theoretical implications of this study are discussed.

Les gisements d’U de type discordance sont associés à des circulations de saumures chlorurées acides et caractérisés par des tonnages et concentrations exceptionnels ce qui amènent à s’interroger sur les processus de transport et de dépôt de l’U contribuant à leur genèse. Cette thèse est donc dédiée à des études expérimentales de la spéciation de l’U6+ et sa précipitation en UO2 par réduction en U4+ en condition hydrothermale. Concernant le transport de l’U, l’étude de la spéciation de l’U6+ dans ces fluides chlorurés (T ≤ 350°C) est réalisée par spectroscopie Raman et XAS. Les résultats montrant la coexistence de plusieurs complexes d’uranyle chlorurés UO2Cln2-n (n=0-5) dont certaines constantes de complexation sont proposées. Ainsi, la complexation de l’uranyle par les chlorures explique la forte capacité de transport en U6+ par les saumures chlorurées acides, condition nécessaire à la formation de gisements de fort tonnage. Pour le dépôt de l’U, les cinétiques de réduction de l’U6+ en U4+ par H2, CH4, Fe2+ et C-graphite sont mesurées et paramétrées en fonction de la température, de la chlorinité, du pH et de la concentration en réducteur. H2, CH4 et le C-graphite sont être très efficaces, contrairement au Fe2+. Le caractère mobile des gaz réducteurs explique en partie les minéralisations massives et focalisées observées dans ces gisements. Enfin des coefficients de partage UO2/fluide d’éléments en traces, dont certaines ETR, sont mesurés, ouvrant de nouvelles perspectives quant à (i) la compréhension de la signature des ETR caractéristiques de chaque type de gisement d’U, et (ii) la composition des fluides à l’origine des minéralisations uranifères / Circulations of acidic chloride brines are associated with unconformity-related uranium (URU) deposits. The spectacular high grade combined with the large tonnage of these deposits is at the origin of the key questions concerning the geological processes responsible for U transport and precipitation. The aim of this work is to performed experimental studies of U6+ speciation and its reduction to U4+ subsequently precipitation to UO2 under hydrothermal condition. About U transport, the study of U6+ speciation in acidic brines at high temperature is performed by Raman spectroscopy and XAS, showing the coexistence of several uranyl chloride complexes UO2Cln2-n (n=0-5). From this study, complexation constants are proposed. The strong capability of chloride to complex uranyl is at the origin of the transport of U6+ at high concentration in acidic chloride brines. Concerning U precipitation, the reactivity of four potential reductants under conditions relevant for URU deposits genesis is investigated: H2, CH4, Fe2+ and the C-graphite. The kinetics of reduction reaction is measured as a function of temperature, salinity, pH and concentration of reductant. H2, CH4, and the C-graphite are very efficient while Fe2+ is not able to reduce U6+ in same conditions. These mobile and efficient gaseous reductant could be at the origin of the extremely focus and massive character of ore in URU deposits. Finally, first partition coefficients UO2/fluid of trace elements are obtained. This last part opens-up new perspectives on (i) REE signatures interpretation for a given type of U deposit (ii) and reconstruction of mineralizing fluids composition

No description available.

No description available.