L’objectif de cette thèse porte sur l’étude de la compartimentalisation cellulaire et de la prise en charge de l’uranium (U) par les protéines cytosoliques des cellules branchiales du poisson zèbre (Danio rerio, espèce modèle en toxicologie aquatique) après exposition contrastées (chronique vs. aiguë, 20 et 250 µg.L-1) par voie directe. Cette étude a nécessité le développement, l’utilisation et le couplage d’outils analytiques de pointe (SEC, IEF hors-gel, RP-UHPLC pour la séparation, ICP-SFMS, ESI-FTMS/MS pour la détection) avec comme défis majeurs la conservation des interactions non-covalentes U biomolécule et une sensibilité maximale pour travailler à des niveaux d’exposition proches de ceux rencontrés dans l’environnement. Après extraction, 24 à 32% de la charge branchiale totale en U est contenue dans le cytosol dans lequel la distribution de l’U sur les biomolécules (en fonction de leur PM mais aussi de leur pI) diffère selon le niveau d’exposition. Enfin, une cartographie des biomolécules cibles de l’U a permis (i) de mettre en évidence une affinité particulière de l’U pour les protéines à caractère acide et/ou contenant du phosphore et (ii) d’identifier 24 protéines candidates pour lier U. / The objective of this thesis is to study the cellular compartmentalization and the chelation of uranium (U) by cytosolic proteins of gill cells of the zebrafish (Danio rerio, model species in aquatic toxicology) under different direct exposure conditions (chronic vs. acute, 20 and 250 µg.L 1). This study required the development of hyphenated techniques (SEC, IEF off-gel, RP-UHPLC for the separation, ICP-SFMS, ESI-FTMS/MS for the detection) with the main challenges of maintaining the non-covalent U-biomolecule interactions and enhancing sensitivity for the analysis of environmentally relevant samples. After extraction, 24% to 32% of the total U detected in the gills were present in the cytosolic fraction, in which the U distribution on the biomolecules (as a function of their MW and pI) varied depending on the exposure level. Finally, U target biomolecules mapping allowed us (i) to highlight a particular affinity of U for acidic and/or P-containing proteins and (ii) to identify 24 protein candidates for U binding.

Following a NEA high priority nuclear data request, an experimental campaign to measure the prompt Î3-ray emissions from 235 U has been performed. This has used the STEFF spectrometer at the new Experimental Area 2 (EAR2) within the neutron time- of-flight facility (n_TOF), a white neutron source facility at CERN with energies from thermal to approximately 1 GeV. Prior to the experimental campaign, STEFF has been optimised for the environment of EAR2. The experimental hall features a high background Î3-ray rate, due to the nature of the spallation neutron source. Thus an investigation into reduction of the background Î3-ray rate, encountered by the NaI(Tl) detector array of STEFF, has been carried out. This has been via simulations using the simulation package FLUKA. Various materials and shielding geometries have been investigated but the effects determined to be insufficient in reducing the background rate by a meaningful amount. The NaI(Tl) detectors have been modified to improve their performance in a high count rate environment, and their behaviour characterised to understand the response to higher count rates. Initial testing demonstrated that the modified detectors maintain a potential to measure Î3-ray multiplicities up to 3 counts per microsecond. However, the energy resolution fails somewhere below 1.75 counts per microsecond. The experimental campaign has produced a large amount of data. The preliminary analysis of phase one data has considered incoming neutron energies ranging from thermal to an upper limit of 1 eV, with a minimum Î3-ray energy threshold of 160 keV. Results have been achieved for the prompt fission Î3-ray multiplicity and total energy of M Î3 = 6.3 ± 0.2 and E S,Î3 = 9.0 ± 0.1 MeV respectively. Further work is ongoing by the STEFF team at Manchester to improve upon these results and analyse the remainder of the data set at higher incoming neutron energies.

Pyroprocessing, via electrorefining in a molten salt bath, is a promising treatment route for spent nuclear fuel reprocessing. In order to implement such a technology and ensure its safe operation it is vital to develop on-line techniques to understand and monitor the molten salt and its contents. These tools are technically challenging because of the high temperatures and corrosive environment experienced in molten salt media. Electrochemical, spectroscopic and spectroelectrochemical methods were developed and used to study actinide and fission product behaviour in molten LiCl-KCl eutectic. A spectroscopic furnace was designed and supporting methodology developed in order to allow the acquisition of reproducible quantitative data. The apparatus monitored the precipitation of NdCl3 by the addition of Li2CO3 and PrCl3 by the addition of Li2O in LiCl-KCl eutectic. The precipitates formed were identified as the respective LnOCl. In order to probe actinide behaviour in this hygroscopic medium, dry actinides chlorides were synthesised. The oxidation of uranium metal by BiCl3 in LiCl-KCl eutectic yielded UCl3 while neptunium and plutonium were prepared as Cs2AnCl6 via precipitation in concentrated aqueous HCl by addition of CsCl. The molar extinction coefficients for U(III), U(IV), Np(IV) and Pu(III) were obtained in LiCl-KCl eutectic at 450 áμ’C. The study of the Np(IV)/Np(III) couple via spectroelectrochemical techniques, enabled the determination of the Np(III) molar extinction coefficients. Uranium was studied in LiCl-KCl eutectic using square wave voltammetry, cyclic voltammetry and chronoabsorptometry. The electrochemical techniques benchmarked the results obtained by spectroelectrochemistry. The results from the different techniques were compared to and explained by determining the Gibbs energy and activation energy of U(III) and U(IV). It was concluded that all the mentioned techniques are suitable for the study of high temperature molten chlorides. Because of its capacity to gather numerous data parameters while minimising the number of experiments required and the quantity of material needed, spectroelectrochemical methods were highlighted as the most promising technique for future studies of radionuclides in high temperature melts.

There is great interest in understanding the contamination of stainless steel by radionuclides across the nuclear fuel cycle. Through study of uptake mechanisms, contaminant localisation and process conditions that affect uptake, decontamination strategies can be tailored to remove built-up radioactive species. This study focusses on understanding stainless steel contamination by inactive lanthanides and radioactive actinide species (U, Np, Pu and Am) in acidic media. Through depth profiling, contamination has been seen to localise on the interface of the oxide layer and the bulk metal (at depths of up to 100 nm) indicating a potentially tenacious contamination mechanism. Furthermore, contaminant was observed at greater depths within the material (up to ~300 nm), suggesting penetration beyond the passive layer in to the bulk of the material. Long term immersion studies (up to 9 months) in 12 M HNO3 have also been undertaken to investigate the effect of surface corrosion on contaminant uptake. After 3 months the surface had undergone intergranular corrosion and grain droppage was observed. Further surface analysis revealed localisation of contaminants within the steel grain boundaries and vacancies. Once again, this may necessitate a more aggressive decontamination strategy. Conditions have been identified that enhance uptake of transuranic contaminants. Highest levels of uptake were seen in polished steel samples immersed in 4 M HNO3. The Np-237, Pu-239 and Am-241 contaminated samples showed surface concentrations of up to 1.2x107, 9.4x105 and 1x109 Bq/m2, respectively. In the case of Np contamination of stainless steel, microfocus X-ray absorption spectroscopy has shown the surface-mediated reduction of Np(V) leading to Np(IV) adsorption.

The Enhanced Actinide Removal Plant (EARP) located at Sellafield, is a key facility for processing nuclear effluents in the UK. The EARP process decontaminates radioactive waste effluent by inducing the coprecipitation of Fe(III) along with any radionuclides in solution. The resulting radioactive solid phase is then separated from the decontaminated aqueous phase by ultrafiltration processes over several weeks. In the future the EARP facility's role will be expanded to treat effluents produced from nuclear decommissioning activities. However there remains a limited understanding around the mechanisms of radionuclide removal from solution and subsequent sequestration within the solid phase under conditions relevant to such industrial effluent treatment facilities. In this work, the fate of U(VI) and Th(IV) were investigated during the EARP process. XRD and TEM analyses revealed that the solid product from the EARP coprecipitation process was 2-line ferrihydrite which transformed over time to form hematite, with some goethite formation observed in the Th containing system. During this coprecipitation process U was initially removed from solution by adsorption to ferrihydrite as a bidentate, edge-sharing surface complex associated with ternary carbonate complexes. As the U containing system was aged, a maximum range of 61 - 75% U became consistently incorporated within the newly formed hematite phase for a wide range of systems containing 6 orders of magnitude total U:Fe molar ratio. Such a constant proportion of incorporated U suggests that this incorporation occurs during a particle mediated mechanism of hematite growth, such as oriented attachment. Interestingly, Th was removed from solution during the EARP coprecipitation process by a combination of both adsorption and occlusion mechanisms. EXAFS analyses revealed that the local coordination environment of Th associated with the solid phase altered considerably with increased aging time, and correspondingly Th became increasingly recalcitrant to remobilisation over time suggesting the formation of further occluded or even incorporated Th species within the transforming iron (oxyhydr)oxide phases. This thesis progresses the fundamental understanding of radionuclide interactions with iron (oxyhydr)oxide phases during coprecipitation and aging processes under conditions relevant to industrial waste treatment processes such as EARP.

Etude expérimentale et modélisation, en fonction du pH et de la concentration en NaCl, du système ternaire U(VI)-NaCl-H2O à T = 155°C et pression de vapeur saturante. Une étude expérimentale sur la solubilité de l'U(VI) dans des saumures de NaCl (0.5 – 6 M) en fonction du pH (3-13) a été réalisée à T = 155°C et pression de vapeur saturante. Les résultats obtenus ont montré que la phase solide initiale UO3 se transforme en de multiples phases solides d'uranates de sodium de formule générale Na2xUyO(x+3y) hydratés dont le rapport molaire Na/U croit avec l'accroissement du pH et de la concentration de NaCl. La solubilité de l'U(VI) est directement gouvernée par trois paramètres physico-chimiques : le pH, le ligand Cl- et le cation Na+. Les deux premiers favorisent fortement la solubilité de l'U(VI) sous forme de complexes d'U(VI) avec les ligands OH- et Cl- à pH = 4. A la différence des deux premiers paramètres, le cation Na+ inhibe la solubilité de l'uranium (VI) en le précipitant sous forme de multiples composés d'uranates de sodium très peu solubles. Les résultats de mesures de solubilité de l'U(VI) obtenues servent de base de données de référence pour calculer les variations de la concentration de chaque complexe soluble d'U(VI) en fonction de deux paramètres, pH et [Na], à l'aide d'une équation de type exponentielle d’un paraboloïde elliptique négatif. Un modèle empirique a également été mis au point, à partir des équations de Pitzer, afin de déterminer, de manière continue, les variations des divers paramètres physico-chimiques des ions solubles présents dans une saumure de NaCl en fonction de quatre paramètres : pH, [Na], T et P du milieu réactionnel. Ce modèle est valable jusqu’à [NaCl] = 6M, T = 300°C et P = 100 MPa. / An experimental study on the solubility of U(VI) in concentrated (0.5-6.0 M) NaCl solutions as a function of pH (3-13) has been realized at 155°C and saturation vapor pressure. The obtained results indicate that the initial solid phase UO3 initial solid phase is transformed into multiple solid phases of hydrated sodium uranates with general formula Na2xUyO(x+3y), the Na/U molar ratio of which increases with increasing pH and NaCl concentration. The solubility of U(VI) is directly dependant of three physico-chemical parameters : the pH, the Cl- ligand, and the Na+ cation. The first two parameters strongly favour the U(VI) solubility in the form of aqueous U(VI) complexes with the OH-and Cl- ligands at a pH = 4, while the Na+ cation inhibits the solubility of U(VI) as it precipitates into various low solubility sodium uranates. The results of solubility measurements obtained for U(VI) serve as a reference data base for the calculation of concentration variations of each soluble U(VI) complex as a function of two parameters, pH and [Na], with the use of a negative elliptic paraboloïd exponential. An empirical model has also been developed from the Pitzer equations in order to determine, in a continuous way, the variations of various physico-chemical parameters of the soluble ions present in the concentrated NaCl solutions as a function of four parameters: pH, [Na], T and P of the reaction medium. This model is valid up to [NaCl] = 6M, T = 300°C and P = 100 MPa.

abstract: Variations of 238U/235U in sedimentary carbonate rocks are being explored as a tool for reconstructing oceanic anoxia through time. However, the fidelity of this novel paleoredox proxy relies on characterization of uranium isotope geochemistry via laboratory experimental studies and field work in modern analog environmental settings. This dissertation systematically examines the fidelity of 238U/235U in sedimentary carbonate rocks as a paleoredox proxy focusing on the following issues: (1) U isotope fractionation during U incorporation into primary abiotic and biogenic calcium carbonates; (2) diagenetic effects on U isotope fractionation in modern shallow-water carbonate sediments; (3) the effects of anoxic depositional environments on 238U/235U in carbonate sediments. Variable and positive shifts of 238U/235U were observed during U uptake by primary abiotic and biotic calcium carbonates, carbonate diagenesis, and anoxic deposition of carbonates. Previous CaCO3 coprecipitation experiments demonstrated a small but measurable U isotope fractionation of ~0.10 ‰ during U(VI) incorporation into abiotic calcium carbonates, with 238U preferentially incorporated into the precipitates (Chen et al., 2016). The magnitude of U isotope fractionation depended on aqueous U speciation, which is controlled by water chemistry, including pH, ionic strength, carbonate, and Ca2+ and Mg2+ concentrations. Based on this speciation-dependent isotope fractionation model, the estimated U isotope fractionation in abiotic calcium carbonates induced by secular changes in seawater chemistry through the Phanerozoic was predicted to be 0.11–0.23 ‰. A smaller and variable U isotope fractionation (0–0.09 ‰) was observed in primary biogenic calcium carbonates, which fractionated U isotopes in the same direction as abiotic calcium carbonates. Early diagenesis of modern shallow-water carbonate sediments from the Bahamas shifted δ238U values to be 0.270.14 ‰ (1 SD) higher than contemporaneous seawater. Also, carbonate sediments deposited under anoxic conditions in a redox-stratified lake—Fayetteville Green Lake, New York, USA— exhibited elevated δ238U values by 0.160.12 ‰ (1 SD) relative to surface water carbonates with significant enrichments in U. The significant U isotope fractionation observed in these studies suggests the need to correct for the U isotopic offset between carbonate sediments and coeval seawater when using δ238U variations in ancient carbonate rocks to reconstruct changes in ocean anoxia. The U isotope fractionation in abiotic and biogenic primary carbonate precipitates, during carbonate diagenesis, and under anoxic depositional environments provide a preliminary guideline to calibrate 238U/235U in sedimentary carbonate rocks as a paleoredox proxy. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

Groundwater is a very scarce and sensitive resource in many parts of the World especially in Africa and in arid areas such as Western Namibia. The Western Namibia hosts the Erongo region which named the Uranium Province world class deposits of uranium and high exploration and mining in the area. The majority of the Erongo region in Namibia depends on groundwater from the Swakop River compartment, hence, is important to understand the mining effects to this precious resource. The safe guarding of groundwater pollution from various sources including mining is vital. The extensive exploration and mining activities in the area raised environmental concerns especially threat to the huge ground water resources and the Aquatic systems in the proximity and hydraulically connected to the Swakopmund and Khan catchments. The study looked the impact of uranium mining in the area specifically focusing on the impact of the unlined uranium tailing dams at Langerheinrich uranium mine on the Gawib River a tributary of the Swakop River. The study reviewed the previous work on the Langerheinrich Uranium Mine that is related to groundwater pollution including the Environmental Impact Assessments carried out by the consultants for the mine. Ten water samples were obtained for the purpose of this study, the samples consists of the groundwater samples, recycled water and the fresh water supply to the mine. The hydrochemistry, stable isotopes and tritium results show that there is contamination from the unlined uranium tailings into the Gawib shallow aquifer system. This could spread to deeper aquifer systems mainly through major structures such as fractures and faults in the area. The contamination plume will also spread downstream to the Gawib River towards the Swakop River unless serious mitigation measures are put in place. There is also a very high risk of the plume to reach the Atlantic Ocean by seasonal flash floods that occurs in the area approximately every after few years. Keywords: Uranium Province, Langerheinrich uranium mine, Groundwater, Pollution, unlined tailings and Gawib River

Dans le cadre de la loi programme relative à la gestion durable des matières et déchets radioactifs du 28 Juin 2006, la France a choisi comme solution de référence le retraitement de ses combustibles usés et le stockage en milieu géologique profond des déchets ultimes vitrifiés. Néanmoins, les études relatives à un stockage direct des combustibles usés se poursuivent par mesure de précaution. Le concept de stockage prévoit de conditionner les assemblages de combustibles usés dans un surconteneur en acier dont l'étanchéité est garantie sur une durée spécifiée de l'ordre de 10 000 ans. L'arrivée d'eau au contact du combustible après dégradation du conteneur initie les processus de dégradation de la matrice UO2 conduisant au relâchement des radionucléides. Il est de ce fait, important de connaître et de comprendre le mécanisme d’altération de la matrice UO2. Pour cela, des techniques électrochimiques (voltammétries cyclique et linéaire) couplées à des techniques de caractérisation du solide et de la solution (XPS, ICP-MS) ont été utilisées.Une étude thermodynamique et bibliographique du système U(VI)/UO2(s) a permis de mettre en évidence l’influence des conditions physico-chimiques de la solution sur le système, et de mettre en évidence les différents mécanismes proposés pour décrire l’oxydation/dissolution d’UO2 dans différents milieux (non-complexant, carbonaté et argileux). L’étude de l’oxydation/dissolution d’UO2 en milieu acide non-complexant (NaCF3SO3 0,1 mol/L à pH = 3), milieu où le couple UO22+/UO2 prédomine et où la formation de précipités est limitée voire évitée, a mis en évidence un mécanisme en deux étapes électrochimiques et un modèle caractéristique de l’oxydation d’UO2 en milieu acide non-complexant. Ensuite, l’étude en milieu neutre non-complexant (NaCl 0,05 mol/L à pH = 7,5) a mis en évidence un mécanisme en deux étapes électrochimiques et une étape chimique (EEC) dans lequel les deux étapes électrochimiques sont similaires à celles proposées en milieu acide. Enfin, une première approche de l’oxydation/dissolution d’UO2 a été réalisée en milieu carbonaté (NaCl 0,05 mol/L + NaHCO3 2.10-3 mol/L à pH = 7,5) puis en présence d’une phase argileuse (MX80) dans la solution d’étude. Ces études ont respectivement montré l’influence des carbonates et de la MX80 sur la dissolution du dioxyde d’uranium. / Within the framework of the geological disposal of spent nuclear fuel, research on the long term behavior of spent fuel is undertaken and in particular the study of mechanisms of UO2 oxidation and dissolution in water-saturated host rock. Under the law program on the sustainable management of radioactive materials and waste of June 28, 2006, France was chose as the reference solution the retreatment of spent fuel and disposal in deep geological repository of vitrified final waste. Nevertheless, studies on a direct disposal of spent fuel will continue for safety. The disposal concept provides for conditioning spent fuel in a steel container whose seal is guaranteed for a period specified in the order of 10,000 years. It is also reasonable to assume that the groundwater comes into contact with the fuel after the deterioration of container and lead to the UO2 matrix degradation and the release of radionuclides. The oxidation/dissolution of UO2 has been studied by means electrochemical methods coupled to XPS and ICP-MS measurements.A thermodynamic and bibliographic study of U(VI)/UO2(s) system allowed to show the effect of the physical and chemical conditions of the solution on the system, and to show the different mechanisms proposed to describe the oxidation and the dissolution of the uranium dioxide in different media (non-complexing, carbonate and clay). The study of the oxidation/dissolution of UO2 in acidic and non-complexing media (0.1 mol/L NaCF3SO3, pH = 3), where UO22+/UO2(s) predominates and the formation of precipitates is limited or even avoided, showed a mechanism with two electrochemical steps and a model characteristic of UO2 oxidation in acidic non-complexing media. Then, the study in neutral non-complexing media (0.05 mol/L NaCl, pH = 7.5) showed a mechanism with two electrochemical steps and one chemical step (EEC) in which both electrochemical steps are similar to those proposed in acidic media. Finally, a first approach of the UO2 oxidation/dissolution was carried out in carbonate media (0.05 mol/L NaCl + 2x10-3 mol/L NaHCO3, pH = 7.5) and in the presence of clay (MX80) in the solution. These studies have respectively shown the influence of carbonates and MX80 on the dissolution of uranium dioxide.

Metal-organic nanotubular (MON) materials have garnered significant attention in the recent years not only due to the aesthetic architecture but also due to the interesting chemical and physical properties that have been reported for these compounds. The number of MONs reported in the literature are limited compared to metal organic frameworks due to synthetic challenges and difficulties in crystal engineering. These types of materials are of interest given their one-dimensional channels that lead to their potential application in advanced membrane technologies. In Forbes group, a uranium-based metal-organic nanotube (UMON) was synthesized using zwitterionic like iminodiacetic acid (IDA) as the ligand. IDA ligand chelates to the U(VI) metal center in a tridentate fashion and doubly protonated IDA linker connects the neighboring uranyl moieties until it forms hexameric macrocycles. These macrocycles stack into a nanotubular array due to supramolecular interactions. Single crystal X-ray diffraction studies displayed there are two crystallographically unique water molecules that can be removed reversibly at 37 °C. UMON indicated selectivity to water, the selectivity of this material was analyzed using solvents with different polarities, sizes, and shapes. In the current body of work, dehydrated UMON crystallites were exposed to these solvents (in liquid and vapor phase) and studied using TGA coupled FTIR set up, confirming the highly selective nature of UMON. Kinetic studies were also conducted using an in-house built vapor adsorption setup confirmed the water uptake rate of the nanotube depends on the humidity of the environment. Uptake rates were estimated using a simple kinetic model and indicated enhanced hydration compared to other porous materials. One of the hypotheses regarding the interesting properties of UMON is that the uranium metal center might play a central role in the selectivity of this material. To test this hypothesis, a similar uranium based metal-organic nanotube containing 2,6-pyridine dicarboxylic acid (UPDC) as the ligand was synthesized and its properties were compared to that of the UMON material. UPDC did display some selectivity based upon size exclusion but did not exhibit the same selectivity to water that is observed for UMON. Different transition metals were also incorporated into the nanotubular structures to determine the influence of dopants on the observable properties. Only small amounts of transition metal dopants were incorporated into the structure, but it increased the stability under high humid environment. Attempts to incorporate transition metal dopants in the UPDC led to the formation of novel chain structures.