Le thème général de cette thèse porte sur le comportement des sols et des roches tendres partiellement saturés. Cette condition de saturation partielle entraîne une complexification du comportement et une augmentation des couplages entre les différents phénomènes existants. Nous avons travaillé sur deux applications différentes qui présentent en fait beaucoup de similitudes. Ce travail s'est effectué principalement dans le code aux éléments finis LAGAMINE. Le premier domaine d'étude concerne le stockage de déchets nucléaires de haute activité. Pour ces derniers, le concept de dépôts dans des couches géologiques profondes a été développé afin de protéger les êtres humains et leur environnement des effets néfastes de la radioactivité. L'idée est de construire un système de galeries dans lesquelles seront placés les déchets vitrifiés ; une barrière d'étanchéité ouvragée (généralement des blocs d'argile compactée) remplira le reste de la galerie et assurera un complément à une barrière géologique naturelle. Pour dimensionner ce système complexe, il est nécessaire de bien connaître les caractéristiques hydrogéologiques, thermiques, mécaniques, chimiques et biologiques, ainsi que de comprendre les processus couplés qui ne manqueront pas de s'y développer. C'est la raison pour laquelle se sont créés des URL (Underground Research Laboratories) dans les couches géologiques potentielles, comme le SCK-CEN à Mol. Les modèles numériques viennent en complément des études expérimentales réalisées dans ces laboratoires et aident à la compréhension des mesures effectuées. En effet, le comportement de la barrière d'étanchéité est très complexe, impliquant des phénomènes thermo-hydro-mécaniques prenant place durant l'échauffement (les déchets dégagent toujours une certaine quantité d'énergie) et l'hydratation (par la formation hôte) de la barrière argileuse ouvragée. Dans ce cadre, nous avons développé un modèle d'écoulement multiphasique avec changement de phase ; il permet d'étudier les transferts hydriques et de chaleur se produisant dans la zone proche de la galerie. Les couplages sont nombreux : les variations de température influencent les propriétés des fluides, ces derniers transportent de la chaleur lors de leur déplacement (flux convectifs), ces conditions de saturation partielle (liées à la succion) induisent également des modifications du comportement mécanique de l'argile. Enfin, dans ces milieux très peu perméables, la prise en compte des transferts hydriques en phase vapeur est primordiale. Ces développements ont été réalisés dans le cadre du projet européen CATSIUS CLAY, ce qui nous a permis une comparaison avec d'autres codes de calculs et la validation de notre travail. Le deuxième domaine d'étude est la subsidence des réservoirs pétroliers de mer du Nord. En effet, certains réservoirs se situent dans des couches de craie à plusieurs milliers de mètres sous le niveau de la mer et ils sont exploités à partir d'installations off-shores. La production du pétrole induit une déplétion du réservoir qui s'accompagne d'une compaction ; cette dernière se répercute jusqu'au fond marin et cela met en danger les stations off-shores. La solution actuellement mise en uvre est l'injection d'eau dans le réservoir afin de le repressuriser et de diminuer ainsi la compaction. Malheureusement, cela a provoqué dans ces formations crayeuses un tassement supplémentaire ! Toutefois, celui-ci n'a pas que des aspects négatifs ; la compaction additionnelle permet une récupération secondaire du pétrole, qui n'aurait pu être obtenue autrement sinon. Il est donc très intéressant de pouvoir contrôler le tassement des couches réservoir. Dans le cadre des projets européens PASACHALK, nous avons développé une loi constitutive élastoplastique suivant l'idée que la sensibilité à l'eau d'une craie initialement saturée d'huile est reliée à l'effet de la succion. Cette dernière comprend des effets purement capillaires mais d'autres également (osmotiques par exemple). Nous avons donc construit un modèle multimécanisme avec influence de la succion, en utilisant les outils et concepts développés en mécanique des sols non-saturés (l'argile notamment). On voit dès lors que les modèles de l'argile de scellement et ceux de la craie de réservoir présentent de nombreuses similitudes ! Cette recherche a été facilitée par le fait qu'une craie, similaire à celles des réservoirs de Mer du Nord, affleure dans notre pays ; on l'exploite notamment dans la carrière de Lixhe, en région liégeoise. Cette craie possède les mêmes caractéristiques et propriétés que celles des formations du réservoir. La seule différence réside dans le fait qu'il n'y a jamais eu de pétrole dans ses pores ! L'analyse de l'ensemble des expérimentations réalisées sur ce matériau, nous a permis de mettre en évidence les caractéristiques du comportement de la craie de manière à calibrer notre loi. Enfin, des essais d'injection dans des échantillons nous fournissent un moyen de validation de nos modèles. Ainsi, nous avons réalisé des simulations à l'échelle du réservoir qui ont confirmé que la variation de succion est bien une explication de certaines compactions dans les réservoirs pétroliers.

A Deep Geologic Repository is proposed for a site on the eastern margin of the Michigan Basin at a depth of 680 metres in the Cobourg Formation. A study of the paleo-hydrogeolgical conditions for the area was conducted using numerical simulation of the distribution of natural tracers and the observed hydraulic head. To conduct the study, simulations of the groundwater flow systems were developed for hydraulic head generated from glacial loading cycles to study its effects on advective solute transport. The hydro-mechanical loading during the glacial cycles is assessed using numerical analysis of coupled stress and porewater pressure. The effect of density-dependent flow was assessed in a second study to estimate the degree of penetration of glacially-derived water driven into the basin during periods of glacial loading. Numerical simulations were used to explore the potential freshwater invasion pathways under a variety of conditions. Finally, profiles of 18O and 2H measured in porewater were combined with our understanding of the paleo-hydrogeological conditions derived from the studies above to test the hypothesis that solute transport was diffusion-dominated in this setting. A series of pure diffusion and advection-diffusion models were developed and the results were compared with profiles of natural water isotopes obtained from the study area. The results of the hydro-mechanical study of glacial impact show the development of significant underpressure during the interstadial periods, especially in the lowest permeability formations. The results also show that the formations have not reached hydrostatic conditions at the present time. These results were verified by comparison to measured environmental heads obtained from the study site. The density-dependent modeling showed that freshwater is capable of reaching the location of the study site through several permeable features. The transport simulations showed that the evolution time starting from a uniform initial condition, and using boundary conditions that are defined by freshwater invasion at several depths agrees with the hydro-geological history of this part of the Basin. The results also show the importance of advection on solute transport from the upper and lower boundaries even in rock of extremely low permeability. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-05-30 10:18:01.286

Welds in materials intended for service at temperatures above the creep activation temperature often develop damage before the base metal. The weld is a discontinuity in the material and stresses and strains often accumulate in the weld. Knowledge of the properties of the weld is essential to the safe operation of the component containing the weld. The work in this thesis has been aimed at the study of welds in service at high temperatures: The work is divided into two main chapters. The first chapter deals with welds in stainlesssteels and dissimilar metal welds and includes three papers, and the second chapter dealswith welds in copper intended for nuclear waste disposal, also including three papers. Common to both parts is that the temperature is high enough for most of the damage in the welds to result from creep. In the first part the role of the weld microstructure on the creep crack propagation properties has been studied. Experiments using compact tension specimens have been performed on service exposed, low alloyed heat resistant steels. The results show good correlation with the crack tip parameter, C*, during steady state creep crack growth. The test methodology has also been reviewed and sensitive test parameters have been identified. The results from the creep crack propagation tests on service exposed material has been modeled using uniaxial creep data on both new and ex-service material. The development of the weld microstructure in a dissimilar metal weld between two heat resistant steels has also been investigated. A weld was made between one ferritic and one martensitic steel and the development of the microstructure during welding and post-weldheat treatments has been studied. The results show that the carbon depleted zone that develops near the weld metal in the lower alloyed steel depends on the formation and dissolution of the M23C6-carbide. Variations of the weld parameters and the post-weld heat treatment affect the size and shape of this zone. The process has been successfully modeled by computer simulation. The second part focuses on oxygen free copper intended for nuclear waste disposal containers. The containers are made with an inner core of cast nodular iron and an outer core of copper for corrosion protection. The copper shell has to be welded and two weld methods has been tested, electron beam welding and friction stir welding. Creep specimens taken from both weld types have been tested as have base metal specimens. The technical specifications of the waste canisters demand that the creep ductility of both the copper shell and the welds has to be as high as possible. The creep test results show that base material doped with at least 30 ppm phosphorus has high creep ductility, and friction stir welds made from this material has almost as high creep strength and creep ductility. Copper without phosphorus does not exhibit the same ductility. The creep properties evaluated from testing has been modeled and extrapolated for the intended purpose / QC20100719

Nuclear power generation is being regarded as a solution to ever increasing demand for electricity, and concerns over global warming and climate change due to the use of fossil fuels. Although nuclear power generation is considered to be reliable, economical, clean, and safe, the wastes produced from the nuclear fuel cycle are not, and can remain hazardous for hundreds of thousands of years. An international consensus has developed over the past several decades that deep geologic disposal of low, intermediate, and high level radioactive wastes is the best option to protect the biosphere. In this thesis, both regional scale and sub-regional scale models are created to simulate groundwater flow and transport for a representative Canadian Shield setting, honouring site-specific topography and surface water features. Sub-surface characteristics and properties are derived from numerous geoscience studies. In addition, a regional scale model is developed, centred on the Bruce Nuclear Power Development (BNPD) site near Tiverton, Ontario, and located within the Michigan Basin. Ontario Power Generation (OPG) has proposed a Deep Geologic Repository (DGR) for low & intermediate level waste (L&ILW) at the BNPD site. Paleoclimate simulations using various combinations of parameters are performed for both the Canadian Shield Sub-Regional model, and the Michigan Basin Regional model. Fracture zone permeability is a very important parameter when modelling crystalline rock settings. Migration of a unit tracer representing glacial recharge water can occur to depth in fractures of high permeability. Representative rock compressibility values are necessary as compressibilities are used to calculate storage coefficients, and the one-dimensional loading efficiency; these affect the subsurface propagation of elevated pore pressures due to glacial loading at surface. Coupled density-dependent flow and transport in paleoclimate simulations affects deep flow systems and provides a measure of flow stability, as well as increasing the mean life expectancy at depth. Finally, hydromechanical coupling is a very important mechanism for reducing vertical hydraulic gradients during a glaciation event when a hydraulic boundary condition equal to the pressure at the base of an ice-sheet is applied at ground surface. Pore water velocities are reduced, thereby retarding migration of surface waters into the subsurface environment.

Nuclear power generation is being regarded as a solution to ever increasing demand for electricity, and concerns over global warming and climate change due to the use of fossil fuels. Although nuclear power generation is considered to be reliable, economical, clean, and safe, the wastes produced from the nuclear fuel cycle are not, and can remain hazardous for hundreds of thousands of years. An international consensus has developed over the past several decades that deep geologic disposal of low, intermediate, and high level radioactive wastes is the best option to protect the biosphere. In this thesis, both regional scale and sub-regional scale models are created to simulate groundwater flow and transport for a representative Canadian Shield setting, honouring site-specific topography and surface water features. Sub-surface characteristics and properties are derived from numerous geoscience studies. In addition, a regional scale model is developed, centred on the Bruce Nuclear Power Development (BNPD) site near Tiverton, Ontario, and located within the Michigan Basin. Ontario Power Generation (OPG) has proposed a Deep Geologic Repository (DGR) for low & intermediate level waste (L&ILW) at the BNPD site. Paleoclimate simulations using various combinations of parameters are performed for both the Canadian Shield Sub-Regional model, and the Michigan Basin Regional model. Fracture zone permeability is a very important parameter when modelling crystalline rock settings. Migration of a unit tracer representing glacial recharge water can occur to depth in fractures of high permeability. Representative rock compressibility values are necessary as compressibilities are used to calculate storage coefficients, and the one-dimensional loading efficiency; these affect the subsurface propagation of elevated pore pressures due to glacial loading at surface. Coupled density-dependent flow and transport in paleoclimate simulations affects deep flow systems and provides a measure of flow stability, as well as increasing the mean life expectancy at depth. Finally, hydromechanical coupling is a very important mechanism for reducing vertical hydraulic gradients during a glaciation event when a hydraulic boundary condition equal to the pressure at the base of an ice-sheet is applied at ground surface. Pore water velocities are reduced, thereby retarding migration of surface waters into the subsurface environment.

Flow instabilities occur at all scales in planetary systems. In this thesis we examine three cases of such instabilities, on three very different length scales. In the first part, we test the idea that Archean granite-greenstone belts (GGBs) form by crustal diapirism, or Rayleigh-Taylor instabilities. GGBs are characterized by large granitic domes (50-100 km in diameter) embedded in narrow keel-shaped greenstones. They are ubiquitous in Archean (> 2.5 Ga) terrains, but rare thereafter. We performed finite element calculations for a visco-elastic, temperature-dependent, non-Newtonian crust under conditions appropriate for the Archean, which show that dense low-viscosity volcanics overlying a felsic basement will overturn diapirically in as little as 10 Ma, displacing as much as 60 % of the volcanics to the lower crust. This surprisingly fast overturn rate suggests that diapiric overturn dominated crustal tectonics in the hot conditions of the Early Earth, becoming less important as the Earth cooled. Moreover, the deposition of large volumes of wet basaltic volcanics to the lower crust may provide the source for the formation of the distinctly Archean granitic rocks which dominate Earth's oldest continents. The second part examines the origin of Venusian coronae, circular volcanic features unique to Venus. Coronae are thought to result from small instabilities (diapirs) from the core-mantle boundary, which are typical of stagnant-lid convection. However, most young coronae are located in a region surrounded by long-lived hotspots, typical of a more active style of mantle convection. Using analogue experiments in corn syrup heated from below, we show that the co-existence of diapirs and long-lived mantle plumes are a direct consequence of the catastrophic overturn of the cold Venusian lithosphere thought to have occurred ~ 700 Ma ago. In the last part we analyze the thermal effect of fluid flow through a full-scale experiment testing clay and concrete tunnel seals in a Deep Geological Repository for nuclear was finite element software, we were able to show that the formation of fissures in the heated chamber between the two seals effectively limited heat flow, and could explain the discrepancy between the predicted and measured temperatures.

Flow instabilities occur at all scales in planetary systems. In this thesis we examine three cases of such instabilities, on three very different length scales. In the first part, we test the idea that Archean granite-greenstone belts (GGBs) form by crustal diapirism, or Rayleigh-Taylor instabilities. GGBs are characterized by large granitic domes (50-100 km in diameter) embedded in narrow keel-shaped greenstones. They are ubiquitous in Archean (> 2.5 Ga) terrains, but rare thereafter. We performed finite element calculations for a visco-elastic, temperature-dependent, non-Newtonian crust under conditions appropriate for the Archean, which show that dense low-viscosity volcanics overlying a felsic basement will overturn diapirically in as little as 10 Ma, displacing as much as 60 % of the volcanics to the lower crust. This surprisingly fast overturn rate suggests that diapiric overturn dominated crustal tectonics in the hot conditions of the Early Earth, becoming less important as the Earth cooled. Moreover, the deposition of large volumes of wet basaltic volcanics to the lower crust may provide the source for the formation of the distinctly Archean granitic rocks which dominate Earth's oldest continents. The second part examines the origin of Venusian coronae, circular volcanic features unique to Venus. Coronae are thought to result from small instabilities (diapirs) from the core-mantle boundary, which are typical of stagnant-lid convection. However, most young coronae are located in a region surrounded by long-lived hotspots, typical of a more active style of mantle convection. Using analogue experiments in corn syrup heated from below, we show that the co-existence of diapirs and long-lived mantle plumes are a direct consequence of the catastrophic overturn of the cold Venusian lithosphere thought to have occurred ~ 700 Ma ago. In the last part we analyze the thermal effect of fluid flow through a full-scale experiment testing clay and concrete tunnel seals in a Deep Geological Repository for nuclear was finite element software, we were able to show that the formation of fissures in the heated chamber between the two seals effectively limited heat flow, and could explain the discrepancy between the predicted and measured temperatures.

In this thesis, fractured rock masses are treated asequivalent continua for large-scale analyses of rockengineering projects. Systematic developments are made for thedetermination of equivalent mechanical and hydraulic propertiesof fractured rock masses using a hybrid discrete fracturenetwork - distinct element method (DFN-DEM) approach. Thedetermined equivalent properties are then used for a far-fieldfinite element analysis of the thermo-mechanical impacts on thestress, deformation and permeability of fractured rockssurrounding a hypothetical geological repository of nuclearwaste. The geological data were extracted from the results ofan extensive site investigation programme at Sellafield, UK,conducted by Nirex UK Ltd. The scale dependencies of the hydraulic and mechanicalproperties were investigated by using multiple realizations ofthe fracture system geometry with increasing model sizes untilproperly defined hydraulic and mechanical representativeelementary volumes (REVs) were reached. The validity of thesecond order permeability tensor and the fourth-ordermechanical compliance tensor were tested for continuum analysesat larger scales. The REV was determined to be around 5 m formechanical and hydraulic data in this study. Analysis of the stress-dependent mechanical and hydraulicproperties shows that the effect of rock stresses is crucial.The elastic moduli increase significantly with the increase ofstress and an empirical equation of stress-dependent elasticmodulus is suggested based on results of numerical experiments.Calculations of the Poisson's ratios suggest greater valuesthan are normally assumed in practice. Depending on the stateof stress, permeability decreases or increases with increasingcompressive stress. Stress-induced flow channeling effect iscaptured by numerical modeling for the first time and detailedmechanisms of shear dilation of fractures are provided. Basedon the numerical experiments, a set of empirical equations wassuggested for the stress-dependent permeability, consideringboth normal deformation and shear dilation of fractures. Thermo-mechanical impact on the performance of ahypothetical repository at a far-field scale (5 km by 1 km) wasinvestigated with the stress-dependent equivalent propertiesdetermined at the REV scale. This analysis shows thatmechanical responses vary significantly depending on how themechanical properties were determined. The change ofpermeability due to the thermal loading is, however, notsignificant in this particular case. The thesis provides a framework for systematic analysis oflarge-scale engineering applications in fractured rock masses,such as geological repositories of nuclear wastes. Keyword:Fractured rock masses, Equivalent Continuum,Discrete Fracture Network (DFN), Distinct Element Method (DEM),Finite Element Method (FEM), Nuclear Waste Disposal, CoupledThermo-Hydro-Mechanical Processes

<p>In this thesis, fractured rock masses are treated asequivalent continua for large-scale analyses of rockengineering projects. Systematic developments are made for thedetermination of equivalent mechanical and hydraulic propertiesof fractured rock masses using a hybrid discrete fracturenetwork - distinct element method (DFN-DEM) approach. Thedetermined equivalent properties are then used for a far-fieldfinite element analysis of the thermo-mechanical impacts on thestress, deformation and permeability of fractured rockssurrounding a hypothetical geological repository of nuclearwaste. The geological data were extracted from the results ofan extensive site investigation programme at Sellafield, UK,conducted by Nirex UK Ltd.</p><p>The scale dependencies of the hydraulic and mechanicalproperties were investigated by using multiple realizations ofthe fracture system geometry with increasing model sizes untilproperly defined hydraulic and mechanical representativeelementary volumes (REVs) were reached. The validity of thesecond order permeability tensor and the fourth-ordermechanical compliance tensor were tested for continuum analysesat larger scales. The REV was determined to be around 5 m formechanical and hydraulic data in this study.</p><p>Analysis of the stress-dependent mechanical and hydraulicproperties shows that the effect of rock stresses is crucial.The elastic moduli increase significantly with the increase ofstress and an empirical equation of stress-dependent elasticmodulus is suggested based on results of numerical experiments.Calculations of the Poisson's ratios suggest greater valuesthan are normally assumed in practice. Depending on the stateof stress, permeability decreases or increases with increasingcompressive stress. Stress-induced flow channeling effect iscaptured by numerical modeling for the first time and detailedmechanisms of shear dilation of fractures are provided. Basedon the numerical experiments, a set of empirical equations wassuggested for the stress-dependent permeability, consideringboth normal deformation and shear dilation of fractures.</p><p>Thermo-mechanical impact on the performance of ahypothetical repository at a far-field scale (5 km by 1 km) wasinvestigated with the stress-dependent equivalent propertiesdetermined at the REV scale. This analysis shows thatmechanical responses vary significantly depending on how themechanical properties were determined. The change ofpermeability due to the thermal loading is, however, notsignificant in this particular case.</p><p>The thesis provides a framework for systematic analysis oflarge-scale engineering applications in fractured rock masses,such as geological repositories of nuclear wastes.</p><p><b>Keyword:</b>Fractured rock masses, Equivalent Continuum,Discrete Fracture Network (DFN), Distinct Element Method (DEM),Finite Element Method (FEM), Nuclear Waste Disposal, CoupledThermo-Hydro-Mechanical Processes</p>

The ultimate goal of this work is providing insights into fundamental (physico-) chemical (redox) behavior of hexavalent uranium (U(VI)), trivalent europium (Eu(III)) and selenium (Se), and upon their interaction with ubiquitous small biomolecules (in case of U(VI) and Eu(III)) or alkaline earth metal ions (in case of Se(IV) and Se(VI)) by application of Nuclear Magnetic Resonance (NMR) spectroscopy. NMR spectroscopy is a powerful method proving its usefulness also to environmental and nuclear waste related studies in aqueous solutions by determination of (potential) binding sites, molecular structures (even conformation and configuration) as well as intra- and intermolecular dynamics, (redox) reaction pathways and mechanisms. The present work comprises extensive NMR spectroscopic investigations in aqueous (D2O) solutions on (i) glutathione (GSH) and glutathione disulfide (GSSG) interactions with trivalent lanthanides (Ln(III), particularly Eu(III)) and U(VI), (ii) molecular structures of citrate (Cit) complexes of U(VI), and their reactions upon light-irradiation, as well as (iii) pH- and temperature-dependent speciation of selenium oxyanions, i.e., Se(VI) (selenate) and Se(IV) (selenite and, notably, hydrogen selenite) as well as Se(VI) and Se(IV) interaction with alkaline earth metal ions. These investigations are supported by time-resolved laser-induced fluorescence spectroscopy (TRLFS), ultraviolet-visible-near infrared (UV-Vis-NIR), IR/Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), as well as quantum chemical calculations on density functional theory (DFT) level. For NMR spectroscopic data on GSH/GSSG complexation towards both Eu(III) and U(VI) are lacking, the herein presented results are new, and nicely complement other spectroscopic studies. Ln(III) complexes of GSH are characterized by their high solubility at least up to 300 mM and pD 5. However, the formation constant of the Eu(III)–GSH 1:1 complex is quite low with log K = 1.71 ± 0.01 as determined by Eu(III)-TRLFS. The diamagnetic La(III) and Lu(III) showed only little effect on the NMR spectra (< 2 ppm) while analogous Eu(III) solutions revealed hyperfine shifts up to 40 ppm. Eu(III)-induced 1H chemical shift changes are solely upfield and attributed to be predominantly due to pseudocontact contribution caused by dipolar interaction. In contrast, Eu(III)-induced 13C chemical shift changes of adjacent atoms – at least for the carboxyl and α-carbons – show alternating signs, indicating spin polarization effects owing to contact contribution. As expected for hard LEWIS acids and shown by other spectroscopies, complexation facilitates by the carboxyl groups. Qualitative differences between the glutamyl and glycyl carboxylate in metal ion complexation are ascribed to COULOMB repulsion due to the positively charged NH3+ in direct vicinity. Investigations of the U(VI)–GSH system covered experiments under both oxidizing and reducing conditions, performed with GSH’s oxidized form, GSSG, at ambient conditions, while samples with reduced GSH were handled under N2 atmosphere. For either condition, U(VI) showed interaction in aqueous (D2O) solution with both GSH and GSSG as determined by U(VI)-induced 1H and 13C chemical shift changes and U(VI) TRLFS, the latter comprising measurements at 25 °C and –120 °C. In principle, the interactions are stronger as compared to the Ln(III) system, and the speciation in both solution and solid is more complex owing to the aqueous chemistry of uranium. Observed binary GSH complexes are [UO2(H2GSH)]2+ for pD values up to ≈ 2.3, and [UO2(HGSH)]+ predominating for pD > 2.3. Complementary to the Eu(III) results, whenever net neutral binary GSH/GSSG or ternary hydroxo GSH/GSSG U(VI) complexes form in solution, both these U(VI) systems revealed extensive precipitation because of the low solubility of these complexes. Binary U(VI) GSSG and ternary U(VI) hydroxo GSSG complexes yield solid phases from pD 2 through 8, even in carbonatic media. The largest quantities of aqueous GSSG–U(VI) complexes are observed for pD ≈ 3.5, with the association constant for pH 3 determined by TRLFS as log K = 4.81 ± 0.08 for a 1:1 complex. GSH cannot compete with hydroxo ligands for complexation as of pD 6, whereas GSSG can at least partially compete with hydroxo and carbonate ligands upon formation of both quaternary U(VI) hydroxo carbonate GSSG, and ternary U(VI) carbonate GSSG (poly-)anionic species of high solubility. Under reducing and near-neutral conditions (pD 6 – 9) GSH immediately reduced U(VI) with subsequent formation of nanocrystalline UO2+x. After centrifugation of the starting material and allowing the decanted supernatant to age, the dissolved nanocrystals assemble network-like as disclosed by TEM, and further analysed by selected-area electron diffraction (SAED), energy-dispersive X-ray (EDX) and UV-Vis spectroscopy, revealing hyper-stoichiometric UO2+x phases. Such network-like assembled actinide containing nanocrystals, with the arrangement most likely provoked by the presence of GSSG, have never been shown before. Complementary, the precipitate that has also been allowed to age as a wet paste, showed color changes from yellow via olive to black, indicating a reaction to proceed. The repeatedly probed and dissolved material exhibited GSSG in NMR spectra, and UV-Vis-NIR absorption bands attributed to U(IV) and, notably, U(V), the latter implying a one-electron transfer with subsequent disproportionation of U(V) to U(IV) and U(VI). Therefore, obtained results advance the understanding of both fundamental redox behavior of uranium and the role of GSH (and related molecules) in U(VI) detoxification processes in vivo. Although investigated for over 70 years, there are still controversial discussions on both speciation and structures of U(VI)–Cit complexes. By means of NMR’s strength in both structure determination and sensitivity to dynamic processes, studies regarding the U(VI)–Cit system allowed further fundamental insights into the structures of the formed complexes on a molecular level. Upon complexation a chiral center is induced in Cit’s central carbon, resulting in the formation of two diastereomeric pairs of enantiomers, whereupon the dimeric complexes exhibit syn and anti configured isomers. In fact, the combination of 17O NMR (note: at natural abundance) and quantum chemical calculations allowed an unambiguous decision on complex geometry and overall configurations. It is evidenced for the first time that the syn isomer is favored in aqueous solution in contrast to the preferably crystallizing anti isomer. Both isomers coexist and interconvert among one another, with a rate estimated to be in the order of 102 s–1 at 25 °C in acidic media, and a corresponding activation energy of approximately 60 kJ mol–1. Moreover, clear indications for uranium chirality is observed for U4+, with the 1:1 U(IV)–Cit complexes also forming two diastereomeric pairs of enantiomers. Comprehensive spectroscopic experiments combined with quantum chemical calculations improved basic understanding of the photo-reaction mechanism in the U(VI)–Cit system. Regardless of sample conditions, Cit is degraded to β-ketoglutarate, acetoacetate, and acetone, while U(VI) was reduced to U(IV) at pD 2 and U(V) at pD 5, suggesting a two- and a one-electron transfer, respectively. NMR signals observed for pD 5 samples at remarkable 1H chemical shift values between 25 and 53 ppm, in combination with UV-Vis-NIR absorptions at about 750 and 930 nm, are assigned to U(V) complexes of citrate. With regard to reported pH dependence on reaction rate and yield in the literature combined with observations in this work, H+/D+ are considered mechanistically crucial constituents. Furthermore, the photoreaction proceeds intermolecularly, requiring for free Cit to be present in solution. In consideration of both the U(VI)–Cit photoreaction and the U(VI)–GSH chemical redox reaction, regardless of the particular mechanism, in both cases the process is intermolecular. This is not only a highly interesting, but the more a very important result, rendering the reductants not required to be bound to U(VI) in order to reduce it. Owing to the suitability of 77Se as NMR-active but non-radioactive Se isotope, this spectroscopy was also applied to study chemical behavior of the nuclear waste related long-lived 79Se. For the first time spectroscopic evidence is given for hydrogen selenite dimerization in aqueous solution upon formation of homo-dimers by hydrogen bonding that are stable up to 60 °C and so are other selenium oxyanionic species. Additionally, a remarkably higher 77Se chemical shift temperature coefficient of the dimer – as compared to corresponding selenite and selenous acid – was found. These findings are attributed to a significant deshielding upon heating due to remarkably different rovibrational modes upon stretching the dimer as a whole instead of its dissociation into monomers owing to the rather strong hydrogen bonds. Interaction of selenium oxyanions with ubiquitous alkaline earth metals, i.e., Ca2+ and Mg2+, showed formation of weak aqueous complexes of both selenite and hydrogen selenite dimer for excessive selenium, however, at high ionic strength (5.6 M) for equimolar Ca2+ and Se(IV) even at pHc 5 crystalline calcium selenite is formed.