In Sweden the encapsulated nuclear waste will be surrounded by compacted bentonite in the granitic host rock. In contact with water-bearing fractures the bentonite barrier may release montmorillonite colloids that may be further transported in groundwater. If large amounts of material are eroded from the barrier, the buffer functionality can be compromised. Furthermore, in the scenario of a leaking canister, strongly sorbing radionuclides, can be transported by montmorillonite colloids towards the biosphere. This thesis addresses the effects of groundwater chemistry on the generation, stability, sorption and transport of montmorillonite colloids in water bearing rock fractures. To be able to predict quantities of montmorillonite colloids released from the bentonite barrier in contact with groundwater of varying salinity, generation and sedimentation test were performed. The aim is first to gain understanding on the processes involved in colloid generation from the bentonite barrier. Secondly it is to test if concentration gradients of montmorillonite colloids outside the barrier determined by simple sedimentation experiments are comparable to generation tests. Identical final concentrations and colloid size distributions were achieved in both types of tests. Colloid stability is strongly correlated to the groundwater chemistry. The impact of pH, ionic strength and temperature was studied. Aggregation kinetics experiments revealed that for colloid aggregation rate increased with increasing ionic strength. The aggregation rate decreased with increasing pH. The temperature effect on montmorillonite colloid stability is pH-dependent. At pH≤4, the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH≥10, the aggregation rate constant decreased with increasing temperature. In the intermediate pH interval, the aggregation rate constant decreased with increasing temperature except at the highest ionic strength, where it increased. The relationship between the rate constant and the ionic strength allowed the critical coagulation concentration (CCC) for Na- and Ca-montmorillonite to be determined. In order to distinguish the contribution of physical filtration and sorption to colloid retention in transport, the different retention mechanisms were quantified. Sorption on different representative minerals in granite fractures was measured for latex colloids (50, 100, 200 nm) and montmorillonite colloids as a function of ionic strength and pH. Despite of the negative charge in mineral surfaces and colloids, sorption was detected. The sorption is correlated to the mineral point of zero charge and the zeta potential of the colloids, and increases with increasing ionic strength and decreasing pH. In transport experiments with latex colloids in columns packed with fracture filling material, the retention by sorption could clearly be seen. In particular at low flow rates, when the contact time for colloids with the mineral surfaces were the longest, sorption contributed to retention of the transport significantly. The retention of latex colloids appeared to be irreversible in contrary to the reversible montmorillonite colloid retention. Generation, stability and sorption of the montmorillonite colloids are controlled by electrostatic forces; hence, the results were in qualitative agreement with DLVO.

One of the proposed solutions to the issue of nuclear waste volume is to transition from once through nuclear fuel cycle to advanced fuel cycles with used fuel recycling option. In any advanced fuel cycles with recycling options, the type and amount of separation technology deployed play a crucial role in the overall performance of the fuel cycle. In this work, a scenario study involving two advanced fuel cycles in addition to the once through fuel cycle were evaluated using VISION nuclear fuel cycle simulation code. The advanced fuel cycles were setup to transition completely to full recycling without any light water reactor by assuming all LWR currently in operation will have 20 years of operating life extension and no new LWR will be constructed thereafter. Several different separation capacities (1kT/yr, 2kT/yr and 4 kT/yr) were deployed and the overall impact of these capacities was analyzed in terms of resources utilization, used fuel and waste material generated and the amount of storage space required. Economic parameter (LCOE, LFCC, etc) analysis was also performed using VISION.ECON. Results presented in this work suggest that the need for LWR-UNF storage can be minimized if sufficient separation capacity is deployed early in the fuel cycle. It can also be concluded that a FuRe system without LEU will not be feasible, thus SFRs must be designed for optional use of LEU fuel. Otherwise LWRs must continue to be part of the mix to keep the near term cost of generating electricity competitive. It was observed that the higher amount of separation capacity deployed in the advanced fuel cycles led to higher LFCC and LCOE, but also translates into less environmental impact on both front and back end of the fuel cycle.

Numerous glacial advances over the past 2 million years have covered the entire Canadian and Fennoscandian Shield outcrop. During glacial advance and retreat, permafrost is expected to form in front of the glacier. The question of how permafrost and freezing impact the formation and evolution of brines in natural systems may be vital to understanding the chemistry of groundwater in crystalline rocks. Investigations of groundwater conditions beneath thick permafrost can provide valuable information that can be applied to assessing safety of deep, underground nuclear waste repositories and understanding analogues to potential life-bearing zones on Mars. However, very little scientific investigation of cryogenic processes and hydrogeology deep within crystalline systems has been published. The purpose of this research is to evaluate the impacts of thick permafrost (>300m) formation on groundwater chemical and flow system evolution in the crystalline rock environment over geologic timescales. A field investigation was conducted at the Lupin Mine in Nunavut, Canada, to characterize the physical and hydrogeochemical conditions within and beneath a thick permafrost layer. Taliks, or unfrozen channels within the permafrost, are found beneath large lakes in the field area, and provide potential hydraulic connections through the permafrost. Rock matrix waters are dilute and do not appear to affect groundwater salinity. Permafrost waters are Na-Cl and Na-Cl-SO4 type, and have been contaminated with chloride and nitrate by mining activities. Sulfide oxidation in the permafrost may be naturally occurring or is enhanced by mining activities. Basal permafrost waters (550 to 570 mbgs) are variably affected by mining. The less contaminated basal waters have medium sulfate concentrations and are Ca-Na dominated. This is similar to deeper, uncontaminated subpermafrost waters, which are Ca-Na-Cl or Na-Ca-Cl type with a wide range of salinities (2.6 to 40 g•L-1). The lower salinity subpermafrost waters are attributed to dissociation of methane hydrate and drawdown of dilute talik waters by the hydraulic gradient created by mine dewatering. This investigation was unable to determine the influence of talik waters to the subpermafrost zone in undisturbed conditions. Pressures are also highly variable, and do not correlate with salinity. Fracture infillings are scarce and calcite δ18O and δ13C values have a large range. Microthermometry indicates a large range in salinities and homogenization temperatures as well, indicative of a boiling system. In situ freezing of fluids and methane hydrate formation may have concentrated the remaining fluids. Field activities at the Lupin mine also provided an opportunity to study the nature of gases within crystalline rocks in a permafrost environment. Gases were generally methane-dominated (64 to 87), with methane δ13C and δ2H values varying between -56 and -42‰ VPDB and -349 to -181 ‰ VSMOW, respectively. The gases sampled within the Lupin mine have unique ranges of chemical and isotopic compositions compared with other Canadian and Fennoscandian Shield gases. The gases may be of thermogenic origin, mixed with some bacteriogenic gas. The generally low δ2H-CH4 ratios are somewhat problematic to this interpretation, but the geologic history of the site, a metaturbidite sequence, supports a thermogenic gas origin. The presence of gas hydrate in the rock surrounding Lupin was inferred, based on temperature measurements and hydrostatic pressures. Evidence also suggests fractures near the mine have been depressurized, likely due to mine de-watering, resulting in dissipation of methane hydrate near the mine. Modeling results indicate methane hydrates were stable throughout the Quaternary glacial-interglacial cycles, potentially limiting subglacial recharge. The effects of deep permafrost formation and dissipation during the Pleistocene glacial/interglacial cycle to deep groundwaters in the Canadian Shield were also investigated by compiling data from thirty-nine sites at twenty-four locations across the Canadian Shield. Impacts due to glacial meltwater recharge and surficial cryogenic concentration of fluids, which had been previously considered by others, and in situ freeze-out effects due to ice and/or methane hydrate formation were considered. At some Canadian Shield sites, there are indications that fresh, brackish, and saline groundwaters have been affected by one of these processes, but the data were not sufficient to differentiate between mixed, intruded glacial meltwaters, or residual waters resulting from either permafrost or methane hydrate formation. Physical and geochemical data do not support the cryogenic formation of Canadian Shield brines from seawater in glacial marginal troughs. The origin and evolution of Canadian and Fennoscandian Shield brines was explored with a survey of chlorine and bromine stable isotope ratios. The δ37Cl and δ81Br isotopic ratios varied between -0.78 ‰ and 1.52 ‰ (SMOC) and 0.01 ‰ and 1.52 ‰ (SMOB), respectively. Variability of chlorine and bromine isotope ratios decreases with increasing depth. Fennoscandian Shield groundwaters tend to be more enriched than Canadian Shield groundwaters for both 37Cl and 81Br. Other sources and processes which may affect δ37Cl and δ81Br composition are also explored. Primary processes such as magmatic and/or hydrothermal activity are thought to be responsible for the isotopic composition of the most concentrated fluids at each site. Positive correlations between δ81Br, and δ37Cl with δ2H-CH4 and δ13C-CH4 were noted. At this time the cause of the relationship is unclear, and may be a result of changing redox, pH, temperature, and/or pressure conditions during hydrothermal, metamorphic, or volcanogenic processes. The data suggest solute sources and fluid evolution at individual sites would be better constrained utilizing a multi-tracer investigation of δ37Cl, δ81Br, and 87Sr/86Sr ratios comparing fluids, rocks, and fracture filling minerals (including fluid inclusions).

Numerous glacial advances over the past 2 million years have covered the entire Canadian and Fennoscandian Shield outcrop. During glacial advance and retreat, permafrost is expected to form in front of the glacier. The question of how permafrost and freezing impact the formation and evolution of brines in natural systems may be vital to understanding the chemistry of groundwater in crystalline rocks. Investigations of groundwater conditions beneath thick permafrost can provide valuable information that can be applied to assessing safety of deep, underground nuclear waste repositories and understanding analogues to potential life-bearing zones on Mars. However, very little scientific investigation of cryogenic processes and hydrogeology deep within crystalline systems has been published. The purpose of this research is to evaluate the impacts of thick permafrost (>300m) formation on groundwater chemical and flow system evolution in the crystalline rock environment over geologic timescales. A field investigation was conducted at the Lupin Mine in Nunavut, Canada, to characterize the physical and hydrogeochemical conditions within and beneath a thick permafrost layer. Taliks, or unfrozen channels within the permafrost, are found beneath large lakes in the field area, and provide potential hydraulic connections through the permafrost. Rock matrix waters are dilute and do not appear to affect groundwater salinity. Permafrost waters are Na-Cl and Na-Cl-SO4 type, and have been contaminated with chloride and nitrate by mining activities. Sulfide oxidation in the permafrost may be naturally occurring or is enhanced by mining activities. Basal permafrost waters (550 to 570 mbgs) are variably affected by mining. The less contaminated basal waters have medium sulfate concentrations and are Ca-Na dominated. This is similar to deeper, uncontaminated subpermafrost waters, which are Ca-Na-Cl or Na-Ca-Cl type with a wide range of salinities (2.6 to 40 g•L-1). The lower salinity subpermafrost waters are attributed to dissociation of methane hydrate and drawdown of dilute talik waters by the hydraulic gradient created by mine dewatering. This investigation was unable to determine the influence of talik waters to the subpermafrost zone in undisturbed conditions. Pressures are also highly variable, and do not correlate with salinity. Fracture infillings are scarce and calcite δ18O and δ13C values have a large range. Microthermometry indicates a large range in salinities and homogenization temperatures as well, indicative of a boiling system. In situ freezing of fluids and methane hydrate formation may have concentrated the remaining fluids. Field activities at the Lupin mine also provided an opportunity to study the nature of gases within crystalline rocks in a permafrost environment. Gases were generally methane-dominated (64 to 87), with methane δ13C and δ2H values varying between -56 and -42‰ VPDB and -349 to -181 ‰ VSMOW, respectively. The gases sampled within the Lupin mine have unique ranges of chemical and isotopic compositions compared with other Canadian and Fennoscandian Shield gases. The gases may be of thermogenic origin, mixed with some bacteriogenic gas. The generally low δ2H-CH4 ratios are somewhat problematic to this interpretation, but the geologic history of the site, a metaturbidite sequence, supports a thermogenic gas origin. The presence of gas hydrate in the rock surrounding Lupin was inferred, based on temperature measurements and hydrostatic pressures. Evidence also suggests fractures near the mine have been depressurized, likely due to mine de-watering, resulting in dissipation of methane hydrate near the mine. Modeling results indicate methane hydrates were stable throughout the Quaternary glacial-interglacial cycles, potentially limiting subglacial recharge. The effects of deep permafrost formation and dissipation during the Pleistocene glacial/interglacial cycle to deep groundwaters in the Canadian Shield were also investigated by compiling data from thirty-nine sites at twenty-four locations across the Canadian Shield. Impacts due to glacial meltwater recharge and surficial cryogenic concentration of fluids, which had been previously considered by others, and in situ freeze-out effects due to ice and/or methane hydrate formation were considered. At some Canadian Shield sites, there are indications that fresh, brackish, and saline groundwaters have been affected by one of these processes, but the data were not sufficient to differentiate between mixed, intruded glacial meltwaters, or residual waters resulting from either permafrost or methane hydrate formation. Physical and geochemical data do not support the cryogenic formation of Canadian Shield brines from seawater in glacial marginal troughs. The origin and evolution of Canadian and Fennoscandian Shield brines was explored with a survey of chlorine and bromine stable isotope ratios. The δ37Cl and δ81Br isotopic ratios varied between -0.78 ‰ and 1.52 ‰ (SMOC) and 0.01 ‰ and 1.52 ‰ (SMOB), respectively. Variability of chlorine and bromine isotope ratios decreases with increasing depth. Fennoscandian Shield groundwaters tend to be more enriched than Canadian Shield groundwaters for both 37Cl and 81Br. Other sources and processes which may affect δ37Cl and δ81Br composition are also explored. Primary processes such as magmatic and/or hydrothermal activity are thought to be responsible for the isotopic composition of the most concentrated fluids at each site. Positive correlations between δ81Br, and δ37Cl with δ2H-CH4 and δ13C-CH4 were noted. At this time the cause of the relationship is unclear, and may be a result of changing redox, pH, temperature, and/or pressure conditions during hydrothermal, metamorphic, or volcanogenic processes. The data suggest solute sources and fluid evolution at individual sites would be better constrained utilizing a multi-tracer investigation of δ37Cl, δ81Br, and 87Sr/86Sr ratios comparing fluids, rocks, and fracture filling minerals (including fluid inclusions).

<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 migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques. In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases. From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes. For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3−, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system. The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered. A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important. A significant different surface complexation is observed for Al2O3. The formation of inner-spheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested. The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces. In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes. The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology. The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed. / Das Migrationsverhalten von Aktiniden und anderen radioaktiven Schadstoffen in der Umwelt wird von wichtigen molekularen Prozessen entlang der Grundwasserfließwege reguliert. Dazu gehören sowohl die Hydrolyse und Komplexierung in wässrigen Lösungen als auch Diffusion und Sorption der Schwermetalle an Mineralen. Diese Reaktionen beeinflussen entscheidend die Mobilität und Bioverfügbarkeit der Metallionen in der Umwelt, insbesondere an den fest-flüssig Grenzflächen. Genaue Kenntnisse über die an diesen Grenzflächen stattfindenden Mechanismen sind somit entscheidend, um Migrationsprozesse verlässlich abschätzen zu können. Die benötigten strukturellen Informationen können mit verschiedenen spektroskopischen Techniken ermittelt werden. Das Ziel der vorliegenden Arbeit war die Untersuchung der Speziation von Uran(VI) und Neptunium(V) an umweltrelevanten Grenzflächen von Oxiden des Titans, Aluminiums, Siliziums und Zinks und von Alumosilikaten mittels ATR FT-IR Spektroskopie. Des Weiteren wurde die Verteilung aquatischer Spezies in mikromolaren Lösungen des U(VI) und Np(V/VI) unter Normalbedingungen charakterisiert. Diese erstmalige Untersuchung wurde mit einer Kombination aus Speziationsmodellierung unter Anwendung aktueller thermodynamischer Daten und ATR FT-IR und NIR Absorptionsspektroskopie realisiert. Die Infrarotspektren zeigen eine deutliche Änderung der Speziesverteilung im Konzentrationsverlauf vom millimolaren zum mikromolaren Bereich. Dies verweist auf die Bildung monomerer U(VI) Hydrolyseprodukte. Im Gegensatz zu berechneten Speziationen werden diese monomeren Komplexe schon bei pH ≥ 2,5 gebildet und dominieren die Speziation bei pH 3. Bei höheren pH-Werten (> 6) konnte eine komplexe Speziesverteilung mit Anteilen von Karbonatkomplexen nachgewiesen werden. Erstmals konnten im Rahmen dieser Arbeit spektroskopische Befunde der Hydrolysereaktionen des Np(VI) im submillimolaren Konzentrationsbereich bis pH 5,3 erhalten werden. Diese wurden im Vergleich mit der U(VI) Speziation diskutiert. Obwohl im sauren Bereich (pH ≤ 4) die Bildung ähnlicher Komplexe nachgewiesen wurde, zeigen die bei höheren pH-Werten erhaltenen Spektren eine unterschiedliche Speziesverteilung. Im Gegensatz zum U(VI) bildet das Np(VI) schon bei pH 5 karbonathaltige aquatische Spezies wie (NpO2)2CO3(OH)3−. Die Ergebnisse der Sorptionsexperimente von U(VI) zeigen die Bildung stabiler Oberflächenkomplexe an allen untersuchten Mineralphasen. Dies umfasst mehrere als Modellsystem dienende Metalloxide wie TiO2, Al2O3 und SiO2, als auch komplexere Alumosilikate wie Kaolinit, Muskovit und Biotit. Für eine detaillierte Charakterisierung der Oberflächenkomplexe wurde eine Vielzahl von in situ Sorptionsexperimenten durchgeführt, die den Einfluss unterschiedlicher Parameter der mineralischen Phase als auch des wässrigen U(VI) Systems berücksichtigen. Die bevorzugte Bildung von innersphärischen Komplexen an TiO2 und SiO2 wird aus den spektroskopischen Daten abgeleitet. Da die in situ FT-IR Spektroskopie eine kontinuierliche Registrierung der Absorptionsänderungen während der ablaufenden Sorptionsprozesse erlaubt, kann somit der Verlauf dieser Prozesse quasi in Echtzeit spektroskopisch verfolgt werden. Es konnte gezeigt werden, dass mit fortschreitender Sorptionsdauer, d.h. bei hohen Beladungsdichten, die Bildung einer weiteren außersphärischen Spezies die Sorption dominert. Die vorliegende kristallographische Modifikation, Anatas und Rutil, ist nicht maßgeblich für das Auftreten unterschiedlicher Sorptionsprozesse verantwortlich, obwohl Parameter wie die spezifische Oberfläche und die Porosität für den Sorptionsprozess von Bedeutung sind. Deutlich verschiedene Oberflächenreaktionen werden für Al2O3 beobachtet. Aus den Spektren kann die Ausbildung einer innersphärischen Spezies bei sehr niedrigen U(VI) Beladungen, niedrigen pH-Werten, hohen Ionenstärken und kurzen Kontaktzeiten abgeleitet werden. Bei fortschreitender Sorption ändert sich die Art der Oberflächenkomplexe. Zunächst bilden sich außersphärische Spezies, während im weiteren Verlauf die Spektren auf eine beginnende Oberflächenausfällung bzw. Polymerisation hinweisen. Weiterhin wird das Auftreten von ternären U(VI) Karbonatkomplexen an γ-Al2O3 aus den spektroskopischen Daten abgeleitet. Die ersten Ergebnisse der Sorptionsexperimente an komplexeren, natürlich auftretenden Mineralphasen (Kaolinit, Muskovit und Biotit) zeigen eine bevorzugte Ausbildung von innersphärischen U(VI) Komplexen. Diese Resultate werden durch die spektralen Befunde der Experimente der Metalloxide gestützt. Erstmalig werden in dieser Arbeit spektroskopische Ergebnisse der Sorptionsprozesse von wässrigen Np(V) an verschiedenen Mineralphasen präsentiert. Wie U(VI) bildet Np(V) stabile innersphärische Oberflächenkomplexe an TiO2. Die Speziesverteilung an der TiO2 Oberfläche ist im pH Bereich 4 – 7,6 konstant. Daher ist zu erwarten, dass eine außersphärische Komplexierung hier nur eine untergeordnete Rolle spielt. Der Vergleich von Spektren der Np(V) Sorptionskomplexe an TiO2, SiO2 und ZnO weist auf die Bildung strukturell ähnlicher bidentater Komplexe hin. Die Vielzahl der hier vorgestellten infrarotspektroskopischen Experimente bietet eine fundierte Sammlung spektroskopischer Daten, die für zukünftige Untersuchungen komplexer aquatischer und mineralischer Systeme unerlässlich ist. Gleichzeitig wurde der Anwendungsbereich der ATR FT-IR Technik auf dem Gebiet der Radioökologie umfassend erweitert. Die im Rahmen dieser Arbeit gewonnenen Ergebnisse tragen zu einem besseren Verständnis der geochemischen Wechselwirkungen von Aktiniden, im Speziellen von U(VI) und Np(V) in der Umwelt bei. Damit unterstützen sie den Aufklärungsprozess der Migration von radioaktiven Kontaminationen und dienen als Grundlage für zuverlässige Prognosen für die Sicherheitsbewertung von Endlagern für nukleare Abfälle.

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The effect of partially saturated conditions on aqueous diffusion was investigated on the Upper Ordovician Queenston Formation shale from the Michigan Basin of southwest Ontario, Canada. Effective diffusion coefficients (De) were determined for iodide tracer on duplicate cm-scale samples from a core segment. Partially saturated conditions were created with a new gas-ingrowth method that takes advantage of the variability of N2 solubility with pressure. The method is designed to create partially saturated pores, quantify the level of partial gas/brine saturation within the tracer-accessible pore space, and measure De under fully porewater-saturated and partially gas-saturated conditions for the same sample. X-ray radiography is used with an iodide tracer for quantifying the degree of partial saturation and measuring De. The saturated De values range from 2.8 x 10-12 to 3.1 x 10-12 m2/s. Following generation of a gas phase in the pores (average gas saturations of 4 to 6.7 %), De values decrease by 20 to 22 % relative to the porewater-saturated condition, indicating that the tortuosity factor (ratio of constrictivity to tortuosity) is sensitive to saturation. Suggesting that a small volume of the pore fraction is responsible for majority of the transport. The gas-ingrowth method was successful for generating partial gas saturation, but the distribution of the gas phase is non-uniform, with relatively high gas saturations near boundaries and lower saturations in the interior of the samples.

In order to increase the waste loading efficiency of nuclear waste glasses, alternative composite structures are sought that trap molybdenum in a water-durable CaMoO4 phase. In this thesis, the formation and stability of CaMoO4 in a borosilicate glass against the attack of internal radiation was investigated. It is a fundamental study that simplified the composition to known contributors of molybdate speciation, and further splits the com- ponents of α and β-decay into integral parts that replicated both nuclear and electronic interactions. Irradiation experiments using 2.5 MeV β, 7 MeV Au, and 92 MeV Xe ions were enlisted to test the hypotheses of whether 100−1000 years of radiation damage given current waste loading standards would: (i) induce phase separation in homogeneous re- gions, (ii) increase the extent of existing phase separation, (iii) induce local annealing that could cause amorphisation of crystalline phases or increase mixing between amorphous phases, or (iv) cause some combination of the above. Results from XRD, SEM, EPR, and Raman spectroscopy suggest that powellite is stable against replicated radiation damage with only minor modifications observed. The main mechanisms of alteration involved: (i) thermal and defect-assisted diffusion, (ii) relaxation from the added ion’s energy, (iii) localised damage recovery from ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain, and led to longer-range modifications. It can be further concluded that no precip- itation or increased phase separation was observed in single-phased glasses. In isolated cases, radiation-induced precipitation of CaMoO4 occurred, but these crystallites were reamorphised at higher doses. At high SHI fluences, minor amorphisation of powellite was also observed, but this occurred alongside bulk-to-surface reprecipitation of CaMo- species. Overall, the components of internal radiation were often found to have opposing effects on the alteration of Si−O−B mixing in the glass, ion migration, and crystallite size. This led to the prediction that a steady-state damage structure could form from cumulative decay processes. These results suggest that CaMoO4 containing borosilicate GCs are resistant to radiation, and that excess molybdenum from increased waste loading can be successfully incorporated into these structures without altering the overall dura- bility of the wasteform. Furthermore, the identified saturation in modifications occurring around 8 x 10¹⁴ Xe ions/cm² can be used as a benchmark in future investigations on more complex systems where the maximum damage state is required.

Dans le cadre de la vitrification des déchets nucléaires de haute activité à vie longue, un nouveau procédé a été mis en service à l’usine de La Hague en 2010 : le procédé creuset froid. Dans ce procédé, des gradients thermiques apparaissent au sein du bain de verre. Celui-ci forme une couche solide au contact de la paroi froide, appelée « auto-creuset ». Dans cette zone, le verre est soumis à des températures où il peut potentiellement cristalliser. L’objectif de ce travail était de déterminer la microstructure de cet auto-creuset en précisant les zones de cristallisation. Parallèlement, il s’agissait d’évaluer l’impact du gradient thermique sur la cristallisation des verres considérés. La cristallisation de deux verres d’intérêt nucléaire a donc été étudiée à l’aide d’une méthode basée sur l’analyse d’images MEB en conditions de traitements isotherme et sous gradient thermique. Les analyses en isotherme mettent en évidence la cristallisation de cristaux d’apatite (660°C-900°C) et de powellite (630°C-900°C) et permettent de quantifier cette cristallisation (vitesses de croissance et de nucléation, fraction cristallisée) qui reste très limitée (< 3%). La comparaison des résultats issus de ces deux types d’expérimentations montre que le gradient thermique n’a pas d’impact mesurable sur les cristallisations observées. Afin de compléter les analyses surfaciques de la cristallisation, des mesures par microtomographie in et ex situ ont été réalisées à l’ESRF sur la ligne ID19. Cette étude a permis de suivre la cristallisation d’apatites dans un verre simplifié et de confirmer la fiabilité de la méthode de quantification de la cristallisation basée sur l’analyse d’images 2D. / In the context of the vitrification of high level nuclear waste, a new industrial process has been launched in 2010 at the La Hague factory: The skull melting process. This setup applies thermal gradients to the melt, which leads to the formation of a solid layer of glass: the “self-crucible”. The question would be to know whether these thermal gradients have an impact or not on the crystallization behaviour of the considered glasses in the self crucible. In order to answer that question, the crystallization of two glass compositions of nuclear interest has been investigated with an image analysis based method in isothermal and thermal gradient heat treatments conditions. The isothermals experiments allow for the quantification (growth speed, nucleation, crystallized fraction) of the crystallization of apatites (660°C-900°C) and powellites (630°C- 900°C). The comparison of the results obtained through these two types of experimentations allows us to conclude that there is no impact of the thermal gradient on the crystallization of the studied glass compositions. In order to complete the image analysis study (based on surfaces), in and ex situ microtomography experiments have been performed at ESRF (Grenoble) on the ID10 beamline. This study allowed us to follow the crystallization of apatites in a simplified glass and to confirm the reliability of the image analysis method based on the analysis of surfaces.