Nuclear energy generation results in the production of effluents and radioactive waste that are very difficult to treat and dispose. A considerable fraction of nuclear waste is discharged in the form of complex mixtures of hazardous organic compounds and metallic radionuclides. The most serious pollution is caused by polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls that are very difficult to remove from the environment. The nuclear industry faces certain challenges related to treatment and safe disposal of these mixed radioactive organic wastes due to the toxicity and recalcitrant nature of the organics. Techniques currently used in treating the waste include physical-chemical processes that have resulted in the generation of the secondary waste requiring further treatment before disposal to the environment. These conventional processes also require the use of strong oxidising agents and higher than natural pH and temperature. Therefore, it is of great importance to develop new environmentally friendly technologies. One suggested method employs specialised cultures of bacteria to completely mineralize the organic compounds without leaving traces of harmful byproducts. The efficiency of bacteria to remove these types of compounds may be improved by in situ application. During in situ application, the bacteria apply a variety of pathways to break down the compounds and use them as their energy and carbon sources. These processes may be carried out within the natural pH and temperature range capable of supporting life forms. In the current study, a more detailed analysis of the biodegradation capability of the organic compounds was conducted and the following were the major findings of the study: <ul><li> Wastewater from an actual radionuclide processing facility was characterised and was found to contain all the 16 priority PAHs in the range 0.001-25 mg/L. Acenaphthene (detected at 25.1 mg/L) was the most abundant. Most of the PAHs in the wastewater samples exceeded the WHO limit of 0.05ìg/L indicating the need for further treatment before final disposal to the environment.</li> <li> After purifying and sequencing the rRNA genes from the soil and mine water bacteria, a total of 5 and 3 bacterial isolates were found, respectively. The rRNA sequences were isolated from bacteria with some tolerance to PAH toxicity and were thus candidate species for naphthalene degradation. The bacteria from soil were predominated by aromatic compound degraders Pseudomonas aeruginosa, Microbacterium esteraromaticum and Alcaligenes sp. In mine water, only Pseudomonas putida was identified as a known aromatic ring cleaving species.</li> <li> The biodegradation of naphthalene by the purified cultures was determined to be limited by its solubility (30mg/L) and toxic effects of the aromatic compounds. A kinetic model was derived based on the metabolism and microbial growth kinetics. The model predicted the concentration remaining in solution under different initial (added) PAH concentrations. A simplified coupled dissolution-degradation model was used to model the kinetics of degradation. With help of the model, parameters were estimated and the sensitivity of parameter value was also evaluated. The aim of model was to help gain a better understanding of biological degradation. This could be used for optimisation of the process and scale up of the process to pilot and full-scale application.</li></ul> / Dissertation (MSc)--University of Pretoria, 2010. / Microbiology and Plant Pathology / unrestricted

This thesis is a qualitative case study of a risk controversy generated by a proposal to construct a high-level nuclear waste repository on the Goshute Indian reservation in rural, northwestern Utah. Using data taken from local newspapers and public hearings, I examine and compare the claims-making activity of project opponents and project proponents. I explore and analyze variability in claims making along four specific dimensions: risk communication, trust and distrust in science and technology, environmental equity, and tribal sovereignty. My analysis is intended to illuminate the sources of contention between opponent and proponent claims-making groups in this case.

One of the greatest challenges to modem society is the management and disposal of hazardous by-products that have accompanied the industrial advances of the twentieth century. One of the most difficult by-products to deal with has been radioactive waste. Previous research has shown that due to the real and perceived risks associated with this type of waste, the burden of storing said waste has fallen on minority communities, including Native American groups. This research examines the proposed temporary nuclear waste storage facility to be located on the Skull Valley Indian Reservation in Utah. Using an ethnographic case study approach, this research examines the claimsmaking activities of opponents and proponents involved in this information campaign. Of specific interest is the rhetoric that each of these groups employ in an attempt to establish a regime of truth. This research focuses on the prominent rhetorical themes and tactics used by the stakeholder groups vying for supremacy and public acceptance.

This thesis was done i cooperation with SKB Clab in Oskarshamn and studies use of sonic waves for detecting voids and irregularities in the weld joints of copper capsules used for long term storage of radioactive waste. Since these could pose material failure and thereby risk radioactive contamination of ground water it is very important to find means of quality control before storage.  During the welding procedure changes occur to the integrity of the material. The homogenous metal – in this case copper – is distorted and voids appear in and around the welded volume. A non-destructive inspection method is needed to make sure that the metal holds for the strains of long term storage. These strains are not completely known at the moment and therefore the goal of this thesis is mainly to add another tool of inspection for future studies. The tests are done using ultrasonic mapping of the welded volume. This is achieved by sending ultrasonic pulse through test samples – welded copper pieces – and recording its reflection. The recorded signals are gathered in data matrices and processed using several different signal processing methods in search of irregularities and voids. To enhance the understanding of the results a graphical user interface (GUI) is developed that allows users to visualize the results.  The welded pieces, the ultrasonic mapping and its resulting data sets were delivered to this thesis and the scope of the thesis is to develop the GUI and apply known signal processing methods to the data set.  It is shown that the irregularities do appear and that ultrasonic detection and use of the processing method is useful for quality control of the material. Further field studies are needed to identify maximum number, size and perhaps shapes of irregularities that can be within tolerance levels of the storage project.

Currently in the UK, composite blends of Portland cement (PC) and blastfurnace slag (up to 90%) are commonly used for the encapsulation of low and intermediate level wastes. The high volume replacement of PC is considered necessary in order to to reduce the high heat generation resulting from cement hydration in 500 litre waste packages. While suited to the majority of waste streams, the high pH environment in such systems (usually around 12.5 -13), will cause the corrosion of certain waste metals such as aluminium. Since aluminium is only passive between pH4 - 8.5, the use of an alternative low-pH cement system could serve to reduce/inhibit the corrosion. However, before such cements can be considered, two main research problems must be addressed, as follows: (1) quantitative evaluation of alternative cement systems based on their corrosion performance with aluminium; (2) high heat generation due to the rapid rate of hydration. The research in this thesis was thus divided into two strands, as follows: (1) The design and development of a novel, scientifically robust testing facility for the quantitative monitoring of aluminium corrosion in cement pastes; (2) the development of novel cement composites based on weakly alkaline calcium sulfoaluminate (CSA) cement for the encapsulation of aluminium from nuclear wastes. The output from this research is considered to be of interest to the UK nuclear industry.

This work focuses on diffusion and advection through cementitious media, the work arises from two research contracts undertaken at Loughborough University: Experiments to Demonstrate Chemical Containment funded by UK NDA and the SKIN project, funded by the European Atomic Energy Community's Seventh Framework Programme. Diffusion will be one of the most significant mechanisms controlling any radionuclide migration from a nuclear waste, deep geological disposal facility. Advection may also occur, particularly as the immediate post closure groundwater rebound and equilibration proceeds but is expected to be limited by effective siting and management during the operational phase of the facility. In this work advection is investigated at laboratory scale as a possible shorter timescale technique for providing insight into the much slower process of diffusion. Radial techniques for diffusion and advection have been developed and the developmental process is presented in some detail. Both techniques use a cylindrical sample geometry that allows the radionuclide of interest to be introduced into a core drilled through the centre of the test material. For diffusion the core is sealed and submerged in a container of receiving solution which is sampled and analysed as the radionuclide diffuses into it. For advection, a cell has been designed that allows inflow via the central core to pass through the sample in a radial manner and be collected as it exits from the outer surface. The radionuclide of interest can be injected directly into the central core without significant disturbance to the advective flow. Minor improvements continue to be made but both techniques have provided good quality, reproducible results. The majority of the work is concentrated on a potential cemetitious backfill known as NRVB (Nirex Reference Vault Backfill) this is a high porosity, high calcium carbonate content cementitious material. The radioisotopes used in this work are 3H (in tritiated water), 137Cs, 125I, 90Sr, 45Ca, 63Ni, 152Eu, 241Am along with U and Th salts. In addition the effect of cellulose degradation products (CDP) on radioisotope mobility was investigated by manufacturing solutions where paper tissues were degraded in water, at 80°C, in the absence of air and at high pH due to the presence of the components of NRVB. All diffusion experiments were carried out under a nitrogen atmosphere. All advection experiments were undertaken using an eluent reservoir pressurised with nitrogen where the system remained closed up to the point of final sample collection. Results for tritiated water and the monovalent ions of Cs and I were produced on a timescale of weeks to months for both diffusion and advection. The divalent ions of Sr, Ca and Ni produced results on a timescale of months to years. Variations of the experiments were undertaken using the CDP solutions. The effects of CDP were much more apparent at radiotracer concentration than the much higher radiotracer with non-active carrier, concentration. In the presence of CDP Cs, I and Ni were found to migrate more quickly; Sr and Ca were found to migrate more slowly. Additional Sr experiments were undertaken at elevated ionic strength to evaluate the effect of the higher dissolved solids content of the CDP solutions. Some of the results for HTO, Cs, I and Sr have been modelled using a simple numerical representation of the system in GoldSim to estimate effective diffusivity and partition coefficient. The diffusion model successfully produced outputs that were comparable to literature values. The advection model is not yet producing good matches with the observed data but it continues to be developed and more processes will be added as new results become available. Autoradiography has been used to visualise the radionuclide migration and several images are reproduced that show the fate of the radiotracers retained on the NRVB at the end of the experiments. As the experimental programme progressed it was clear that results could not be produced in a suitable timescale for Eu, Am U and Th. These experiments have been retained and will be monitored every six months until either diffusion is detected or the volume of receiving liquid is inadequate to ensure the NRVB is saturated.

The objective through my PhD has been to investigate radiation damage effects in materials related to fusion and to safe encapsulation of nuclear waste, using Molecular Dynamics (MD) methods. Particularly, using MD, we acquire essential information about the multi-scale phenomena that take place during irradiation of materials, and gain access at length and time-scales not possible to access experimentally. Computer simulations provide information at the microscopic level, acting as a bridge to the experimental observations and giving insights into processes that take place at small time and length-scales. The increasing computer capabilities in combination with recently developed scalable codes, and the availability of realistic potentials set the stage to perform large scale simulations, approaching phenomena that take place at the atomistic and mesoscopic scale (fractions of m for the first time) in a more realistic way. High-energy radiation damage effects have not been studied previously, yet it is important to simulate and reveal information about the properties of the materials under extreme irradiation conditions. Large scale MD simulations provide a detailed description of microstructural changes. Understanding of the primary stage of damage and short term annealing (scale of tens of picoseconds) will lead to better understanding of the materials properties, best possible long-term use of the materials and, importantly, new routes of optimization of their use. Systems of interest in my research are candidate fusion reactor structural materials (iron and tungsten) and materials related to the radioactive waste management (zirconia). High-energy events require large simulation box length in order for the damage to be contained in the system. This was a limitation for previous simulations, which was recently shifted with my radiation damage MD simulations. For the first time high-energy radiation damage effects were simulated, approaching new energy and length scales, giving a more realistic view of processes related to fusion and to high-energy ion irradiation of material.

The U.S. Department of Energy (DOE) has been engaged in a viability study for a potential underground geological repository in Yucca Mountain, Nevada. The repository is being designed for disposal of high level nuclear waste. A reference design for the repository has focused on the use of natural and manmade barriers to assure that radionucleide release will not be significant though an extended time period on the order of 10,000 years. The reference design utilizes manmade metallic components that are expected to last for this time period. The specified metallic materials depend on a phenomenon known as metallic passivity to achieve their expected service lives. It is difficult to demonstrate this type of service life for these metallic materials as they have only been in commercial use for less than 100 years. There have been metal artifacts and metallic materials that have survived for long time periods, however, little is known about whether these artifacts have been exposed to conditions where they have been immune to corrosion, exhibiting passive behavior, or actively corroding at an extremely low rate. A demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste package materials. Long-lived metallic materials, such as iron, copper, nickel, and alloys based on these metals are materials that demonstrate passive behavior and have been identified in the literature as possible analogues, potentially useful to provide additional confidence in making projections of such long-term passive behavior.1, 4, 28, 45 This paper presents a study into some aspects of the corrosion behavior of Josephinite. Josephinite is a naturally occurring assemblage of a metallic alloy of nickel and iron in conjunction with a host rock. The typical metallic composition is approximately 70% nickel and 30% iron. The material has been reported in association with geologic features with age into the millions of years. The study used corrosion measurement techniques to assess the behavior of the mineral immersed in aqueous solutions of various pH. Corrosion measurement techniques utilized included potentiodynamic polarization, open circuit corrosion potential, and electrochemical impedance spectroscopy. Other techniques utilized in the study included visual and metallographic examinations with both optical and scanning electron microscopy. Test results from this study indicate that passive behavior characterizes Josephinite specimens immersed in naturally aerated buffered aqueous solutions in a range of pH from 6 to 9. This range has been reported for the geographic area where Josephinite materials are found in southwest Oregon. This suggests that passive behavior may be responsible for the material longevity as opposed to the material being immune or undergoing slow but active corrosion.

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.

Stainless steel – zirconium alloys were developed by the US Department of Energy Laboratories as metallic waste forms for noble metal fission products. This thesis evaluates iron–zirconium–rhenium alloys to establish a technical basis for using metal waste form alloys for technetium-99 immobilization. Rhenium is used as a surrogate for Tc-99 since Tc is not naturally available and Re is metallurgically similar to Tc. The iron-zirconium system has two eutectic compositions, Fe-15 wt % Zr and Zr- 16 wt% Fe. Ten test samples were successfully cast in yttrium oxide crucibles at 1600°C, half near each eutectic composition, with Re amounts varying from 2.5 to 12.5 weight percent. A scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) capability was employed to determine the phase structure and phase composition of each sample. Iron rich samples were found to form up to three phases, with the rhenium content favoring the intermetallic phases: 1) an Fe solid solution phase, 2) an FeZr2-type intermetallic with 11 wt % or less Re, and 3) a second intermetallic with about 18 wt % Re. Zirconium rich samples formed as many as five distinct phases: 1) a Zr solid solution phase, 2) a Zr3Fe-type intermetallic with as much as 13 wt% Re, 3) a rhenium-zirconium intermetallic, 4) another Fe-Zr intermetallic with very little Re, and 5) a Fe-Re intermetallic. Potentiostatic and potentiodynamic electrochemical tests were performed using sulfuric acid to evaluate the corrosion resistance of each sample. These tests found that the zirconium rich samples were very corrosion resistant but became increasingly susceptible at higher rhenium concentrations. The iron rich samples were not very resistant to corrosion under the test conditions; there was no notable trend in corrosion behavior related to the introduction of rhenium.