Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 207-244).

No description available.

Thesis (M.A.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on January 11, 2008) Includes bibliographical references.

Thesis (M.Sc.)--York University, 2007. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 149-159). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38802

This thesis investigates three problems in the general area of environmental fluid mechanics. The first two problems are related to liquid or gas flow through clay-water suspensions, with relevance for the underground storage of radioactive waste and also for understanding the mechanism of eruption in mud volcanoes. The third problem centres on the different problem of mixing in a turbulent buoyant plume. First, the injection of gas and water from a central source into a two-dimensional layer of clay confined between two circular horizontal plates is investigated. This provides a model of the potential pressurisation and failure of the seal rock around a radioactive waste repository as may arise if gas is continuously generated in the repository. As the gas injection pressure is gradually increased the cell walls deform and the clay moves radially outwards. However, at a critical radius, the liquid-clay interface becomes unstable and a series of channels propagate through the clay. When one of the channels reaches the edge of the domain the gas escapes and the pressure is released. As a result, the domain relaxes by elastic deformation and the clay seals the channel. In this way, continuous fluid injection leads to episodic release of gas from the cell. The second problem concerns the flow of mud along a vertical conduit driven by the combined effect of reservoir pressure and buoyancy associated with the gas injected at the base of the conduit. This represents an analogue model of the eruption of a mud volcano, in which mud rises from a deep reservoir to the surface. I find that the pressure associated with the reservoir and any buoyancy force produced by the migration of gas from deep in the reservoir to the surface leads to a continuous eruption if the net pressure is greater than the yield stress of the clay. If the reservoir pressure falls during such an event, the eruption will eventually stop, once the pressure reaches a dynamic yield stress condition. Only later, if the reservoir pressure increases to the static yield stress of the clay will the eruption start again, and this can lead to a series of eruption cycles which depend on the non-Newtonian rheology of the clay. In contrast, if this pressure is smaller than the yield stress of the clay, a series of episodic gas burst events can occur until the conduit is cleared of mud. The third problem relates to the mixing in a turbulent buoyant plume. Through a series of new experiments and some complementary theoretical modelling I show that the mixing in a turbulent plume is strongly affected by the eddies and leads to significant longitudinal dispersion in the flow. The implications of the modelling for determining the residence time distribution of the fluid in the plume is discussed.

Coupled Thermo-Hydro-Mechanical (THM) behavior in geological porous media has been a subject of great interest in many geoengineering disciplines. Many attempts have been made to develop numerical prediction capabilities associated with topics such as the movement of pollutant plumes, gas injection, energy storage, geothermal energy extraction, and safety assessment of repositories for radioactive waste and spent nuclear fuel. This thesis presents a new numerical modeling approach and a new computer code for simulating coupled THM behavior in geological porous media in general, and compacted bentonite clays in particular, as buffer materials in underground radioactive waste repositories. New governing equations were derived according to the theory of mixtures, considering interactions among solid-phase deformation, flows of water and gases, heat transport, and phase change of water. For three-dimensional problems, eight governing equations were formulated to describe the coupled THM processes. A new thermal conductivity model was developed to predict the thermal conductivity of geological porous media as composite mixtures. The proposed model considers the combined effects of solid mineral composition, temperature, liquid saturation degree, porosity and pressure on the effective thermal conductivity of the porous media. The predicted results agree well with the experimental data for MX80 bentonite. A new water retention curve model was developed to predict the suction-saturation behavior of the geological porous media, as a function of suction, effective saturated degree, temperature, porosity, pore-gas pressure, and the rate of saturation degree change with time. The model was verified against experimental data of the FEBEX bentonite, with good agreement between measured and calculated results. A new finite element code (ROLG) was developed for modeling fully coupled thermo-hydro-mechanical processes in geological porous media. The new code was validated against several analytical solutions and experiments, and was applied to simulate the large scale in-situ Canister Retrieval Test (CRT) at Äspö Hard Rock Laboratory, SKB, Sweden, with good agreement between measured and predicted results. The results are useful for performance and safety assessments of radioactive waste repositories. / QC20100720 / THERESA

The purpose of this research is to develop a methodology for a thorium fuel recycling analysis that provides results for isotopics and radio-toxicity evaluation and analysis. This research is motivated by the need to reduce the long term radiological hazard in spent nuclear fuel, which mitigates the mixing hazard (radiotoxicity and chemical toxicity) and decay heat load on the repository. The first part of the thesis presents comparison of several once-through cases with uranium and thorium fuels to show how transuranics build up as fuel is depleted. The once-through analysis is performed for the following pairs of comparison cases: low enriched uranium dioxide (UOX) vs. thorium dioxide with 233UOX (233U-ThOX), natural uranium dioxide mixed with transuranic oxides (U-TRUOX) vs. thorium dioxide mixed with transuranic oxides (Th-TRUOX), natural uranium dioxide mixed with weapons grade plutonium dioxide (U-WGPuOX) vs. thorium dioxide mixed with weapons grade plutonium dioxide (Th-WGPuOX), natural uranium dioxide mixed with reactor grade plutonium dioxide (U-RGPuOX) vs. thorium mixed with reactor grade plutonium dioxide (Th-RGPuOX). The second part of the research evaluates the thorium fuel equilibrium cycle in a pressurized water reactor (PWR) and compares several recycling cases with different partitioning schemes. Radio-toxicity results of the once-through cycle and multi-recycle calculations demonstrate advantages for thorium fuel and reprocessing with respect to long term nuclear waste management.

Den här uppsatsen hanterar ämnet om ett nukleärt arv och minne genom en fallstudie bunden till fyra identifierade aktörer. Alla fyra arbetar med etablerandet av ett slutförvar för högaktivt och långlivat radioaktivt avfall vilket förväntas vara fortsatt farligt under 100,000-tals år. På grund av det enorma tidsspann det gäller lyfter uppsatsen även koncept så som djup tid och den antropocena tidsåldern som bakgrund till sitt ämnesmaterial. Uppsatsen håller även ett fokus på ansvarsfrågan, då det visade sig att det inte fanns något tydligt svar på frågan om vem som höll det primära ansvaret i frågan av informationsbevaring hos aktörerna, om det ens skulle falla fullkomligen till någon av dem, i deras egna ögon. Uppsatsen är centrerad kring arbetet i Sverige, och inte på en explicit internationell nivå. Genom att använda värdebaserade teorier tillsammans med Pierre Noras teori om platser av minne närmar sig uppsatsen frågan om hur aktörer arbetar med informationsbevaring och kunskapshantering, samt hur minnesinstitutioner så som arkiv kan bidra i deras arbete. Generellt visade det sig att aktörernas arbete med informationsbevaring låg på en primärt teoretisk nivå med lite försök till konkretisering av planer. Olika ideer som är menade att underlätta i processen för långtidsinformationsbevaring presenteras, så som markörer, markeringssystem, och immateriella och materiella minnesplatser. Minnesinstitutioner skulle kunna spela en viktig roll inom informationsbevaring för aktörerna som är ansvariga för slutförvaret, två primära sätt presenteras i uppsatsen, (1) arkivhandlingar, och (2) involverandet av Riksantikvarieämbetet. Detta är en två-årig masteruppsats inom musei- och kulturarvsvetenskap. / This thesis handles the subject of nuclear heritage and memory through a case study surrounding the work with information preservation of 4 identified main actors. The information preservation is in turn centred around the potential establishing of a future final repository for highly active and long-lived radioactive waste, which is expected to still be dangerous within 100,000’s of years. Because of these immense time frames the thesis also takes concepts such as deep time and the Anthropocene into account as background to its subject matter. The thesis holds a focus on the responsibility question, as there turned out to be no unambiguous answer to the question of who were to hold responsibility, if any of them were to hold responsibility, in the eyes of the actors.  The case study is centred around the work in Sweden, and not on an explicitly international scale. By using value-based theories as well as Pierre Nora’s theory of sites of memory the thesis approaches the issue of how actors work with information preservation as well as how memory institutions such as archives can contribute to their efforts.   In general, it is found that the actors’ work with information preservation is primarily theoretical with little attempt at concrete executions of solid plans. Different ideas that are meant to facilitate long-term information preservation are presented, such as markers and marking systems, as well as tangible and intangible sites of memory. Memory institutions could play an important role in information preservation for the actors in charge of the repository, two primary ways this could be the case is presented in this thesis, (1) archival records, and (2) involvement of the Swedish National Heritage Board. This is a two-year master’s thesis in Museum and Cultural Heritage Studies.

About 60 percent of the electricity production in Belgium originates from nuclear power plants. Belgium owns 7 nuclear pressurized water reactors, which are located in two sites: 4 reactors in Doel and 3 reactors in Tihange. Together they have a capacity of approximately 5900 MWe. All these reactors use classical uranium oxide fuel assemblies. Two of them (Doel3, Tihange2) have also accepted a limited number of mixed (uranium and plutonium) oxide fuel assemblies. These mixed fuel assemblies came from the reprocessing of spent uranium oxide fuel assemblies in La Hague (France). The reprocessing of spent fuel gives birth to vitrified high-level waste, and to different isotopes of uranium and plutonium, which can be used in the manufacture of mixed oxide fuel assemblies. Each country producing radioactive waste must find a solution to dispose them safely. The internationally accepted solution is to dispose high-level radioactive waste in a deep and stable geological layer. This seems to be the most secure and environment-friendly way to get rid of the high-level radioactive waste. One of the few stable geological layers, which could accept radioactive waste in Belgium, is the Boom clay layer. Another possible layer is the Ypresian clay layer, but it is not the reference option for the moment. The Boom clay layer is quite thin (about 100 m thick) and is not at a large depth (about 240 m below the ground surface) at the proposed disposal site, beneath the SCK CEN Nuclear Research Centre in Mol. A large number of studies have already been performed on the Boom clay layer, and on the possibility of building a high-level radioactive waste repository in this geological medium. Since 1993, the Belgian government has promulgated a moratorium on the reprocessing of spent uranium oxide fuels in La Hague. Since then, spent fuel assemblies are considered as waste, and ONDRAF/NIRAS (the Belgium Agency for Radioactive Waste and Enriched Fissile Materials) has thus to deal with them as waste. This rises a number of questions on how to deal with this new kind of waste. A solution is to directly dispose these spent fuel assemblies in containers in a repository, just like the other high-level radioactive waste. This repository would be build in the Boom clay layer at a depth of about 240 m beneath the SCK CEN. One of the questions raised by this new kind of waste is: "could the direct disposal of the spent nuclear fuel assemblies lead to nuclear criticality risks in the future?". Nuclear criticality is the ability of a system to sustain a nuclear fission chain reaction. This question was not a key issue with vitrified high-level waste because these do not include fissile uranium and plutonium isotopes, which could lead to a criticality event. The spent fuel repository will be designed in order to totally avoid the occurrence of a criticality event at the closure time. But in the future history of the repository, external events could possibly affect this. These events could maybe lead to criticality inside the repository, and this has also to be avoided. This work tries to answer this question, and to determine how to avoid a long-term criticality event inside the repository. The only complete research work answering this question has been performed in the U.S. for the Yucca Mountain repository but this design is fully different from the Belgian one studied here: for example, the waste are not only spent fuel waste, and the geological layer is volcanic tuff.<p>The main achievements of this work are: <p>*A first set of in-package criticality scenarios for different design options for a Belgian spent fuel repository in the Boom clay layer. <p>*A large number of criticality calculations with different parameters (fuel type, fuel burnup, fuel enrichment, distance between the fuel assemblies, distance between the fuel rods, water fraction inside the overpack) for the different design options. <p>*A preliminary study of the effects of the spent fuel assemblies isotopic evolution with time on the multiplication factor. <p>*For the first time, a coupling between the in-package criticality scenarios and the criticality calculations has been performed. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Les études du risque du stockage de déchets radioactifs comprennent, comme toute étude du risque, un traitement de l'incertitude. L'outil de calcul du risque, appelé outil PRA (Probabilistic Risk Assessment), est formé d'un code de calcul d'écoulement des eaux souterraines et de transport de chaînes de radionucléides. Ce type d'outil est essentiel pour l'évaluation de performance de la barrière géologique. Le manque de connaissances au sujet de la variabilité (dans l'espace et le temps) des propriétés hydrogéologiques de cette barrière est la raison primaire de l'incertitude et des méthodes stochastiques ont été développées en hydrogéologie pour le traiter.<p>Dans cette thèse, l'analyse d'incertitude liée à la composition du milieu géologique est partagée entre l'écoulement et le transport de la manière suivante: a) une solution moyenne de l'écoulement est tout d'abord déterminée à l'aide d'un code basé sur la méthode des différences finies. Cette solution est ensuite soumise à une analyse de sensibilité. Cette analyse débouche sur la résolution d'un problème inverse afin d'améliorer l'estimation initiale des paramètres moyens d'écoulement; b) l'effet de la variation aléatoire de la vitesse d'écoulement est envisagé lors du transport des radionucléides. Le transport est résolu à l'aide d'une méthode Monte Carlo non analogue.<p><p>L'analyse de sensibilité du problème d'écoulement est réalisée à l'aide d'une méthode variationnelle. La méthode proposée a comme avantage celui de pouvoir quantifier l'incertitude de structure; c'est-à-dire l'incertitude liée à la géométrie du milieu géologique.<p>Une méthodologie Monte Carlo non analogue est utilisée pour le transport de chaînes de radionucléides en milieu stochastique. Les apports de cette méthodologie pour le calcul du risque reposent sur trois points:<p>1) L'utilisation d'une solution de transport simple (sous la forme d'une solution adjointe) dans les mécanismes de la simulation Monte Carlo. Cette solution de transport permet de résumer, entre deux positions successives du marcheur aléatoire, les processus chimicophysiques (advection, diffusion-dispersion, adsorption, désorption,) apparaissant à l'échelle microscopique. Elle rend possible des simulations efficaces de transport en accélérant les mécanismes de transition des marcheurs aléatoires dans le domaine géologique et dans le temps.<p>2) L'application de la méthode des arbres d'événements continus au transport de chaînes de radionucléides. Cette méthode permet d'envisager les transitions radioactives entre éléments d'une chaîne selon un même formalisme que celui qui prévaut pour les simulations de transport d'un radionucléide unique. Elle permet donc de passer du transport d'un radionucléide au transport d'une chaîne de radionucléides sans coûts supplémentaires en temps de calcul et avec un coût supplémentaire en mémoire limité.<p>3) L'application de techniques dites de "double randomization" au problème de transport de radionucléides dans un milieu géologique stochastique. Ces techniques permettent de combiner efficacement une simulation Monte Carlo de paramètres avec une simulation Monte Carlo de transport et ainsi d'inclure l'incertitude associée à la composition du milieu géologique explicitement dans le calcul du risque.<p><p>Il ressort de ce travail des perspectives prometteuses de développements ultérieurs de la méthodologie Monte Carlo non analogue pour le calcul du risque.<p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished