Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

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The feasibility of capital projects in an uncertain world can be determined in several ways. One of these methods is real options valuation which arose from financial option valuation theory. On the other hand fuzzy set theory was developed as a mathematical framework to capture uncertainty in project management. The valuation of real options using fuzzy numbers represents an important refinement to determining capital projects' feasibility using the real options approach. The aim of this study is to determine whether the deferral of the decommissioning time (by a decade) of an electricity-generating nuclear plant in South Africa increases decommissioning costs. Using the fuzzy binomial approach, decommissioning costs increase when decommissioning is postponed by a decade whereas use of the fuzzy Black-Scholes approach yields the opposite result. A python code was developed to assist in the computation of fuzzy binomial trees required in our study and the results of the program are incorporated in this thesis. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The management of radioactive wastes is a significant environmental issue facing the international nuclear community today. The current international consensus is for disposal of higher activity waste from a variety of sources in deep geological disposal facilities (GDFs). Hydraulic seals, often planned to consist of compacted bentonite-sand blocks, are an important part of the closure phase of a GDF. As such, an understanding of the hydro-mechanical (HM) behaviour of these seals, and the ability to model and predict their behaviour is fundamental to support many planned safety cases and licence applications. Bentonite is well suited for use as a hydraulic seal due to its high swelling capacity that enables it to swell into voids while maintaining a low permeability sealed barrier to advective flow, and to provide structural support by generating a swelling pressure on the excavation walls. The hydro-mechanical process of bentonite hydration is a highly non-linear problem. As such, coupled process models that are able to account for the strong inter-dependence of the hydraulic and mechanical processes are employed to simulate the behaviour of bentonite under repository conditions. This thesis reports the development of an HM coupled model in the open source finite element code OpenGeoSys (OGS), and its application to the simulation of a range of hydraulic seal test conditions. The developed model couples Richards’ equation for unsaturated flow to a new strain dependent non-linear elastic mechanical model that incorporates a Lagrangian moving finite element mesh to inform the material non-linearity. Stress and volumetric dependent water retention behaviour are incorporated through the implementation of the Dueck suction concept extended to take into account non-recoverable strains during consolidation. A number of permeability functions are implemented and tested against experimental data. The mechanical model is extended to account for wetting-induced collapse behaviour by the definition of a failure curve derived from experimental results. Similar in definition to the Loading-Collapse curve in elasto-plastic models, this failure curve triggers the application of a source term to account for wetting-induced collapse. Coupling between the hydraulic and mechanical processes is achieved through the stress dependency of the water retention behaviour, the inclusion of a new coupling factor for the hydraulic contribution to the mechanical process, and the dependency of numerical convergence criteria on net mean stress. An explicit iterative calculation approach is employed. As a result, the hydraulic and mechanical moving meshes are decoupled to allow volumetric dependent parameters to be updated within process iterations. The model is calibrated and compared to experimental data from the SEALEX experiments conducted by the Institut de Radioprotection et de S ˆ uret´e Nucl´eaire (IRSN) at the Tournemire URL, France. The experimental programme comprises standardised laboratory tests, a 1/10th scale mock-up of a hydraulic seal with a uniform technological void, and a full scale in situ performance test with a non-uniform technological void due to its horizontal geometry. Using a model with 5 hydraulic parameters, 8 mechanical parameters with an experimentally defined failure curve, and one coupling parameter, the major trends of behaviour in all the SEALEX experiments can be recreated, including axial stress build up, water uptake, and final deformation. However, the elastic method employed leads to an over prediction of the rebound on loss of axial confinement in the 1/10th scale mock-up test. Simulations suggest that the non-symmetric technological void in the full scale performance test could have lasting effects on the development of heterogeneity in the hydraulic seal. The development of heterogeneity does not adversely affect the permeability with respect to the design criteria, but may have significant consequences for the development of a heterogeneous swelling pressure.

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Made available in DSpace on 2014-10-09T12:34:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:18Z (GMT). No. of bitstreams: 0 / Um aspecto fundamental da aceitação pública da energia nuclear é a crença de que os rejeitos radioativos podem ser gerenciados de maneira segura, no intuito de proteger os seres humanos dos possíveis efeitos prejudiciais, tanto nas gerações atuais como nas futuras. Neste sentido, é essencial compreender como as pessoas percebem o risco associado com rejeitos radioativos e quais são os principais fatores que conduzem suas atitudes em relação à eliminação destes. Uma das maneiras para alcançar esse entendimento é através de pesquisas de opinião. Neste estudo, foi proposto um questionário focado na questão da aceitabilidade da energia nuclear e sua associação com a gestão de rejeitos radioativos, cobrindo os seguintes aspectos: atitudes em relação à energia nuclear e aos rejeitos radioativos, credibilidade das instituições e setores responsáveis pela segurança nuclear, identificação dos benefícios percebidos; percepção do risco de determinadas tecnologias e atividades, percepção do risco real, compreensão das reações emocionais e princípio da precaução. Resultados obtidos a partir de uma aplicação piloto do questionário são apresentados e discutidos neste trabalho. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:28:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:44Z (GMT). No. of bitstreams: 0 / Fontes radioativas seladas são largamente empregadas no mundo. A Agência Internacional de Energia Atômica AIEA estima em dezenas de milhões de fontes radioativas no mundo. No Brasil, este número é próximo de 500 mil unidades, considerando-se as fontes de pára-raios e detectores de fumaça. Uma fonte selada pode tornar-se desnecessária, seja devido ao seu decaimento ou outro motivo, sendo classificada como fontes radioativas seladas fora de uso (FRS). No Brasil, a maioria das FRS é considerada rejeito radioativo e são encaminhadas a um dos institutos da CNEN. Sem uma estratégia definida para a deposição das FRS, estas são armazenadas aguardando uma solução. A Gerência de Rejeitos Radioativos - GRR do IPEN-CNEN/SP é o principal centro de recepção desse material e até meados de 2010 havia recebido cerca de 14.000 fontes. O processo proposto para a gestão dessas FRS consiste em retirá-las de suas blindagens originais e transferi-las a outra blindagem, projetada para esse fim. As operações de transferência são realizadas em uma cela quente, garantindo a segurança radiológica. Uma das exigências da CNEN é que todas as fontes seladas sejam caracterizadas. No processo estudado, a avaliação da atividade de cada fonte será feita utilizando-se um detector, do tipo câmara de ionização tipo poço. O presente trabalho tem por objetivo desenvolver uma metodologia para aferir ou determinar a atividade de FRS armazenadas na GRR de acordo com sua geometria e determinar suas incertezas. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Down-hole injection and sampling equipment was designed and constructed in order to perform diverging-flow tracer tests. The tests were conducted at a field site about 8 km southeast of Oracle, Arizona, as part of a project sponsored by the U. S. Nuclear Regulatory Commission to study mass transport of fluids in saturated, fractured granite. The tracer injection system was designed to provide a steady flow of water or tracer solution to a packed off interval of the borehole and allow for monitoring of down-hole tracer concentration and pressure in the injection interval. The sampling system was designed to collect small volume samples from multiple points in an adjacent borehole. Field operation of the equipment demonstrated the importance of prior knowledge of the location of interconnecting fractures before tracer testing and the need for down-hole mixing of the tracer solution in the injection interval. The field tests were designed to provide data that could me analyzed to provide estimates of dispersivity and porosity of the fractured rock. Although analysis of the data is beyond the scope of this thesis, the detailed data are presented in four appendices.