The goal of this research was to identify and fabricate zeolitic membranes that can separate radioisotope krypton-85 (half-life 10.72 years) and xenon gas released during spent nuclear fuel reprocessing. In spent nuclear fuel reprocessing, fissionable plutonium and uranium are recovered from spent nuclear fuel and recycled. During the process, krypton-85 and xenon are released from the spent nuclear fuel as process off-gas. The off-gas also contains NO, NO2, 129I, 85Kr, 14CO2, tritium (as 3H2O), and air and is usually vented to the atmosphere as waste without removing many of the radioactive components, such as 85Kr. Currently, the US does not reprocess spent nuclear fuel. However, as a member of the International Framework for Nuclear Energy Cooperation (IFNEC, formerly the Global Nuclear Energy Partnership), the United States has partnered with the international nuclear community to develop a “closed” nuclear fuel cycle that efficiently recycles all used nuclear fuel and safely disposes all radioactive waste byproducts. This research supports this initiative through the development of zeolitic membranes that can separate 85Kr from nuclear reprocessing off-gas for capture and long-term storage as nuclear waste. The implementation of an 85Kr/Xe separation step in the nuclear fuel cycle yields two main advantages. The primary advantage is reducing the volume of 85Kr contaminated gas that must be stored as radioactive waste. A secondary advantage is possible revenue generated from the sale of purified Xe. This research proposed to use a zeolitic membrane-based separation because of their molecular sieving properties, resistance to radiation degradation, and lower energy requirements compared to distillation-based separations. Currently, the only commercial process used to separate Kr and Xe is cryogenic distillation. However, cryogenic distillation is very energy intensive because the boiling points of Kr and Xe are -153 °C and -108 °C, respectively. The 85Kr/Xe separation step was envisioned to run as a continuous cross-flow filtration process (at room temperature using a transmembrane pressure of about 1 bar) with a zeolite membrane separating krypton-85 into the filtrate stream and concentrating xenon into the retentate stream. To measure process feasibility, zeolite membranes were synthesized on porous α-alumina support discs and permeation tested in dead-end filtration mode to measure single-gas permeance and selectivity of CO2, CH4, N2, H2, He, Ar, Xe, Kr, and SF6. Since the kinetic diameter of krypton is 3.6 Å and xenon is 3.96 Å, zeolites SAPO-34 (pore size 3.8 Å) and DDR (pore size 3.6 Å) were studied because their pore sizes are between or equal to the kinetic diameters of krypton and xenon; therefore, Kr and Xe could be separated by size-exclusion. Also, zeolite MFI (average pore size 5.5 Å) permeance and selectivity were evaluated to produce a baseline for comparison, and amorphous carbon membranes (pore size < 5 Å) were evaluated for Kr/Xe separation as well. After permeation testing, MFI, DDR, and amorphous carbon membranes did not separate Kr and Xe with high selectivity and high Kr permeance. However, SAPO-34 zeolite membranes were able to separate Kr and Xe with an average Kr/Xe ideal selectivity of 11.8 and an average Kr permeance of 19.4 GPU at ambient temperature and a 1 atm feed pressure. Also, an analysis of the SAPO-34 membrane defect permeance determined that the average Kr/Xe selectivity decreased by 53% at room temperature due to unselective defect permeance by Knudsen diffusion. However, sealing the membrane defects with polydimethylsiloxane increased Kr/Xe selectivity by 32.8% to 16.2 and retained a high Kr membrane permeance of 10.2 GPU at ambient temperature. Overall, this research has shown that high quality SAPO-34 membranes can be consistently fabricated to achieve a Kr/Xe ideal selectivity >10 and Kr permeance >10 GPU at ambient temperature and 1 atm feed pressure. Furthermore, a scale-up analysis based on the experimental results determined that a cross-flow SAPO-34 membrane with a Kr/Xe selectivity of 11.8 and an area of 4.2 m2 would recover 99.5% of the Kr from a 1 L/min feed stream containing 0.09% Kr and 0.91% Xe at ambient temperature and 1 atm feed pressure. Also, the membrane would produce a retentate stream containing 99.9% Xe. Based on the SAPO-34 membrane analysis results, further research is warranted to develop SAPO-34 membranes for separating 85Kr and Xe.

Submitted in fulfillment for the requirements for the degree of Doctor of Technology: Biotechnology, Durban University of Technology, Durban, South Africa, 2015. / Main focus of this study is to investigate the enzymatic-conversion of microalgal lipids to biodiesel. However, preceding steps before conversion such as drying of microalgal biomass and extraction of lipids were also studied. Downstream processing of microalgae has several challenges and there is very little literature available in this area. S. obliquus was grown in the pilot scale open pond cultivation system for biomass production. Different techniques were studied for biomass drying and extraction of lipids from harvested microalgal biomass. Effect of these drying and extraction techniques on lipid yield and quality was assessed. Energy consumption and economic evaluation was also studied. Enzymatic conversion of microalgal lipids by extracellular and whole cell lipase application was investigated. For both applications, free and immobilized lipases from different sources were screened and selected based on biodiesel conversion. Process parameters were optimized using chosen extracellular and whole cell lipases; also step-wise methanol addition was studied to improve the biodiesel conversion. Immobilized lipase was studied for its reuse. Final biodiesel was characterized for its fuel properties and compared with the specifications given by international standards. Enzymatic conversion of microalgal lipids was compared with the conventional homogeneous acid-catalyzed conversion. Enzymatic conversion and chemical conversion were techno-economically investigated based on process cost, energy consumption and processing steps. Freeze drying was the most efficient technique, however at large scale economical sun drying could also be selected as possible drying step. Microwave assisted lipid extraction performed better compared to sonication technique. Immobilized P. fluorescens lipase in extracellular application and A. niger lipase in whole cell application showed superior biodiesel conversion. The extracellular immobilized P. fluorescens lipase showed better biodiesel conversion and yields than the immobilized A. niger whole cell lipase. Both the enzyme catalysts showed lower biodiesel conversion compared to conventional chemical catalyst and higher processing cost. However, techno-economic analysis showed that, the reuse potential of immobilized lipases can significantly improve the economics. Fewer purification steps, less wastewater generation and minimal energy input are the benefits of enzymatic route of biodiesel conversion. Microalgae as a feedstock and lipase as a catalyst for conversion makes overall biodiesel production process environmentally-friendly. Data from this study has academic as well as industrial significance. Conclusions from this study form the basis for greener and sustainable scaling-up of microalgal biodiesel production process. / D

The laminar burning velocity is an important fundamental property of a fuel-air mixture at given conditions of temperature and pressure. Knowledge of burning velocities is required as an input for combustion models, including engine simulations, and the validation of chemical kinetic mechanisms. It is also important to understand the effect of stretch upon laminar flames, to correct for stretch and determine true (unstretched) laminar burning velocities, but also for modelling combustion where stretch rates are high, such as turbulent combustion models. A constant volume combustion vessel has been used in this work to determine burning velocities using two methods: a) flame speed measurements during the constant pressure period, and b) analysis of the pressure rise data. Consistency between these two techniques has been demonstrated for the first time. Flame front imaging and linear extrapolation of flame speed has been used to determine unstretched flame speeds at constant pressure and burned gas Markstein lengths. Measurement of the pressure rise during constant volume combustion has been used along with a numerical multi-zone combustion model to determine burning velocities for elevated temperatures and pressures as the unburned gas ahead of the spherically expanding flame front is compressed isentropically. This burning velocity data is correlated using a 14 term correlation to account for the effects of equivalence ratio, temperature, pressure and fraction of diluents. This correlation has been modified from an existing 12 term correlation to more accurately represent the dependence of burning velocity upon temperature and pressure. A number of fuels have been tested in the combustion vessel. Biogas (mixtures of CH₄ and CO₂) has been tested for a range of equivalence ratios (0.7–1.4), with initial temperatures of 298, 380 and 450 K, initial pressures of 1, 2 and 4 bar and CO₂ fractions of up to 40&percnt; by mole. Hydrous ethanol has been tested at the same conditions (apart from 298 K due to the need to vaporise the ethanol), and for fractions of water up to 40&percnt; by volume. Binary, ternary and quaternary blends of toluene, n-heptane, ethanol and iso-octane (THEO) have been tested for stoichiometric mixtures only, at 380 and 450 K, and 1, 2 and 4 bar, to represent surrogate gasoline blended with ethanol. For all fuels, correlation coefficients have been obtained to represent the burning velocities over wide ranging conditions. Common trends are seen, such as the reduction in burning velocity with pressure and increase with temperature. In the case of biogas, increasing CO₂ results in a decrease in burning velocity, a shift in peak burning velocity towards stoichiometric, a decrease in burned gas Markstein length and a delayed onset of cellularity. For hydrous ethanol the reduction in burning velocity as H₂O content is increased is more noticeably non-linear, and whilst the onset of cellularity is delayed, the effect on Markstein length is minor. Chemical kinetic simulations are performed to replicate the conditions for biogas mixtures using the GRI 3.0 mechanism and the FlameMaster package. For hydrous ethanol, simulations were performed by Carsten Olm at Eötvös Loránd University, using the OpenSMOKE 1D premixed flame solver. In both cases, good agreement with experimental results is seen. Tests have also been performed using a single cylinder optical engine to compare the results of the hydrous ethanol tests with early burn combustion, and a good comparison is seen. Results from tests on THEO fuels are compared with mixing rules developed in the literature to enable burning velocities of blends to be determined from knowledge of that of the pure components alone. A variety of rules are compared, and it is found that in most cases, the best approximation is found by using the rule in which the burning velocity of the blend is represented by weighting by the energy fraction of the individual components.

The human effort to continuously improve their standard of living in conjunction with the rapid growth of world‟s population, the reckless and the wasteful misuse of energy reserves threaten to lead mankind in an energy deadlock. In an effort to realize the size of the waste of our planet‟s available energy resources, we only need to point out that people have spent the last century stocks of raw materials and energy, which were saved and produced during the lifetime of our planet. The management of the energy systems in a proper and best way is considered to be essential worldwide. In this project the energy system of Greece is studied. The power production systems used in different sectors of life were analyzed. The study emphasized in the electricity production from different sources. Lignite electricity power plants were first introduced in the country followed by the gas power plants and Renewable Energy Sources (RES) installations. The deregulation of electricity market formed the new energy scenery of the country. Electricity grid reinforcements with smart metering and energy storage proved to be necessary in order the RES to be fully penetrated to the national grid, so as Greenhouse Gas (GHG) emissions to be reduced as much as possible. The further expansion of RES could help to cope with the barriers of the country‟s electrification due to singularity of hundred islands that are not yet interconnected to the mainland. Analytical theory methods and numerical skills used to derive the appropriate data and results. Installed capacity of the power sources was verified as well as costs and polluted emissions per unit and type of sources involved. Weaknesses and abnormalities of the electric system were pointed out. Proved gains from the RES use were verified for ensuring the sustainability of the country‟s energy system

Ces travaux ont été développés dans le contexte de l'analyse vibratoire des assemblages combustibles. Ce type de structure est très complexe et a, du fait de sa géométrie, une très forte densité modale. Ainsi, afin de calculer la réponse d'une telle structure, une modélisation simplifiée est préférable. L'objectif est d'identifier des forces stochastiques induites par l'écoulement en utilisant un modèle numérique incertain et des réponses expérimentales. Pour ce problème, 4 sources d'incertitudes sont à prendre en considération : (1) Les incertitudes de modèle induites par les simplifications du modèle. (2) Les incertitudes sur les forces induites par les fluctuations statistiques de la pression turbulent. (3) Les incertitudes concernant la modélisation des forces stochastiques. (4) Les incertitudes induites par les erreurs de mesures. Les forces stochastiques ainsi identifiées sont appliquées sur le modèle simplifié stochastique pour calculer des statistiques sur les quantités d'intérêt / The present research has been developed in the context of the dynamical analysis of fuels assemblies which is a very complex nonlinear dynamical systems due to the high modal density of such a structure. Therefore, the computational model has to be simplified. The objective of this research is to identify stochastic forces induced by the turbulent fluid which are applied to the structure, using an uncertain stochastic simplified computational model and experimental responses. In this problem, there are four sources of uncertainties : (1) The model uncertainties induced by the simplifications in the model. (2) The uncertainties on the loads induced by the statistical fluctuations of the applied turbulent pressure. (3) The uncertainties concerning the model of the stochastic loads. (4) The uncertainties induced by measurement. The identified stochastic loads and the stochastic simplified computational model are then used to construct statistics on quantities of interest

<p>The research described in this dissertation focuses on several areas: developing analytical methods to distinguish structural isomers, identifying the chemical compositions of aviation fuels and evaluating the effectiveness of organic dopants to swell aircraft o-ring seals. Chapter 2 discusses fundamental aspects of mass spectrometry, and ionization methods and the instrumentation used to complete this research. </p> <p>Chapter 3 discusses and compares two activation methods used to distinguish ionized structural isomers. Ionized naphthene-containing aromatic structural isomers were subjected to collision-activated dissociation (CAD) in an ion trap (ITCAD) and to medium-energy collision-activated dissociation (MCAD) in an octupole collision cell, both in the energy-resolved mass spectrometry mode (ERMS). MCAD was shown to be superior over ITCAD at the structural differentiation of the ionized isomers. </p> <p>Determination of the chemical compositions of petroleum-based jet and diesel fuels, potential alternative fuels and fuel blending components by using a GCxGC/(EI)TOF MS is discussed in chapter 4. The ability to determine the chemical compositions of fuels and to correlate the identified compounds and their concentrations to the physical and chemical properties and aircraft performance of the fuels is vital for the development of future resilient, alternative fuels. The chemical compositions of petroleum-based fuels were found to be different from potential alternative fuels.</p> <p>Chapter 5 discusses the effectiveness of aromatic and nonaromatic compounds in swelling air craft o-ring seals, which prevents leaks in the fuel circulation systems. The aim of this study was to identify aromatic and nonaromatic compounds that most effectively swell o-ring seals. Steric effects were shown to decrease the efficiency of the compounds to swell seals. Ethylbenzene and indane were found to swell o-ring seals more effectively than any other compounds studied, including a currently approved alternative fuel. </p>

A contaminação de águas subterrâneas por hidrocarbonetos provenientes de postos de abastecimento de combustível tem sido objeto de crescente preocupação dos organismos ambientais de todo o mundo. Os compostos Benzeno, Tolueno, Etilbenzeno e Xilenos (BTEX), presentes nesses combustíveis, são extremamente tóxicos à saúde humana e podem inviabilizar a exploração de aqüíferos por eles contaminados e conseqüentemente os poços utilizados para abastecimento. Neste trabalho, foi realizado um diagnóstico da qualidade da água, com informações e análises, com o objetivo de retratar a situação dos poços artesianos destinados ao abastecimento de água, doméstico e comercial, na área urbana do município de Santo André, São Paulo. Foram avaliadas a presença dos micro poluentes BTEX, após a ocorrência de vazamentos de gasolina de tanques de armazenamento de combustível próximos a estes poços, em diferentes locais do município. Foram avaliados também parâmetros físico-químicos (cor, turbidez e cloro residual) bem como os elementos-traço, metais e os ânions fluoreto, sulfato, cloreto, nitrato e fosfato, como também os bacteriológicos (coliformes totais e termotolerantes, bactérias heterotróficas). Na definição dos locais amostrados, procurou-se primeiramente avaliar a série histórica de contaminação ambiental por postos de gasolina, avaliando o conjunto de informações do órgão ambiental do Estado e a representatividade espacial do problema. Para gerenciamento da qualidade da água subterrânea foi adotada a metodologia utilizada pela Companhia de Tecnologia de Saneamento Ambiental (CETESB), sendo realizado uma identificação prévia de Áreas Potenciais (AP) de contaminação, organizando um banco de dados sobre &#61472;&#61472;lixões e locais abandonados; cadastramento dos postos de serviço e poços utilizados pela população e inventário industrial com plantas ativas e abandonadas, levando-se em consideração o porte e a geração de resíduos (com o SEMASA), dessa forma priorizando os locais de monitoramento. Foi feito um cadastro dos locais e realizada uma investigação preliminar das áreas suspeitas. A amostragem e o monitoramento foram realizados e os resultados foram comparados com os valores orientadores para água subterrânea estabelecidos pela CETESB. Os resultados mostraram que nos doze poços avaliados, não foram encontrados valores de BTEX acima do permitido pela Portaria 518/2004 do Ministério de Saúde, em que o teor máximo permitido para o benzeno é de 5 µg L-1. Foi observado que em três poços há contaminação por nitrato, que é responsável pela indução da metaemoglobinemia. Foram avaliados também os possíveis processos ou mecanismos de remediação natural (biodegradação) ou induzida. / The contamination of underground waters by hydrocarbons originated from gas stations has been object of increasing preoccupation in environmental organization all over the world. The organic compounds Benzene, Toluene, Ethylbenzene and Xylene (BTEX), present in these fuels, are extremely toxic to human health and could make impracticable the exploration of these contaminated waters by these kinds of pollutants and consequently the gasoline wells used for this purpose. In this work, it was carried out a diagnosis of the water quality with information and analyses, with the goals to snap shot the situation of the wells destinated to domestic and commercial supply of water in the urban area of Santo André city, São Paulo state. There have been evaluated the presence of micron pollutants BTEX, after contamination due to leaks in fuel storage tanks close to the wells, in different places of the city. The physical chemistry parameters like color, turbidity and residual chlorine were also evaluated as well as trace elements, metals, anions like fluorine, sulphates, chlorine, nitrates and phosphates and bacteriological (total coliphorms, themostable coliphorms, heterotrophic bacterias). On definition of the sampling area, it was sought, at first, the evaluation of environmental contaminations historical series by gas stations, evaluating the set of information available at government environmental organizations and spacial representativety of the problem. For administration of the underground water quality it was adopted the methodology used by Companhia de Tecnologia de Saneamento Ambiental (CETESB), being accomplished a previous identification of contamined potencial areas and organizing a data base on landfills disposal and negleted places; registration of gas station services and, wells used by the population, industrial inventory with active and negleted maps taking into consideration the size and residues generation (such as SEMASA), prioritizing in this way the monitoring places. It was made registrations of places and preliminary investigation of suspicious areas was accomplished. The sampling and monitoring were carried out and the results were compared with the standard values for underground water that are established by CETESB. The results showed that in the twelve wells evaluated were not found values of BTEX above the recommended by Law 518/2004 of the Health Ministry in which the allowed value for benzene is 5 µg L-1. It was observed that three of the twelve wells studied were contamined with nitrate, which is responsible for Methemoglobinemia induction. They were appraised also the processes or mechanisms of natural (biodegradation) or induced remediation.

As emissões veiculares constituem-se em uma das mais graves ameaças a qualidade de vida da população, principalmente nos grandes centros urbanos. Poluentes de origem veicular podem induzir alterações no material genético de organismos a eles expostos, pois nessas emissões, destacam-se entre outros, os hidrocarbonetos policíclicos aromáticos (HPAs), que são substâncias consideradas carcinogênicas e mutagênicas. A utilização de indicadores sensíveis a ação de agentes genotóxicos serve para avaliar a presença destes compostos no ambiente. Portanto, o objetivo deste trabalho foi avaliar comparativamente o risco mutagênico das emissões provenientes da combustão dos combustíveis fósseis (gasolina e diesel) e renováveis (álcool e biodiesel), utilizando o bioensaio Trad-SH. Os ensaios foram realizados utilizando veículos do ciclo Diesel (Citröen JUMPER 2.8 L, 2006) e do ciclo Otto (VW FOX 1.6 Flex, 2005 sem o conversor catalítico), em um dinamômetro de chassi, submetidos a um ciclo de condução urbano padronizado (FTP-75) modificado, para a coleta dos gases de escapamento. Os gases foram misturados com o ar ambiente e homogeneizados para simular o que ocorre no trânsito urbano. As inflorescências do clone KU-20 de Tradescantia foram expostas a mistura de poluentes, provenientes dos veículos, dentro de uma câmara de fumigação, por duas horas. Para a avaliação do efeito mutagênico foi feita uma comparação entre as inflorescências não expostas aos poluentes (grupo 1) e as inflorescências expostas as emissões do álcool (grupo 2), do biodiesel (grupo 3), da gasolina (grupo 4) e do diesel (grupo 5). Os dados obtidos dos experimentos foram analisados estatisticamente onde se observou que a freqüência média das mutações no grupo 1 (controle), foi significativamente mais baixa do que aquela dos grupos 2, 3, 4, e 5. Os resultados indicam que as emissões dos veículos abastecidos com combustíveis fósseis (gasolina e diesel), são mais mutagênicas do que as emissões provenientes da combustão dos combustíveis renováveis (álcool e biodiesel). / The vehicle emissions constitute a major serious threat to the population\'s quality of life, especially in the large urban areas. Pollutants from vehicle origin may lead to changes concerning the genetic material of some organisms that have been exposed to them, and within these emissions it is stood out among others the polycyclic aromatic hydrocarbons (PAH\'s), which are carcinogenic and mutagenic compounds. The use of sensitive indicators to the action of genotoxic agents is useful to prevent and to evaluate the presence of these compounds in the environment. Therefore, this work is aimed at evaluating comparatively the mutagenic risk of emissions from the burning of fossil fuel (gasoline and diesel) and renewable ones (ethanol and biodiesel) by the use of Trad-SH bioassay. The assays were carried out using vehicles from the diesel cycle (Citröen JUMPER 2.8 L, 2006) and the Otto cycle (VW FOX 1.6 Flex, 2005, without a catalytic converter), in a chassis dynamometer, submitled to a standard urban driving cycle (FTP-75) in order to collect the gases of exhaust. The gases were mixed up to the atmosphere air and homogenized to simulate what happens in urban traffic. The inflorescences of KU-20 clone of Tradescantia were exposed to a mixture of pollutants from vehicles, in a fumigation chamber for two hours. To evaluate the mutagenic effect it was necessary to establish a comparison between the inflorescences which were not exposed to pollutants (group 1) and inflorescences exposed to emissions of alcohol (group 2), biodiesel (group 3), gasoline (group 4) and diesel (group 5). Data obtained from experiments were statistically analyzed in which appears that the average frequency of mutations in group 1 (control) was significantly lower than that of groups 2, 3, 4 and 5. The results indicate that emissions from vehicles fueled by fossil fuels (petrol and diesel) are more mutagenic than emissions from the combustion of renewable fuels (ethanol and biodiesel).

O objetivo do presente trabalho é avaliar o uso de borracha triturada de pneu como carburante substituto do coque após a fusão e durante o refino primário oxidante em um forno elétrico a arco na produção de aço 1020. Para o teste foram produzidas 40 toneladas de borracha de pneu triturado em condições granulométricas semelhantes ao coque e abastecido nos silos que alimentam injetoras que adicionaram este material durante o refino primário oxidante. No sistema existem 3 silos e 3 injetoras que são capazes de operar com vazões independentes. O silo n° 1 e o silo n° 3 foram abastecidos com borracha triturada, enquanto que o silo n° 2 foi abastecido com o coque. Testou-se durante 152 corridas situações com injeção de borracha em 4 níveis como substituto do coque: 0% de borracha (somente coque), 33% de borracha, 66% de borracha e 100% de borracha. As vazões e quantidades totais injetadas de carburante foram mantidas em relação ao processo usual. Para evitar interferências manteve-se a receita de carga fria metálica para abastecer o forno bem como os programas elétricos e químicos. Em todas as corridas testadas foram coletadas amostras do aço e da escória no momento antes do vazamento. As amostras foram analisadas através de um espectrômetro de RX. Os resultados obtidos mostraram que é possível a substituição total do coque pela borracha de pneu triturada sem incorrer prejuízos ao processo. Não se observou incorporação de Enxofre no aço, preocupação esta que existia pelo fato da borracha triturada conter teores mais elevados deste elemento em comparação com o coque. / The purpose of this research is to evaluate the use of grinded wasted rubber tires as a carbon source to substitute the coke during the refine in an Electric Arc Furnace to produce steel - grade 1020. For the tests, it was produced 40 tons of grinded rubber in similar size grains of the coke and the material was filled up inside the tanks that feeds the carbon injectors and added the carbon source during the primary oxidant refine. The system is composed by 3 tanks and 3 injectors that can be operate independent. The tank number 1 and number 3 were filled up with grinded rubber, and the tank number 2 was filled up with coke. It was tested during 152 heats 4 different levels of rubber injection to substitute coke: 0% of rubber, 33% of rubber, 66% of rubber and 100% rubber. The flow and injected quantities were kept in the same levels of the normal process. The metallic raw material and electrical and chemical profile were kept the same to avoid interferences. Samples of the steel and the slag were taken before the tap. The samples were analyzed in the RX Spectrometer. The results showed that is it possible to substitute completely the coke with rubber without causing any issues to process. The sulfur content in the rubber did not contaminated the steel, although the rubber contains higher sulfur compared to the coke.

Nenhuma / Uma das principais etapas na fabricação de combustíveis nucleares tipo placa, para a utilização em reatores de pesquisa e de propulsão naval, consiste no desenvolvimento de métodos e técnicas de ensaios não destrutivos para a avaliação do combustível nuclear durante a fabricação, assim como para análises do combustível pós-irradiação. Os ensaios não destrutivos podem contribuir para a detecção de descontinuidades durante as etapas de fabricação do combustível, como trincas e falhas na união entre o cerrne e o revestimento, que podem provocar a falha do combustível durante o seu uso em reatores nucleares. Métodos de ensaio como visual, radiográfico, correntes parasitas e ultra-som podem ser utilizados para essa finalidade. Neste trabalho foi abordado o uso do ensaio não destrutivo por ultra-som para a avaliação de combustíveis nucleares tipo placa. Devido às pequenas espessuras dos combustíveis tipo placa, assim como aos diferentes materiais presentes nos mesmos, foram utilizados, nos experimentos, transdutores ultra-sônicos de contato com sapatas de atraso e transdutores de imersão. Os ensaios foram realizados em um protótipo de combustível tipo placa constituído por um núcleo de UO2 disperso em uma matriz metálica de aço inoxidável, com revestimento em aço inoxidável. Neste protótipo foram usinados diferentes tipos de refletores artificiais, simulando a presença de descontinuidades naturais. Para os testes com os transdutores de imersão foi desenvolvido um dispositivo para a obtenção do perfil do feixe sônico emitido pelos mesmos, de forma a identificar a região de maior sensibilidade do feixe para o ensaio. Foram ainda fabricadas algumas lentes acústicas para a focalização do feixe, neste caso, sem sucesso. O uso dos diferentes tipos de transdutores ultra-sônicos possibilitou o estabelecimento de uma metodologia para a detecção de descontinuidades com diferentes geometrias e dimensões. O protótipo de combustível desenvolvido para os experimentos demonstrou ser adequado para estudos de sensibilidade do sistema de ensaio. / One of the most important steps in the fabrication processes of plate type nuclear fuels, intended to be used in research reactors or naval propulsion, is the development of nondestructive testing (NDT) methods and techniques for their quality assessment during fabrication and post-irradiation analysis. Those tests can contribute to detect discontinuities such as cracks and fails in meat-cladding junctions, that can lead to failures when installed and used in reactors. Examples of NDT methods that may be used for this purpose are visual inspection, radiography, eddy current and ultrasound. The objective of this study is to present the utilization of ultrasound methods to evaluate plate type nuclear fuels. Due to the small thicknesses of such kind of fuels, as well as the presence of different materials, the ultrasonic transducers used to perform the experiments were immersion type or contact with delay shims. Furthermore, a dummy plate fuel, constituted by a dispersion of UO2 in stainless steel matrix, with stainless steel cladding, was specially constructed. In the surface of such plate, several kinds of artificial reflectors, simulating the presence of natural flaws were machined. For immersion type ultrasonic transducers, a mechanical scanning system was developed to allow the determination of their sonic beam profiles and identification of the highest sensitivity beam region. Additionally, some acoustic lenses, useful to help on beam focalization, were fabricated and used, but the expected performance was not achieved. The use of different kinds of ultrasonic transducers allowed the establishing of a methodology to detect discontinuities of different geometry and sizes. The developed dummy fuel demonstrated to be adequate for the studies of sensitivity of the test system.