Two topics from nuclear engineering field are included in this dissertation. One study is the air-ingress phenomenon during a loss of coolant accident (LOCA) scenario, and the other is a 5-by-5 bundle assembly problem under a design of PWRs. The objectives are to investigate the Kelvin-Helmholtz instability of the gravity-driven stratified flows inside a coaxial pipe and the effects caused by two types of spacers at the downstream of the rod bundle problem. Richardson extrapolation is used for the grid independent study. Simulation results give good agreements with the experiments. Wavelet analysis and Proper Orthogonal Decomposition (POD) are used to study the flow behaviors and flow patterns. For the air-ingress phenomenon, Brunt-Vaisala frequency, or buoyancy frequency, predicts a frequency of 2.34 Hz, which is confirmed by the dominant frequency of 2.4 Hz obtained from the wavelet analysis between times 1.2 s and 1.85 s. For the rod bundle study, the dominant frequency at the center of the subchannel is given as 2.4 Hz with a secondary dominant frequency of 4 Hz and a much minor frequency of 6 Hz. Generally, wavelet analysis has much better performance than POD in the air-ingress phenomenon that is a strongly transient scenario; they both appropriate for the rod bundle study. Based on this study, when the fluid pair in a real condition is used, the time which air intrudes into the reactor is predictable.

This project addresses the actuation system architecture of future All-electric aircraft (AEA) with electrically powered actuators (EPA). Firstly, the information of EPAs is reviewed, and then an electro-hydrostatic actuator (EHA) and electro-mechanical actuator (EMA) are selected for further system research. The actuation system architecture of Boeing and Airbus is then presented as a conventional design where the new design concepts are also researched and the distributed architecture was proposed as another design trend. To find out which one is better, both of them are selected for further research. The easily available data makes the Flying Crane a better choice for the case study. Stall load, maximum rate and power are the main elements for electric actuator requirements and power consumption, weight, cost and safety are the most important aspects for civil aircraft actuation systems. The conventional and distributed flight actuation system design considered the redundancy of systems and actuators, and also the relationship of the power, control channel and actuator work mode. But only primary flight actuation control system specifications are calculated since this data has better precision and also the limited time has to be taken into consideration. Brief comparisons of the two system specifications demonstrate that the higher power actuator have has higher efficiency and distributed actuators could reduce the system weight through reduce the system redundancy with a power efficiency decline. The electrically powered actuation system for future aircraft design is a balance between actuator number, system weight and power consumption.

Made available in DSpace on 2014-10-09T12:36:47Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:28Z (GMT). No. of bitstreams: 1 04288.pdf: 4625254 bytes, checksum: 9001b53adf99cafca24341f1052507a2 (MD5) / Dissertacao (Mestrado) / IPEN/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

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Submitted by Almir Azevedo (barbio1313@gmail.com) on 2013-12-04T12:50:22Z No. of bitstreams: 1 dissertacao_mestrado_ien_2013_05.pdf: 1528233 bytes, checksum: f68d87785bc45e2f76ceb65d2ba1ef23 (MD5) / Made available in DSpace on 2013-12-04T12:50:22Z (GMT). No. of bitstreams: 1 dissertacao_mestrado_ien_2013_05.pdf: 1528233 bytes, checksum: f68d87785bc45e2f76ceb65d2ba1ef23 (MD5) Previous issue date: 2013 / Programa: Ciência e Tecnologia Nucleares – IEN/CNEN A reatividade de um reator refrigerado a água é controlada utilizando-se barras de controle ou diluição de boro na água do refrigerante do circuito primário. O boro 10 (10B) é considerado um absorvedor de nêutrons eficiente, principalmente quando utilizado na absorção de nêutrons térmicos. Estudos transitórios com deficiência na homogeneização de boro em reatores PWR tornam-se importante, pois a solução de ácido bórico é adicionada ao refrigerante do circuito primário auxiliando no controle das taxas de fissão no núcleo do reator. Após desligamento do reator, o boro presente no refrigerante tem a função de manter o reator no estado de subcriticalidade. Caso haja a introdução de água borada com baixa concentração no circuito primário, torna-se necessário fazer um aumento da concentração desta solução e assegurar que o refrigerante esteja bem homogeneizado, evitando que água com pouca quantidade de boro atinja o núcleo. O objetivo deste trabalho é simular a homogeneização do boro no pressurizador de um reator nuclear avançado. É utilizada uma seção de testes, que representa ¼ de um pressurizador de um reator nuclear modular. Através da utilização do código CFX, programa computacional que permite análises termohidráulica de diferentes tipos de escoamento, foram simulados três exemplos em diferentes condições de operação. A partir destes resultados foram analisados parâmetros que podem influenciar nesta homogeneização. Estudos de casos como variação das dimensões da tubulação de entrada e saída, variação da vazão e mudança de posicionamento das entradas e saídas, foram feitos com o objetivo de encontrar parâmetros que podem auxiliar na otimização da homogeneização do boro. Os resultados encontrados mostram que os fatores analisados podem ser alterados no projeto a fim de se obter melhores condições de operação. / The reactivity of a water cooled reactor is controlled using control rods or boron dilution in water of the primary circuit. The boron-10 (10B) is an efficient neutron absorber, especially when used in the absorption of thermal neutrons. Transient studies with disabilities in the homogenization of boron in PWR reactors become important as the boric acid solution is added to the primary circuit coolant in order to help control the rate of fission in the reactor core. After the reactor shutdown, the boron present in the coolant has the function of maintaining reactor subcriticality. If low concentrated boron solution enters in the primary circuit, it becomes necessary to inject boron and to assure that the coolant will be well homogenized in order to increase the concentration and thus preventing water with small amounts of boron to reach the core. The aim of this study is to simulate the boron homogenization in the pressurizer of an advanced nuclear reactor. It is used a test section, which represents a quarter of a modular nuclear reactor pressurizer. By using the CFX code, a computer program that allows thermal hydraulic analysis of different types of flow, three examples were simulated using different operating conditions. With the results, it was analyzed the parameters that could influence this homogenization. Case studies such as variation of the dimensions of the water inlet and outlet tubes, flow variation and change in positioning of entrances and exits were made with the goal of finding parameters that could help the optimization of the homogenization of boron. The results confirm that the issues analyzed can be changed in the project in order to obtain the best operating condition.

Submitted by Almir Azevedo (barbio1313@gmail.com) on 2013-12-09T15:57:53Z No. of bitstreams: 1 dissertacao_mestrado_ien_2010_03.pdf: 1621960 bytes, checksum: e63c49dff927a279c98b2d05d4b60a04 (MD5) / Made available in DSpace on 2013-12-09T15:57:53Z (GMT). No. of bitstreams: 1 dissertacao_mestrado_ien_2010_03.pdf: 1621960 bytes, checksum: e63c49dff927a279c98b2d05d4b60a04 (MD5) Previous issue date: 2010 / Procedimentos e técnicas para maximizar a confiabilidade e a disponibilidade de plantas industriais têm sido usados ao longo das últimas décadas por especialistas e profissionais de manutenção. Contudo, a extensão dos modernos sistemas industriais e a crescente complexidade e interdependência entre seus componentes vêm tornando o planejamento desta atividade uma tarefa cada vez mais difícil. Considerando este contexto, o objetivo do presente trabalho é oferecer uma ferramenta computacional que possa auxiliar na tomada de decisão e no planejamento das políticas de manutenção praticadas em plantas termonucleares. A ferramenta desenvolvida baseia-se na utilização de redes neurais artificiais (RNA) para o reconhecimento de padrões e estabelecimento de correlações entre eventos ocorridos nos componentes de sistemas típicos de reatores pressurizados refrigerados a água leve (PWR). As RNA atuam como mineradoras de dados nos bancos de eventos de falhas e são capazes de identificar ligações e estabelecer inferências imperceptíveis até para os mais experientes especialistas em manutenção de sistemas nucleares. Os resultados foram obtidos a partir de dados realistas e são confrontados com as clássicas políticas de manutenção atualmente praticadas em centrais tipo PWR. Estes resultados demonstram a solidez da técnica em avaliar e predizer falhas em uma planta real, podendo vir a ser utilizada como ferramenta de suporte a decisão no planejamento das políticas de manutenção de um PWR típico. / Proceedings and techniques in order to maximize the reliability and the availability of industrial plants have been used along the last decades by specialists and professionals of maintenance. However, the modern industrial systems’ sizing, and the increasing complexity and interdependence among its components have become this activity’s planning a more and more difficult task. Considering this scenario, the objective of the present work is to provide a computational tool which is able to help about the taking decision's task, and about planning policies of maintenance practiced in thermonuclear plants. The tool developed is based on the artificial neural networks (ANN) for the recognition of standards and establishment of correlations among events occurred in the components of pressurized water reactor (PWR) typical systems. The ANN work as miners of database of failure events, and are able to identify connections and to establish imperceptible inferences even for the most experienced specialists in maintenance of nuclear systems. The results were attained from realistic data and are confronted against the maintenance's classic policies which are practiced nowadays on PWR thermonuclear plants. These results show the solidity of the technique in valuing and predicting failures in a real powerplant, and is able to be used as a tool for supporting decisions about planning maintenance policies on a typical PWR.