Epistemic uncertainty (related to lack of knowledge), often found in the documentation of nuclear facility engineering projects, can affect the decision-making process of managers and analysts on safety and risk issues. This article conceptualizes the nature of the major uncertainties involved in engineering projects and describes a knowledge base developed to gather data and information related to the project of an Open-Pool Light-water Research Reactor (OPLRR) and whose purpose is to assist professionals who work in the areas of nuclear facilities. To reduce the epistemic uncertainties that may arise in the project, the OPLRR knowledge base is designed with a set of information that allows identifying and facilitating the forwarding of solutions to address inconsistencies, and /or pending issues that may exist in the project. In this sense, the information and the documents related to the project are organized in a graphical and hierarchical architecture, allowing the knowledge base users to quickly and easily obtain information regarding the systems, processes, equipment, and components of the project. Besides that, a set of documents containing descriptions, reliability data, and some other information about the systems and components are specially created to the knowledge base and it is crucial to reduce epistemic uncertainties, once it raises the issues and the inconsistencies of the project, as well as it clarifies the interrelations between the systems, the functioning of the equipment, their failures modes and the consequences of their failures, and some other data, which are not originally contained in the documents of the project.
Durability still represents one of the major barriers to the commercialization of Proton Exchange Membrane Fuel Cells (PEMFCs) in the market. Therefore, it is important to understand the main phenomena involving the long-term operation of PEMFCs in order to elucidate the degradation issues of these devices. Thus, in this work long-term experiments of 500 hours at steady state were performed with variations of the operational parameters such as relative humidity, cell temperature and the reactant flow rates. According to the results obtained, the test which presented the lowest global loss of performance (132μV.h-1, with reversible and irreversible losses measured all together) was the one with the temperatures of the humidifiers and cell set all at 75°C and the reactants flow rates set as 300 ml.min-1 and 200 ml.min-1 for the H2 and O2, respectively. For this test, the irreversible loss of performance was assessed as 38μV.h-1. On the other hand, the test performed with higher humidification degree presented much higher global and irreversible losses of performance (318 and 52μV.h-1, respectively), showing that the degree of humidification, which is a function of the operational parameters, strongly influence on the long-term performance. Therefore, the water management is a key point to obtain better performances in long-term operation of PEMFCs.
The development of power conversion systems based on fuel cells has been demanding reliability studies since the requirements associated with cost and durability of these technological products have become fundamental to their acceptance by the energy market. The experimental part of the reliability study presented in this work consisted of performing life tests with single proton exchange membrane fuel cells (PEMFCs). The proposed reliability analysis methodology covered the application of qualitative and quantitative techniques. In the qualitative approach, a Failure Mode and Effect Analysis was developed in order to identify and evaluate all potential failures associated with the operation of fuel cells. In the quantitative approach, a statistical analysis was applied to the sample data generated in long-term steady-state tests of these devices. A two-parameter exponential distribution was fitted to data and the maximum likelihood estimate for the mean time to failure (MTTF) of the fuel cells was calculated. It is important to point out that the tests performed under the scope of this study were the first long-term experiments performed with the fuel cells produced in the laboratories of IPEN-CNEN/SP, Brazil. Although the results indicated that fuel cell performance and durability were still at a level below the targets normally established for similar commercial devices, the improvement of the main components of PEMFCs has been the objective of several projects developed at the institute. Thus, the main benefit brought by this study is the proposed methodology, which can be implemented as part of a reliability growth analysis of the fuel cells and can be integrated into the design process of these devices.
Agradeço imensamente à minha família e minha esposa por todo o amor, compreensão e paciência. Meus sinceros agradecimentos à minha orientadora, Dra. Elisabete Inacio Santiago pela orientação, oportunidade, amizade e confiança em mim depositada. Não devo deixar de agradecer ao meu co-orientador, Dr. Fabio Coral Fonseca pelas colaborações, disposição, sugestões e amizade. Em especial, devo muita gratidão ao Dr. Marcelo Linardi por ter idealizado este projeto e depositado em mim toda a confiança em realizá-lo desde o meu trabalho de mestrado. Agradeço enormemente à Joana Ramos, pela amizade e também pela grande contribuição na realização deste trabalho, sempre disposta a resolver os incontáveis problemas e processos burocráticos deste projeto. Um especial agradecimento à pessoa mais querida do CCCH, Dona Verinha, pelos cafés, bolos, pipocas e, principalmente, pelo carinho e cuidado legítimos de uma mãe, comigo e com todos do laboratório. Devo muita gratidão também ao Dr. Thiago Lopes pelas orientações, sugestões e amizade. Agradeço imensamente ao Dr. Alexandre Lanfredi pela colaboração e disposição em obter as imagens de microscopia. Ademais, agradeço imensamente aos colegas, funcionários e pesquisadores do CCCH/IPEN pelo companheirismo, aprendizado e, acima de tudo, amizade conquistada.
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