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Lopes D.A.,Centro Tecnologico da Marinha em Sao Paulo | Guisard Restivo T.A.,University of Sorocaba | Guisard Restivo T.A.,University of Sao Paulo | Padilha A.F.,University of Sao Paulo
Journal of Nuclear Materials | Year: 2013

Nuclear fuels composed of uranium alloys in monolithic and dispersed forms are being considered for research and compact power reactors due to their density properties (greater than 15 g-U/cm3) and fast heat transfer. U-Nb-Zr and U-Mo alloys are the most promising systems for plate fuel elements owing to their broad γ-phase stability field, which shows higher ductility and isotropic behaviour, allowing extensive fabrication capability. In the present work, γ-phase stabilized U-7.5Nb-2.5Zr and U-10Mo alloys were characterized by mechanical and thermal analyses for comparison of their behaviour under deformation and heat-treatment. The results demonstrate that the alloys have substantially different properties regarding deformation, kinetics phase transformation and recovery/recrystallization. The main results show that U-Nb-Zr is superior regarding fabrication capabilities although the γ-phase is less stable than U-Mo alloys. © 2013 Elsevier B.V. All rights reserved. Source


Lopes D.A.,Centro Tecnologico da Marinha em Sao Paulo | Lopes D.A.,University of Sao Paulo | Restivo T.A.G.,University of Sao Paulo | Restivo T.A.G.,University of Sorocaba | Padilha A.F.,University of Sao Paulo
Nuclear Engineering and Design | Year: 2013

Phase transformation diagrams provide fundamental informations for designing thermomechanical processes being a must regarding uranium alloys nuclear fuels. The work shows the evaluation of a kinetic transformation diagram for U-7.5Nb-2.5Zr (wt.%) based on both calorimetry experiments and dilatometry allied to X-ray diffraction analysis. Calorimetry measurements in scanning and drop modes can detect enthalpies of heating and transformation onset points from ambient up to select isotherms while the dilatometer is used to scan for sample volume changes related to phase transformations. The resulted kinetic diagram shows the gamma phase is stable for this alloy, guiding the rolling deformation process to temperature ranges where this phase remains for longer periods. Comparing to the literature results, the low temperature transformation (300-400 C) is shifted to longer times accordingly to the disclosed TTT kinetic diagram. Therefore, two forming process windows can be proposed at 200 C and 400 C neighborhood where gamma-phase remains for enough time to accomplish total reduction. © 2013 Elsevier B.V. All rights reserved. Source


Da Silva Serra A.,University of Sao Paulo | Da Silva Serra A.,Centro Tecnologico da Marinha em Sao Paulo | Pascholati P.R.,University of Sao Paulo | Dos Santos A.,Brazilian Nuclear Energy Research Institute (IPEN) | And 2 more authors.
AIP Conference Proceedings | Year: 2011

The reactivity measurement of subcritical fissile arrangements (subcriticality) is a featured subject among those in reactor physics, because it is necessary to handle, process, and transport fissile material from nuclear installations safely. None of the many available experimental methods of subcriticality measurements used nowadays allows its direct determination; however, the third order correlation of neutron counting allows subcriticality estimation from a fissile material without any previous knowledge of its kinetic parameters or any pulsed neutron source. Despite of its intrinsic advantages, high order statistics requires a careful planning and an optimized procedure because this type of experiment demands a long acquisition time when compared to the usual methods. It is estimated that such procedure could ask for acquisition times a few orders of magnitude longer than those required by the usual methods of subcriticality estimation (for similar uncertainties). The main experimental results of this work, undertaken in the IPEN/MB-01 facility (a zero power reactor), which agreed with the simulated results obtained by dedicated Monte Carlo codes, were: the long time for data acquisition to obtain an useful result (hundreds hours of acquisition time), and the higher efficiency of using saturation time channels different from those which were used by others researches. © 2011 American Institute of Physics. Source


Van Der Giet M.,RWTH Aachen | Lange E.,RWTH Aachen | Correa D.A.P.,Centro Tecnologico da Marinha em Sao Paulo | Chabu I.E.,University of Sao Paulo | And 2 more authors.
IEEE Transactions on Industrial Electronics | Year: 2010

The approach presented in this paper consists of an energy-based fieldcircuit coupling in combination with multiphysics simulation of the acoustic radiation of electrical machines. The proposed method is applied to a special switched reluctance motor with asymmetric pole geometry to improve the start-up torque. The pole shape has been optimized, subject to low torque ripple, in a previous study. The proposed approach here is used to analyze the impact of the optimization on the overall acoustic behavior. The fieldcircuit coupling is based on a temporary lumped-parameter model of the magnetic part incorporated into a circuit simulation based on the modified nodal analysis. The harmonic force excitation is calculated by means of stress tensor computation, and it is transformed to a mechanical mesh by mapping techniques. The structural dynamic problem is solved in the frequency domain using a finite-element modal analysis and superposition. The radiation characteristic is obtained from boundary element acoustic simulation. Simulation results of both rotor types are compared, and measurements of the drive are presented. © 2006 IEEE. Source


Carneiro A.L.G.,Brazilian Nuclear Energy Research Institute (IPEN) | Porto Jr. A.C.S.,Centro Tecnologico da Marinha em Sao Paulo
Chemical Engineering Transactions | Year: 2013

The reliability question of the components, specifically the process control valves, became an important point to be investigated in nuclear power plants and others areas such as oil refinery or offshore oil platform, considering security and extension life of the plant. Therefore, the necessity of improvements in monitoring and diagnosis methods started to be the extreme relevance in the maintenance predictive field, as mentioned by Guimarães Carneiro (2007), establishing as main goal the reliability and readiness of the components systems. The development of nonintrusive monitoring and diagnostics method makes it possible to identify malfunctions in plant components during normal plant operation. The purpose is to present an analysis and diagnostic of a water flow control valve that charges a steam generator, simulating part of the secondary circuit of a power water reactor. This facility is part of the laboratory of tests of propulsion equipment of the Brazilian Navy, in São Paulo - Brazil (2007). The methodology of this project is based on the graphic analysis of two parameters; the valve actuator air pressure and the valve plug displacement. The data come from intelligent positioner; it is a kit of Delta V™ Automation System (2010). The analysis is implemented on detection of anomalies approach using Expert Systems by Fuzzy Logic technique based on rules and knowledge base. A distinct approach as mentioned by Choudhury ( 2005), Desborough (2001), Gerry (2001) or Camila Pinto (2010). Once the baseline measurements of control valves are taken, it is possible to detect fault symptoms, leaking, attrition, clamping, damage, etc. The system of monitoring and diagnostic was designed at the MATLAB™ platform "FUZZY LOGIC TOOLBOX". Copyright © 2013, AIDIC Servizi S.r.l. Source

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