JAVIER GONZALES MANTECON

JAVIER GONZALES MANTECON

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Analytical and experimental analysis on safety related aspects of the RMB research reactor
2020 - BELCHIOR JUNIOR, A.; SANTOS, A.A.C. dos; FREITAS, R.L.; SOARES, H.V.; JUNQUEIRA, F.C.; MANTECON, J.G.; MATTAR NETO, M.; MENZEL, S.C.; TORRES, W.M.; UMBEHAUN, P.E.
This paper presents some numerical and experimental safety related activities developed at the Brazilian Multipurpose Reactor (RMB) project by CNEN research institutes. Brief comments on the models and results are presented with emphasis to their relation to the safe design and operation of the reactor. Thermal-hydraulic analysis for Siphon Breaker of the Core Cooling System (CCS); pools hot water layer; core chimney of CCS and spent fuel transport cask are presented, showing results, advantages, difficulties and drawbacks for each analyzed case. All are very distinct cases, involving phenomena that range from two-phase flow and thermal-stratification to lead melting. Beside the one-dimensional thermal hydraulic system Code RELAP5, Computational Fluid Dynamics (CFD) is shown to play an important role in the analysis being performed as it can detail the flow and temperature fields of complex components and phenomena, which are extremely difficult to model analytically or experimentally. Two experimental circuits designed to test RMB fuel elements performance are also presented.
Simplified CFD model of coolant channels typical of a plate-type fuel element
2019 - MANTECON, J.G.; NETO, M.M.
The use of parallel plate-type fuel assemblies is common in nuclear research reactors. One of the main problems of this fuel element configuration is the hydraulic instability of the plates caused by the high flow velocities. The current work is focused on the hydrodynamic characterization of coolant channels typical of a flat-plate fuel element, using a numeri-cal model developed with the commercial code ANSYS CFX. Numerical results are compared to accurate analytical solutions, considering two turbulence models and three different fluid meshes. For this study, the results demonstrated that the most suitable turbulence model is the k- model. The discretization error is estimated using the Grid Conver-gence Index method. Despite its simplicity, this model generates precise flow predictions.
Preliminar mechanical evaluation of the structure of a nuclear plate-type fuel element
2019 - SANTOS, MARCELO M. dos; MATTAR NETO, MIGUEL; MANTECON, JAVIER G.
The improvement in the efficiency and safety aspects of compact nuclear reactors is directly linked to innovations in fuels and in the geometry of fuel elements (F.E), as is the case of plate-type fuel elements. From the mechanical viewpoint, to ensure that the structure of a fuel element is safe to operate in a compact PWR reactor is important to confirm that it meets the functional design requirements for structures of this type and application, present in ANSI/ANS-57.5-1996 and, also, that the stresses resulting from the loads imposed are less than the permissible mechanical limits for their structural materials, in accordance with ASME III, division 1, subsection NB. In order to develop a methodology of mechanical analysis to verify compliance with the criteria of the cited standards, a numerical model of a plate-type fuel element was developed, taking into consideration the main active loads admitted from the full power operation event belonging to the normal operating condition of a compact PWR type nuclear reactor. The results of the analyses demonstrated that the fuel element designed did not show signs of mechanical failure with respect to the modes of plastic collapse and excess of mechanical deformation.
Numerical analysis on stability of nuclear fuel plates with inlet support comb
2019 - MANTECON, JAVIER G.; MATTAR NETO, MIGUEL
Many nuclear research reactors use or are planned with cores containing flat-plate-type fuel elements. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the narrow channels that separate the plates can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. In particular, in real fuel elements and experimental tests, flowinduced deflections at the leading edge and along the length of the plates have been detected. Some authors have indicated that the use of a support comb removes the leading-edge static divergence, but it has been also suggested that, even with the comb, there are significant deflections away from the inlet. In this work, a fluid-structure interaction study is conducted to examine the effectiveness of using an inlet comb on the mechanical stability of fuel plates. The system consists of two fuel plates bounded by three-equal coolant channels. The pressure loadings caused by the fluid flow are calculated using a CFD model and the structural response of the plates and the support comb are determined by means of an FEA model. The two-way fluid-structure interaction method was employed for coupling the fluid and solid solvers. The results presented here show that the static divergence at the inlet end is effectively eliminated with the installation of a support comb. Nevertheless, the main contribution of this work is the detection of deformation of the plates along their length and that it was an increasing function of the fluid velocity in the channels. As a consequence, the flow channels could be constricted or completely closed, thus affecting the safe operation of the nuclear reactor. To the best of our knowledge, this is the first numerical analysis reported in the literature that models the fluid-structure interaction phenomenon of adjacent plates with the support comb located at the midpoint of their inlet end.
Evaluation of mechanical stability of nuclear fuel plates under axial flow conditions
2019 - MANTECON, JAVIER G.
Several nuclear research reactors use or are planned with cores containing flat-plate- type fuel elements. The nuclear fuel is contained in parallel plates that are separated by narrow channels through which the fluid flows to remove the heat generated by fission reactions. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the channels can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. As a consequence, the safe operation of the reactor may be affected. In this work, a numerical fluid-structure interaction study was conducted for evaluating the mechanical stability of nuclear fuel plates under axial flow conditions. Five different cases were analyzed. In all cases, the system consisted of two fuel plates bounded by fluid channels but, in case 5, a support comb at the leading edge of the plates was inserted. The pressure loadings caused by the fluid flow were calculated using a Computational Fluid Dynamics model created with ANSYS CFX. The structural response was determined by means of a Finite Element Analysis model generated with ANSYS Mechanical. Both models were coupled using the two-way fluid-structure interaction approach. The results from Case 1 allowed proposing a methodology to predict the critical velocity of the assembly without an inlet support comb. The maximum deflection of the plates was detected at their leading edges. It was detected that, for flow rates in the channels less than a certain value, the maximum deflection increased linearly with the square of the coolant velocity. In contrast, for greater flow rates, a nonlinear behavior was observed. Therefore, that fluid velocity was identified as the critical velocity of the system. Besides, above the critical velocity, an extra deflection peak was observed near the trailing edge of the plates. In cases 2, 3 and 4, the influence of manufacturing deviations and the change of materials properties due to the increment of temperature on the critical velocity was investigated. With these conditions, the critical velocity of the system was found at lower values. Lastly, in Case 5, the effectiveness of using a support comb at the leading edge of the plates was investigated. The results showed that the static divergence at the inlet end is effectively eliminated with the installation of the comb. In addition, the flow-induced deflections along the length of the plates were significantly diminished with the comb.
One-way fluid-structure interaction model to study the influence of the fluid velocity and coolant channel thickness on the stability of nuclear fuel plates+
2017 - MANTECON, JAVIER G.; MATTAR NETO, MIGUEL
In nuclear research reactors, the fuel elements are frequently composed of parallel, flat or curved plates. A major problem of that fuel element configuration is the hydraulic instability of the plates caused by high coolant velocities. Thin plates contain the fuel and they are separated by narrow channels through which the coolant flows to remove the heat generated. In this study, a numerical analysis was conducted to examine the fluid-structure interaction of a flat fuel plate bounded by two coolant channels. The loads caused by the fluid flow are calculated using a Computational Fluid Dynamics model implemented in ANSYS CFX, and the plate structural responses are determined using a Finite Element Analysis model implemented in ANSYS Mechanical. The goal of the present work is to estimate the amount of deformation of a fuel plate when there is an increment of the fluid velocity and a variation in the thickness of the coolant channels.
Numerical methodology for fluid-structure interaction analysis of nuclear fuel plates under axial flow conditions
2018 - MANTECON, JAVIER G.; MATTAR NETO, MIGUEL
Shell-type fuel elements are widely used in nuclear research reactors. The nuclear fuel is contained in parallel shells, flat or curved, that are separated by narrow channels through which the fluid flows to remove the heat generated by fission reactions. A major problem of this fuel assembly design is the hydraulic instability of the shells caused by the high flow velocities. The objective of the study presented here is the development of a fluid-structure interaction methodology to investigate numerically the onset of hydroelastic instability of flat-shell-type fuel elements, also known as plate-type fuel assemblies, under axial flow conditions. The system analyzed consists of two nuclear fuel plates bounded by three-equal coolant channels. It is developed using the commercial codes ANSYS CFX for modeling the fluid flow and ANSYS Mechanical to model the plates. The fluid-structure interaction methodology predicts a behavior consistent with other theoretical and experimental works. Particularly, the maximum deflection of the plates is detected at the leading edge and it is a linear function of the square of the fluid velocity up to the Miller’s theoretical value. For velocities above this value, a nonlinear relationship is observed. This relationship indicates that structural changes are taking place in the plates. Furthermore, for fluid velocities greater than the Miller’s velocity, an extra deflection peak is observed near the trailing edge of the plates. Thus, structural alterations also happen along the length of the flat-shells.
Simplified CFD model of coolant channels typical of a plate-type fuel element: an exhaustive verification of the simulations
2017 - MANTECON, JAVIER G.; MATTAR NETO, MIGUEL
The use of parallel plate-type fuel assemblies is common in nuclear research reactors. One of the main problems of this fuel element configuration is the hydraulic instability of the plates caused by the high flow velocities. The current work is focused on the hydrodynamic characterization of coolant channels typical of a flat-plate fuel element, using a numerical model developed with the commercial code ANSYS CFX. Numerical results are compared to accurate analytical solutions, considering two turbulence models and three different fluid meshes. For this study, the results demonstrated that the most suitable turbulence model is the k- model. The discretization error is estimated using the Grid Convergence Index method. Despite its simplicity, this model generates precise flow predictions.