Modeling of Local Steam Condensation on Walls in Presence of Non-condensable Gases. Application to a Loca Calculation in Reactor Containment Using the Multidimensional Geyser/tonus Code PDF Download
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Languages : en
Pages : 13
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This paper reports part of a study of possible severe pressurized water reactor (PWR) accidents. The need for containment modeling, and in particular for a hydrogen risk study, was reinforced in France after 1990, with the requirement that severe accidents must be taken into account in the design of future plants. This new need of assessing the transient local hydrogen concentration led to the development, in the Mechanical Engineering and Technology Department of the French Atomic Energy Commission (CEA/DMT), of the multidimensional code GEYSER/TONUS for containment analysis. A detailed example of the use of this code is presented. The mixture consisted of noncondensable gases (air or air plus hydrogen) and water vapor and liquid water. This is described by a compressible homogeneous two-phase flow model and wall condensation is based on the Chilton-Colburn formula and the analogy between heat and mass transfer. Results are given for a transient two-dimensional axially-symmetric computation for the first hour of a simplified accident sequence. In this there was an initial injection of a large amount of water vapor followed by a smaller amount and by hydrogen injection.
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Category :
Languages : en
Pages : 13
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This paper reports part of a study of possible severe pressurized water reactor (PWR) accidents. The need for containment modeling, and in particular for a hydrogen risk study, was reinforced in France after 1990, with the requirement that severe accidents must be taken into account in the design of future plants. This new need of assessing the transient local hydrogen concentration led to the development, in the Mechanical Engineering and Technology Department of the French Atomic Energy Commission (CEA/DMT), of the multidimensional code GEYSER/TONUS for containment analysis. A detailed example of the use of this code is presented. The mixture consisted of noncondensable gases (air or air plus hydrogen) and water vapor and liquid water. This is described by a compressible homogeneous two-phase flow model and wall condensation is based on the Chilton-Colburn formula and the analogy between heat and mass transfer. Results are given for a transient two-dimensional axially-symmetric computation for the first hour of a simplified accident sequence. In this there was an initial injection of a large amount of water vapor followed by a smaller amount and by hydrogen injection.
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Category : Fluid dynamics
Languages : en
Pages : 794
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Category : Power resources
Languages : en
Pages : 896
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Languages : en
Pages : 21
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This paper presents several approaches in the modelling of wall condensation in the presence of noncondensable gases for containment codes. The lumped-parameter modelling and the local modelling by 3-D codes are discussed. Containment analysis codes should be able to predict the spatial distributions of steam, air, and hydrogen as well as the efficiency of cooling by wall condensation in both natural convection and forced convection situations. 3-D calculations with a turbulent diffusion modelling are necessary since the diffusion controls the local condensation whereas the wall condensation may redistribute the air and hydrogen mass in the containment. A fine mesh modelling of film condensation in forced convection has been in the developed taking into account the influence of the suction velocity at the liquid-gas interface. It is associated with the 3-D model of the TRIO code for the gas mixture where a k-[xi] turbulence model is used. The predictions are compared to the Huhtiniemi`s experimental data. The modelling of condensation in natural convection or mixed convection is more complex. As no universal velocity and temperature profile exist for such boundary layers, a very fine nodalization is necessary. More simple models integrate equations over the boundary layer thickness, using the heat and mass transfer analogy. The model predictions are compared with a MIT experiment. For the containment compartments a two node model is proposed using the lumped parameter approach. Heat and mass transfer coefficients are tested on separate effect tests and containment experiments. The CATHARE code has been adapted to perform such calculations and shows a reasonable agreement with data.
Author: Dhongik Samuel Yoon
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Category :
Languages : en
Pages : 0
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Condensation of steam vapor is an important mode of energy removal from the reactor containment in postulated design basis accidents where high-energy steam escapes into the reactor containment. Due to its passive nature and magnitude of heat transfer associated with phase change, condensation can be used as an effective energy removal mechanism, especially for reactors with a passive containment cooling system. Therefore, there has been a great interest in modeling condensation phenomena in the reactor containment for the purpose of accident analysis. Until recently, the focus has been the presence of noncondensable gas since traditional reactor designs operate at near atmospheric pressure with substantial amount of noncondensable gas in the containment, which hinders the process of condensation heat transfer. In this case, the phase change is dominated by diffusion resistance in the gas mixture phase and the thermal resistance of condensate film layer can be neglected. Recent advanced reactor designs, on the other hand, are designed to allow very low air pressure in the containment. In this case, the heat transfer resistance due to the presence of noncondensable gas is reduced significantly and the thermal resistance of condensate film layer can no longer be neglected. Moreover, it has been reported that condensation on the micro or nano-engineered surfaces shows substantially different behavior compared to traditional untreated surfaces. Those engineered surfaces with modified wetting characteristics can affect the condensation rates by affecting the condensate film behavior on such surfaces, proposing a potential way of affecting the heat removal from reactor containment by wall surface modification. Consequently, it has become relevant and necessary to study and characterize the effect of thermal resistance and kinetic conditions of the condensate film layer on the overall condensation heat transfer in the reactor containment regarding conditions with very low noncondensable gas concentration where the presence of condensate film layer can no longer be neglected. The current condensation model in MELCOR was evaluated in order to assess its capability to predict condensation heat transfer for traditional containment conditions. By modeling sets of containment condensation experiments, satisfactory performance of MELCOR in predicting condensation phenomena was confirmed for conditions with significant noncondensable gas concentration. It has to be noted that, as a result of this assessment, few adjustments has been implemented to guarantee more accurate predictions of MELCOR in specific conditions addressed in those experiments. However, it is observed that MELCOR may be inaccurate in predicting condensation for conditions with very low noncondensable gas concentrations where the effects of condensate film layer is more prominent. However, MELCOR's correlation-based models prevent further investigations on the parameters that have not been already implemented. In an effort to better understand the effect of thermal resistance and kinetic conditions of the condensate film layer for conditions with very low noncondensable gas concentrations, a condensation model was developed in the framework of a Computation Fluid Dynamics (CFD) to include thermal and kinetic conditions of the condensate film layer. The developed condensation model includes heat transfer resistances in both phases without directly simulating the two-fluid problem and proposes that the liquid-gas interface can be represented as a free surface. Case studies were conducted to show its theoretical validity. The developed condensation model including the thermal resistance of the condensate film layer and the free surface assumption was validated against two sets of separate effects experiments, one in traditional reactor containment conditions and the other in a pure steam condition. The results indicate that a free surface assumption can greatly improve the prediction of condensation heat transfer, even for traditional reactor containment conditions where the concentration of noncondensable gas is significant. Including the thermal resistance of the condensate film layer does not provide a significant change in the results for high noncondensable gas concentration cases, as expected. For near-pure steam conditions, however, the effect of the condensate film is not only significant but also increases with decreasing noncondensable gas concentration as expected. The proposed modeling approach is also able to account for this effect.
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Languages : en
Pages : 225
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This NEUP funded project, NEUP 12-3630, is for experimental, numerical and analytical studies on high-pressure steam condensation phenomena in a steel containment vessel connected to a water cooling tank, carried out at Oregon State University (OrSU) and the University of Wisconsin at Madison (UW-Madison). In the three years of investigation duration, following the original proposal, the planned tasks have been completed: (1) Performed a scaling study for the full pressure test facility applicable to the reference design for the condensation heat transfer process during design basis accidents (DBAs), modified the existing test facility to route the steady-state secondary steam flow into the high pressure containment for controllable condensation tests, and extended the operations at negative gage pressure conditions (OrSU). (2) Conducted a series of DBA and quasi-steady experiments using the full pressure test facility to provide a reliable high pressure condensation database (OrSU). (3) Analyzed experimental data and evaluated condensation model for the experimental conditions, and predicted the prototypic containment performance under accidental conditions (UW-Madison). A film flow model was developed for the scaling analysis, and the results suggest that the 1/3 scaled test facility covers large portion of laminar film flow, leading to a lower average heat transfer coefficient comparing to the prototypic value. Although it is conservative in reactor safety analysis, the significant reduction of heat transfer coefficient (50%) could under estimate the prototypic condensation heat transfer rate, resulting in inaccurate prediction of the decay heat removal capability. Further investigation is thus needed to quantify the scaling distortion for safety analysis code validation. Experimental investigations were performed in the existing MASLWR test facility at OrST with minor modifications. A total of 13 containment condensation tests were conducted for pressure ranging from 4 to 21 bar with three different static inventories of non-condensable gas. Condensation and heat transfer rates were evaluated employing several methods, notably from measured temperature gradients in the HTP as well as measured condensate formation rates. A detailed mass and energy accounting was used to assess the various measurement methods and to support simplifying assumptions required for the analysis. Condensation heat fluxes and heat transfer coefficients are calculated and presented as a function of pressure to satisfy the objectives of this investigation. The major conclusions for those tests are summarized below: (1) In the steam blow-down tests, the initial condensation heat transfer process involves the heating-up of the containment heat transfer plate. An inverse heat conduction model was developed to capture the rapid transient transfer characteristics, and the analysis method is applicable to SMR safety analysis. (2) The average condensation heat transfer coefficients for different pressure conditions and non-condensable gas mass fractions were obtained from the integral test facility, through the measurements of the heat conduction rate across the containment heat transfer plate, and from the water condensation rates measurement based on the total energy balance equation. 15 (3) The test results using the measured HTP wall temperatures are considerably lower than popular condensation models would predict mainly due to the side wall conduction effects in the existing MASLWR integral test facility. The data revealed the detailed heat transfer characteristics of the model containment, important to the SMR safety analysis and the validation of associated evaluation model. However this approach, unlike separate effect tests, cannot isolate the condensation heat transfer coefficient over the containment wall, and therefore is not suitable for the assessment of the condensation heat transfer coefficient against system pressure and noncondensable ...
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Category :
Languages : en
Pages : 18
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This paper presents a simple modelling of mass diffusion effects on condensation. In presence of noncondensable gases, the mass diffusion near the interface is modelled using the heat and mass transfer analogy and requires normally an iterative procedure to calculate the interface temperature. Simplifications of the model and of the solution procedure are used without important degradation of the predictions. The model is assessed on experimental data for both film condensation in vertical tubes and direct contact condensation in horizontal tubes, including air-steam, Nitrogen-steam and Helium-steam data. It is implemented in the Cathare code, a french system code for nuclear reactor thermal hydraulics developed by CEA, EDF, and FRAMATOME.
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Languages : en
Pages : 16
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The Westinghouse Electric Corporation has designed an advanced pressurized light water reactor, AP600. This reactor is designed with a passive cooling system to remove sensible and decay heat from the containment. The heat removal path involves condensation heat transfer, aided by natural convective forces generated by buoyancy effects. A one-twelfth scale rectangular slice of the proposed reactor containment was constructed at the University of Wisconsin to simulate conditions anticipated from transients and accidents that may occur in a full scale containment vessel under a variety of conditions. Similitude of the test facility was obtained by considering the appropriate dimensionless group for the natural convective process (modified Froude number) and the aspect ratio (H/R) of the containment vessel. An experimental investigation to determine the heat transfer coefficients associated with condensation on a vertical and horizontal cooled wall (located in the scaled test section) at several different inlet steam flow rates and test section temperatures was conducted. In this series of experiments, the non-condensible mass fraction varied between (0.9-0.4) with corresponding mixture temperatures between 60-90°C. The heat transfer coefficients of the top horizontal surface varied from (82-296)W/m2K and the vertical side heat transfer coefficients varied form (70-269)m2K. The results were then compared to boundary layer heat and mass transfer theory by the use of the McAdams correlation for free convection.
Author: Warren M. Rohsenow
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ISBN:
Category :
Languages : en
Pages : 537
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Author: Argonne National Laboratory
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Category : Boiling water reactors
Languages : en
Pages : 254
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