Abstract
In water-cooled nuclear power reactors, significant quantities of steam and hydrogen could be produced within the primary containment following the postulated design basis accidents (DBA) or beyond design basis accidents (BDBA). For accurate calculation of the temperature/pressure rise and hydrogen transport calculation in nuclear reactor containment due to such scenarios, wall condensation heat transfer coefficient (HTC) is used. In the present work, the adaptation of a commercial CFD code with the implementation of models for steam condensation on wall surfaces in presence of noncondensable gases is explained. Steam condensation has been modeled using the empirical average HTC, which was originally developed to be used for “lumped-parameter” (volume-averaged) modeling of steam condensation in the presence of noncondensable gases. The present paper suggests a generalized HTC based on curve fitting of most of the reported semiempirical condensation models, which are valid for specific wall conditions. The present methodology has been validated against limited reported experimental data from the COPAIN experimental facility. This is the first step towards the CFD-based generalized analysis procedure for condensation modeling applicable for containment wall surfaces that is being evolved further for specific wall surfaces within the multicompartment containment atmosphere.
Highlights
Steam condensation in the presence of noncondensable gases is a relevant phenomenon in many industrial applications, including nuclear reactors
Condensation on the containment structures during an accident and associated computations are important for the containment design of all the existing reactors for LOCA design basis accidents (DBA), DBA, and beyond design basis accidents (BDBA) hydrogen distribution and recombination and passive emergency systems in the nuclear reactors of new generation
The present fit has been derived taking a fixed value of liquid film thickness and temperature gradient. This can be improved based on specific requirement, and inputs can be generated for complex intercompartmental configurations within CFD framework. This result advocates the replacement of simplified condensation model with a new improved simple heat transfer coefficient (HTC) in CFD-based approach which can be used to model real large containment geometry for safety evaluation in a more consistent manner
Summary
Steam condensation in the presence of noncondensable gases is a relevant phenomenon in many industrial applications, including nuclear reactors. The most popular way is to include heat or mass transfer correlations that were originally developed for “lumped-parameter” (volumeaveraged) calculations and apply them in the layer of cells contiguous to the condensation surface These correlations use the temperature and steam mass fraction value from bulk flow and calculate the condensing heat transfer coefficient, since the corresponding sink term is applied for the very first fluid cell near the condensing wall, and the bulk flow parameters and thermophysical properties are evaluated at these cell centres. In this approach rate of heat and mass transfer depends on the cell width near the condensing wall. The simulation was performed with the knowledge of experimental results
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