Numerical investigation on critical heat flux for 5 × 5 fuel assemblies with a wide range of working conditions

Abstract

To determine the safe boundary of fuel assembly operation and improve the heat transfer performance of fuel assembly, it is necessary to accurately calculate the thermohydraulic characteristics and the critical heat flux (CHF) in rod bundles. The Eulerian two-phase model coupled with extended wall boiling model was used to numerically investigate the 5 × 5 fuel rod bundle flows with four sets of mixing vane spacer grids. A wide range of working conditions were analyzed to validate the numerical method. The results indicate that the current numerical model can not only accurately calculate the CHF values but also predict the location of heat transfer crisis. Based on CFD (Computational Fluid Dynamics) results, the detailed two-phase flow distributions were provided to analyze the CHF performance under special structures, such as bowed rod and spacer backward shift. The quantitative results were obtained on the analyses of spacer position influence on CHF and the penalty effect of bowed rod. Furthermore, the prediction of present numerical model under low inlet subcooling conditions and cold rod CHF were discussed. The research of this paper provides support for the design and optimization of fuel assemblies.