Modeling of Time-Averaged Film Thickness Distribution Downstream of BWR Functional Spacers

Abstract

Functional spacers play an important role for the annular steam-water flow in boiling water reactors. They are designed to enhance droplet deposition and therefore delay dryout by sustaining the liquid film. Spacers also have an impact on the liquid film thickness on the fuel rod by their effect on the ve- locity field in the gas core of the flow. This work presents a CFD-based approach to predict the film thickness distribution in proximity of functional spacers based on a two-dimensional mass conservation equation for the liquid film coupled to a steady-state RANS simulation of the gas flow field. The model is validated by experiments with highly resolved film thickness data. For the experiments the gas flow rate, the liquid flow rate, the gas density and the spacer shape are varied. The model and experiments are in good agreement in regard to film thickness distributions downstream of spacers. A model sensi- tivity analysis shows the key parameters of the model and the potential for future development. The model aims to contribute to the development methodology of functional spacer optimization.