Developing a two-phase coarse grid model for nuclear thermal-hydraulics

Nuclear reactor core thermal-hydraulics are evaluated using system-level codes, subchannel analysis codes, and Computational Fluid Dynamics (CFD) solvers. System and subchannel codes generate solutions with limited flow details. CFD captures detailed flow structures, albeit with a significant computational effort. To alleviate the limitations of the existing codes, Subchannel CFD (SubChCFD), a coarse-grid CFD model, is developed at the University of Sheffield. SubChCFD applies a subchannel approach to compute wall effects so as to create a computationally cost-effective model for evaluating the flow dynamics within the nuclear reactor core. The single-phase model of SubChCFD has been developed in OpenFOAMT M and verified against a resolved CFD solution. This study aims to expand on the SubChCFD capability to solve for two-phase flow dynamics observed within nuclear reactor cores, specifically boiling flows. In a first step, the homogeneous equilibrium model (HEM) approach is adopted to predict two-phase flow characteristics (mixture enthalpy, mixture density, void fraction, and pressure drop). The results obtained from the SubChCFD model developed in this study match very well against the 1D HEM model, displaying the potential to develop a reliable low-resolution two-phase CFD model with much reduced computational effort.