This project focuses on the validation and enhancement of the Eulerian Multiphase (EMP) boiling flow model available in the STAR-CCM+ Computational Fluid Dynamics (CFD) code. The STAR-CCM+® EMP models will be enhanced to include the latest NEK-2P model extensions during this activity. The model extensions will be implemented in STAR-CCM+® as a set of user functions referred to as the Advanced Boiling Framework (ABF). It is important to note that the STAR-CCM+® EMP models are based on the two-phase models inherited from the predecessor CFD code STAR-CD, which were developed by ANL in collaboration with CD-adapco. This new development can be used as a supporting tool for safety analysis of Pressurized Water Reactor (PWR) and Boiling Water Reactors (BWR).

Simulations of boiling flow in a heated pipe were performed and results were compared with corresponding experimental data (Fig. 1). In our previous work, the two-phase CFD codes NEK-2P and STAR-CD codes were validated through comparison with Becker Critical Heat Flux (CHF) benchmark tests. In both codes, the extended boiling framework (EBF) was implemented. The EBF was developed for the fine-mesh, 3-dimensional simulation of the two-phase flow phenomena that occur in a Boiling Water Reactor (BWR) fuel assembly. These phenomena include coolant phase changes and multiple flow topologies that directly influence the reactor performance. The EBF boiling models, which describe the inter-phase mass, momentum, and energy transfer phenomena specific for various local flow topologies, allow the simulation of a wide spectrum of flow regimes expected in a BWR fuel assembly. Also, the same formulated model validated with 5x5 spacer grid for PWR conditions (not shown).