Computational Fluid Dynamics Modeling of Compact Steam Generators

Abstract

Compact Steam Generators (CSGs) are vital components in Small Modular Reactors (SMRs), particularly within Integral Pressurized Water Reactor (iPWR) configurations where compactness and high performance are essential. This thesis explores the use of Multiphase Computational Fluid Dynamics (M-CFD) to simulate two-phase flow boiling in CSGs based on Printed Circuit Heat Exchanger (PCHE) technology. Using the commercial CFD code STAR-CCM+, two modeling approaches—the Volume of Fluid (VOF) model and the Two-Phase Thermodynamic Equilibrium (TPTE) model—are applied to simulate both adiabatic and heat transfer conditions within mini-channels. The simulations are validated against experimental data from two sources: an R-134a-based vertical test loop developed at MIT’s Greenlab and a water-based PCHE test section from Kromer’s prior work. Key two-phase flow parameters such as void fraction, pressure drop, and heat duty are evaluated and compared to experimental benchmarks. Calibration methodologies are implemented to improve predictive accuracy. The validated models are then used to simulate realistic CSG operating conditions based on Babcock \& Wilcox and NuScale reactor designs. Results indicate that PCHE-based CSGs, despite being smaller, are capable of delivering favorable thermal and hydraulic performance, with slightly better results compared to the existing steam generator design. Overall, the study demonstrates the potential of M-CFD tools to support the design and optimization of CSGs for next-generation nuclear applications.