Development of STEAM code: a steam generator tube-level three-dimensional thermal–hydraulic analysis platform

The steam generator (SG) serves as a critical component for ensuring the safe removal of heat from the reactor core and maintaining the integrity of the primary loop pressure boundary. Acquiring accurate three-dimensional thermal–hydraulic parameters distribution characteristics in the SG is essential for safety analysis. The STAF series, which are SG three-dimensional thermal–hydraulic analysis codes, have been developed based on the drift-flux model by NuTHeL (Nuclear Thermal-hydraulic Laboratory) at XJTU (Xi'an Jiaotong University) since 2012. To further improve the code's accuracy in analyzing SG flow fields—particularly regarding the local flow characteristics in the bending tube zone and the flow distribution in the primary side tube bundle—a high-precision SG three-dimensional thermal–hydraulic analysis code, STEAM (Steam generator Tube-level three-dimensional thErmal-hydraulic Analysis platforM), has been developed as an upgrade to STAF series, based on the two-fluid model. In the STEAM code, the two-fluid model is constructed using the two-group bubble method to cover various two-phase flow regimes on the secondary side, while tube-level modeling of SGs is employed to enhance the resolution of the flow field. Validation studies are carried out using the MHI SG and FRIGG experiments, and the mean relative errors of the predicted void fraction are 7.02% and 9.54% respectively. The applicability and accuracy of the STEAM code's mathematical model are confirmed. The STEAM code is employed to simulate the Westinghouse MB-2 SG, the distribution characteristics of key thermal–hydraulic parameters—including pressure drop, temperature, flow, void fraction, velocity, cross flow energy, and heat transfer—are analyzed. The local flow characteristics in the bending tube zone are revealed. The analysis capability can serve as a guide and reference for the safety analysis of in-service SGs and the design optimization of next-generation SGs.