Optimization of the Heat Transfer Model for Superheated Steam Condensation Inside Tubes and Its Evaluation with the SPACE Code

This study focuses on condensation heat transfer of superheated steam inside tubes of once-through steam generators, which are utilized in various small modular reactors (SMRs). This work specifically investigates innovative SMR (i-SMR) and its passive auxiliary feedwater system (PAFS). The primary objective is to implement an optimized heat transfer model for superheated steam condensation into the Safety and Performance Analysis Code for Nuclear Power Plants (SPACE) code and subsequently validate it. To achieve this, a review of previous studies on superheated steam condensation heat transfer inside tubes was conducted to identify the best existing model for the PAFS operating conditions. The model identified from the literature review was first implemented in the SPACE code and evaluated against relevant experimental data. This evaluation revealed a key weakness, as the model underpredicted heat transfer in the high-superheat region. To address this shortcoming, an optimized model was developed by improving the single-phase forced convection heat transfer correlation for superheated steam based on a previous experimental study. This optimized model was subsequently implemented in the SPACE code. Validation calculations confirmed that the optimized model offers significantly improved prediction accuracy, especially in the high-superheat region, establishing it as the final model for the i-SMR PAFS.