Predictability Evaluation of the SPACE Code for Condensation in a Nearly Horizontal Tube

The passive auxiliary feedwater system (PAFS) is a key passive safety feature adopted in the innovative Small Modular Reactor (i-SMR). This system removes decay heat through condensation occurring inside slightly inclined (3 ° ) heat exchanger tubes submerged in an emergency cooling tank. Accurate prediction of the condensation heat transfer within the tubes is essential for evaluating the heat removal capability of the PAFS. In addition, it is also crucial to predict the flow regime inside the tube because the condensation heat transfer mechanism is strongly dependent on it. In this study, SPACE code analyses were conducted for three experiments simulating the condensation heat transfer in a nearly horizontal tube, to evaluate the predictability of the SPACE code for the condensation heat transfer and flow regime in a PAFS. An improved PAFS model based on an original condensation model was used with the improved horizontal stratification criteria suggested in a previous study. The SPACE code analysis results demonstrated that the improved PAFS model significantly enhanced the predictability of the SPACE code for the condensation heat transfer rate and flow regime in the condensation experiments.