Development of Heat Transfer Model Package for Horizontal U-Shaped Heat Exchanger Submerged in Pool of Passive Safety System

A horizontal U-shaped heat exchanger (HX) submerged in a pool is under development as a piece of key equipment for a passive safety system in a nuclear power plant (NPP). For the successful design of the HX and the safety analysis of the NPP, reliable prediction of the heat transfer performance of the HX is important. At present, the design and the safety analysis of the passive safety systems are performed mainly using best-estimate thermal-hydraulic analysis codes such as RELAP5 and MARS. However, those codes do not have suitable models for both condensation heat transfer in the horizontal tube and natural convective and nucleate boiling heat transfer on the horizontal tube, both of which ultimately determine the heat transfer performance of the HX. This study developed a heat transfer model package for the horizontal U-shaped HX submerged in a pool by improving the horizontal in-tube condensation model and developing the out-tube natural convective and nucleate boiling model. From the validation results, the proposed model provides an improved prediction of HX performance (condensation, natural convection and nucleate boiling, and heat removal rate of the HX) compared to the default model in MARS.