Improvement of the heat transfer modeling in ATHLET for safety analysis of supercritical water-cooled reactor (VERA). Final report

Since Supercritical Water-Cooled Reactor (SCWR) has such advantages as system simplification and higher efficiency, research activities on it are ongoing worldwide. In the frame of improving the accuracy of System Thermal-hydraulics (STH) code, one of the most challenging tasks is to develop an accurate prediction of heat transfer between the cladding and fluid. However, due to the large variation of thermal-physical properties in the vicinity of the pseudo-critical point, heat transfer of supercritical water shows an abnormal behavior compared with that of conventional fluids, especially when the fluid bulk temperature is close to the pseudo-critical point. In order to design the SCWR Fuel Assembly (FA), it is necessary to investigate the heat transfer phenomenon and characteristics of supercritical water flowing in typical channels. The overall objective of this project is the development of new models to predict the heat transfer in supercritical water for a wide parameter range. Based on the large amount of test data, new heat transfer models with high accuracy were developed, implemented into the STH program ATHLET and validated with the experimental results of transient experiments with supercritical water in a 2x2 rod bundle.