Multi-dimensional thermal-hydraulic phenomena in advanced nuclear reactor systems: current status and perspectives of the R and D program at KAERI

This paper introduces the current status and perspectives of the research works on the multi-dimensional thermal-hydraulic phenomena which are related to the development of advanced nuclear reactor systems like APR1400, of advanced system analysis codes like MARS or TRAC and also of new safety analysis methodology with enhanced effectiveness and reliability. One research area is related to the multi-dimensional behavior of the Safety Injection (SI) water in a Reactor Pressure Vessel (RPV) downcomer, which is directly associated with adopting the DVI (Direct Vessel Injection) type of the SI system in the APR1400. It includes the ECC bypass phenomena in a RPV downcomer during a LBLOCA reflood phase, steam venting through a DVI line break in a upper downcomer of the RPV during a SBLOCA, and the boron mixing phenomena in both the RPV downcomer and core inlet regions during a MSLB event. The other area is associated with the direct contact condensation of steam and the resultant thermal mixing in a large pool. This area is directly related to the depressurization system in advanced reactor systems. Our work, based on both experiments and analyses, is believed to contribute to the understanding of the new thermal-hydraulic phenomena relevant to advanced reactor system designs as well as evaluating the prediction capabilities of the analysis tools for multi-dimensional flow behavior especially in complicated geometries