Integral effect test on operational performance of PAFS (passive auxiliary feedwater system) for long term cooling under an SBO (Station Black Out) condition

PAFS (Passive Auxiliary Feedwater System) is one of the advanced safety features adopted in APR+ (Advanced Power Reactor Plus) which is intended to completely replace a conventional active auxiliary feedwater system. PAFS cools down the steam generator secondary side and eventually removes the decay heat from the reactor core by adopting a natural convection mechanism; i.e., condensing steam in nearly-horizontal U-tubes submerged inside PCCT (Passive Condensation Cooling Tank). With an aim of validating the operational performance of PAFS, the experimental program of an integral effect test has been performed at KAERI (Korea Atomic Energy Research Institute). In this study, PAFS-LTC-01 test was performed with ATLAS-PAFS facility for evaluating the cooling performance of PAFS under an SBO (Station Black Out) condition. The main objectives of this test were not only to provide a physical insight into the system response of APR + but also to evaluate the cooling performance of PAFS for the long term operation. From the present experimental result, it was observed that the cooling rate of the core decreased as PAFS operated during long time. The maximum limit that PAFS retains its cooling capability was until the time that the collapsed water level of PCCT reduced to the bending point of PCHX. It took about 30 h in the present test which corresponds to 42.4 h in the prototype nuclear power plant with consideration of time scaling ratio.