Analyses of operation performance of advanced secondary passive residual heat removal system in PWR

Abstract The newly designed advanced secondary passive heat removal system (ASP) was one of the most important cooling systems to cope with station blackout (SBO) accident in the generation II + 1000 MWe PWR nuclear power plant (NPP). Advanced secondary passive heat removal system test facility (ASPTF) was constructed to obtain the operation performance of ASP under SBO conditions. The geometrical scaling ratio of ASPTF is 1/4 in the height and 1/208 in the volume with respect to the generation II + 1000 MWe PWR. The drag coefficient experiments were conducted to match the prototypical resistance characteristics of ASP in this paper firstly. Then, a prolonged SBO accident sequence was experimentally investigated in ASPTF. The experimental results reveal that the secondary side pressure of steam generator (SG) maintained at the set value in the early stage with the reciprocating opening of vapor discharge to atmosphere valve (VDA). After the startup of ASP, the secondary side pressure of SG decreased and heat generated in core simulator was effectively removed by natural circulation through ASP within 3 h (h) of the design value. Three hours later, the flow rate of ASP became unstable with the baring of heat exchanger (HX) tube. The stable natural circulation of ASP was recovered after the injection of water in the water tank (WT) after 4 h. A sensitivity investigation on operation performance of ASP also was performed based on RELAP5 code. This study not only helps to improve the understanding of important thermal hydraulic phenomena in ASP, but also sheds some lights on operation optimization for the PWRs with ASP.