Calculation analysis on the natural circulation of a passive residual heat removal system for IPWR

The passive residual heat removal system (PRHRS) is designed to increase the inherent safety features of the integrated pressurized water reactor (IPWR). The PRHRS consists of once though steam generator (OTSG) secondary side, a heat exchanger (HX), a cooling water tank (CWT), and corresponding pipes and valves. On the accident conditions, residual heat is transferred to the CWT by the single-phase natural circulation in primary loop and two-phase natural circulation in PRHRS loop, and then the water in CWT is heated and finally evaporates into the air. The calculate results using RELAP5 code show that the PRHRS is sufficient enough to take heat away from primary coolant system. The effect of main parameters on the PRHRS was studied. The results indicate that the effective height between OTSG and HX, the HX areas, the volume of CWT, and the isolation valve actuation time are important parameters which are worth being considered seriously in the design of the PRHRS.