Design and transient analyses of emergency passive residual heat removal system of CPR1000. Part: Air cooling condition

The steam generator secondary emergency passive residual heat removal system (EPRHRS) is a novel design for the conventional generation + reactor CPR1000. The EPRHRS is designed to improve the safety and reliability of CPR1000 by completely or partially replacing the traditional emergency water cooling system in the event of the feed line break (FLB) or loss of heat sink accident. The EPRHRS consists of a steam generator (SG), a heat exchanger (HX), an air cooling tower, an emergency makeup tank (EMT), and corresponding pipes and valves for air cooling condition. In order to improve the safety and reliability of CPR1000, a model of the primary loop system and the EPRHRS was developed using RELAP5/MOD3.4 to investigate the residual heat removal capability of the EPRHRS and the transient characteristics of the primary loop system affected by the EPRHRS. The transient characteristics of the primary loop system and the EPRHRS were calculated in the event of the feed line break accident. Sensitivity studies were also conducted to investigate effects of the main parameters of the EPRHRS on the transient characteristics of the primary loop and the EPRHRS. The EPRHRS could supply water to the SG shell side from the EMT successfully. The calculation results showed that the EPRHRS could take away the decay heat from the primary loop effectively for air cooling condition, and that the single-phase and two-phase natural circulations were established in the primary loop and the EPRHRS loop, respectively. The present work is instructive for engineering design of the EPRHRS for Chinese NPPs.