The comparison of designed water-cooled and air-cooled passive residual heat removal system for 300 MW nuclear power plant during the feed-water line break scenario

The steam generator (SG) secondary water-cooled and air-cooled passive residual heat removal systems (PRHRSs) are proposed and designed for 300 MW Pressurized Water Reactor (PWR). The RELAP5/MOD3.4 code is utilized to study the behavior of the PRHRSs and transient characteristics of primary loop system during Feed-water Line Break (FLB) accident. The characteristic comparison between water-cooled and air-cooled PRHRSs is also conducted in this study. The results show that both water-cooled and air-cooled PRHRSs can establish stable natural circulations in PRHRS loops, which realize the effective core decay heat removal from primary loop. Results illustrate that both water-cooled PRHRS and air-cooled PRHRS designed in the study have great significance for improving the inherent safety of 300 MW nuclear power plant. However, the water-cooled PRHRS heat transfer ability is stronger in the initial time, while it becomes weaker as the system tank water evaporates in the later stage. In contrast, the air-cooled PRHRS, ensuring the main reactor operation parameters to decrease to a more safety value, is more effective than water-cooled PRHRS for long term cooling.