Numerical study on improved design of passive residual heat removal system for China pressurizer reactor

The core residual heat removal system of the pressurized water reactor (PWR) is a vital facility to ensure the reactor safety, and its failure after shutdown will inevitably lead to the meltdown of the core. However, the existing core residual heat removal system of CPR1000 only guarantee the 72-hour grace period, after which the core decay heat can still melt the core within one day. The present study proposes an improved design of passive residual heat removal system (PRHRS) that utilizes natural forces to realize a passive self-start. Meanwhile, an innovative method is also proposed to use the atmosphere as the final heat sink in this paper. Subsequently a numerical study is conducted to verify the performance of the improved design during accident condition. Numerical results show that the improved design of PRHRS maintains a timeless safety cooling capacity during the station blackout (SBO) scenario. Finally, the parameter sensitivity study is performed to investigate a reasonable design value of chimney height. And numerical results prove that the proposed PRHRS is still capable of removing the core residual heat continuously even if the atmosphere temperature is variable. All component functions of new designed PRHRS are completely driven only by the action of natural factors without any external energy power. Therefore, the improved design of PRHRS can actually eliminate the risk of severe accident and lays the necessary technical foundation for the faster and larger-scale development of PWR.