Study on Optimization of Allowable Outage Time for Essential Service Water System in HPR1000

The risk-informed integrated decision-making method combining deterministic and probability theories was adopted for the optimization analysis and demonstration of the allowed outage time (AOT) in the terms of operational technical specifications for the essential service water system (WES) of Hualong One (HPR1000), including the determination of proposed changes, defense-in-depth analysis, safety margin analysis and probabilistic safety assessment (PSA). The results show that it is acceptable to extend the AOT from 72 h to 96 h for the unavailable train of the WES of HPR1000; the principle of defense-in-depth and safety margin requirements of HPR1000 are met; the increased risk meets the acceptance guidelines of the U.S. Nuclear Regulatory Commission (NRC) regulatory guidelines RG1.174 and RG1.177. On the premise of risk control, the flexibility of power plant operation can be further improved.