Decay heat removal performance analysis of AP1000 startup feed water during non-LOCA accident

In order to verify if the supply performance of startup feed water (SFW) can meet the Defense in Depth Criterion of decay heat removal after non-LOCA accident, it is conservatively supposed that the reactor has been shut down, and the inner/external power grid, main feed water, and condenser heat sink have been lost. In additional hypothesis, the steam generator (SG) backpressure is the lowest setting value of safety valve, and only one series of SG and SFW pump is available. Firstly, whether the minimum supply of SFW pump can satisfy the criterion of 118.1m3th is verified, when the condensate tank (CST) is at the lowest level. Secondly, after the accident, when the standby AC power and SFW pump needs 140s to loading, whether the buffering capacity of SG can carry out the decay heat without trigger the safety system is illustrated. Thirdly, 140s later, whether the SFW can stabilize SG level is discussed. Fourthly, whether the capacity of CST can satisfy the criterion of continuously supply during 24 hours after the accident. Through the analysis of the minimum SFW supply, the SG buffering capacity, the SG level control and the CST capacity, the design reliability and consistency to Defense in Depth criterion of AP1000 are verified. (authors)