Identification of Success Criteria for Automated Function Using Feed and Bleed Operation

Since NPP has lots of functions and systems, operated procedure is much complicated and the chance of human error to operate the safety systems is quite high. In the case of large break loss of coolant accident (LBLOCA) and station black out (SBO), the dependency of operator is very low. However, when many mitigation systems are still available, operators have several choices to mitigate the accident and the human error can be increased more. To reduce the operator's workload and perform the operation accurate after the accident, automated function for safe cooldown based on the feed and bleed (F and B) operation was suggested. The automated function can predict whether the plant will be safe after the automated function is initiated, and perform the safety functions automatically. To expect the success of cooldown, success criteria should be identified. To perform the operation accurately after the accident, the automated function for safe cooldown based on the F and B operation is suggested. To expect the success of cooldown, sequence of RCS situation when heat removal by secondary system fails is identified. Based on the sequence of RCS situation, four levels of necessity of F and B operation are classified. To obtain the boundary of levels, the TH analysis will be performed