Development of a symptom-based transient mitigation method for feedwater system failure in the ABWR plant

A transient mitigation method for feedwater system failure in the ABWR has been developed using a symptom method which detects system failures based on the trends of the plant parameter changes. This concept was derived from a correlation between the trends of the main plant parameters when a transient event occurs. Based on simulation results and the plant dynamics model, the trends of the main plant parameters confirm that the occurrence of a feedwater now changing event can be distinguished from other types of transient events. The transient detection logic and threshold are developed to be able to detect the transient event early in an abnormal event. This system detects the failure of the feedwater system based on the changes of the plant parameters, and it uses counter control to avoid a scram event caused by the low-water-level scram interlock logic. With early detection the plant power can be kept as high as possible corresponding to the remained water feeding ability. Based on the simulation results, the transient mitigation system was confirmed able to detect the transient event and avoid the plant scram in the case of the feedwater system failure. Furthermore it can distinguish the type of transient event and does not initiate any counter control in other types of transient events.