A Study on the Operator Decision Support for Feed-and-Bleed Operation

In the case of a combined accident that includes a failure of the secondary cooling system, it is difficult for operators to recognize the necessity of an feed and bleed (F and B) operation because a lot of parameters and alarms should be checked before a decision, and operators may spend a considerable amount of time arriving at the entry for a proper emergency operating procedure that contains the procedure for an F and B operation. Therefore, a clear identification of the success boundary of an F and B operation would help operators in their decision-making when a combined accident that includes a secondary cooling system failure occurs. This study will provide a useful guideline for the initiation of an F and B operation for operators. Cooling the RCS after a scram is one of the most important safety functions for preventing core damage. To support the operator in decision making whether to initiate the F and B operation, plant conditions requiring the initiation of an F and B operation were identified. Plant conditions are affected by the steam generator inventory, RCS inventory, core inventory, and safety injection availability. The combination of accident types, component availabilities, and the initiation time of an F and B operation affect the success of the F and B operation. Operators need clear information about the RCS condition when the steam generators, the RCS's main residual heat removal mechanism, become unavailable. When this happens, the initiation of an F and B operation becomes necessary. As the number of the state increases, the necessity of an F and B operation increases. Especially, the operator should initiate an F and B operation when the RCS condition enters State 3 for Type 1 incidents or State 3-2 for Type 2 incidents. The results of this study may be useful in providing information regarding the necessity and effects of an F and B operation in a quantitative manner. In particular, in the case of a combined accident including a secondary cooling system failure, the provision of clear information will play a critical role in the operators' decision to initiate an F and B operation