Dynamic sequence analysis for feed-and-bleed operation in an OPR1000

Abstract

A feed-and-bleed (F&B) operation in an OPR1000 provides residual heat removal when the secondary cooling system is not available. Operators may hesitate to initiate F&B operation if a clear cue is not provided because its initiation will result in the release of radioactive coolant into the containment structure. An analysis of the necessity and effects of F&B operation was performed systematically. The plant conditions requiring F&B operation were categorized as type of transients. The factors which affect the necessity and effects of F&B operation are water inventory in the primary and secondary cooling systems, break size and timing of the break-up in the case of loss-of-coolant accident, the availability of the safety injection system and safety depressurization system, and timing of the F&B operation initiation. The boundary of each state in an OPR1000 was identified and the effects of factors were investigated to support the operator’s decision to initiate F&B operation under various reactor conditions. A thermohydraulic analysis was performed using the MARS code to determine this success boundary. This study is expected to provide a useful guideline for the initiation of F&B operation for operators. 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 F&B operation.