Accident sequence analysis of a main feed line break for the KSNP

A main feed line break (MFLB) accident and a main steam line break (MSLB) accident have been summed as a large secondary side break (LSSB) accident sequence in the current PSA model for the Korea Standard Nuclear Power Plant (KSNP). This was because of the estimation that both accidents showed a similar behavior in the KSNP. Each sequence, however, had been analyzed much differently in the Final Safety Analysis Report (FSAR) of the KSNP. According to the FSAR, the MSLB accident showed a typical reactivity-related transient behavior, i.e., a main concerning point of the MSLB accident was the 'return to power' due to reactivity impact by an over cooling effect. While the MFLB accident showed a typical pressure-related transient behavior, i.e., a main concerning point of the MFLB accident was the Reactor Coolant System (RCS) pressure behavior which can threaten the RCS integrity. The MFLB accident was described as a decrease of heat removal by the secondary side event in the FSAR, so the RCS pressure is rapidly arisen to the set point of the Pressurizer Safety Valves (PSVs). Although the MFLB accident sequence in the FSAR was too conservative to describe a realistic behavior of the RCS pressure, a remarkable thing of this fact is the difference between the MSLB accident sequence and the MFLB accident sequence from the viewpoint of a PSA modeling. Now we tried to deal with this fact in order to improve the PSA model. In the present paper, a LSSB accident sequence in the current PSA separated as a MSLB accident sequence and a MFLB accident sequence. The MFLB accident sequence analysis as a part of the PSA model has been performed for the estimation of its impact on the entire risk profile of the KSNP