Shahabeddin Kamyab - Shiraz University, Mechanical Engineering Department
Mohammadreza Nematollahi - Shiraz University, Mechanical Engineering Department
Meisam Rafiee - Shiraz University, Mechanical Engineering Department
Mohsen Ebrahimian - Shiraz University, Mechanical Engineering Department

The availability of alternating current electrical power is essential for the safe operation and accident recovery in commercial nuclear power plants (NPPs). Offsite power sources normally supply essential power from the grid. Loss of Offsite Power (LOOP) initiating event is a simultaneous loss of electrical power to all safety-related buses that causes emergency power generators to start and supply power to the safety-related buses.The results of current Probabilistic Safety Analysis (PSA) show that LOOP event is a large contributor to the Core Damage Frequency (CDF). Thus, plant designers resort into using redundant and reliable preferred power source to NPPs to lessen the occurrence frequency of LOOP, and the resultant LOOP induced CDF.This study surveys the effect of electrical offsite power reliability on total CDF resulted by internal events in the Advanced Pressurized Water Reactor (APWR). Sensitivity cases are defined regarding the potential variation of offsite power grid connection to the NPPs and plant design features, for each frequency of occurrence of LOOP, as an initiating event, is estimated, then. Thereafter, total induced CDFs, are reevaluated, corresponding to each configuration. The results are, finally, compared for two cases of passive and active APWRs.The results show that LOOP contributes almost nearly more than 20% up to 80% in total CDF of active APWRs, for possible LOOP frequencies. Although such contribution is, by far, lower for passive APWRs (less than 1% to 5% in AP1000 as a case study). The results of sensitivity cases for active reactors, however, much more signify the requirement for exploiting redundant and reliable offsite electrical power sources in active power plants, in order to maintain a reasonable value of CDF. Moreover, the results emphasize on the need to prepare NPPs with two independent lines of grid. Besides, house load capability of NPP can be nominated as a conspicuous way-out to reduce the LOOP induced CDF (15% decrease in total CDF, if the NPPs benefits from full load rejection capability). However, no tangible change happens in total CDF of those NPPs rely on passive designs, over various LOOP frequencies.

Loss of Offsite Power, Advanced PWR, Core Damage Frequency, Electrical Grid, Sensitivity Analysis