APR1400 Electrical Power System Conformance to SECY-91-078

In this paper, the APR1400 electric power system for NRC-DC was described. In addition, the conformance to SECY 91-078 was evaluated. Enclosure 1 of the SECY provides an overview of the issue and states that the staff concludes that feeding the safety buses from the offsite power sources through non-safety buses or from a common transformer winding with non-safety loads is not the most reliable configuration. Such an arrangement increases the difficulty in properly regulating voltage at the safety buses, subjects the safety loads to transients caused by the non-safety loads, and adds additional failure points between the offsite power sources and safety loads. Therefore, it is the staff's position that at least one offsite circuit to each redundant safety division should be supplied directly from one of the offsite power sources with no intervening non-safety buses, in such a manner that the offsite source can power the safety buses upon a failure of any non-safety bus. The APR1400 does not have an intervening nonsafety bus in the current offsite to onsite electrical configuration; however, the design does include nonsafety and safety buses coming from the same secondary side 4.16 kV transformer winding. Nevertheless, the APR1400 has designed the electrical interface system between offsite and onsite power with enhanced reliability measures to ensure that the nonsafety system will not impact the safety loads. The design complies with GDC 17 and also conforms to SECY-91-078