Document: NUREG-0800
Document ID: 81256f55-72dd-4777-9472-f373c71c4554
Document Type: srp
Title: AC POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550065.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
pendence of GDCs 34, 35, 38, 41, and 44; that is, for onsite power system operation (assuming offsite power is not available), the system safety function can be accomplished assuming a single failure. To determine that the physical independence of the preferred power circuits to the Class 1E buses is consistent with satisfying the requirements of GDC 17 and the recommendations of IEEE Std 308, the physical arrangement drawings are examined to verify that each circuit is physically separate and independent from its redundant counterparts. In addition, the final feeder-isolation breaker in each circuit through which preferred power is supplied to the safety buses should be designed and physically separated in accordance with the criteria for the onsite power system. Following the loss of preferred power, the safety buses are powered solely from the standby power supplies. Under this situation, the design of the feeder-isolation breaker in each preferred power circuit should preclude the automatic connection of preferred power to the respective safety bus upon the loss of standby power. In this regard, an acceptable design should include the capability for restoring preferred power to the respective safety bus by manual actuation only. The staff has determined that supplying power to the Class 1E buses from offsite power sources through non-Class 1E buses, or from a common winding to that supplying non-Class 1E loads, is not the most reliable configuration. Such configurations make it difficult to obtain suitable voltage regulation at the Class 1E buses and subject the Class 1E loads to transients caused by non-Class 1E loads (e.g., Reactor Coolant Pump). Such configurations could also result in additional failure points between the offsite power source and the Class 1E buses/loads. Therefore, the staff has concluded that the design should include at least one offsite circuit supplied directly to each redundant safety division from one of the offsite power sources with