Document: NUREG-0800
Document ID: 9cfc38bf-7808-446e-a43d-4ca9ff55df2a
Document Type: srp
Title: AC POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1007/ML100740289.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
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 no intervening non- safety buses in such a manner that the offsite source can power the safety buses in the event of failure of any non-safety bus. 8.3.1-24 Revision 4 - May 2010 In plants where there is no alternate source to supply power to balance of plant loads such as Reactor Coolant Pumps, Reactor Recirculation Pumps, Feedwater Pumps, etc.; the loss of power to these loads due to a plant trip or a 100% load rejection caused by the opening of the main generator high-side circuit breaker will result in a loss of forced circulation in the reactor coolant system and reduced feedwater flow. Therefore, the electrical drawings should also be examined to ensure that the design includes an alternate power source for non-safety loads, unless it has been demonstrated that the design margins will result in transients for loss-of non-safety-power events that are no more severe than those associated