Document: NRC Regulatory Guide
Document ID: da55f4e3-0344-4286-b684-2ebd9c82115e
Document Type: regulatory_guide
Title: Independence Between Redundant Standby
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739924.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.6
CFR Part: 
CFR Title: 

Content:
ilize a swing bus. A diesel generator that swings between the load groups of different units at a multiple unit site is not an example of the foregoing since such load groups are not redundant to each other. D. Regulatory Position 1. The electrically powered safety loads (a-c and d-c) should be separated into redundant load groups such that loss of any one group will not prevent the minimum safety functions from being performed. 2. Each a-c load group should have a con nection to the preferred (offsite) power source and to a standby (onsite) power source (usually a single diesel genera tor). The standby power source should have no automatic connection to any other redundant load group. At mul tiple nuclear unit sites, the standby power source for one load group may have an automatic connection to a load group of a different unit. A preferred power source bus, however, may serve redundant load groups. 8. Each d-c load group should be energized by a battery and battery charger. The battery-charger combination should have no automatic connection to any other redundant d-c load group. 4. When operating from the standby sources, redundant load groups and the redundant standby sources should be independent of each other at least to the following extent: a. The standby source of one load group should not be automatically paralleled with the standby source of another load group under acci dent conditions; b. No provisions should exist for auto matically connecting one load group to another load group; c. No provisions should exist for auto matically transferring loads be tween redundant power sources; d. If means exist for manually con necting redundant load groups tu gether, at least one interlock should be provided to prevent an operator error that would parallel their standby power sources. 5. A single generator driven by a single prime mover is acceptable as the standby power source for each a-c load group of the size and characteristics typical of recent applications.