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:
ers immediately following an accident condition concurrent with the LOOP are reviewed to ascertain that the independence of the redundant portions of this system is established given a single failure. Operating experience has shown that potential single failure and fire vulnerabilities may exist whereby a circuit failure could result in safety bus lockouts and prevent reenergization of the redundant safety bus (see Reference 12). Certain safety bus protection schemes involving three current transformers for individual phase overcurrent relays and a ground overcurrent relay connected in a basic residual scheme were identified, which also included connection to a single common watt-hour meter summing the power for redundant safety buses. A fire-induced fault or watt-hour meter failure resulting in an open circuit could be interpreted by the bus differential protection system as an electrical fault on both safety buses causing in multiple bus lockouts. The reviewer should examine the electrical protection and metering schemes to verify that no such interconnections exist between protection and metering circuits that would constitute a common-mode failure vulnerability. C. To ensure physical independence, the criteria governing the physical separation of redundant equipment, including cables and raceways and their implementation as depicted on preliminary or final physical arrangement drawings, are reviewed to determine that the design arrangements satisfy the recommendations set forth in IEEE Std. 384 as augmented by RG 1.75. This standard and RG set forth acceptance criteria for the separation of circuits and electrical equipment contained in or associated with the Class 1E power system. To determine that the independence of the redundant cable installation is consistent with satisfying the recommendations set forth in IEEE Std. 384 as augmented by RG 1.75, the proposed design criteria governing the separation of Class 1E cables and raceways are reviewed, including