Document: NUREG-0800
Document ID: f9d2d9cb-1d13-407e-ad7a-523fff64de06
Document Type: srp
Title: DC POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1007/ML100740391.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.2
CFR Part: 
CFR Title: 

Content:
n systems, including their connected loads, to assess the independence between redundant portions of the system. To ensure electrical independence, the staff will review the design criteria, analyses, description, and implementationCas depicted on functional logic diagrams, electrical single-line diagrams, and electrical control and schematicsCto determine whether the design meets the positions of RGs 1.153, 1.53, 1.32, and 1.6. As endorsed by RG 1.153, IEEE Std. 603 provides a method acceptable to the staff for evaluating all aspects of the electrical portions of safety-related systems and the onsite power system. For guidance related to the application of the single-failure criterion, IEEE Std. 603 8.3.2-14 Revision 4 - May 2010 references IEEE Std. 379. In addition, as endorsed by RG 1.53, IEEE Std. 379 provides an acceptable methodology for satisfying the Commission=s regulations for the application of the single-failure criterion to onsite dc power systems. The following aspects of the design need special review attention to confirm that the electrical independence and physical separation have not been compromised: A. The reviewer will examine interconnections between redundant load centers through bus tie breakers and multifeeder breakers used to connect extra redundant loads to either of the redundant distribution systems to ensure that no single failure in the interconnections or inadvertent closure of interconnecting devices will compromise division independence in a manner that will cause the paralleling of the dc power supplies. To ensure this, the control circuits of the bus tie breakers or multifeeder breakers must preclude automatic transferring of load centers or loads from the designated supply to the redundant counterpart upon loss of the designated supply (Regulatory Position 4 of RG 1.6). Regarding the interconnections through bus tie breakers, an acceptable design will provide for two tie breakers connected in series and physically separated from