Document: NUREG-0800
Document ID: 61198d64-419c-45ea-aebb-cf34c3b171fe
Document Type: srp
Title: Revision 0 – July 2015
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1505/ML15057A085.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
ffsite power source circuit breaker. One of the three phases in the circuit breaker failed to open, resulting in a double open phase condition in the power circuit (i.e., two open phases). Some of the operating loads tripped due to phase unbalance, while some safety-related and nonsafety-related loads overheated and failed. The undervoltage relays on the safety buses did not detect the degraded voltage conditions because the induced voltage was higher than the trip setpoint of the relays. 3. On April 27, 2014, the Dungeness B power plant in United Kingdom experienced random tripping of large loads resulting from the loss of one of three phases in the 400kV electrical supply to the site. The open phase condition was the result of inadequate contact in one pole of the circuit breaker. In the events discussed above, the protective relaying schemes did not detect the open phase(s) conditions due to inadequate detection schemes. As a result, degraded power sources continued to supply plant safety-related and nonsafety-related loads. In addition, the emergency diesel generators (onsite power system) did not automatically connect to the safety buses because the plant design did not have features to detect and automatically isolate the open phase conditions in the offsite power source. Based on the Byron Station operating event, the staff issued NRC, Information Notice 2012-03, “Design Vulnerability in Electric Power System,” dated March 1, 2012 (ADAMS Accession No. ML120480170). On July 27, 2012, the staff issued NRC Bulletin 2012-01, “Design Vulnerability in Electric Power System,” (ADAMS Accession No. ML12074A115) to confirm that licensees comply with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(h)(2), 10 CFR 50.55a(h)(3), and Appendix A, “General Design Criteria for Nuclear Power Plants,” to 10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities,” General Design Criterion (GDC) 17, “Electric Power Systems,” or