Document: NUREG-0800
Document ID: b75d082b-2493-4543-981a-2ee136d737cf
Document Type: srp
Title: BTP 8-9-1
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1405/ML14057A433.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
due to loss of seal cooling water may have resulted in a loss-of-coolant event within a few more minutes. A second event also occurred at Byron Station Unit 1 on February 28, 2012. This event was also initiated by a failed inverted porcelain insulator which resulted in an open phase as well as a phase to ground fault on the line side of the circuit. In this event, the fault current was high enough to actuate protective relaying on the 345 kV system. The 4.16-kV ESF buses experienced an undervoltage condition due to the opening of 345 kV system breakers, which resulted in separation of SATs from the 4.16-kV buses. The 1A and 1B EDGs started and energized the 4.16-kV ESF buses as designed. Past operating experience has identified design vulnerabilities associated with single-phase open circuit conditions at South Texas, Unit 2; Beaver Valley Power Station, Unit 1; James A. Fitzpatrick Nuclear Power Plant; and Nine Mile Point, Unit 1. These events involved offsite power circuits that were rendered inoperable by an open-circuited phase. In each BTP 8-9-2 Draft Revision 0 – May 2014 instance (except South Texas, Unit 2), the condition went undetected for several weeks because offsite power was not aligned to ESF buses during normal operation and the surveillance procedures, which recorded phase-to-phase voltage, did not identify the loss of the single phase. At South Texas, Unit 2, offsite power was normally aligned to ESF and nonsafety plant buses and the reactor was manually tripped by the operator when circulation water pump was tripped by the open phase condition. Recently, two related international events occurred. First, the Bruce Power Plant in Canada identified that the protective relaying scheme is vulnerable to open-phase, or loss-of-phase events based on an event that occurred on December 22, 2012, where one of the 3-phases of 230 kV overhead line connections was broken. Second, the Forsmark, Unit 3 in Sweden reported that protective relaying scheme is