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:
ebruary 26, 2013 (ADAMS Accession No. ML13052A711). Safety Significance of open phase condition: At Byron, both offsite and onsite electric power systems were not able to perform their intended safety functions due to the design vulnerability. Manual actions were necessary to restore ESF safety functions. A design-basis event concurrent with this open phase condition could have resulted in the plant exceeding the guidance contained in 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors.” The accident sequence precursor analyses conducted by the staff calculated a conditional core damage probability of 1×10-4. The purpose of this BTP is to provide guidance to the staff in reviewing various licensing actions related to electric power system design vulnerability due to open phase conditions in offsite electric power system in accordance with Appendix A to 10 CFR Part 50, GDC 17 or principal design criteria specified in the updated final safety analysis report, and 10 CFR 50.36(c)(2) and (c)(3). B. BRANCH TECHNICAL POSITION The design of the electrical system should address the following open phase conditions: (i) Electric power from the transmission network to the onsite electric distribution system is supplied by two physically independent circuits. The system should address loss of one of the three phases of the independent circuits on the high BTP 8-9-3 Draft Revision 0 – May 2014 voltage side of a transformer connecting an offsite power circuit to the transmission system under all operating electrical system configurations and loading conditions: a. with a high impedance ground fault condition; and b. without a high impedance ground fault condition; and (ii) loss of two of the three phases of the either offsite power circuit on the high voltage side of a transformer connecting an offsite power circuit to the transmission system under all operating electrical system configurations and loading conditions.