Document: NUREG-0800
Document ID: a2680f96-0e15-402d-89ab-688ff09806a8
Document Type: srp
Title: with respect to the specified station blackout event/duration.13
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070497.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.2
CFR Part: 
CFR Title: 

Content:
r concurrent with turbine trip and failure of the onsite emergency ac power system, but not the loss of available ac power to buses fed by station batteries through inverters or the loss of power from "alternate ac sources." The concern about station blackout arose because of the accumulated experience regarding the reliability of ac power supplies. The issue of station blackout involves the likelihood of a loss of offsite power and its duration, the redundancy and reliability of the onsite emergency ac power systems, and the potential for severe accident sequences after a loss of all ac power. The results of risk studies indicate that estimated core meltdown frequencies from station blackout vary considerably for different plants and that station blackout could be a significant risk contributor for some plants. In order to reduce this risk and resolve the safety concerns stemming from station blackout events, the Nuclear Regulatory Commission (NRC) has promulgated 10 CFR 50.63, "Loss of All Alternating Current Power," and issued a supporting Regulatory Guide 1.155, "Station Blackout." Regulatory Guide 1.155 endorses NUMARC-8700 (Reference 6) as supplemented by its regulatory positions and describes a means acceptable to the staff for meeting the requirements of 10 CFR 50.63. The overall review of compliance with station blackout requirements is described in SRP Section 8.4 (proposed). One option for meeting the requirements of 10 CFR 50.63 involves the provision of an alternate ac (AAC) source (an adequate AAC source is mandatory based upon the staff's position for new applications) as defined in 10 CFR 50.2 and described further in 10 CFR 50.63. This appendix describes the staff's review of proposed AAC sources.119 B. Staff Review Process All licensees/applicants are required to determine by analysis (1) an acceptable minimum time for which a plant can withstand or cope with a station blackout (station blackout duration) and (2) the plant's capability for