Document: NUREG-0800
Document ID: 805f7e09-51a2-413b-92af-e23bb9073497
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070493.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
ossibility of adverse effects on plant safety systems. Failure or bypass of a protective function should not be a credible consequence of failures occurring in the indication equipment, and the bypass indication should not reduce the required independence between redundant safety systems. 6. The indication system should include a capability of assuring its operable status during normal plant operation to the extent that the indicating and annunciating function can be verified. C. REFERENCES 8A-13 DRAFT Rev. 3 - April 1996 1. Regulatory Guide 1.47, "Bypassed and Inoperable Status Indication for Nuclear Power Plant Safety Systems." 2. Regulatory Guide 1.153, "Criteria for Power, Instrumentation, and Control Portions of Safety Systems."31 3. IEEE Std 603-1980, "Criteria for Safety Systems for Nuclear Power Generating Stations."32 DRAFT Rev. 3 - April 1996 8A-14 BRANCH TECHNICAL POSITION PSB-1 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES A. BACKGROUND Events at the Millstone station have shown that adverse effects on the Class 1E loads can be caused by sustained low grid voltage conditions when the Class 1E buses are connected to offsite power. These low voltage conditions will not be detected by the loss of voltage relays (loss of offsite power) whose low voltage pickup setting is generally in the range of .7 per unit voltage or less. See Reference 2 for further background information regarding these events.33 The above events also determineddemonstrated that improper voltage protection logic can itself 34 cause adverse effects on the Class 1E systems and equipment such as spurious load shedding of Class 1E loads from the standby diesel generators and spurious separation of Class 1E systems from offsite power due to normal motor starting transients. An more recent event at Arkansas Nuclear One (ANO) station and the subsequent analysis 35 performed disclosed the possibility of degraded voltage conditions existing on the Class 1E buses even with normal grid