Document: NUREG-0800
Document ID: e1169529-d2cb-4947-9efe-b23d927f4aa9
Document Type: srp
Title: NUREG40800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350520.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
e 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 1. Regulatory Guide 1.47, "Bypassed and Inoperable Status Indication for Nuclear Power Plant Safety Systems.' 8A-12 Rev. 2 - July 1981 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 lE 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. The above events also determined that imporper voltage protection logic can itself cause adverse effects on the Class lE systems and equipment such as spurious load shedding of Class 1E loads from the standby diesel generators and spurious separation of Class lE systems from offsite power due to normal motor starting transients. A more recent event at Arkansas Nuclear One (ANO) station and the subsequent analysis performed disclosed the possibility of degraded voltage conditions existing on the Class lE buses even with normal grid voltages, due to deficiencies in equipment between the grid and the Class lE buses or by the starting transients experienced during certain accident events not originally considered in the sizing of these circuits. 8. BRANCH TECHNICAL POSITION 1. In addition to the undervoltage scheme provided to detect loss of offsite power at the Class 1E buses, a second level of undervoltage protection with time delay should also be provided to protect the Class 1E