Document: NRC Regulatory Guide
Document ID: fe0fff83-b171-47c6-a3a7-46faf8de3252
Document Type: regulatory_guide
Title: Criteria for The Protection of Safety-Related
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2415/ML24158A041.pdf
Revision Date: 2024-08
Chapter: 
Section ID: RG-1.238
CFR Part: 
CFR Title: 

Content:
monic Filters” (Ref. 27), provide additional information on monitoring power quality and on harmonic filters, respectively. The NRC staff reviewed IEEE Stds. 519, 1159, and 1531 and found that these documents contain information on power quality, harmonics, and harmonic filters. However, this revision of RG 1.238 does not endorse IEEE Std. 519, 1159, or 1531. The NRC’s Research Information Letter 2023-09, “An Assessment of the Harmonics Effects on Undervoltage Relays in Nuclear Power Plants,” issued January 2024 (Ref. 28), contains information on how harmonic distortion affects electrical protection relay operation. There are wide variations in Degraded Voltage Relay (DVR) time delay settings for nonaccident conditions (i.e., conditions other than loss-of-coolant accident conditions) at nuclear power plants depending on plant technical specifications or final safety analysis reports. Some power plants have a single set of DVR time delay settings (typically a few seconds), which apply in both accident and nonaccident conditions (i.e., there are no separate time delay settings for nonaccident conditions). Other DG-1354, Page 7 power plants have two sets of DVR time delay settings: one for accident conditions (for which the delay is short), and other for nonaccident conditions (for which the delay may be longer). The DVR time delay settings for nonaccident conditions may range from a few seconds to a much longer period, such as a few minutes, or may involve only an alarm. Based on operating experience of a dual-unit trip at Calvert Cliffs Nuclear Power Plant in 2015 (see the licensee event report (Ref. 29) and the NRC’s special inspection report (Ref. 30)), if separate (longer) time delay settings do not exist for nonaccident conditions, then the short time delay settings used for accident conditions may lead to an unplanned or unexpected plant trip under nonaccident conditions during a significant switchyard voltage transient. Consideration of International