05000400/LER-2016-005

LER-2016-005, Offsite Power Undervoltage Caused Actuation of Several Systems

Shearon Harris Nuclear Power Plant, Unit 1
Event date:	10-08-2016
Report date:	12-07-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
4002016005R00 - NRC Website

LER 16-005-00 for Shearon Harris Nuclear Power Plant, Unit 1 Regarding Offsite Power Undervoltage Caused Actuation of Several Systems

ML16342C391
Person / Time
Site:	Harris
Issue date:	12/07/2016
From:	Jones B K Duke Energy Progress
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-005-00
Download: ML16342C391 (5)

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Inf000llects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

05000- Shearon Harris Nuclear Power Plant - Unit 1 400 Energy Industry Identification System (EllS) and component codes are identified in the text as [XX].

A. Background

On October 8, 2016, Shearon Harris Nuclear Power Plant (HNP), was preparing for a planned refueling outage. At the time of the event, the unit was in Mode 4 and experiencing high winds and rain due to the effects of Hurricane Matthew.

HNP is connected to the transmission grid via a switchyard and 8 transmission lines. The transmission line initiating this event was the Cape Fear 230 kV line.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in valid manual or automatic actuation of any of the following systems: reactor protection system, general containment isolation signals, emergency core cooling systems, auxiliary or emergency feedwater system, containment heat removal and depressurization systems, emergency AC electrical systems, emergency service water systems.

B. Event Description

On October 8, 2016, at approximately 1310 EDT, while in Mode 4 in preparation for a planned refueling outage, HNP experienced an undervoltage (UV) condition for approximately 1.5 seconds. The duration exceeded the UV relay time delay due to failure of transmission system relays to clear the faulted line within design parameters. This condition triggered the UV relays for both emergency 6.9 kV buses and for several of the non-safety related 6.9kV auxiliary buses, resulting in the respective supply breakers opening. The interruption in power caused the actuation of several safety systems.

Both Emergency Diesel Generators (EDGs) [EK] started and loaded as designed. The EDGs were allowed to run until 2154 EDT, after the grid had been declared stable by the Energy Control Center at 2033 EDT and grid performance had been verified by operations personnel. Additionally, the Containment Ventilation Isolation system [JM] and the Auxiliary Feedwater system [BA] actuated and performed as designed.

An Unusual Event was declared for the loss of offsite power to emergency buses for greater than 15 minutes.

C. Causal Factors Several causes were found to contribute to the UV condition. One cause was determined to be a line fault along the Cape Fear - West End 230kV line. A fallen tree was discovered near the location of the fault. Additionally, contact resistance was discovered at the protective relay within the Cape Fear 230 kV Substation which caused the delay in clearing the line fault. Further, a substation timing relay tripped at 88 cycles, which was beyond the 24 cycle design time. All causal factors, not within the authority of HNP, combined to decrease grid voltage to about 68% nominal, which is below the HNP UV relay setpoints.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Inf000llects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

05000- Shearon Harris Nuclear Power Plant, Unit 1 400

D. Corrective Actions

Completed: The Cape Fear — West End 230kV line was restored to its normal configuration on 10/8/2016. An additional feeder relay check was performed on 10/9/2016. The affected relays were calibrated or replaced as necessary.

Planned: An end-to-end test of the feeder/relay scheme is planned.

E. Safety Analysis

The safety significance of these events is low per Probabilistic Risk Assessment analysis. The station was in Mode 4 during a planned refueling outage. Station equipment operated as designed. Throughout the events, there were no significant adverse impacts to the health and safety of the public.

F. Additional Information

There is no prior operational experience at HNP involving the loss of offsite power to both emergency buses over the past three years.