05000338/LER-2016-001

LER-2016-001, 1 OF 3

Event date:	01-23-2016
Report date:	03-16-2016
3382016001R00 - NRC Website

LER 16-001-00 for North Anna, Units 1 and 2, Regarding Emergency Diesel Generators Automatic Start Due to Loss of Power to "C" Reserve Station Service Transformer

ML16099A386
Person / Time
Site:	North Anna
Issue date:	03/16/2016
From:	Bischof G T Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
16-035 LER 16-001-00
Download: ML16099A386 (4)

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send 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 intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.

1.0 DESCRIPTION OF THE EVENT On January 23, 2016,

• at approximately 1703 hours0.0197 days <br />0.473 hours <br />0.00282 weeks <br />6.479915e-4 months <br />, Switchyard breaker L102 (EIIS System — EA, Component — BKR), supply to 34.5kV bus #3, tripped open from the' Sulfur Hexafluoride (SF6) gas pressure switch. This resulted in the loss of "C" Reserve Station Service Transformer (RSST) (EIIS System — EA, Component — XFMR) which supplies "F" transfer and 2G intake structure 4160VAC buses (EIIS System — EB, circulating water, pumps to continue to run being supplied by Unit 1. The "F" transfer bus supplies the 1H and 2J emergency buses (EIIS System — EK, Component — BU).

Their associated Emergency Diesel Generators (EDG) (EIIS System —EK, Component — DG) started and loaded to recover those buses. The 1H bus.was swapped to its alternate supply from 1B station service and the 1H EDG was shutdown and returned to auto standby. Limiting actions on Unit 1 were cleared at that time. The 2J EDG continued to carry the 2J bus. At 1948 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.41214e-4 months <br /> on January 23, 2016, an 8-hour Non- Emergency Report was made to the NRC in accordance with 10 CFR 50.72(b)(3)(iv)(A) .as a condition that resulted in valid actuation of ESF.

As a result of the event, the Unit 2 Moisture Separator Reheater (MSR) flow control valves (FCVs) (EIIS System — SB, Component — FCV) went closed and reactor power reduced to approximately 96 percent. In addition, the Unit 1 "B" Charging pump (EIIS System — CB, Component — P) auto-started due to the under-voltage condition on the 1H bus. The pump was secured and returned to auto at 1720 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.5446e-4 months <br /> on January 23, 2016. The MSR FCVs were reopened at 0332 hours0.00384 days <br />0.0922 hours <br />5.489418e-4 weeks <br />1.26326e-4 months <br /> on January 24, 2016. At 1528 hours0.0177 days <br />0.424 hours <br />0.00253 weeks <br />5.81404e-4 months <br /> on January 24, 2016, the "C" RSST was energized and normal power restored to the 2J Emergency bus. The 2J EDG was secured at 1541 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.863505e-4 months <br />. Repairs to breaker L102 were completed and the Unit 2 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limiting action was exited at 1706 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.49133e-4 months <br /> on January 24, 2016.

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS Units 1 and 2 continued to operate, as designed, following the loss of offsite power. No significant safety consequences resulted from this event because the 1H and 2J EDGs powered the emergency busses, as designed. Offsite power sources were restored in a timely manner and the associated EDGs were secured and returned to automatic. The health and safety of the public were not affected by this event.

3.0 CAUSE The direct cause for the opening of the L102 breaker was an internal switch contact.

failure due to moisture. Snow/moisture intrusion inside the cabinet likely shorted across the electrical terminals for the SF6 gas pressure switch (63G) and caused the 63X relay to pick up, which tripped and locked out the breaker.

The SF6 pressure switch vendor was unable to find anything wrong with the calibration of the switch. Subject matter experts (SME) within the company along with the breaker manufacturer were also unable to find anything physically wrong, with the switch.

4.0 IMMEDIATE CORRECTIVE ACTION(S) The L102 SF6 gas pressure switch was replaced and the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limiting action for Unit 2 was exited.

5.0 ADDITIONAL CORRECTIVE ACTIONS In accordance with the manufacturer's and Dominion SME recommendations, all 34.5KV breakers in the North Anna switchyard have had weather sealant applied to prevent moisture intrusion (rain/snow) where air gaps were noted to be around the conduit access plate and the mechanism access plate .at the bottom of the breaker cabinet which .are the most likely intrusion areas. Additionally the L102 and .L202 breakers had weather sealant applied to the area where the breaker cabinet top meets the breaker cabinet side walls along the front and two sides.

6.0 ACTIONS TO PREVENT RECURRENCE The preventive maintenance procedure is being revised to include an additional check for snow and moisture intrusion paths into cabinets and seal as appropriate for the breakers in question. Monitoring of all the 34.5KV breakers for moisture intrusion will occur to determine if additional actions to seal the breakers are required for the remaining. nine (9) breakers. Inspections of the sealant will also be performed to ensure it remains intact. The monitoring period will be for approximately one year to allow the breakers to be exposed to all seasonal conditions.

7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION Component: 63G pressure switch Manufacturer Solon Model 6TC Bulb type