05000338/LER-2016-003

LER-2016-003, 1 OF 3

North Anna Power Station, Unit 1
Event date:
Report date:
3382016003R00 - NRC Website

LER 16-003-00 for North Anna, Unit 1, Regarding Engineered Safety Feature Actuation Due to Loss of Power to "A" Reserve Station Service Transformer

ML16175A424
Person / Time
Site:	North Anna
Issue date:	06/16/2016
From:	Bischof G T Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
16-193 LER 16-003-00
Download: ML16175A424 (4)

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1.0 DESCRIPTION OF THE EVENT On April 29, 2016, at approximately 2214 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.42427e-4 months <br />, with Units 1 and 2 operating at 100 percent power in Mode 1, the load side leads of switchyard Transformer 3 (EIIS System- FK, Component- XFMR) faulted, causing 34.5kV Bus 5 lockout relays (BITS System- EA, Component- RLY) to actuate. This resulted in the loss of "A" Reserve Station Service Transformer (RSST) (EIIS System- EA, Component- XFMR) whiCh supplies the Unit 1 "J" (1J) Emergency Bus (EIIS System- EK, Component- BU). The 1J Emergency Diesel Generator (EDG) (EIIS System —EK, Component — DG) automatically started and loaded to re-energize the bus as designed. The 1J Emergency Bus was transferred to its 2B Station Service alternate supply and the 1J EDG was secured and returned to automatic at approximately 2334 hours0.027 days <br />0.648 hours <br />0.00386 weeks <br />8.88087e-4 months <br />.

As a result of the event, the Unit 1 Moisture Separator Reheater (MSR) flow control valves (FCVs) (BITS System- SB, Component- FCV), went closed and reactor power reduced to approximately 96 percent. In addition, the Unit 1 "A" Charging Pump (EIIS System- CB, Component- P) automatically started due to the under-voltage condition on the 1J Emergency Bus. The MSR FCVs were reopened at approximately 2257 hours0.0261 days <br />0.627 hours <br />0.00373 weeks <br />8.587885e-4 months <br /> and Unit 1 "A" Charging Pump was secured and returned to automatic at approximately 2346 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.92653e-4 months <br />. Following a post incident inspection and testing, Transformer 3 and Bus 5 were returned to service.

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 1J EDG powered the emergency bus, as designed. Offsite power sources were restored in a timely manner and the associated EDG was secured and returned to automatic. The health and safety of the public were not affected by this event.

3.0 CAUSE It was determined that the cause of this event was due to raccoons contacting between the radiator (ground) and the load side leads of the Switchyard Transformer 3 just below the "A" phase conductors going from the transformer low side bushings to the Bus 5 "A" phase pipe bus, creating a phase to ground fault.

Animal guards are being installed. on Switchyard Bus 3, Bus 4, Bus 5. These are being installed per Engineering Technical Evaluation ETE-NA-2015-0054 and tracked through the corrective action and work management processes.

7.0 SIMILAR EVENTS LER, N1-2014-001-00, Engineered Safety Feature Actuation Due to Loss of Power to "C" Reserve Station Service Transformer due to a crow making contact with Bus 5 "A", phase to ground.

8.0 MANUFACTURER/MODEL NUMBER None 9.0 ADDITIONAL INFORMATION Unit 2 continued to operate at 100 percent power in Mode 1 during the event.

There were no failures of any system or component, all protective relaying worked as designed.

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