05000338/LER-2014-001
| North Anna Power Station | |
| Event date: | |
|---|---|
| Report date: | |
| 3382014001R00 - NRC Website | |
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1.0 DESCRIPTION OF THE EVENT At 1920 on May 15, 2014, with Units 1 and 2 operating at 100% power, the load side of switchyard transformer (EIIS System — EA, Component — XFMR) #3 faulted, causing a loss of the "C" Reserve Station Service Transformer (RSST) (EIIS System — EA, Component — XFMR). The loss of the "C" RSST caused a power loss on the Unit 1 "H" (1H) and the Unit 2 "J" (2J) Emergency busses (EIIS System — EK, Component — BU) and the associated Emergency Diesel Generators (EDGs) (EIIS System —EK, Component — DG) auto-started and re-energized the busses. An 8-hour report per 10CFR50.72(b)(3)(iv)(A) was made at 2310 hours0.0267 days <br />0.642 hours <br />0.00382 weeks <br />8.78955e-4 months <br /> on May 15, 2014 for automatic actuation of an Engineered Safety Feature (ESF) system.
At 2046 on May 15, 2014, the 1H Emergency bus offsite power source was restored and the 1H EDG was secured.
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 96 percent. In addition, the Unit 2 "A" Charging pump (EIIS System — CB, Component — P) auto-started due to the under-voltage condition on the 2J bus. The pump was secured and returned to auto at 1938 on May 15, 2014. At that same time, the MSR FCVs were reopened and by 2230 on May 15, 2014, power returned to approximately 100 percent. At 0410 on May 16, 2014, the "C" RSST was energized and normal power restored to the 2J Emergency bus and the 2J EDG was secured.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS 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 cause of the event was due to a crow making contact with Bus #5 "A" phase to ground. The Apparent Cause is a less than adequate prevention of a bird, or other animal, from making contact with an open air energized bus to ground.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The immediate corrective actions were to restore offsite power to the 1H and 2J Emergency busses. Once offsite power was restored, the 1H and 2J EDGs were secured, and all event related TS actions were cleared by 0440 on May 16, 2014.
5.0 ADDITIONAL CORRECTIVE ACTIONS No additional corrective actions were identified by the Apparent Cause Evaluation.
6.0 ACTIONS TO PREVENT RECURRENCE The fleet and industry standard design is to not have any electrical covers on open air non-insulated electrical conductors/tube bus work. Engineering is evaluating installation of electrical protective covers on susceptible areas of switchyard bus to help prevent future faults from animal contact.
7.0 SIMILAR EVENTS No similar events have occurred at North Anna Power Station.
8.0 ADDITIONAL INFORMATION Unit 1 continued operating in Mode 1, 100 percent power during this event.