Alert Emergency Action Level Declaration due to Loss of Offsite Power Resulting from a Seismic Event

Print View Posted on: 29 August 2011

On 23 August 2011, Units 1 and 2 of the North Anna Power Station declared an Alert, Emergency Action Level due to a loss of offsite power following a 5.8 seismic event on the Richter Scale. As of August 24, 2011, Unit 1 and Unit 2 are proceeding to cold shutdown conditions to allow for inspections inside containment. Normal offsite power has been restored to the North Anna Power Station.

At 1403 (EDT), on August 23, 2011, Units 1 and 2 of the North Anna Power Station declared an Alert, Emergency Action Level due to a loss of offsite power.

The North Anna Power Station is located in Louisa, Virginia which is about 90 miles (145 km) southwest of Washington, D.C. The Alert was declared following a seismic event rated as a 5.8, using the Richter Scale, by the U.S. Geological Survey; the epicenter of the seismic event occurred at a distance of about 14 miles (23 km) from the North Anna Power Station.

Both North Anna units experienced a complete loss of offsite alternating current (AC) power (LOOP) sourcesto emergency electrical buses due to the actuation of transformer pressure relays from the effects of seismic action. The four onsite emergency diesel generators (EDGs) started and powered the station emergency electrical buses after the LOOP. About 40 minutes after the EDGs started, one of the EDGs supplying power to the Unit 2 emergency buses, designated as the 2H EDG, was shut down by operators in response to a radiator leak. A backup, station blackout diesel generator was started to assume the loads that were being supplied by the 2H EDG.

As of August 24, 2011, Unit 1 and Unit 2 are proceeding to cold shutdown conditions to allow for inspections inside containment. Normal offsite power has been restored to the North Anna Power Station. All EDGs have been shut down and returned to a standby condition. The 2H EDG has been repaired and is awaiting retest; however, it is considered available if needed. Reactor coolant chemistry sample results are normal with no indications of any fuel damage. All reactor coolant pressure boundaries and containment boundaries are intact as designed.

Additionally, a number of plants in the eastern United States declared a Notice of Unusual Event (NOUE) due to seismic activity at their respective sites. Plants declaring NOUEs due to the potential for a decrease in plant safety include Peach Bottom, Three Mile Island, Susquehanna and Limerick in Pennsylvania; Salem, Hope Creek and Oyster Creek in New Jersey; Calvert Cliffs and a research reactor in Maryland; Surry in Virginia; Shearon Harris and a research reactor in North Carolina; and D.C. Cook and Palisades in Michigan. All of these plants exited their NOUE declarations after completing inspections and receiving confirmation of normal conditions.

The USNRC’s participation in the International Nuclear and Radiological Event Scale is described in Information Notice 2009-27, dated November 13, 2009, Agencywide Documents Access and Management System Accession No. ML092510055. USNRC generic communications can be found on the USNRC public website http://www.nrc.gov, under NRC Library/Document Collections.

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