In the aftermath of an earthquake on August 23, 2011 that automatically shut down the two nuclear reactors at North Anna Power Station, the Nuclear Regulatory Commission approved the restart of the units on Nov. 11. Unit 1 was restarted and connected to the grid on Nov. 15, 2011, and Unit 2 was restarted and connected to the grid on Nov. 22, 2011.
Additional information:
The two nuclear reactors at North Anna Power Station in Mineral, Va., automatically shut down following a 5.8 magnitude earthquake in Central Virginia on Aug. 23, 2011, at 1:51 p.m. ET. The epicenter was approximately 11 miles west-southwest from the station.
The North Anna staff "responded to the event in a manner that protected the public health and safety," an inspection team from the U.S. Nuclear Regulatory Commission (NRC) reported on Oct. 3. While the ground motion at the site during the earthquake exceeded levels for which the plant was originally licensed, the NRC team report said "safety system functions were maintained" and "reviews of the plant equipment, systems and structures did not reveal significant damage."
The station has been unaffected by aftershocks that have occurred in the region.
Another inspection team from the NRC worked at the station through Oct. 14 to determine what further measures – if any – need to be taken before the units can be restarted. Dominion officials and NRC staff members provided a report to the NRC commissioners on Oct. 21. The NRC held a public hearing on Nov. 1 that featured a restart readiness update from Dominion.
The Nuclear Regulatory Commission, in a news release dated Nov. 11, 2011, concluded that Dominion's North Anna Unit 1 and 2 reactors can be restarted. Dominion Virginia Power subsequently began the restart.
North Anna was hardened against earthquakes and other potential disasters in the early 1990s after the NRC enacted new seismic requirements. Subsequent reviews indicated the station was able to withstand and safely shutdown in a much larger quake than the one that occurred on Aug. 23, 2011.
A program of extensive analysis by Dominion engineers and outside seismic experts, hundreds of detailed inspections and numerous tests have been conducted since the Aug. 23 earthquake. The company followed the guidance documents for post-seismic inspections from the U.S. Nuclear Regulatory Commission and the Electric Power Research Institute. Those detailed inspections showed that North Anna Power Station did not suffer any significant damage from the earthquake. Dominion Virginia Power informed the U.S. Nuclear Regulatory Commission of the findings on Sept. 8, 2011. (> View the news release.)
The earthquake’s vibrations exceeded North Anna’s design analysis at some frequencies, but no significant damage has been seen. Analysis shows that the earthquake’s intensity and duration were not sufficient to cause significant damage at the station. (> View Dominion's presentation to the NRC.)
Also, based upon the instrument data and the inspection observations, the Service Water Reservoir and the main Lake Anna Dam also sustained no significant physical or functional damage and remain capable of performing their intended design functions.
A special NRC inspection team has been reviewing earthquake data and analyzing the quake’s impact on the station.
A public meeting on the findings was held Oct. 3 at the North Anna Nuclear Information Center. The inspection team said it has found no significant damage, but more evaluation is needed for some "anomalies" that were observed on safety-related equipment (> View the NRC presentation and Exit Meeting summary. The NRC team also said the plant's safety system functions were maintained and Dominion's staff reacted in a manner that protected public health and safety. |
View a video of the complete public meeting held Oct. 3, 2011.
Thorough and detailed inspections, testing and analysis by Dominion, the Nuclear Regulatory Commission (NRC) and respected outside experts has shown that North Anna received only cosmetic damage from the Aug. 23 earthquake. There was no damage to safety-related systems and the NRC has noted the station responded "in a manner that protected public health and safety." The company has gone well beyond inspection procedures established by the NRC for just such an event and has found no issues that should prevent a restart.
When the earthquake occurred, sensors reported a slight reduction in power in the two reactors at North Anna and that initiated the automatic shutdowns. One second after the shutdowns, the station lost off-site power, just as reactor operators were shutting down the reactors manually. Emergency diesel generators began operating automatically and promptly following the shutdowns.
Initial reports indicted the loss offsite power or actions by station operators responding to the earthquake resulted in the units being shut down. However, a subsequent investigation showed that the automatic shutdown was initiated when sensors reported a slight reduction in power in the two reactors. The events illustrate the multiple layers of safety in the station operations.
Detailed inspections have found only cosmetic damage to items not related to station safety. Some electrical components on transformers in the switchyard were damaged and were replaced. Insulation on some piping systems was knocked down (this would be similar to insulation used in commercial buildings on pipes). In on-site office buildings built to commercial – not nuclear – standards adjacent to or near the power station, some ceiling tiles fell and some small minor mortar cracks were found in walls.
At the power station itself, there was visible but very minor damage to one of the four bases that support a large piece of filtering equipment on the turbine deck that removes impurities from water. This damage was not significant and did not affect the operation of the filtering system. A picture of this damage was included in the company’s presentation to the Nuclear Regulatory Commission. It shows that some of the exterior concrete of one of the bases had come off.
No. The dam was inspected by an experienced civil engineer from North Anna shortly after the event. The engineer, who had knowledge of the dam from earlier inspections, performed a thorough walk down and visual inspection of the dam, spillway and gates, looking for any indications of leakage, cracks, fissures or movement -- any sign of distress. No problems were found.
Instruments that measure the underlying condition of the dam were also checked. No unusual indications were found. Several subsequent inspections were made with similar results following a series of aftershocks after Aug. 23.
Also, four professors from Virginia Tech with experience in various aspects of geology, seismology and civil engineering, including a recognized authority on seismic issues and earthen dams, also inspected the facility not long after the quake. They found no problems.
The Lake Anna dam also passed an independent, five-year inspection by an outside earthen dam expert in July. This examination was required by the Federal Energy Regulatory Commission. The consultant reported that the dam was in good shape and met all regulatory requirements.
Our inspection teams went above and beyond the requirements already established by the NRC for inspections following a seismic event, putting in more than 12,000 hours of inspections, testing and analysis.
The units will not be restarted until the company demonstrates to the NRC and itself that they are safe to restart and the NRC gives its permission to restart.
Unit 2 was scheduled for a refueling outage and unloading the full core is part of that process. Based on the results of that inspection and a series of visual, ultrasonic and other tests done on Unit 1, removal of the fuel from Unit 1 was not needed. Both the company and the NRC are satisfied that no significant damage occurred in either unit.
Since the earthquake Dominion and outside experts have performed various inspections to ensure the integrity of its underground piping. Some of the underground piping was uncovered and inspected directly to ensure that it was intact. These inspections included direct visual inspections as well as ultrasonic inspections to confirm wall thickness. Additionally, increased monitoring of system parameters was performed to ensure that there were no indications of leaks. All piping and system parameters indicated that the underground piping was intact and no damage was incurred as a result of the earthquake.
Dominion continues to monitor and maintain its underground piping systems in accordance with industry guidance and best practices.
For several reasons:
Dominion has completed all detailed inspections, testing and analysis of structures, systems, and components at Unit 1 to ensure that all systems function properly and is completing these inspections on Unit 2, which is in a scheduled refueling outage. Unit 1 is ready to return to service and Unit 2 will be ready at the end of October, when its refueling is complete. However, the company will not restart the two units until it demonstrates to the Nuclear Regulatory Commission that the units can operate safely and reliably, and it receives permission from the NRC to restart.
In its Confirmatory Action Letter of Sept. 30, the NRC said that it must complete its review of Dominion’s information, perform its confirmatory inspections and complete its safety evaluation review before allowing the units to restart.
That has yet to be determined.
North Anna Power Station is one of the most cost-effective sources of electricity for the customers of Dominion Virginia Power. When the station is offline, the company operates other generating units or purchases power to meet the needs of customers. Dominion is working diligently to find the lowest-cost replacement power and – fortunately – the outage is occurring during a time of year when overall demand is lower. The company expects to incorporate any additional costs for replacement power in its annual fuel and purchased power filing with the Virginia State Corporation Commission. Costs for fuel and purchased power are passed through dollar-for-dollar to customers.
The Aug. 23 earthquake that caused both units to shut down also caused 25 of the 27 TN-32 dry nuclear fuel storage containers to move from 1 inch to 4.5 inches on the storage pad. They remained upright and stayed fully intact. The quake also caused cosmetic damage to several of the concrete modules that hold horizontal canisters, but retained their structural integrity, maintaining the used fuel canisters stored inside in a safe condition.
No. The containers are designed to keep them safe and they were not damaged.
Pressure monitoring systems on each container that connect by wire to a nearby monitoring panel were not damaged and were all functional during the earthquake.
The 27 TN-32 containers were loaded and placed from July 1998 through January 2007.
Each container is 16 feet tall and 8 feet in diameter. When fully loaded with 32 used nuclear fuel assemblies, each container weighs about 115 tons.
This storage pad has 26 horizontal modules installed and 13 loaded with fuel.
No movement was observed.
Early in the design phase of North Anna, the company retained outside seismic specialists to review the plant site. Based on their reports the company told the Nuclear Regulatory Commission that no faults existed at the site. Later, after excavation revealed faulting, it was alleged that the company made false statements to the Nuclear Regulatory Commission about seismic conditions at the site. While all parties to the case agreed the company never had any intent to deceive the Commission and that it believed the statements were true at the time they were made, the company was fined $32,500.
In a related proceeding, Nuclear Regulatory Commission licensing and licensing appeal boards subsequently concluded that there were no seismic safety issues at the site to prevent construction and operation of North Anna because the fault that had been found later was considered inactive. Both the fine and the findings of the licensing board were upheld in federal appeals court.
The epicenter of the earthquake that occurred on Aug. 23 was about 11 miles from North Anna and was not related to the fault discovered at the station.
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