The Nuclear Regulatory Commission (NRC) said that Dominion Generation’s (NYSE: D) North Anna Unit 1 and 2 reactors, that together generate 1,806 MW, can be restarted. The North Anna reactors, in Louisa, Va., have been shut down since Aug. 23, when a magnitude 5.8 earthquake occurred about 11 miles from the plant.
“The earthquake shook the reactors more strongly than the plant’s design anticipated, so Dominion had to prove to us that the quake caused no functional damage to the reactors’ safety systems,” said Eric Leeds, director of the NRC’s Office of Nuclear Reactor Regulation.
The restart process for each unit normally takes about four days from cold shutdown to normal power operations in which electricity is produced and placed on the electric grid. During the restart process, hundreds of pumps, motors, valves and other systems are restarted in a carefully prescribed and observed sequence. Because the units will be starting up after the first earthquake to shut down a nuclear unit in the United States, the restart process will be prolonged to allow for additional equipment tests that can only be performed when the units are in various stages of start-up as an extra, deliberate safety precaution.
The NRC said it issued Dominion a letter describing the staff’s review, which started with existing guidance for determining a reactor’s response to an earthquake. The staff used more recent experience, including insights learned from a reactor site in Japan damaged by a 2007 earthquake, in asking Dominion additional questions regarding proper examination of technical areas that included piping systems, including buried segments; nuclear fuel assemblies; steam generators; pumps and valves; and emergency diesel generators.
The NRC’s actions included an Augmented Inspection Team (AIT) that examined the plant shortly after the quake, as well as a restart readiness inspection in mid-October. Both Dominion and NRC’s results showed only minor damage that did not affect North Anna’s safety systems.
"As always, safety is our first priority," said David A. Heacock, president and chief nuclear officer-Dominion Nuclear. "We have demonstrated to ourselves and to the NRC and are confident that North Anna is safe and ready to be restarted. The station suffered no functional damage from the quake and is ready to resume generating clean, low-cost energy safely for our customers."
The NRC has issued Dominion a separate letter documenting the company’s commitment to several additional quake-related actions, including:
· Updating North Anna’s Final Safety Analysis Report to incorporate information from the quake and subsequent analysis;
· Additional characterization of the fault responsible for the Aug. 23 quake, as well as any special ground motion effects at North Anna;
· Re-evaluating plant equipment (including an assessment of potential improvements) identified in earlier seismic reviews;
· Developing any needed inspections or evaluations for components within the North Anna reactor vessels; and
· Permanently updating seismic monitoring equipment for the North Anna reactors and dry-cask spent fuel storage facility.
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