With approval from the Nuclear Regulatory Commission, Dominion Virginia Power is restarting two nuclear reactors that shut down near the epicenter of the East Coast Earthquake in August.
After “careful analysis of inspection findings and related information,” the NRC said it had approved the restart of North Anna Units 1 and 2—the first nuclear reactors in the United States to have been shut down by an earthquake.
Dominion Resources Inc.
|The North Anna reactors are the first in the United States to have been shut down by an earthquake. Bringing them back online will involve more testing, inspections and staffing than a regular restart.|
The 1,800-megawatt twin reactors are in Louisa, VA, about 11 miles from the epicenter of the 5.8 magnitude earthquake that rocked the East Coast on Aug. 23.
The quake automatically shut down both North Anna reactors, knocked out an offsite power connection, and triggered alerts at 13 other nuclear plants from South Carolina to Michigan.
Jolt Exceeded Design Plan
Before the quake, Dominion had said that the reactors were designed to withstand an earthquake of up to magnitude 6.1.
However, an NRC official said in a statement this week that the August quake “shook the reactors more strongly than the plant’s design anticipated.”
Therefore, said Eric Leeds, director of the Office of Nuclear Reactor Regulation, “Dominion had to prove to us that the quake caused no functional damage to the reactors’ safety systems.”
“We’ve asked Dominion dozens of detailed questions, and our experts have examined Dominion’s answers, as well as information from our own inspections,” said Leeds.
“We’re satisfied the plant meets our requirements to restart safely, and we’ll monitor Dominion’s ongoing tests and inspections during startup of both reactors.”
Dominion began the restart process for Unit 1 on Nov. 11. The utility planned to bring that unit to full operation before it began the restart on Unit 2.
The process for each unit normally takes about four days from cold shutdown to normal operation, as hundreds of pumps, motors, valves and other systems are restarted in a carefully prescribed sequence.
However, because the units are the first in the United States to have been shut down by an earthquake, the normal 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,” Dominion said in a statement.
The company said it had increased staff and would add several days to the restart schedule.
“The additional time and tests reflect Dominion's commitment to carefully monitoring systems and equipment during startup to ensure proper and safe operation,” the company said.
In April, an NRC inspection noted earthquake “vulnerabilities” at North Anna, according to the Center for Public Integrity. The NRC found that some parts of water and gaseous suppression systems and hose stations were “not seismically designed,” the center reported.
The report cited a risk of leaks “through penetrations following a seismic event” and said Dominion would “evaluate the issues … to determine if additional mitigation strategies are required.”
Last week, the NRC issued Dominion a letter describing the agency’s own response since the quake.
That process began with existing guidance for determining a reactor’s response to an earthquake, then incorporated more recent experience, the NRC said.
The review included “insights learned from a reactor site in Japan damaged by a 2007 earthquake” and extensive questioning of Dominion about examination of piping systems, including buried segments; nuclear fuel assemblies; steam generators; pumps and valves; and emergency diesel generators.
An NRC Augmented Inspection Team (AIT) examined the plant shortly after the quake, and the agency conducted “a restart readiness inspection” in October. NRC also held two public meetings about its inspection.
“Both Dominion and NRC’s results showed only minor damage that did not affect North Anna’s safety systems,” NRC said in a statement.
The NRC said Dominion had taken additional measures after the quake, including:
- Updating the plant’s Final Safety Analysis Report to incorporate information from the quake and subsequent analysis;
- Re-evaluating plant equipment;
- Developing inspections or evaluations for components within the reactor vessels; and
- Updating seismic monitoring equipment for the reactors and dry-cask spent fuel storage facility.
Dominion said these and other post-quake measures had involved more than 100,000 staff hours of work and cost more than $21 million.