Every nuclear energy facility in the United States is built with layer upon layer of safety systems. So, when a rare 5.8-magnitude earthquake shook the East Coast on August 23, this built-in margin of safety ensured that all 14 nuclear energy facilities from North Carolina to Michigan that were impacted by the quake safely withstood nature’s challenge.
Dominion’s North Anna Power Station in central Virginia, located just 11 miles from the epicenter of the quake, felt the most impact. Shortly after the earthquake began, North Anna’s two 1,800-megawatt reactors shut down safely and automatically as designed. Four locomotive-sized diesel generators activated to keep the facility’s safety systems running when power was lost.
“A 5.8-magnitude earthquake is highly unusual for the region,” said Eugene S. Grecheck, vice president of nuclear development at Dominion, “but the energy that was imparted to the plant by the quake was relatively minor. In fact, a detailed evaluation of the duration and energy of the August 23 event shows that it was actually less than one-third as strong as for which the facility was built.”
When an earthquake exceeds the ground accelerations specified in a plant’s operating license, as it did in this case, U.S. Nuclear Regulatory Commission (NRC) regulations require that the plant operators demonstrate that the facility did not sustain damage to safety systems or components and does not pose a risk to the health and safety of the public before it is granted permission to restart.
Following guidance developed by the Electric Power Research Institute (EPRI) and endorsed by the NRC in 1997, Dominion began a series of inspections, testing and seismic analyses to confirm that North Anna did not sustain any functional damage and could safely restart. In the two-and-half months the facility was off-line because of the earthquake, Dominion employees and outside seismic and engineering experts worked more than 110,000 hours on the comprehensive review, equivalent to the work of 200 people per day since the earthquake.
The facility increased staffing levels to help with inspections and created a cross-functional restart organization to prepare the plant to return to service. Members of the team were on-site 24/7 to examine critical equipment, safety systems, and structures and were prepared to fill key emergency response organization positions, if needed.
“We have gone over North Anna very systematically—every safety system, structure and component—and found only cosmetic damage,” Grecheck said. “Multiple layers of designed-in safety margin, including the seismic design, provided more than enough strength for the station to withstand the earthquake and safely shut down.”
Dominion shared the findings from these inspections with the NRC, which also conducted its own independent review of the plant. NRC resident inspectors monitored the plant’s safe shutdown on August 23 and performed initial inspections. Information gathered by subsequent technical reviews in September and October confirmed that the facility was undamaged and capable of safely restarting.
The NRC formally approved North Anna’s restart on November 11, concluding in a letter that “safety system functions were maintained” and “reviews of the plant equipment, systems and structures did not reveal significant damage.” The agency also praised the facility’s reactor operators for “responding to the event in accordance with established procedures and in a manner that protected public health and safety.”
The nuclear energy industry’s focus on continuous safety training played a key role in preparing operators for the quake. Nuclear plant operators are trained and tested every five weeks to safely manage extreme events, including earthquakes.
“This event demonstrated that the industry’s rigorous training standards, in addition to the plant’s robust design and the company’s emergency response procedures, prepared North Anna for an unanticipated event of this nature,” Grecheck said. “You can’t predict an earthquake, but when it occurred, the operators responded as they were trained and the plant responded as designed.”
Virginia Governor Bob McDonnell issued a statement on November 11 thanking both Dominion and the NRC for “putting public safety first from the moment this earthquake occurred” and asserting his confidence that “every possible precaution was taken prior to returning the facility to normal operations.”
The first of North Anna’s two reactors began transmitting electricity to the grid on the morning of November 15, followed by the second unit on November 22. Safety checks during the start-up process ensured that equipment functioned as designed. Dominion employees analyzed data and inspected safety systems throughout the restart to confirm that all equipment operated properly.
The facility returned to full power on November 26, providing clean, emission-free electricity to approximately 450,000 homes and businesses throughout Virginia. Dominion will continue to regularly analyze and confirm North Anna’s capability to withstand earthquakes to the NRC.
DID YOU KNOW?
- Each U.S. nuclear plant has sensitive monitoring instruments systems to detect seismic activity and operators are required to shut down a facility if ground motion exceeds a specified level. This means that during an earthquake, a highly trained reactor operator will shut down the nuclear reactor to ensure the safety of the plant and its employees.
- Nuclear power plant designs are based on a detailed evaluation of potential earthquake-induced ground motion at the site. This is followed by thorough analysis, testing and qualification of the plant structures and equipment, using simulated seismic vibrations.
- The Richter scale is not an accurate measure of the impact of an earthquake quake on a nuclear energy facility. Rather, the Nuclear Regulatory Commission requires that reactors be able to withstand a predicted level of ground motion specific to a given site, not a specific magnitude on the Richter scale. The Richter scale is an expression of how much energy an earthquake releases, but is not an indicator of ground acceleration.
For more information on how nuclear plants are built to withstand earthquakes and other natural disasters, see our fact sheet.