The earthquake that prompted the shutdown of a Virginia nuclear power plant last week may have been more severe than the plant’s reactors were designed to withstand, federal regulators said.
The revelation is likely to put increased pressure on the Nuclear Regulatory Commission (NRC) to quickly implement a series of safety recommendations intended in part to protect plants from major natural disasters like earthquakes.
NRC said Monday that its preliminary analysis indicates that the ground motion caused by the magnitude-5.8 earthquake near the North Anna Power Station in Louisa County, Va., exceeded the maximum level the two reactors at the plant were built to handle.
But the commission noted in a statement Monday that “data is still being collected and analyzed to determine the precise level of shaking that was experienced at key locations within the North Anna facility.”
NRC decided to send additional inspectors to the North Anna power plant after conducting the analysis, the commission said Monday.
“The fact that we’re sending an [augmented inspection team] should not be interpreted to mean that Dominion staff responded inappropriately or that the station is less safe as a result of the quake,” NRC Region II Administrator Victor McCree said in a statement. “An AIT provides us with the resources needed to completely understand all the effects at North Anna and gather important information for the NRC’s continuing evaluation of earthquake risk at all U.S. nuclear plants.”
Analysis conducted by plant operator Dominion echoes NRC’s findings.
"We have informed the NRC that preliminary reports from instruments show the earthquake potentially exceeded the design basis," Dominion spokesman Ryan Frazier said. "All reports are not final, and probably will not be until the end of the week."
Frazier stressed that inspections have found no major damage to the plant.
"All safety systems operated as designed and built," he said.
Dominion told The Hill last week that the North Anna reactors were designed to withstand the equivalent of a 5.9 to 6.1 magnitude earthquake. The company said the reactors have additional safety measures in the event of a larger seismic event.
But these numbers are just estimates because the NRC and the nuclear industry use ground motion, not earthquake magnitude, to determine the threat to nuclear power plants from seismic activity.
The two reactors at the North Anna nuclear plant shut down Tuesday after the earthquake. The plant lost offsite power and ran on diesel generators through much of the day.
Dominion restored power to the plant late Tuesday night and lifted an emergency alert the following day.
While there have been no reports of major damage at the plant, nuclear critics have pounced on the incident, arguing that it highlights the vulnerability of the U.S. nuclear fleet to major natural disasters.
A federal task force said in a report released last month that the NRC should make wide-ranging improvements to the “existing patchwork of regulatory requirements and other safety initiatives.” The task force was mandated by President Obama in the aftermath of the nuclear disaster at Japan’s Fukushima Daiichi power plant.
But the report also said current NRC regulations pose no “imminent threat” to safety and stressed that a disaster on the scale of the one that occurred in Japan following a massive earthquake and tsunami is unlikely in the United States.
Nuclear Regulatory Commission Chairman Gregory Jaczko has called on his fellow commissioners to review the report’s recommendations within 90 days and implement any regulatory changes within five years.
But Jaczko has faced some resistance from the NRC commissioners on that timeline, which represents a breakneck pace for an agency known for its deliberate and lengthy regulatory process.
Earlier this month, the commissioners agreed to a compromise timeline for analyzing the recommendations. The NRC gave staff 45 days to review most of the recommendations. But the commissioners gave staff 18 months to analyze the report’s most sweeping recommendation — that the NRC broadly rethink its regulatory framework.
Nuclear power critics say last week’s earthquake shows it's time to quickly implement the recommendations.
"This event affirms that reactors located outside active earthquake zones are also at risk and that increased steps to protect against earthquakes must be implemented at all sites. It is time to push aside industry and NRC foot-dragging and strengthen nuclear reactor safety regulations,” Tom Clements, southeastern nuclear campaign coordinator at Friends of the Earth, told The Hill last week.
Rep. Edward Markey (D-Mass.) wrote to Jaczko on Monday to urge the NRC to quickly implement regulations to protect nuclear plants from extreme weather, pointing to Hurricane Irene and last week’s earthquake.
“In light of the widespread challenges to nuclear power plants caused by Hurricane Irene, as well as the potential that global warming could increase both the frequency and intensity of extreme weather events such as hurricanes, I urge you to quickly incorporate hurricanes and other strong storms into the safety and emergency response upgrades the Commission is currently undertaking,” Markey said in the letter.
But the nuclear industry insists that the nuclear plants are designed to withstand major natural occurrences including earthquakes and hurricanes.
“Nuclear power plants are designed to withstand natural occurrences greater than those encountered in the regions where they are located. They are built to withstand floods, earthquakes and high winds, and have numerous safety systems that will operate and safely shut the reactor down in the event of a loss of off-site power,” the Nuclear Energy Institute said in a statement Sunday after Hurricane Irene prompted the shutdown of nuclear reactors in Maryland and New Jersey.
“These plant designs are routinely reviewed and modifications are made to assure their integrity and safety.”