To show the power of the magnitude 5.8 earthquake that hit central Virginia, 25 spent-fuel storage casks, weighing 115 tons apiece, shook and shifted on their concrete pad at Dominion Virginia Power’s North Anna nuclear power plant.
The shifting of these massive casks holding used nuclear fuel was the first caused by an earthquake in the U.S., according to the U.S. Nuclear Regulatory Commission (NRC).
None of the metal cylinders suffered damage and they released no radiation, Dominion Virginia Power said.
The 16-foot tall casks shifted from an inch to 4½ inches, said Dominion spokesman Rick Zuercher.
“They just moved because of the vibration,” Zuercher said. “They remained upright and fully intact.”
Federal regulators will examine data from the spent-fuel storage area as part of the inspection of the plant the NRC began Tuesday, said Scott Burnell, a spokesman with the federal agency’s headquarters in Rockville, MD.
“The information available indicates the shifting did not affect safety in any way,” Burnell said. “It is an instance of an event we had not previously seen, so were trying to learn as much as possible.”
Used nuclear fuel rods from commercial atomic power plants are highly radioactive.
Dominion Virginia Power has 27 of the massive TN-32 storage casks standing vertically outdoors on the concrete pad. The casks, made from thick steel, do not connect to the ground; gravity holds them in place.
Concrete bunkers for other used-fuel containers stored horizontally at the Louisa County power station experienced “cosmetic” damage, he said. “None of these moved.”
NRC regulations specify the spacing of the vertically set dry casks from one another mainly to ensure workers do not suffer exposure to unexpected levels of radiation, Burnell said.
“If the spacing shifts a slight amount, the dose shifts a very slight amount,” he said. “Those doses have to be taken into account. The doses would be very low in any case.”
The NRC requires a nuclear plant’s assemblies of spent fuel rods to cool in water pools for at least five years before transferring to dry casks.
Spent-fuel storage in casks is safe, the NRC said. Such storage systems should resist floods, tornadoes, projectiles, temperature extremes and other unusual scenarios, the federal agency said.
During the past 20 years, the NRC said, there have been no radiation releases affecting the public, no radioactive contamination, and no attempts to sabotage spent-fuel casks or their storage sites across the U.S.
August’s magnitude-5.8 earthquake shook protective electrical devices at the North Anna Power Station strongly enough to cause the plant to shut down automatically, the first time this has occurred in the United States.
The power station remained out of service this week as company and NRC officials continued detailed inspections of its two 980-megawatt reactors and other station structures and systems.
“To date, there has been no significant earthquake-induced damage in safety-related structures or systems important to safety and shutdown cooling,” Zuercher said.
The 27 vertically stored casks are each 16 feet tall and 8 feet in diameter. Each has steel walls 18 inches thick.
The containers hold 32 fuel assemblies and weigh 115 tons when loaded with the used-fuel assemblies.