Earthquake caused massive nuclear storage casks to move at North Anna

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Last week’s central Virginia earthquake caused 25 spent-fuel storage casks — each weighing 115 tons — to move on their concrete pad.

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.

Like hockey pucks on a jostled tray, the 16-foot tall casks shifted from an inch to 4½ inches, utility company spokesman Rick Zuercher said.

Federal regulators will examine data from the spent-fuel storage area as part of the inspection of the plant that 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.”

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, are not fastened to the ground, being held in place by gravity.

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 are not exposed 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.”

“I am a strong advocate of accelerating the transfer of irradiated fuel from spent fuel pools to dry casks,” said nuclear engineer David Lochbaum with the Union of Concerned Scientists.

The two spent-fuel storage pads cover 11.4 acres at North Anna — one pad holds the 27 cylinders and the other has the concrete bunkers for the horizontal storage containers. The first container was placed in storage in July 1998.

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.

Also, some spent fuel at North Anna is stored horizontally in concrete bunkers, using 50-ton metal containers that are 16 feet long and 6 feet in diameter. These are placed in concrete modules 19 feet high, 10 feet wide and 21 feet long. The modules have 3-foot-thick concrete end walls, and each holds a single container.

 

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Earthquake Update

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 A 3.4-magnitude earthquake shook Mineral, Va., early Thursday morning — the latest in a series of aftershocks following last Tuesday’s 5.8-magnitude quake that rocked the Washington area.

The latest quake rumbled at 5:09 a.m. just four miles from Mineral and 81 miles southwest of D.C.

There have been more than 20 aftershocks since the original quake, ranging from 1.8 to 4.5.

There were also two aftershocks on Wednesday that registered 1.8 and 2.1, respectively.

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