It was a week that tested the nuclear industry’s strength, only months after a high-profile leakage cast a shadow over the entire sector.

Though Dominion’s North Anna nuclear plant in Northern Virginia shook in last week’s earthquake, and shut down automatically as a result; and although Southern Maryland Calvert Cliffs plant was knocked offline when Hurricane Irene blew a piece of aluminum siding into a transformer, nuclear plants along the East Coast largely remained operational and withstood the summer storms.

At the North Anna nuclear plant–which is still down for routine maintenance until the Nuclear Regulatory Commission gives Dominion a green light to power it back up–perhaps the most dramatic affect of the earthquake can be seen at the dry cask storage facility some half a mile from the station itself.

There, about 25 of the plant’s 27 steel dry cask storage containers, each approximately 18 inches thick and holding 32 used fuel assemblies, shook and moved between one and four inches during the quake. The containers store the fuel assemblies vertically and, according to Dominion spokesperson Rick Zuercher, none of them shifted from their upright position.

Each container remained fully intact, he said and remained connected to a pressure monitoring device. All seals held and no extra radiation was released into the air.

But even though a few inches of movement may seem insignificant, each of the containers weighs approximately 115 tons. Such movement may mean that the plant was not designed to withstand an earthquake of such magnitude, Zuercher told Breaking Energy.

The NRC sent an inspection team to the facility on Tuesday and the results are being evaluated.

NRC spokesperson Dave McIntyre called the dry cask movement “unexpected and unprecedented.”

Seismic Uncertainty

In 2003, the NRC noticed that some of its seismic data of fault lines that would, among other things, help predict earthquakes was being collected with outdated tools. Since then, the agency has been working to update its seismic data and make better decisions about future plant locations.

In response to some of the uncertainty with seismic data, the NRC released a statement on September 1, calling for public comments on a proposed Generic Letter that would re-examine the seismic risks facing American nuclear plants. Comments on the draft letter will be accepted until October 31 on www.regulations.gov.

But for the time being, McIntyre told Breaking Energy, its too early to tell if there were any real design problems at North Anna or if any new and stricter regulations will be necessary.

The NRC is waiting to approve the plant restarting, he said, only to determine if there was any still unseen damage from the earthquake.

Good Night Irene

The impact of Hurricane Irene on nuclear facilities was also less severe than anticipated. Though the Calvert Cliffs nuclear plant was automatically shut down when one of its pieces went blowing in the wind and hit a transistor, the shutdown was quick and followed procedure.

Only one other plant on the East Coast was forced to shut down from the hurricane: Exelon’s Oyster Creek Generating Station.

Inspectors were sent ahead of time to 9 other plants in the path of Hurricane Irene, but only a few reduced power in anticipation of possible shutdowns, none of which occurred.

Breaking Energy covered some of the power outages and damages to nuclear plants after Hurricane Irene. Read more: Bracing For Widespread Power Outages From Irene.

Photo Caption: A man walks past a downed tree following Hurricane Irene in Central Park on August 29, 2011 in New York City.