Virginia earthquake, Nuclear plant design exceeded?, Dominion Resources North Anna nuclear plant, Nuclear Regulatory Commission inspection team

From Reuters August 29, 2011.

“Virginia quake may have exceeded nuclear plant design”

“The historic earthquake that shut Dominion Resources Inc’s North Anna nuclear plant in Virginia last week may have shaken the facility more than it was designed to withstand, the U.S. nuclear regulator said on Monday.

The Nuclear Regulatory Commission said it had sent a special inspection team to the plant rocked by the 5.8-magnitude quake, after initial reviews from Dominion indicated the ground motion may have exceeded North Anna’s design parameters.

The plant cannot be restarted until the operator can show no “functional damage” occurred to equipment needed for safe operation, the NRC said.

“The company and the NRC will continue to carefully evaluate information to determine if additional actions may be necessary,” the regulator said in a statement.

It will probably take about three or four weeks before the team’s preliminary findings are released, NRC spokesman Roger Hannah said. He would not speculate on how long the plant might be closed, saying it would depend on the team’s assessment.

If it does turn out that the quake exceeded North Anna’s design specifications, Hannah said the team’s analysis could find that the plant could withstand quakes stronger than what was originally intended.

But the team could also call for changes such as back fitting or reinforcing equipment for more powerful earthquakes.

“It could be they would be shut down for a while, we just don’t know at this point,” Hannah said.

MORE KNOWN MIDWEEK

Dominion said the North Anna reactors, which entered service in 1978 and 1980, were designed for an earthquake of up to 6.2 magnitude, but the NRC does not use that scale to measure seismic design specifications. Instead, the commission looks at ground-motion measurements.

Dominion spokesman Rick Zuercher said on Monday that more will be known by midweek about whether the quake exceeded the station’s design as further analysis is conducted on seismic plates from the station’s containment building.”

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http://www.reuters.com/article/2011/08/29/us-usa-dominion-quake-idUSTRE77S66I20110829