Nuclear expert: U.S. should review worst case scenarios

MONTPELIER, Vermont Tue Mar 15, 2011 4:09pm EDT

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MONTPELIER, Vermont (Reuters) - The U.S. nuclear industry and regulators need to reexamine disaster planning and worst-case scenarios, especially in reactors such as the Vermont Yankee with the same design as the crippled plant at the center of the Japanese crisis, a top expert says.

Vermont Yankee and similar plants are vulnerable to a similar cascade of events as in Japan, where reactors were crippled after the massive earthquake, said Arnold Gundersen, a nuclear engineer who advises the Vermont legislature, the only U.S. legislature with nuclear plant oversight.

The March 11 quake in Japan knocked out electric power needed for pumps used to cool the reactors. Back-up generators failed when they were flooded by the tsunami and emergency batteries ran out of power after eight hours, he said.

With no electricity to drive the pumps, the radioactive fuel at the Fukushima Daiichi Nuclear Power Station has dangerously overheated.

"We're not going to have a tsunami in the Connecticut River," said Gundersen. But a power failure coupled with a flood could threaten the reactor by disabling pumps that draw cooling water from the river, he said.

"What we called a maximum credible accident last week is no longer maximum credible. We really need to go back and evaluate what really is the worst case," Gundersen said. "I don't think we've take a hard look at what the worst case is for Vermont Yankee's flood issues."

The Japanese accident shows back-up emergency power supplies are inadequate as well, he said.

Vermont Yankee -- a 39-year-old, 605-megawatt reactor on the Connecticut River in southern Vermont with a similar General Electric design as Fukushima Daiichi -- relies on eight-hour batteries as did the Japanese plant, he said.

"They always assume they can solve the problem in eight hours or less," said Gundersen. "Of course, in Japan they can't solve the problem in eight hours or less."

Neil Sheehan, a spokesman for the U.S. Nuclear Regulatory Commission, said federal regulators will study the Japanese accident to improve safety at U.S. reactors.

"There's no question we're going to be looking for lessons learned to come out of this," he said.

"Whether that would mean increasing battery power or some other measure it's too soon to say," he added.

The NRC recently decided to allow Entergy Corp's Vermont Yankee to operate for another 20 years.

But under state law, the plant needs approval from the legislature to run past March 21, 2012, making its fate uncertain.

The state Senate in 2010 voted to shut the plant in 2012 due to pollution issues, though the full legislature has yet to vote on the issue.

Yankee is lobbying for another vote, but legislative leaders say it is unlikely Vermont lawmakers will take up the issue again.

(Additional reporting by Chris Baltimore; Editing by Barbara Goldberg, Ellen Wulfhorst and Greg McCune)

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