Minnesota accident prompts alert to other nuclear plants

By TOM MEERSMAN
Thursday, January 18, 2007

Federal officials have alerted the owners of four nuclear power plants about a potential safety problem that caused an automatic shutdown last week at Xcel Energy's Monticello nuclear plant in Minnesota.

"Typically when there's a problem at one plant, we look to see if any aspects have the potential of applying to other plants," said Jan Strasma, spokesman for the Nuclear Regulatory Commission. "It's a precautionary or prudent notification."

At the time of the Jan. 10 incident, Monticello had been operating for a record 637 consecutive days, 161 days longer than ever before, according to Xcel officials. Typically nuclear plants shut down for refueling every 18 to 20 months, and are out of service for four to five weeks, during which utilities also schedule major maintenance and inspections.

The Monticello plant remained closed a week after a 35,000-pound control box broke loose from its support beams and fell about a foot onto a large pipe carrying radioactive steam. The pipe did not rupture or leak.

Strasma said his agency has notified managers of four Northeast plants similar to Monticello in age, design, and layout about the incident in Minnesota. The plants are Vermont Yankee, Oyster Creek in New Jersey, Nine Mile Point in New York and Pilgrim in Massachusetts, he said.

The Monticello plant, about 45 miles northwest of the Twin Cities, began operating in 1970.

Two months ago Xcel received federal permission to extend the plant's license for 20 years after its current license expires in 2010. State regulators have also given the utility permission to expand radioactive-waste storage in casks outside the plant, but the Minnesota Legislature has the option to review that decision.

Suspicion has focused on the control box's welds, which may have been weakened by vibrations.

Charles Bomberger, Xcel's general manager for nuclear asset management, said the steam pipe struck by the falling box didn't rupture. He said steam pipes are designed, anchored and tensioned to withstand much more severe shocks and stresses, including earthquakes.

Even if the pipe had leaked, only a small amount of steam would have been released and isolated within the plant, Bomberger said.

"I don't want to sugarcoat it; this was a significant problem," Bomberger said. "It's got the full attention of Xcel." The utility will fully evaluate the cause of the problem, repair it, check for other possible damage and report everything to federal authorities, he said.

Reach Tom Meersman at meersman(at)startribune.com