The problems first surfaced last week at the Monticello power plant outside the facility's nuclear reactor. The malfunctioning equipment is in a part of the plant where pipes carry superheated steam to a power generating turbine.
Nuclear Regulatory Commission spokesman Jan Strasma says last Wednesday afternoon, a 13-ton box containing valves that control steam pressure fell.
"The weld supporting that (box) broke allowing one end of this device to drop down eight to twelve inches. It came to rest on top of several steam lines that are located below it," Strasma says.
That caused a drop in steam pressure into the turbine.
The plant's monitoring system detected the change in pressure immediately, according to Arline Datu, spokesperson for the Wisconsin-based Nuclear Managment Company which operates the plant for Xcel Energy.
"What happens then is all the plant's safety systems kick in automatically and it shuts down the reactor," Datu says.
The reactor is still shut down while company officials investigate what caused the welds to fall.
The NRC's Jan Strasma says initial indications are that it may have been improperly welded in place when the plant was built back in the early 1970s.
"Apparently it's a combination of some inadequate welds when it was originally installed 30 years ago, coupled with fatigue induced by vibration," he says.
Strasma says the incident in Monticello has prompted the NRC to ask four other nuclear power plants in the northeastern part of the country with similar designs to check their equipment for the same problem.
The NRC recently granted the Monticello nuclear power plant, owned by Xcel Energy, a 20 year extension on its operating license. The plant's original 40 year license is set to expire in 2010.
Some people are concerned that failing equipment at nuclear power plants is a sure sign of aging facilities that can't be trusted to operate for another two decades.
George Crocker, with the North American Water Group, a Twin Cities-based environmental organization concerned with energy issues says this incident is a warning that Minnesota should think twice before investing it's energy future in aging nuclear power plants.
"When the things that break have the potential to have such utterly catastrophic consequences, why I think it's time to seriously review and that type of commercial relationship," Crocker says.
Crocker hopes Minnesota invests more money on renewable forms of energy, like wind power, to meet the region's future energy needs.
Officials at the Monticello nuclear power plant say their facility is far from falling apart, and is subject to constant maintenance and inspection overseen by federal officials. Officials at the Monticello nuclear power plant say their facility is far from falling apart, and is subject to constant maintenance and inspection overseen by federal officials.
Xcel officials say the shutdown of the plant won't have any affect on the price or supply of electricity for their customers.