Xcel Energy's nuclear power plant in Monticello, Minn., continues to undergo testing, after a series of problems caused the reactor to shut down automatically.
In October the plant shut down for ten days because an underground cable failed. In November, the main turbine experienced fluctuating oil pressure, which also caused a shutdown.
Xcel was starting the reactor up again when operators noticed a new flaw in the turbine. It took more than a week to identify the problem. Engineers from an industry group suggested installing a new monitoring device for the turbine, which has now been done.
All three incidents involved generating equipment, not the nuclear reactor, said Tim O'Connor, Xcel vice president at the Monticello.
"The nuclear side is absolutely safe, the systems are working, the safety systems are working," O'Connor said. "We're talking about fixing actually production of electricity."
Xcel recently received a license to operate the 40-year-old plant for another 20 years. But the company is postponing a power boost at Monticello because of additional safety reviews following the meltdown in Fukushima, Japan.
Xcel buys electricity on the open market when its plant is offline.