The federal government has again decided that Xcel Energy's Prairie Island nuclear power plant needs an extra inspection, because of problems with its back up power supply for safety equipment.
The NRC says tests showed two battery chargers at the plant's Unit 1 reactor might not have performed properly in certain conditions.
The NRC only recently lifted the plant from its extra-inspections category after Xcel worked through a backlog of problems.
The battery problem has apparently existed ever since the batteries were installed more than 15 years ago.
In a statement, Xcel Energy says the problem has been corrected, and a similar problem in the Unit 2 reactor will be corrected when that unit is down for refueling.
The company has until mid-September to contest the NRC's decision.
Starting next year, Xcel plans to spend more than $! billion to refurbish the plant so it can operate until 2034.