This post has been modified to correct language from the NRC.
The Palisades nuclear power plant is returning to service. It was shut down earlier this month to repair a water leak in the building where the actual reactor is located.
Workers found water was leaking through several cracks in a device that sits atop the nuclear reactor. Palisades Spokesman Mark Savage says they completely replaced that control rod device.
"We did ultrasonic testing on eight others on the reactor head to ensure that that was not occurring in those as well and it was not," Savage said. There are 45 control rods total at the plant.
Nuclear Regulatory Commission spokeswoman Viktoria Mytling says initially federal inspectors on site had questions about how the plant evaluated the extent of the problem in testing the additional eight control rod drive mechanisms.
“They did some tests. They provided us with the results and we said ‘hey this doesn’t give you the full picture’. So they had to go back and do it differently so that they had a whole picture," Mytling said.
Mytling says as a result the company had to repeat the tests on 8 control rod drive mechanisms so that they included the entire area of interest.
The NRC and Entergy, the company that owns Palisades, know where the leak was. Mitlying says the stress from the pressure and corrosion caused the crack, but the root cause has not been determined. A special investigation is underway.
This is the second time this summer Palisades had to shut down to repair some kind of leak.
Federal nuclear regulators are keeping a closer eye on the plant this year. Regulators have given Palisades one of the worst safety ratings in the country after a series of problems last year.