Worker's in New Jersey took the Oyster Creek Generating Station's reactor off line at 6:30 a.m. Wednesday.
The plant's owner says Oyster Creek has three feedwater heaters, which are used to maximize efficiency by recovering heat that would otherwise be lost.
Exelon Corp. says the heaters are not related to the plants safety equipment.
Earlier this month, plant officials said a monitor that measures radiation emissions was found to be inoperable. But officials said the problem didn't pose a public health threat because other monitors were available.
The 40-year-old plant in Lacey Township generates enough electricity to power 600,000 homes a year and provides 9 percent of New Jersey's electricity.
