First Energy said that an unplanned outage at its Beaver Valley nuclear power station unit 2 reactor has been executed due to generator malfunction.
The Beaver Valley power station covering an area of 1,000 acres is located near Shippingport in Pennsylvania.
US Nuclear Regulatory Commission (NRC) has confirmed that due to vibrations in the main generator, operations at the unit had to be temporarily shut down.
NRC public affairs officer Neil Sheehan was quoted by Times Online as saying that the vibrations in the main generator resulted from parts in the main generator stator that have either broken or became loose.
"Remember that these machines rotate at 1,800 rpm and will have some wear from actual mechanical vibrations, as well as from repeated heating and cooling cycles," Sheehan added.
"The generators are large electrical components that are cooled by hydrogen."
The unit is currently offline and is not producing electricity.
It was noted that the company could not confirm how long the forced outage will keep the unit offline.