A spokesperson for the Nuclear Regulatory Commission told Action News that the Unit 1 reactor experienced an electrical fault in a transformer, which led to the manual shutdown.
Exelon, the owner of the plant, declared it an "Unusual Event," which the NRC said is the lowest of four levels of emergency classification.
In a statement, Exelon said the electrical problem occurred on the non-nuclear side of the plant.
While Unit 1 will remain offline until all repairs can be made, Exelon said Unit 2 continues to operate at full power.
Exelon said it notified all appropriate federal, state and local government officials of the event, adding "there is no threat to the health and safety of the public associated with this event."
The NRC said it is closely monitoring the shutdown, with resident inspectors assigned to the plant gathering information.
There do not appear to be any complications at this point, the NRC said.
Limerick Generating Station is located approximately 21 miles northwest of Philadelphia. With both units at full power, the site can produce enough electricity for two million homes, Exelon said.
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