The Limerick Generating Station is operated by Exelon.
From Excelon's press release on 7/18/2012, announcing that the Unit 1 has been taken offline:
Limerick Operators Take Unit 1 Offline
Operators at Limerick Generating Station took Unit 1 offline this morning following an electrical disturbance on the non-nuclear side of the plant.
POTTSTOWN – Operators at Limerick Generating Station took Unit 1 offline this morning following an electrical disturbance on the non-nuclear side of the plant.
Unit 1 will remain offline until repairs, inspections and testing can be completed. Limerick Unit 2 continues to operate at full power.
As a result of the electrical disturbance, an Unusual Event was declared at 8:39 a.m. and terminated at 9:46 a.m. in keeping with NRC procedures. An Unusual Event is the lowest of four Nuclear Regulatory Commission emergency classifications.
Exelon Generation notified all appropriate federal, state and local government officials of the event. There is no threat to the health and safety of the public associated with this event.
Limerick Generating Station is located approximately 21 miles northwest of Philadelphia. With both units at full power, the site can produce enough carbon-free electricity for 2 million homes
An excellent example of not saying anything like "where exactly" and "what exactly".
According to reports, a transformer blew up in the turbine building. Here's from The Times Herald (7/18/2012):
‘Unusual event’ reported at Limerick power plant
(Updated at 10:55 a.m.) LIMERICK — The Nuclear Regulating Commission said it is closely monitoring events at the Limerick Generating Station after a manual scram around 8:15 a.m. shut down the reactor at the nuclear power plant.
According to NRC spokesman Neil Sheehan, an electrical fault was reported in a transformer in a turbine building that spurred the scram and that the transformer is not a main transformer.
The event was listed as an “unusual event” around 8:39 a.m., the lowest of the event ratings, Sheehan said. No one was injured in the incident and no outside help was requested, Sheehan said.
Sheehan said the transformers have been known to fail from time to time and that the reactor was safely shut down.
Sheehan said there are no complications at the power plant at this time and there is no danger to the public from the incident.
EARLIER VERSION OF THIS STORY
LIMERICK — An “unusual event” was reported Wednesday morning in Unit 1 of the Limerick Nuclear Generating Station.
According to Frank Custer, communications director with Montgomery County, the county received an email from Exelon, parent company of the nuclear power plant, stating that an explosion had occurred causing the “unusual event,” in Unit 1 but the event did not pose any threat to the public.
Custer said the notice reported the “unusual event” had been terminated.
A call placed to the Limerick Generating Station’s media relations spokesperson was not picked up or returned as of 11 a.m. Wednesday.