Last updated 9:48 p.m. Wednesday
The Unit 1 nuclear reactor at Exelon's Limerick Generating Station was shut down at 8:15 a.m. Wednesday following an electrical fault in a transformer, the Nuclear Regulatory Commission said in a statement sent to area media outlets.
The reactor was manually shut down from the power station's control room following the fault, according to the NRC.
"The NRC is closely monitoring the shutdown, with our Resident Inspectors assigned to the plant gathering information from the control room and sharing it with NRC staff. There do not appear to be any complications at this point. We will want to know more about Exelon’s root cause evaluation of what caused the event and about any and all corrective action," NRC spokesperson Neil Sheehan said.
The NRC has two inspectors permanently assigned to the facility.
Sheehan said Exelon had declared an "Unusual Event," which is the lowest of four levels of emergency classification used by the NRC.
An "electrical disturbance caused a loss of power to generator cooling equipment" at the plant, Exelon Nuclear spokesperson Dana Melia said in a statement.
"There is no threat to the health and safety of the public associated with this event," Melia said.
The company said the Unit 1 plant will remain offline until repairs, testing, and inspections are complete. The generating station's other power plant, Unit 2, continued to operate at full power.
Melia denied reports that there had been an explosion at the plant.
"It wasn't an explosion," Melia said, instead referring to the fault as an "electrical flash-out," comparable to a circuit breaker being tripped.
Sheehan said the failed transformer was in the building that also houses the plant's control room.
"The 13-kv (kilovolt) transformer that failed was located in the plant’s control structure, not the turbine building. The control structure in where the control room is housed but it usually also is location of electrical switchgear rooms, battery rooms and other equipment rooms. There was no impact on the control room from this event," Sheehan said via e-mail.
"There can be a loud noise when an electrical transformer experiences a failure. That may be what [the reports] are referring to," Sheehan said.
The plant, which is in the process of applying for license extensions that would keep it operating until 2049, experienced three unscheduled shutdowns between February and June of 2011.