Transformer explodes at Exelon's Pa. Limerick nuke

Security personnel at the plant conducted a "thorough walk-down of all areas and had no concerns," the company said in the report. Both 1,196 megawatt units 1 and 2 at the plant, which can produce enough power to serve more than 2.2 million homes, remained at full power during the incident.

The affected transformer, located in the non-nuclear portion of the plant, provides internal power to plant equipment such as heating, ventilation and air conditioning equipment and other components, the company said in a separate statement.

The malfunction was isolated to the individual transformer and did not affect the safety of the plant, the company said.

Following the explosion, Exelon declared an unusual event, which is the lowest of four levels of emergency classification used by the NRC. The company exited the event within about two hours. The company said it was investigating the cause of the transformer failure.

The Limerick station is located in Pottstown, Pennsylvania, about 21 miles northwest of Philadelphia. Exelon Nuclear operates the nuclear units of its parent Exelon Corp. of Chicago.