An environmental review issued by federal regulators Friday suggested the agency might renew the operating permit of a unit of the Three Mile Island nuclear power plant in Pennsylvania.

Exelon Corp. (EXC) unit Exelon Generation Group LLC, which owns the reactor, in Middletown, Pa., applied last year to renew the operating license for the power plant's Unit 1 for another 20 years. The unit's initial 40-year operating license, issued by the Nuclear Regulatory Commission, expires in April 2014.

NRC staff concluded in its environmental review that continuing operations at the plant wouldn't present any environmental impacts that would "preclude" the issuance of a 20-year renewed license.

The plant's Unit 2, owned by FirstEnergy Corp. (FE) and monitored by Exelon, experienced a partial meltdown of its reactor core in 1979 and was permanently shut down and defueled.

-By Cassandra Sweet, Dow Jones Newswires; 415-439-6468; cassandra.sweet@dowjones.com