Three Mile Island has returned to service following a refueling and maintenance outage.
Exelon spokesman Ralph DeSantis said TMI returned to service Tuesday and reached full power Thursday evening.
During the outage, workers replaced nearly a third of the reactor's fuel, performed inspections and made significant upgrades to the plant.
The upgrades included the replacement of a large reactor coolant pump motor, an overhaul of the turbines used to make electricity, and the installation of new control rod drive mechanisms to control nuclear reaction in the reactor, DeSantis said.
More than 1,700 highly trained technical workers supported the refueling outage which began in late October.
Refueling outages are conducted every two years.