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Operators at Three Mile Island Generating Station in Pennsylvania returned Unit 1 to full power Friday following a 26-day refueling and maintenance outage.

During the outage, which began on Oct. 30, TMI’s 700 employees and 1,600 supplemental workers replaced nearly one-third of the reactor’s fuel and performed tests, inspections and maintenance activities that cannot happen while the unit is operating.

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Three Mile Island Generating Station is approximately 12 miles south of Harrisburg, PA.

ExelonGeneration said the plant produces enough electricity to power approximately 800,000 homes.

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In May, had a five-day unplanned shutdown after a control rod and steam bypass valve malfunctioned.

The nuclear plant ended up manually shut down after a control rod that controls the nuclear fission process dropped. There are dozens of control rods in the reactor.

During the shutdown, a main steam bypass valve closed even though it was supposed to open. That resulted in a release of steam to the atmosphere multiple times, heard by residents surrounding the plant.

Exelon said at the time no radiation detectable by monitors released.

The Nuclear Regulatory Commission (NRC) said two resident inspectors at TMI were continuing to monitor Exelon’s evaluation of the problem, the repairs made and the restart.

A relief valve on the coolant side of the reactor that operated opposite of what its design called for contributed to the partial meltdown of the core at TMI in the infamous 1979 accident.

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