Three Mile Island's Unit 1 went back into service Saturday after an automatic shutdown last week took the station offline.
Plant operators connected the plant's turbine generator to the regional power grid at 9:12 a.m., according to an Exelon Corp. official.
TMI spokesman Ralph DeSantis had said four pumps circulate water through the reactor coolant system to keep the plant operating at proper temperatures. One of them experienced a problem about 2:20 p.m. Thursday and shut itself down, which automatically shut down the entire Dauphin County plant, he said.
A loud noise coming from the plant during the shutdown might have drawn attention from nearby residents. Steam was released into the atmosphere, creating an audible sound of steam rushing through pipe.
The automatic shut-down was caused by an unexpected actuation of a relay switch on a reactor coolant pump.
Plant personnel replaced the relay, installed additional monitoring capabilities for the relay and tested the pump prior to restarting the plant.
"We performed the necessary repairs safely and efficiently and are committed to a reliable operating cycle," said Rick Libra, TMI site vice president.
Other shutdowns: Plants don't typically shut down automatically very often, and TMI has gone as long as 10 years between automatic shutdowns. But that's not a recent record.
The plant also shut down automatically on Aug. 22, as workers were in the process of manually shutting it down to replace a heating element.
Electric customers were not affected by the plant's being off-line most recently.
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