The money-losing Three Mile Island, the 1979 site of the United States' worst commercial nuclear power accident, was shut down Friday by its energy giant owner.

The end of the 45-year electricity-producing career of Three Mile Island Unit 1 came after Chicago-based Exelon Corp. tried and failed to get financial aid from Pennsylvania in the spring.

Three Mile Island's Unit 1 opened in 1974 and was licensed to operate through 2034, but Exelon complained the plant was losing money in competitive electricity markets.

Three Mile Island also faced particularly difficult economics because the 1979 accident that destroyed Unit 2 left it with just one reactor.

Decommissioning Unit 1, dismantling its buildings and removing spent fuel could take six decades and cost more than $1 billion, Exelon estimates, although companies specializing in the handling of radioactive material are buying retired U.S. nuclear reactors and promising to do it in under a decade.

The destroyed Unit 2 is sealed, and its twin cooling towers remain standing. Its core was shipped years ago to the U.S. Department of Energy's Idaho National Laboratory. What is left inside the containment building remains highly radioactive and encased in concrete.

Work to dismantle Unit 2 is scheduled to begin in 2041 and be completed in 2053, its owner, FirstEnergy, has said.

No nuclear plant proposed after the 1979 accident has been successfully completed and put into operation in the United States.