HARRISBURG, Pa. —  The owner of Three Mile Island, site of the United States’ worst commercial nuclear power accident, said Monday that it will shut down the plant in 2019 without a financial rescue from Pennsylvania.

Exelon Corp.’s announcement comes after what it called more than five years of losses on the single-unit power plant and its recent failure in an auction to sell Three Mile Island’s power into the regional grid.

In the meantime, the Chicago-based energy company wants Pennsylvania to give nuclear power megawatts the kind of preferential treatment and premium payments that are given to renewable energies, such as wind and solar.

Nuclear power plants have been hammered by the natural gas boom that has slashed electricity prices in competitive markets.

In March 1979, equipment failure and operator errors led to a partial core meltdown of one of Three Mile Island’s two reactors.

The damaged reactor has been mothballed since, but the other reactor is still in use. Exelon said that its operating costs for just one unit at the plant are high, further damaging Three Mile Island’s financial viability.

Perhaps nuclear power’s biggest nemesis is the cheap natural gas flooding the market from the northeast’s Marcellus Shale reservoir, the nation’s most prolific gas field. Meanwhile, electricity consumption hit a wall after the recession, while states have emphasized renewable energies and efficiency.

So-called nuclear bailouts have thus far won approval in Illinois and New York. The potential for higher utility bills in Pennsylvania and other states is drawing pushback from rival energy companies, manufacturers and consumer advocates.
Pennsylvania is the nation’s No. 2 nuclear power state.