On Wednesday, power company Exelon said that it would be closing the single reactor that it operates on Three Mile Island by September 30.

Three Mile Island (TMI) is notorious for its role as the site of the United States' first commercial power plant accident in 1979. The Nuclear Regulatory Commission was not able to correlate the accident to any deaths or ill health effects in the Middletown, Pennsylvania, area, but the threat galvanized environmentalists against nuclear power and led to sweeping regulatory reforms in throughout the nation.

TMI-1, the 819 megawatt (MW) reactor that Exelon owns, was not affected by the 1979 accident. Exelon says it has been operating the reactor at a loss.

No government support

Exelon's Wednesday statement placed the blame for the reactor's impending shutdown at the feet of Pennsylvania legislators. Lawmakers had recently introduced two similar bills in the state House and Senate to reclassify nuclear power so it could take advantage of a 2004 law requiring electric utilities to buy a certain amount of renewable energy, according to WHYY.

But legislators declined to act on the bills. "With only three legislative session days remaining in May and no action taken to advance House Bill 11 or Senate Bill 510, it is clear a state policy solution will not be enacted before June 1, in time to reverse the premature retirement of the plant," Exelon wrote in its Wednesday statement. Exelon announced its intention to close the plant in 2017, barring some legislative deus ex machina.

WHYY noted that in mid-April Pennsylvania's utility regulators were neutral-to-negative about the nuclear-boosting bills, saying that the TMI plant was the only "financially troubled" nuclear plant in the state. (However, FirstEnergy Solutions, which owns the Beaver Valley Nuclear Power Station in Pennsylvania, has also said that it will shut down its plant in 2021.)

One regulator told the station that state legislation is "quite an expensive solution to the issue" if TMI is the only plant in dire financial straits. The state's nuclear legislation was estimated to cost between "$459 million and $551 million each year," which would be shouldered by ratepayers.

Some 700 people are currently employed at Three Mile Island according to The New York Times, and the nuclear industry supports 16,000 jobs in Pennsylvania, according to the Pittsburgh Post-Gazette. Exelon says it will offer jobs to employees who are willing to relocate.

Still, nuclear watchers are concerned about the industry's health on a national scale, as decades-old reactors are retired at a faster pace than they're being replaced.

Three Mile Island's Unit 2 was permanently shut down after the 1979 accident caused a partial meltdown. A mechanical or electrical failure prevented water from being fed to the steam turbine, leading to an automatic system shutdown, according to the Nuclear Regulatory Commission. The automatic shutdown required a pressure release, but the pressure-release valve became stuck. "As a result, the plant staff was unaware that cooling water in the form of steam was pouring out of the stuck-open valve," the NRC writes.