Three Mile Island failed to clear PJM's auction of future electricity generation for the third year in a row, making the nuclear power plant's closure more likely.

The auction would have allowed TMI to sell guaranteed power in 2020 and 2021. While there are other ways to sell electricity, the auction generally brings in the most revenue.

For Exelon, which operates TMI and 22 other reactors nationwide, their failure to clear the auction was another serious blow. Earlier this week, a TMI official told PennLive that the iconic facility had lost about $300 million spread across the last eight years.

The nuclear industry has struggled nationwide due to stagnating electric consumption and a glut of natural gas from the Marcellus Shale region.

Joseph Dominguez, another Exelon official, told PennLive in a previous interview that TMI's performance at this year's auction would weigh heavily on the decision of whether to close the plant.

"We have effectively tried everything we can to weather the storm," he said. "I think the question in front of us now is how much longer we're willing to go."

The company operates Unit 1 at TMI and maintains the other, owned by FirstEnergy, which partially melted down in 1979. Unit 2's cooling towers and other buildings could not be demolished until the closure of Unit 1.

Exelon currently employs 675 at TMI in Londonderry Township. The plant's license is set to expire in 2034.

Those jobs would not go away immediately if Exelon chooses to decommission its reactor. It would first need to transfer spent fuel into a specialized structure, which is expected to begin construction in 2018.

The spent fuel would remain on the site for decades because the federal government has not designated a place where it can be permanently discarded.

According to a filing with the Nuclear Regulatory Commission, Exelon reported that it had set aside $626 million in decommissioning funds for TMI. In its most recent FEC filing, the company reported having $11.1 billion across all of its facilities.

Another nuclear plant, Quad Cities in Illinois, also failed to clear PJM's capacity auction. In a written statement, Dominguez said Exelon "remains fully committed to keeping the Quad Cities plant open."

Last year, Illinois created a zero emissions credit to bolster its reactors and give them a leg up on the competition.

Exelon has lobbied for a similar measure in Harrisburg, highlighting the fact that nuclear power does not emit any greenhouse gases that contribute to climate change.

Three Mile Island nuclear generating station 16 Gallery: Three Mile Island nuclear generating station

If nuclear reactors like TMI closed, they would likely be replaced with gas-fired plants. Exelon's representatives have argued that a less competitive energy market would eventually lead to higher electricity rates as currently low natural gas prices increase.

Critics, including the gas lobby, said any attempt to bail out the nuclear industry would lead to more taxpayer spending, higher energy costs to ratepayers or possibly both. Meanwhile, the country still hasn't figured out a permanent solution to the question of what to do with spent fuel.

State lawmakers from both chambers and both parties have formed a "nuclear caucus" with the goal of rescuing the industry. So far, it hasn't coalesced around a solution. The group will hold several hearings on its way toward a final proposal this fall.

Wallace McKelvey may be reached at wmckelvey@pennlive.com. Follow him on Twitter @wjmckelvey. Find PennLive on Facebook.