Exelon is threatening to shutter three nuclear plants in northern Illinois, which together power the equivalent of 5.5 million homes in the region.

The Chicago-based parent of Commonwealth Edison and the largest nuclear power generator in the country issued the warning about the potential for “early retirement” of its Byron, Dresden and Braidwood nuclear stations in a Feb. 8 Securities & Exchange Commission filing. While Exelon has hinted in the past that Byron and Dresden are financially at risk for closure, it was the first time the company explicitly identified Braidwood as vulnerable.

Braidwood, located in Will County, and Byron, near Rockford, have operating licenses from the Nuclear Regulatory Commission that don’t expire until the late 2040s. One of Dresden’s two reactors in Grundy County is licensed until 2029 and the other until 2031.

“Dresden, Byron, and Braidwood nuclear plants in Illinois are … showing increased signs of economic distress, which could lead to an early retirement, in a market that does not currently compensate them for their unique contribution to grid resiliency and their ability to produce large amounts of energy without carbon and air pollution,” Exelon said in the filing.

Setting the table for a bailout request in Illinois, Exelon added that it “continues to work with stakeholders on state policy solutions, while also advocating for broader market reforms at the regional and federal level.”

In a statement to Crain’s, Exelon said, “We are working with Illinois policymakers and other stakeholders on solutions to not only maintain Illinois’ clean energy progress but to further advance efforts to reduce and eliminate carbon emissions in the electric power and other sectors.”

The earliest the company could move to shutter Dresden is 2021. It’s committed to operating Dresden until June 2021 with regional grid managers. But Dresden bid too high to qualify for “capacity” payments from consumers in northern Illinois in the most recent auction held by PJM Interconnection, which is responsible for managing wholesale power markets in all or part of 13 states and the District of Columbia from Illinois east to the mid-Atlantic.

The earliest Exelon could move to close Byron and Braidwood is mid-2022. Those plants have committed with PJM to operate until then.

That gives the state some time to determine what to do about potential closures. Springfield could act on wide-ranging energy legislation as early as this session, but its timetable depends at least in part on actions not yet taken by federal energy regulators.

PJM has proposed changes to its capacity auction—how it determines prices all consumers and businesses pay to plants for their promise to produce during the highest-demand periods of the year. State energy regulators have criticized those proposals as “punishment” for Illinois’ 2016 decision to subsidize two other Exelon-owned nukes that were slated to close, its Quad Cities station on the Mississippi River and its Clinton plant in central Illinois. If the Federal Energy Regulatory Commission approves PJM’s changes, the state could well move to take over the responsibility of adequate power generation from PJM.

In the short term, it’s highly unlikely that Exelon would be permitted to close all three plants should it come to that. The loss of all three could well jeopardize adequate power supplies to the nation’s third largest city.

But recent capacity auctions have made clear that northern Illinois enjoys a glut of power supplies currently. The closure of a single nuke clearly wouldn’t jeopardize that.

Capacity isn’t the only issue, though. Nuke closures could threaten Gov. J.B. Pritzker’s goal of eventually powering Illinois only through sources that don’t emit carbon. Exelon has been successful arguing that carbon-free nukes are a crucial component of state plans to address climate change by “de-carbonizing.”

Pritzker’s predecessor, Gov. Bruce Rauner, signed the last wide-ranging energy bill, the Future Energy Jobs Act, which slaps a surcharge on electric bills statewide to funnel more than $200 million a year to Exelon’s Quad Cities and Clinton nukes.

Interestingly, Exelon is budgeting 31 percent less for nuclear fuel in 2022 than it expects to spend this year, according to a Feb. 8 investor presentation. A spokesman says, though, that the reduction doesn't reflect any assumed closures other than Pennsylvania's Three Mile Island, which already has been announced.