A nearly four-decade moratorium on the construction of nuclear plants in Illinois will end next year under a measure signed Friday by Gov. J.B. Pritzker, who vetoed an earlier version of the bill.

Legislators passed a new iteration of the bill last month that addressed concerns Pritzker raised in an August veto message about the size of nuclear plants that would be allowed under the initial legislation.

With Pritzker’s signature, Illinois joins a number of other states that recently have rescinded similar bans as policymakers are taking a fresh look at nuclear power as another alternative to generate energy without increasing carbon output.

The revamped measure, which takes effect June 1, sets limits on the size of new nuclear plants that would be allowed and focuses on small modular reactors, a new generation of technology that supporters argue could be an important tool to help the state reach its goal of carbon-free power generation by midcentury.

The proposal to lift the moratorium exposed a rift between two core groups within the Democratic Party coalition, with labor unions lining up in support and environmental groups standing in opposition. Environmentalists argued that allowing new nuclear power generation could be an expensive distraction from developing more renewable power sources in the state.

Pritzker surprised some supporters with his veto of the original proposal after previously expressing an openness to nuclear power continuing to be a part of the state’s energy mix.

But in his veto message, Pritzker said he believed the original language would have left the door open to the development of new large-scale plants like the six that already exist in Illinois, which he did not support.

The measure Pritzker signed Friday was the result of negotiations between lawmakers in both parties, labor unions, manufacturers and environmental groups. In limiting the size of new nuclear reactors, it aligns the state with the federal definition of a “small modular reactor.”

The measure also authorizes a study to identify any potential gaps in the state’s regulations for nuclear power.

In addition to swaying Pritzker, the changes were enough to convince some legislators who opposed the original proposal to support the revamped version.

Some environmental groups, however, remained opposed.

It’s unclear whether or how quickly the new law, which lifts a ban that’s been in place since Sept. 11, 1987, will lead to the construction of nuclear power plants in the state.

Experts who spoke with the Chicago Tribune this summer said a variety of economic factors and policy decisions at the federal level ultimately will determine whether a new nuclear power boom happens in Illinois or elsewhere in the U.S.

“There’s no one waiting here to start building a nuclear power plant as soon as the law changes,” Robert Rosner, a theoretical physicist and founding co-director of the Energy Policy Institute at the University of Chicago, told the Tribune at the time.

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