The Obama administration’s new carbon proposals appear likely to boost the long-troubled but enormous U.S. nuclear sector.

The proposed rules, unveiled on Monday, would require states to reduce greenhouse gas emissions from power plants by 2030. Since nuclear facilities emit no carbon when they operate, nuclear offers a relatively straightforward way for states to achieve those reductions.

But many of the nation’s nearly 100 nuclear reactors are struggling economically, either because of stiff competition from cheap natural gas or because conducting necessary repairs and retrofits are too expensive to complete. Four nuclear reactors recently retired early in California, Florida, Vermont and Wisconsin for a mix of those reasons.

To encourage investments in economically at-risk facilities, the Environmental Protection Agency (EPA) allows states to count 6 percent of their existing nuclear generation toward their reduction goals. States where new nuclear facilities are already under construction -- two in Georgia, two in South Carolina and one in Tennessee -- can count electricity generation from those new plants as part of their reductions as well.

The accompanying chart shows how much nuclear generation -- both existing and under construction -- each state can apply toward their emissions targets, according to EPA data. The EPA’s proposal offers states a variety of options for meeting those goals. So some states might not opt to invest in their existing nuclear fleet if they can achieve similar reductions elsewhere, for instance by supporting energy-efficiency retrofits or renewable energy projects. And other states, especially those with strong nuclear power lobbies, might push to have more than 6 percent of existing generation count toward those targets, said Steve Clemmer of the Union of Concerned Scientists.