US Nuclear Power by State: The Quiet Carbon-Free Giant

Nuclear power is the most underappreciated piece of the U.S. grid: it generates about a fifth of the nation's electricity and is by far its largest source of carbon-free power — more than wind and solar combined for most of the past two decades. Yet its output has barely changed in 20 years, even as renewables exploded. This guide charts U.S. nuclear generation, maps which states depend on it, and explains why this carbon-free giant has stood still.

How much U.S. electricity is nuclear?

Nuclear reactors generate roughly a fifth of all U.S. electricity — close to 800 terawatt-hours a year — from a fleet of plants mostly built in the 1970s and 1980s. The national output line is strikingly flat: nuclear generation today is about the same as it was 20 years ago. That stability is itself notable, because almost every other source has moved dramatically; nuclear has been the grid's steady, around-the-clock workhorse.

America's largest carbon-free source

Here's what surprises many people: nuclear is the biggest source of carbon-free electricity in the United States — for most of the past two decades it produced more than wind, solar, and hydro individually, and often more than wind and solar combined. Because reactors emit no carbon dioxide while generating, the existing nuclear fleet quietly prevents a vast amount of emissions every year. Losing a nuclear plant typically means burning more natural gas to replace it, raising emissions.

Which states rely on nuclear?

Nuclear generation is concentrated in about 30 states that host reactors. Illinois is the largest producer by far, with more reactors than any other state, followed by states across the South and East like Pennsylvania, South Carolina, and Tennessee. Some states get more than half their electricity from a single nuclear plant. The map and ranking show how uneven the footprint is — much of the West and Mountain region has little or no nuclear at all.

Why nuclear has stayed flat

The flat line reflects a near-total halt in new construction. After the 1979 Three Mile Island accident and rising costs, almost no new U.S. reactors were ordered for decades; the steady output comes from running existing plants reliably, plus efficiency upgrades. A few plants have closed, offset by others running better. Now interest is reviving — driven by climate goals and surging electricity demand from data centers — with talk of new reactors and small modular designs, but building them remains slow and expensive.