Compared to using coal for electricity production, nuclear power plants result in

Nuclear power plants heat water to produce steam. The steam is used to spin large turbines that generate electricity. Nuclear power plants use heat produced during nuclear fission to heat water.

In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains uranium fuel.

The uranium fuel is formed into ceramic pellets. Each ceramic pellet produces about the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. A bundle of fuel rods, some with hundreds of rods, is called a fuel assembly. A reactor core contains many fuel assemblies.

The heat produced during nuclear fission in the reactor core is used to boil water into steam, which turns the blades of a steam turbine. As the turbine blades turn, they drive generators that make electricity. Nuclear plants cool the steam back into water in a separate structure at the power plant called a cooling tower, or they use water from ponds, rivers, or the ocean. The cooled water is then reused to produce steam.

Nuclear reactors in the United States may have large concrete domes covering the reactors, which are required to contain accidental releases of radiation. Not all nuclear power plants have cooling towers. Some nuclear power plants use water from lakes, rivers, or the ocean for cooling.

Containment dome of a nuclear reactor

Source: Stock photography (copyrighted)

Nuclear power plants have generated about 20% of U.S. electricity since 1990

As of July 1, 2022, 92 nuclear reactors were operating at 54 nuclear power plants in 28 states. Thirty-two of the plants have two reactors, and three plants have three reactors. Nuclear power plants have supplied about 20% of total annual U.S. electricity since 1990. Learn more about the U.S. nuclear energy industry.

The United States generates more nuclear power than any other country

In 2020, 33 countries had commercial nuclear power plants, and in 17 of the countries, nuclear energy supplied at least 20% of their total annual electricity generation. The United States had the largest nuclear electricity generation capacity and generated more nuclear electricity than any other country. France, with the second-largest nuclear electricity generation capacity and second-highest nuclear electricity generation, had the largest share—about 69%—of total annual electricity generation from nuclear energy.

Top five nuclear electric generation capacity countries, 2020

Last updated: July 12, 2022

The popular conception of nuclear power is straight out of The Simpsons: Springfield abounds with signs of radioactivity, from the strange glow surrounding Mr. Burn's nuclear power plant workers to Homer's low sperm count. Then there's the local superhero, Radioactive Man, who fires beams of "nuclear heat" from his eyes. Nuclear power, many people think, is inseparable from a volatile, invariably lime-green, mutant-making radioactivity.

Coal, meanwhile, is believed responsible for a host of more quotidian problems, such as mining accidents, acid rain and greenhouse gas emissions. But it isn't supposed to spawn three-eyed fish like Blinky.

Over the past few decades, however, a series of studies has called these stereotypes into question. Among the surprising conclusions: the waste produced by coal plants is actually more radioactive than that generated by their nuclear counterparts. In fact, the fly ash emitted by a power plant—a by-product from burning coal for electricity—carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy. * [See Editor's Note at bottom]

At issue is coal's content of uranium and thorium, both radioactive elements. They occur in such trace amounts in natural, or "whole," coal that they aren't a problem. But when coal is burned into fly ash, uranium and thorium are concentrated at up to 10 times their original levels.

Fly ash uranium sometimes leaches into the soil and water surrounding a coal plant, affecting cropland and, in turn, food. People living within a "stack shadow"—the area within a half- to one-mile (0.8- to 1.6-kilometer) radius of a coal plant's smokestacks—might then ingest small amounts of radiation. Fly ash is also disposed of in landfills and abandoned mines and quarries, posing a potential risk to people living around those areas.

In a 1978 paper for Science, J. P. McBride at Oak Ridge National Laboratory (ORNL) and his colleagues looked at the uranium and thorium content of fly ash from coal-fired power plants in Tennessee and Alabama. To answer the question of just how harmful leaching could be, the scientists estimated radiation exposure around the coal plants and compared it with exposure levels around boiling-water reactor and pressurized-water nuclear power plants.

The result: estimated radiation doses ingested by people living near the coal plants were equal to or higher than doses for people living around the nuclear facilities. At one extreme, the scientists estimated fly ash radiation in individuals' bones at around 18 millirems (thousandths of a rem, a unit for measuring doses of ionizing radiation) a year. Doses for the two nuclear plants, by contrast, ranged from between three and six millirems for the same period. And when all food was grown in the area, radiation doses were 50 to 200 percent higher around the coal plants.

McBride and his co-authors estimated that individuals living near coal-fired installations are exposed to a maximum of 1.9 millirems of fly ash radiation yearly. To put these numbers in perspective, the average person encounters 360 millirems of annual "background radiation" from natural and man-made sources, including substances in Earth's crust, cosmic rays, residue from nuclear tests and smoke detectors.

Dana Christensen, associate lab director for energy and engineering at ORNL, says that health risks from radiation in coal by-products are low. "Other risks like being hit by lightning," he adds, "are three or four times greater than radiation-induced health effects from coal plants." And McBride and his co-authors emphasize that other products of coal power, like emissions of acid rain–producing sulfur dioxide and smog-forming nitrous oxide, pose greater health risks than radiation.

The U.S. Geological Survey (USGS) maintains an online database of fly ash–based uranium content for sites across the U.S. In most areas, the ash contains less uranium than some common rocks. In Tennessee's Chattanooga shale, for example, there is more uranium in phosphate rock.

Robert Finkelman, a former USGS coordinator of coal quality who oversaw research on uranium in fly ash in the 1990s, says that for the average person the by-product accounts for a miniscule amount of background radiation, probably less than 0.1 percent of total background radiation exposure. According to USGS calculations, buying a house in a stack shadow—in this case within 0.6 mile [one kilometer] of a coal plant—increases the annual amount of radiation you're exposed to by a maximum of 5 percent. But that's still less than the radiation encountered in normal yearly exposure to X-rays.

So why does coal waste appear so radioactive? It's a matter of comparison: The chances of experiencing adverse health effects from radiation are slim for both nuclear and coal-fired power plants—they're just somewhat higher for the coal ones. "You're talking about one chance in a billion for nuclear power plants," Christensen says. "And it's one in 10 million to one in a hundred million for coal plants."

Radiation from uranium and other elements in coal might only form a genuine health risk to miners, Finkelman explains. "It's more of an occupational hazard than a general environmental hazard," he says. "The miners are surrounded by rocks and sloshing through ground water that is exuding radon."

Developing countries like India and China continue to unveil new coal-fired plants—at the rate of one every seven to 10 days in the latter nation. And the U.S. still draws around half of its electricity from coal. But coal plants have an additional strike against them: they emit harmful greenhouse gases.

With the world now focused on addressing climate change, nuclear power is gaining favor in some circles. China aims to quadruple nuclear capacity to 40,000 megawatts by 2020, and the U.S. may build as many as 30 new reactors in the next several decades. But, although the risk of a nuclear core meltdown is very low, the impact of such an event creates a stigma around the noncarbon power source.

The question boils down to the accumulating impacts of daily incremental pollution from burning coal or the small risk but catastrophic consequences of even one nuclear meltdown. "I suspect we'll hear more about this rivalry," Finkelman says. "More coal will be mined in the future. And those ignorant of the issues, or those who have a vested interest in other forms of energy, may be tempted to raise these issues again."

*Editor's Note (12/30/08): In response to some concerns raised by readers, a change has been made to this story. The sentence marked with an asterisk was changed from "In fact, fly ash—a by-product from burning coal for power—and other coal waste contains up to 100 times more radiation than nuclear waste" to "In fact, the fly ash emitted by a power plant—a by-product from burning coal for electricity—carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy." Our source for this statistic is Dana Christensen, an associate lab director for energy and engineering at Oak Ridge National Laboratory as well as 1978 paper in Science authored by J. P. McBride and colleagues, also of ORNL.

As a general clarification, ounce for ounce, coal ash released from a power plant delivers more radiation than nuclear waste shielded via water or dry cask storage.