Nuclear Energy: How It Works, Safety, Pros and Cons

This article contains affiliate links: if you buy through them we may earn a commission, at no extra cost to you. Learn more.

Nuclear energy is the energy stored in the nucleus, or core, of an atom. Nuclear power plants release it by splitting uranium atoms, a process called fission. The heat boils water into steam, and the steam spins turbines that make electricity, with no carbon dioxide from the reactor itself.

Nuclear power is closer to your daily life than it may seem. In the U.S., about one in every five or six kilowatthours that light your kitchen or charge your car comes from a reactor somewhere on the grid. And the radiation question that worries many people has a surprising home angle: the biggest natural source most families are exposed to is not a power plant at all, but radon gas seeping up from the ground under the house.

Nuclear energy at a glance

• What it is: energy released when the nuclei of atoms split (fission) or join (fusion). Today’s power plants all use fission.
• Fuel: uranium, a common metal found in rocks worldwide; plants use the rarer U-235 form because its atoms split easily.
• Renewable? No. Uranium is a mined, finite resource, but nuclear power is low-carbon.
• Share of U.S. electricity: about 18% of utility-scale generation in 2025 (U.S. EIA), and about 20% every year since 1990.
• Share of world electricity: about 9% in 2025, from about 440 reactors (World Nuclear Association).
• Main upside: steady, around-the-clock power with no air pollution or CO2 while running.
• Main downside: very expensive and slow to build, and long-lived radioactive waste with no permanent U.S. disposal site yet.

How nuclear energy works

The simple version: a nuclear plant is a steam power plant with a very unusual fire. Instead of burning coal or gas, it uses the heat from splitting atoms.

1. Fuel. Uranium is mined, processed and pressed into small ceramic pellets. EIA says each pellet holds about as much energy as 150 gallons of oil. The pellets are stacked inside 12-foot metal fuel rods, which are bundled into fuel assemblies.
2. Fission. Inside the reactor, a neutron hits a uranium-235 atom and splits it into two smaller atoms. That releases a lot of heat and radiation, plus more neutrons.
3. Chain reaction. Those new neutrons split more uranium atoms, which release more neutrons, and so on. Operators control how fast the reaction runs, keeping it steady.
4. Steam. The heat boils water, either directly in the reactor (a boiling water reactor) or through a separate loop (a pressurized water reactor).
5. Electricity. The steam spins turbine blades that drive a generator.
6. Cooling. The steam is cooled back into water, using cooling towers or water from a lake, river or the ocean, and sent around again.

Why so much energy from so little fuel? When an atom splits, the pieces weigh slightly less than the original atom. That tiny bit of missing mass becomes energy, following Einstein’s E = mc². Because the speed of light (c) is enormous, a very small amount of mass makes a huge amount of heat. Fission is one kind of nuclear energy; the other is fusion energy, which joins light atoms together the way the sun does and is still experimental on Earth.

A short history of nuclear power

• December 2, 1942: a team led by Enrico Fermi ran the first self-sustaining nuclear chain reaction, Chicago Pile-1, at the University of Chicago.
• December 20, 1951: Experimental Breeder Reactor I in Arco, Idaho, made the first electricity from nuclear energy, lighting four light bulbs.
• December 8, 1953: President Eisenhower gave his “Atoms for Peace” speech at the United Nations; the Atomic Energy Act of 1954 followed.
• December 2, 1957: the first large-scale U.S. nuclear power plant began operating at Shippingport, Pennsylvania, serving the Pittsburgh area.
• March 28, 1979: a loss-of-coolant accident at Three Mile Island in Pennsylvania, the worst accident in U.S. commercial reactor history. The DOE reports no one was injured; safety rules were tightened afterward.
• April 26, 1986: explosions at Chernobyl in the Soviet Union, a reactor design with weak containment that would not be licensed in the U.S.
• March 11, 2011: a magnitude 9.0 earthquake and a 15-meter tsunami knocked out cooling at Fukushima Daiichi in Japan, and three reactor cores melted.
• 2023 and 2024: Vogtle Units 3 and 4 in Georgia started up, the first new U.S. reactors since Watts Bar 2 in 2016.

Types of nuclear reactors

• Light-water reactors. Every commercial power reactor running in the U.S. today uses ordinary water to cool the core and carry the heat. They come in two main designs, pressurized water reactors and boiling water reactors. Vogtle’s two newest units use the Westinghouse AP1000 design.
• Small modular reactors (SMRs). Smaller reactors designed to be built in standard units. The Tennessee Valley Authority’s planned 300-megawatt BWRX-300 at Clinch River is one example.
• Advanced (non-light-water) reactors. Designs that use something other than ordinary water to carry heat. TerraPower’s Natrium, which pairs its reactor with molten salt energy storage, is the first of these to get a U.S. construction permit.
• Fusion reactors. Still research machines; see our page on fusion energy.

Where nuclear energy is used today

In the United States

The U.S. has the largest nuclear fleet in the world. According to EIA, as of March 2026 there were 96 operating commercial reactors at 57 power plants in 28 states, with about 98,441 megawatts of capacity. The average reactor is about 44 years old; the oldest still running, Nine Mile Point Unit 1 in New York, started in December 1969. Georgia’s Plant Vogtle, with four reactors and 4,530 megawatts, is the largest plant, and Illinois has the most reactors of any state (11 at six plants).

Nuclear plants run almost all the time. Their average capacity factor in 2025 was 91%, meaning they produced 91% of the power they could make if they ran flat out all year. That reliability is why about 18% of U.S. electricity came from nuclear in 2025, even though nuclear is a much smaller share of total power plant capacity. Most of the uranium is imported: in 2022, U.S. plant owners bought 40.5 million pounds, with Canada (27%) and Kazakhstan (25%) the top suppliers, followed by Russia, Uzbekistan and Australia.

Around the world

The World Nuclear Association counts 441 operable reactors in 31 countries in 2025, with about 404 gigawatts of capacity. They made about 2,700 terawatthours, roughly 9% of the world’s electricity, and 81 more reactors were under construction. The U.S. generated the most (about 786 TWh, 17.7% of its power), followed by China and France. France gets about 68% of its electricity from nuclear.

Nuclear energy at home: what it means for you

You can’t put a reactor in your basement, but nuclear touches your home in a few practical ways.

• Your power mix. If your utility owns or buys from a nuclear plant (Illinois has the most reactors of any state), a big part of your electricity is already low-carbon. Your utility’s yearly report shows its mix.
• Living near a plant. The U.S. Nuclear Regulatory Commission (NRC) estimates the extra dose from living within 50 miles of a pressurized water reactor at about 0.0009 millirem a year. The average American gets about 620 millirem a year from all sources, about half of it natural and half mostly from medical scans. A single chest X-ray is about 10 millirem.
• Radon is the real radiation risk at home. Radon is a natural radioactive gas that comes up from the ground. The EPA says it causes about 21,000 lung cancer deaths a year, making it the second leading cause of lung cancer and the top cause among nonsmokers. Nearly one in 15 U.S. homes has a radon level that should be fixed (4 picocuries per liter or more). Testing is cheap and easy; start in the lowest lived-in level of the house.
• If your test is high. A professional radon mitigation system can cut levels by up to 99%, according to the EPA. Use a certified radon mitigation contractor, and a licensed electrician for any new wiring.
• Use less, whatever the source. An energy-saving habit lowers your bill no matter what powers your grid, and home solar or battery storage can cover part of your own needs.

Products for radiation and radon at home

Prices change often. The prices below are what we saw on Amazon in October 2026; check the current price before you buy.

PRO-LAB short-term radon test kit (about $10, seen October 2026, plus a $20 lab fee per detector): the low-cost way to follow the EPA’s advice and test. You set the detectors out, mail them in, and get lab results. Two detectors let you test two spots, or run a side-by-side check.

Check the PRO-LAB radon test kit price on Amazon

Airthings Corentium Home (about $143, seen October 2026): a battery-powered digital radon monitor that shows short-term and long-term averages on its screen. Radon goes up and down day to day, so a monitor that keeps reading is handy after a high test or once a mitigation system is in.

GQ GMC-800 (about $89, seen October 2026): a handheld Geiger counter that detects beta, gamma and X-ray radiation, with a dosimeter mode and several alarm types. It is a fun, educational tool for checking background radiation, old ceramics or rocks. It is not a radon test; use a radon kit or monitor for that.

Pros and cons of nuclear energy

Pros	Cons
No air pollution or CO2 while running (EIA)	Mining, processing and building plants still cause emissions
Runs day and night; 91% average capacity factor in 2025	Very high cost to build new plants: $141–$220 per MWh unsubsidized (Lazard 2025)
Tiny fuel volume: one pellet ≈ 150 gallons of oil	Long-lived spent fuel with no permanent U.S. disposal site
Cheap fuel: Lazard assumes $0.85 per million Btu, versus $3.45 for gas	Rare but serious accidents (Chernobyl, Fukushima) and public concern
About 20% of U.S. power every year since 1990	New projects take many years and often run over budget (Vogtle topped $30 billion)
Strict federal oversight, tightened after Three Mile Island	Much of the uranium is imported

Environmental and safety impact

Waste

The hardest problem is spent fuel. The DOE says U.S. reactors make about 2,000 metric tons of spent fuel each year and about 90,000 metric tons since the 1950s. That sounds like a lot, but it is dense: all of it would fit on one football field stacked less than 10 yards high. It sits in cooling pools and then in steel and concrete dry casks at more than 70 sites in 35 states, because the U.S. still has no permanent disposal facility. Congress picked Yucca Mountain in Nevada in 1987, but that site never opened. Even after five years in a reactor, spent fuel still holds more than 90% of its potential energy.

Accidents in perspective

• Three Mile Island (1979): a partial meltdown; DOE reports no injuries and no overexposure to radiation.
• Chernobyl (1986): two workers died in the explosion and 28 more within weeks from radiation sickness. The UN’s science committee links about 5,000 thyroid cancers (15 fatal) to the accident.
• Fukushima (2011): no deaths or radiation sickness from the radiation itself, per the World Nuclear Association, but more than 100,000 people were evacuated, and Japan counted 2,313 disaster-related deaths among evacuees from Fukushima prefecture, mostly elderly people under the stress of evacuation.

EIA notes that U.S. plants rely on several barriers and backup safety systems, inside containment structures built to withstand extreme weather and earthquakes. Plants also need a lot of cooling water, and uranium mining leaves tailings that must be sealed to keep radon from escaping.

What nuclear power costs

Nuclear is cheap to run and expensive to build. Lazard’s 2025 Levelized Cost of Energy study estimates power from a new U.S. nuclear plant at about $141 to $220 per megawatthour without subsidies, based on Vogtle’s costs; that is the highest of the major sources it compares. Vogtle Units 3 and 4 began construction in 2009, were first expected to run in 2016, and came online in 2023 and 2024, with the total project cost above $30 billion, according to EIA. Fuel is a small part of the cost, so existing plants that are already paid off can keep producing power at a steady price.

The future of nuclear energy

Here is what is real and announced as of October 2026, as opposed to hopes:

• Federal goals. Executive orders signed in May 2025 set a goal of growing U.S. nuclear capacity from about 100 gigawatts to 400 gigawatts by 2050, with 10 new large reactors under construction by 2030. These are goals, not funded projects.
• TerraPower Natrium, Wyoming. In March 2026 the NRC issued a construction permit for Kemmerer Unit 1, a 345-megawatt advanced reactor that can boost to 500 megawatts using molten salt heat storage. Operation is expected around 2030.
• TVA Clinch River, Tennessee. On September 29, 2026, the NRC issued a construction permit for a 300-megawatt BWRX-300 small modular reactor, expected to run in the early 2030s.
• Restarts. Holtec is working to restart the Palisades plant in Michigan, which shut in May 2022; it would be the first U.S. nuclear plant to restart after entering decommissioning. In July 2026 Holtec said the major projects were done and the site had moved on to testing and readiness work.
• The long view. EIA’s projections show nuclear’s share of U.S. power slipping from 17% in 2025 to between 12% and 15% by 2050, as demand grows and older reactors age, unless a lot of new building happens.

How nuclear compares with other energy sources

Source	Share of U.S. electricity (2025)	CO2 while running	New-build cost, $/MWh (Lazard 2025)	Runs when needed?
Nuclear	About 18%	None	$141–$220	Yes, around the clock
Coal	About 17%	2.31 lb/kWh (2023)	$71–$173	Yes
Natural gas	About 41%	0.96 lb/kWh (2023)	$48–$109	Yes
Wind (onshore)	About 11%	None	$37–$86	Only when the wind blows

Nuclear energy FAQs

Is nuclear energy renewable?

No. Nuclear plants run on uranium, a metal that is mined and will not be replaced on a human timescale, so EIA classes it as nonrenewable. It is, however, a low-carbon source: reactors give off no carbon dioxide or air pollution while running. That is why nuclear is often grouped with wind and solar as “clean” energy.

How much U.S. electricity comes from nuclear power?

About 18% of U.S. utility-scale electricity came from nuclear in 2025, according to the U.S. Energy Information Administration, and nuclear has supplied about 20% every year since 1990. As of March 2026, 96 reactors at 57 plants in 28 states were operating, more than in any other country.

Is it safe to live near a nuclear power plant?

For normal operation, the added radiation is extremely small. The NRC estimates about 0.0009 millirem a year for someone within 50 miles of a pressurized water reactor, compared with about 620 millirem a year that the average American gets from all sources. A single chest X-ray is about 10 millirem, more than ten thousand times that yearly amount.

What happens to nuclear waste?

Spent fuel is first cooled in deep pools of water, then moved into sealed steel and concrete dry casks stored at the plant. The U.S. has about 90,000 metric tons at more than 70 sites in 35 states, and adds about 2,000 tons a year. There is still no permanent national disposal site.

What is the difference between fission and fusion?

Fission splits heavy atoms like uranium into smaller ones; it powers every nuclear plant today. Fusion joins very light atoms, like forms of hydrogen, into heavier ones; it powers the sun. Both turn a little mass into a lot of energy, but fusion power plants do not exist yet. Scientists first got more energy out of a fusion reaction than the laser energy put in during 2022.

Should I test my home for radon?

Yes. Radon is invisible and has no smell, it has been found at high levels in every state, and the EPA says testing is the only way to know your level. Nearly one in 15 U.S. homes is at or above the 4 pCi/L action level. Test kits cost little, and if your level is high, a certified contractor can install a system that lowers it.

Are new nuclear plants being built in the U.S.?

A few. Vogtle Units 3 and 4 in Georgia were finished in 2023 and 2024. In 2026 the NRC issued construction permits for TerraPower’s Natrium reactor in Wyoming and TVA’s small modular reactor at Clinch River, Tennessee. Both are expected to run around 2030 or in the early 2030s, if schedules hold.

Keep exploring

See where nuclear sits among all the types of energy, learn how its experimental cousin fusion works, or compare it with coal and natural gas. Curious how “clean” and “renewable” differ? Our clean energy guide explains it.