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Nuclear Power Plants

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.
Photo of nuclear power plant

Source: Stock photography (copyrighted)

Nuclear power comes from nuclear fission

Most power plants, including nuclear power plants, use heat to produce electricity. Power plants rely on steam from heated water to spin large turbines that generate electricity. Instead of burning fossil fuels to produce steam, nuclear power plants use heat produced during nuclear fission.

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 the uranium fuel.

The uranium fuel is formed into ceramic pellets. Each ceramic pellet produces roughly 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, sometimes hundreds, 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 turbine blades. As the turbine blades turn, they drive generators that make electricity. Afterward, the steam is cooled back into water in a separate structure at the power plant called a cooling tower. The water can then be reused.

Nuclear power plants generate about 20% of U.S. electricity

The United States has 61 operating nuclear power plants with 99 nuclear reactors.1 Of the 61 operating nuclear power plants, 35 of the plants have 2 or more reactors. There are nuclear power plants in 30 U.S. states, and 46 plants are located east of the Mississippi River. Nuclear power has supplied about one-fifth of annual U.S. electricity each year since 1990. Nuclear power provides about as much electricity as the total electricity used in California, New York, and Texas combined.

The United States generates more nuclear power than any other country

Of the 30 countries in the world that have commercial nuclear power plants, the United States has the most nuclear capacity and generation. France, the country with the second-highest nuclear capacity, relies on nuclear power for nearly 75% of its electricity. Fourteen other countries generate more than 20% of their electricity from nuclear power.

Nuclear generation, 2012

Source: U.S. Energy Information Administration


    1 As of January 1, 2015.

Last updated: June 9, 2015

Diagram of a boiling water nuclear reactor
Diagram of a boiling water nuclear reactor.

Source: U.S. Nuclear Regulatory Commission (public domain)

Did you know?

About 70% of the reactors operating in the United States are pressurized-water reactors.

Diagram of a pressurized nuclear water reactor
Diagram of a pressurized nuclear water reactor.

Source: U.S. Nuclear Regulatory Commission (public domain)

Nuclear reactors are machines that contain and control nuclear chain reactions while releasing heat at a controlled rate.

A nuclear power plant uses the heat supplied by a nuclear reactor to turn water into steam, which then drives turbine generators that generate electricity.

There are two types of reactors used in the United States

Boiling-water reactors and pressurized-water reactors are the two types of reactors used in the United States.

Boiling-water reactors

In a boiling-water reactor, water heated by the reactor core turns directly into steam in the reactor vessel, and the steam is then used to power the turbine generator.

Pressurized-water reactors

In a pressurized-water reactor, water heated by the reactor core is kept under pressure so that it does not turn to steam at all, it remains liquid. This hot radioactive water flows through a piece of equipment called a steam generator.

A steam generator is a giant cylinder with thousands of tubes that hot radioactive water can flow through to heat up. Outside these hot tubes in the steam generator is nonradioactive water (or clean water), which eventually boils and turns to steam.

The radioactive water flows back to the reactor core, where it is reheated and then sent back to the steam generator. The clean water may come from one of several sources like oceans, lakes, or rivers.

What are Small Modular Reactors?

Small Modular Reactors (SMRs) are about one-third the size of the reactors currently under construction. SMRs have simple compact designs that can be assembled in a factory and transported by train or truck directly to the power plant site, potentially reducing the time it takes to construct a new nuclear power plant. The U.S. Department of Energy is supporting the design, certification, and commercialization of SMRs in the United States.

Last reviewed: April 27, 2015