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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

Many power plants, including nuclear power plants, heat water to produce electricity. These power plants use steam from heated water 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 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 100 nuclear reactors at 60 operating nuclear power plants located in 30 states.1 Thirty-six of the plants have 2 or more reactors, and 46 plants are located east of the Mississippi River. Nuclear power has supplied about one-fifth of annual U.S. electricity since 1990.

The United States generates more nuclear power than any other country

Of the 31 countries in the world that have commercial nuclear power plants, the United States has the most nuclear capacity and generation. France has the second-highest nuclear electricity generation and obtains about 75% of its total electricity from nuclear energy. Fifteen other countries generate more than 20% of their electricity from nuclear power.

Nuclear generation, 2014

Source: U.S. Energy Information Administration


    1The newest U.S. reactor, Watts Bar Unit 2 in Tennessee, began initial operation in June 2016.

Last updated: July 21, 2016

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 that a nuclear reactor produces to turn water into steam, which then drives turbine generators that generate electricity.

U.S. nuclear power plants use two types of nuclear reactors

Nuclear power plants in the United States have either a boiling-water reactor or a pressurized-water reactor.

Boiling-water nuclear reactors

In a boiling-water reactor, the reactor core heats water, which turns directly into steam in the reactor vessel. The steam is used to power a turbine generator.

Pressurized-water nuclear reactors

In a pressurized-water reactor, the reactor core heats water and keeps it under pressure to prevent the water from turning into steam. This hot radioactive water flows through tubes in a steam generator.

A steam generator is a giant cylinder filled with nonradioactive water (or clean water). Inside the giant water-filled cylinder are thousands of tubes filled with the hot radioactive water from the reactor core that eventually bring the clean water to a boil and turn it into steam.

The radioactive water flows back to the reactor core to be reheated, and once reheated, returns to the steam generator. The clean water may come from one of several sources like oceans, lakes, or rivers.

What are small modular reactors?

The U.S. Department of Energy is supporting the design, certification, and commercialization of small modular reactors (SMRs). SMRS are about one-third the size of the reactors that are operating and under construction in the United States. SMRs have simple, compact designs that can be assembled in a factory and transported by train or truck to the power plant site. The size and simplicity of the SMRs could reduce the time it takes to construct a new nuclear power plant.

Last reviewed: July 15, 2016