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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

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

As of January 2018, there were 99 operating nuclear reactors at 61 nuclear power plants in 30 states. Thirty-six of the plants have 2 or more reactors. Nuclear power has supplied about one-fifth of total annual U.S. electricity since 1990.

The United States generates more nuclear power than any other country

Of the 31 countries in the world with commercial nuclear power plants in 2015, the United States had the most nuclear electricity generation capacity and generated more electricity from nuclear energy than any other country. France had the second-highest nuclear electricity generation capacity and electricity generation and obtained about 78% of its total electricity generation from nuclear energy, the largest share of any other country. Fourteen other countries generated at least 20% of their electricity from nuclear power.

Top five nuclear electricity generation countries, 2015

Country Nuclear electricity generation capacity (million kilowatts) Nuclear electricity generation (billion kilowatthours) Share of country's total electricity generation
United States 99 797 19.5%
France 63 419 77.6%
Russia 25 183 18.1%
China 27 161   2.9%
South Korea 22 157 30.4%

Source: U.S. Energy Information Administration, International Energy Statistics, as of August 8, 2018

Last updated: August 8, 2018

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?

Sixty-five of the 99 nuclear power reactors operating in the United States are pressurized-water reactors (as of May 2018).

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 updated: August 22, 2018