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How Nuclear Reactors Work

America’s 100 nuclear power plants generate almost 20 percent of the nation’s electricity while emitting no carbon dioxide or controlled pollutants.

How Nuclear Plants Generate Electricity

Nuclear plants, like plants that burn coal, oil and natural gas, produce electricity by boiling water into steam. This steam then turns turbines to produce electricity. The difference is that nuclear plants do not burn anything. Instead, they use uranium fuel, consisting of solid ceramic pellets, to produce electricity through a process called fission.

Nuclear power plants obtain the heat needed to produce steam through a physical process. This process, called fission, entails the splitting of atoms of uranium in a nuclear reactor. The uranium fuel consists of small, hard ceramic pellets that are packaged into long, vertical tubes. Bundles of this fuel are inserted into the reactor.

Watch NEI's easy-to-understand video tutorial below on the design and safe operation of a nuclear reactor. (Note: Select "Full screen" at the bottom right of the video to see an enlarged version of the video.)


To see this video and other video tutorials on nuclear energy topics, visit NEI's YouTube channel.

Two Types of Uranium

Nuclear fuel consists of two types of uranium, U-238 and U-235. Most of the uranium in nuclear fuel is U-238, but U-235 splits—or fissions—easily. In U-235 atoms, the nucleus, which is composed of protons and neutrons, is unstable. As the nuclei break up, they release neutrons.

When the neutrons hit other uranium atoms, those atoms also split, releasing neutrons of their own, along with heat. These neutrons strike other atoms, splitting them. One fission triggers others, which triggers still more until there is a chain reaction. When that happens, fission becomes self-sustaining.

Rods inserted among the tubes holding the uranium fuel control the nuclear reaction. Control rods, inserted or withdrawn to varying degrees, slow or accelerate the reaction.

Water separates fuel tubes in the reactor. The heat produced by fission turns this water into steam. The steam drives a turbine, which spins a generator to create electricity.

Types of Nuclear Power Plants

Commercial nuclear power plants in the United States are either boiling water reactors or pressurized water reactors.

Both boiling water reactors and pressurized water reactors are cooled by ordinary water. The water is the main link in the process that converts fission energy to electrical energy.

Boiling water reactors heat the water surrounding the nuclear fuel directly into steam in the reactor vessel. Pipes carry steam directly to the turbine, which drives the electric generator to produce electricity.

Pressurized water reactors heat the water surrounding the nuclear fuel, but keep the water under pressure to prevent it from boiling. The hot water is pumped from the reactor vessel to a steam generator. There, the heat from the water is transferred to a second, separate supply of water. This water supply boils to make steam. The steam spins the turbine, which drives the electric generator to produce electricity.

Approximately two-thirds of the 100 reactors in the United States are pressurized water reactors, and one-third of them are boiling water reactors.