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Although they are tiny, atoms have a large amount of energy holding their nuclei together. Certain isotopes of some elements can be split and will release part of their energy as heat. This splitting is called fission. The heat released in fission can be used to help generate electricity in powerplants. Uranium-235 (U-235) is one of the isotopes that fissions easily. During fission, U-235 atoms absorb loose neutrons.  This causes U-235 to become unstable and split into two light atoms called fission products.

The combined mass of the fission products is less than that of the original U-235. The reduction occurs because some of the matter changes into energy. The energy is released as heat. Two or three neutrons are released along with the heat. These neutrons may hit other atoms, causing more fission.

A series of fissions is called a chain reaction. If enough uranium is brought together under the right conditions, a continuous chain reaction occurs. This is called a self-sustaining chain reaction.  A self-sustaining chain reaction creates a great deal of heat, which can be used to help generate electricity. Nuclear powerplants  generate electricity like any other steam-electric powerplant.   Water is heated, and steam from the boiling water turns turbines and generates electricity. The main difference in the various types of steam-electric plants is the heat  source.  Heat  from a self-sustaining chain reaction boils the water in  a nuclear powerplant.  Coal, oil, or gas is burned in other powerplants to heat the water.

Watch a video and learn more about the history of nuclear power in the United States in our blog post 60 Years Since Nuclear Turned on The Lights.