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The sun is basically a giant ball of hydrogen gas undergoing fusion and giving off vast amounts of energy in the process.
The sun is basically a giant ball of hydrogen gas undergoing fusion into helium gas and giving off vast amounts of energy in the process.

Source: NASA (public domain)

Did you know?

All nuclear power in the United States is used to generate electricity.

Drawing of how fission splits the uranium atom.

Source: Adapted from National Energy Education Development Project (public domain)

Nuclear energy is energy in the core of an atom

Atoms are the tiny particles in the molecules that make up gases, liquids, and solids. Atoms themselves are made up of three particles called protons, neutrons, and electrons. An atom has a nucleus (or core) containing protons and neutrons, which is surrounded by electrons. Protons carry a positive electrical charge and electrons carry a negative electrical charge. Neutrons do not have an electrical charge. There is enormous energy present in the bonds that hold the nucleus together. This nuclear energy can be released when those bonds are broken. The bonds can be broken through nuclear fission, and this energy can be used to produce electricity.

In nuclear fission, atoms are split apart, which releases energy. All nuclear power plants use nuclear fission, and most nuclear power plants use uranium atoms. During nuclear fission, a neutron hits a uranium atom and splits it, releasing a large amount of energy in the form of heat and radiation. More neutrons are also released when a uranium atom splits. These neutrons go on to hit other uranium atoms, and the process repeats itself over and over again. This is called a nuclear chain reaction. This reaction is controlled in nuclear power plant reactors to produce a desired amount of heat.

Nuclear energy can also be released in nuclear fusion, in which atoms are combined or fused together to form a larger atom. This is the source of energy in the sun and stars. Nuclear fusion is the subject of ongoing research as a source of energy for heat and electricity generation, but it is not yet clear whether or not it will be a commercially viable technology because of the difficulty of controlling a fusion reaction.

Nuclear fuel—uranium

Uranium is the fuel most widely used by nuclear plants for nuclear fission. Uranium is considered to be a nonrenewable energy source, even though it is a common metal found in rocks worldwide. Nuclear power plants use a certain kind of uranium, referred to as U-235, for fuel because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare.

Most U.S. uranium ore is mined in the western United States. Once uranium is mined, the U-235 must be extracted and processed before it can be used as a fuel.

Last reviewed: October 26, 2015

U.S. nuclear statistics

2014 data except where noted.

Total operable reactors United States—99
Nuclear electricity net generation 797,067 million kilowatthours
Nuclear percentage of electricity generation 19.54%
Nuclear net summer generating capacity 98.6 million kilowatts
Nuclear share of total U.S. electric generating capacity (2013) 9% (net summer)
Nuclear annual capacity factor 91.7%
Largest U.S. nuclear plant Palo Verde—3,937 megawatts (three nuclear reactors)
Number of states with commercial nuclear plants 30
U.S. uranium expenditures $239.7 million
U.S. uranium concentrate (U3O8) production 4.6 million pounds
Average price for purchased uranium concentrate U3O8 $46.16 per pound U3O8
Fuel cost: nuclear vs. fossil steam (2012) 0.76 cents/kilowatthour vs. 2.83 cents/kilowatthour

World nuclear statistics

2012 data

Nuclear share of total electricity production for selected countries
  • France
  • United States
  • United Kingdom
  • Germany
  • Japan
  • 77%
  • 19%
  • 19%
  • 16%
  • 2%
Share of world nuclear electricity generation (six largest)
  • United States
  • France
  • Russia
  • South Korea
  • Germany
  • China
  • 33%
  • 17%
  • 7%
  • 6%
  • 4%
  • 4%

Last updated: October 26, 2015