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Glossary of Nuclear Terms

  • Atom: The basic building block of all matter. The smallest particle of an element that has the same properties as the element. It consists of a central core called the nucleus that is made up of protons and neutrons. Electrons revolve in orbits in the region surrounding the nucleus.

  • Dry-cask storage: A method for storing spent fuel. Dry casks are large, rugged containers made of steel or steel-reinforced concrete, 18 or more inches thick. The casks use materials like steel, concrete and lead - instead of water - as a radiation shield. Depending on the design, a dry cask can hold from seven to 56 12-foot-long fuel assemblies.

  • Fission: The splitting of atoms that results in the release of large amounts of energy. Two or three neutrons are usually released during this event. Fission occurs either naturally or when an atom's nucleus is bombarded by neutrons.

  • Fossil fuel: Carbon based fuel resulting from millions of years of biological decay. Coal, oil, and natural gas are the most common examples.

  • Fuel assembly: Assemblies of fuel rods that are placed in the reactor vessel to form the core. Each fuel assembly may contain from approximately 60 to 300 fuel rods.

  • Fuel pellets: The Uranium fuel for nuclear reactors in the form of ceramic cylinders about one-half of an inch long and three-eighths of an inch in diameter. These "pellets" are stacked in long tubes to form fuel rods.

  • Fuel rod: A long, slender tube that holds the fuel pellets; fuel rods are assembled into bundles called fuel elements or fuel assemblies that are loaded individually into the reactor core.

  • NRC: Nuclear Regulatory Commission, a U.S. agency chartered to develop and administer rules for regulating commercial nuclear applications (including nuclear power plants, medical and industrial uses).

  • Nuclear energy: Energy, usually in the form of heat or electricity, produced by the process of nuclear fission within a nuclear reactor. The coolant that removes the heat from the nuclear reactor is normally used to boil water, and the resultant steam drives steam turbines that rotate electrical generators.

  • Pressurized water reactor (pwr): A reactor designed in which water flowing through the reactor is heated by nuclear energy but is kept at high pressure to keep the water from boiling. This heated water then transfers its heat to a secondary water system that boils into steam to drive the turbine.

  • Pressurizer: A device to keep water in the primary system within pressure limits needed to operate the reactor.

  • Radioactivity: The spontaneous transformation of an unstable atom and often results in the emission of radiation. This process is referred to as a transformation, a decay, or a disintegration of an atom.

  • Radiation: Particles (alpha, beta, neutrons) or rays (gamma) emitted from the nucleus of an unstable radioactive atom as a result of radioactive decay.

  • Radon: A naturally occurring radioactive gas formed when the element radium decays.

  • Reactor vessel: A device in which nuclear fission may be sustained and controlled in a self-supporting nuclear reaction. It houses the core (made up of fuel rods, control rods, and instruments contained within a reactor vessel) of most types of power reactors.

  • Spent fuel: Fuel rods which no longer have enough fissionable uranium in them to be efficiently used to produce power.

  • Steam generator: The heat exchanger used in some reactor designs to transfer heat from the primary reactor coolant system to the secondary (steam system).

  • Uranium: A naturally radioactive and very dense element. Mine Uranium contains 0.7 percent of the isotope Uranium-235, needed for fission. Uranium-235 is the principal nuclear fuel material used in today's nuclear power reactors.

  • "Watch list": Twice a year the United States Nuclear Regulatory Commission (NRC) evaluates the performance of the operating nuclear power plants in the United States and identifies those which require additional regulatory oversight because of declining performance. Those plants are placed on a list commonly called the "watch list". Once placed on the "watch list" a plant must demonstrate consistent improved performance before it is removed from the list.


    Edelson, Edward. The Journalist's Guide to Nuclear Energy. 4th ed., Nuclear Energy Institute, 1994.

    Florida Power & Light Nuclear Notebook. Florida Power & Light Company, 1990.

    Emergency Public Communications Manual. lim. ed., Institute of Nuclear Power Operations December, 1993.

    Waltar, Alan E., Ph.D. America the Powerless: Facing our Nuclear Energy Dilemma. Madison, Wisconsin: Cogito Books, 1995.

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