Nuclear Energy: Glossary

atom: the smallest unit of an element. It is made up of electrons, protons, and neutrons. Protons and neutrons make up the atom's nucleus.

breeder reactor: a nuclear reactor that makes more fuel than it uses.

cadmium: a soft, blue-white metal used as control rods because it absorbs neutrons.

chain reaction: a continuous fission reaction where atoms split to form new atoms and release neutrons that cause more atoms to split.

critical mass: the amount of uranium needed to cause a self-sustaining chain reaction.

deuterium: an isotope of hydrogen used in fusion.

fission: the process in which the nucleus of an atom is split to produce heat.

fission products: light atoms that result from fission. The combined mass of fission products is less than that of the original whole atom because energy and neutrons are released.

fusion: the process in which atoms are joined to produce energy.

isotope: a form of an element that contains an unusual number of neutrons in its nucleus.

light-water reactor (LWR): the typical commercial nuclear power reactor. It uses ordinary water (light water) to produce steam. The steam turns turbines and generates electricity.

Manhattan Project: the code name for production of the atomic bombs developed during World War II. The name comes from the Manhattan Engineering District, which ran the program.

moderator: substance causing slowing down of fast neutrons by collision; necessary for thermal reactors

radioisotope: a radioactive isotope of an element.

radioactivity: emission of alpha or beta particles, or gamma rays from substances by radioactive decay

reactor: device utilizing nuclear chain reaction for power production

reactor core: Assembly of fuel elements in a reactor vessel for sustaining a chain reaction and power production

self-sustaining chain reaction: a continuous chain reaction.

spent fuel: Fuel removed from reactors at end of its useful life; typically stored in water pools for cooling for ~10 years or more

spent fuel dry storage: Stored after ~ 10 years in shielded concrete casks.

uranium: a heavy, silver-white, radioactive metal.

uranium-235 (U-235): an isotope of uranium that is used as fuel in nuclear power plants.