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Glossary of Terms

Heat energy produced by the process of nuclear fission within a nuclear reactor. The coolant that removes heat from the reactor core is normally used to boil water. The resultant steam drives turbines that rotate electrical generators.

Alpha particle
Particle emitted in certain types of radioactive decay. It is positively charged and made up of two neutrons and two protons (which is a helium atom nucleus.) It is easily stopped, and cannot penetrate a piece of paper or the skin.

The smallest part of an element that still has all properties of that element. Its nucleus consists of protons and neutrons, and is surrounded by orbiting electrons.

Atoms for Peace
President Eisenhower's 1954 initiative to allow the peaceful uses of atomic energy to be available to other nations.

Background radiation
Radiation that comes from natural sources and is always present in the environment. This includes solar and cosmic radiation as well as radioactive elements in the ground, building materials, and the human body. Average annual dose of background radiation for an American is about 360 millirems.

Beta particle
Another type of particle, a negatively charged electron--emitted in certain types of radioactive decay. It can be stopped by a thin piece of aluminum or by traveling a short distance in the air.

Breeder reactors
A special design of nuclear reactor that generates more usable fuel than it consumes.

Chain reaction
When neutrons produced in one fission event cause another fission event to occur. A continuing series of these nuclear fissions takes place inside a reactor.

An atom with a unique number of protons in its nucleus. Oxygen has eight protons in its nucleus, and plutonium has 94.

The process of splitting a heavy atom into two or more lighter atoms upon absorption of a neutron. This process generates a large amount of energy and usually at least two neutrons. The act of fissioning is also referred to as burning.

Fuel cycle
All the steps involved in using nuclear fuel in reactors: supply, use, processing and disposal of waste.

Gamma ray
A highly penetrating, short wavelength electromagnetic radiation emitted during the radioactive decay of many nuclides.

The length of time for a radioactive substance to lose half its radioactivity from decay. At the end of one half-life, only 50% of the original radionuclide remains.

High level waste
Current definition: the highly radioactive solid material that results from the chemical reprocessing of spent nuclear fuel. It contains mainly fission products, trace amounts of uranium and plutonium and other transuranic elements.

Integral Fast Reactor. A type of reactor based on a closed fuel cycle at the site. The key to this design is that the plutonium fission product never occurs in a pure form. This feature is considered proliferation-resistant. Developed by the Argonne National Laboratory.

Ionizing radiation
Radiation of such high energy that it can remove electrons from a struck atom, leaving positively charged particles behind. High doses of IR can cause cellular damage.

Atoms of the same element but with different mass numbers. They have the same number of protons in their nucleus but different numbers of neutrons. For example, helium-3, an isotope of helium, contains two protons and one neutron. Helium-4 has two protons and two neutrons.

Low-level waste
Waste materials containing very low levels of radioactivity, requiring essentially no shielding or heat removal.

A millirem is a unit of radiation dose equivalent to one-thousandth of a rem (which stand for Roentgen equivalent man). It measures the amount of damage to human tissue from a dose of ionizing radiation.

A general term used to describe the full range of elements and their family of isotopes.

A fuel cycle in which spent fuel is not reprocessed but sent to short or long term storage.

A very heavy element formed when uranium-238 absorbs neutrons. Like uranium, it has two principal isotopes that are fissile.

Particles or rays emitted by radioactive substances from the unstable nuclei of their atoms. (See alpha particle, beta particle and gamma ray)

Any species of an atom that is radioactive.

A natural radioactive gas produced by the decay of radium, a decay product of uranium.

AKA recycling. The mechanical and chemical process of separating out usable products (like uranium and plutonium) from spent nuclear fuel. Ideally, these fissile products can be used again in a reactor.

Spent fuel
Nuclear fuel elements that are discharged from a nuclear reactor after they have been used to produce power.

Transuranics (TRU)
Elements with an atomic number greater than uranium, or greater than 92 protons. Examples of transuranics are neptunium (No. 93), plutonium (94), and americium (No. 95).

The heaviest element normally found in nature. The principal fuel material used in today's nuclear reactors is the fissile isotope uranium-235.


America the Powerless by Alan E. Waltar, Ph.D. (1995)

Understanding Radioactive Waste by Raymond L. Murray (1994)

The Nuclear Waste Primer by The League of Women Voters (1993)

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