Glossary

* Italicized words are defined in glossary.

Activated. Describes non-fissile material that has become radioactive as a result of neutron irradiation.

Alpha particle. A particle that consists of two protons and two neutrons, given off by the decay of many elements, including uranium, plutonium, and radon. Alpha particles cannot penetrate a sheet of paper; however, alpha-particle emitting isotopes in the body can be damaging.

Americium. A man-made transuranic element. Americium is the next element above plutonium on the periodic table.

Assay. The qualitative or quantitative analysis of a substance often used to determine the proportion of isotopes in radioactive materials.

Atomic Energy Act. This act administers and regulates the production and uses of atomic power. The act was passed in 1946 and amended in 1954 and several times since then.

Atomic Energy Commission (AEC). Civilian agency created by the U.S. Congress in 1946 as the agency responsible for the production of nuclear weapons as well as research and regulation of atomic energy. The AEC was disbanded in 1975. Today its nuclear weapons production and research activities are the responsibility of the Department of Energy .

Beta particle. Emitted in the radioactive decay of many radionuclides . A beta particle is identical to an electron. It has a short range in air and low ability to penetrate most other materials.

Canyon. A slang term for a chemical separations plant; inspired by the plant's long, high, narrow structure. Not all chemical separations plants are canyons.

Chain reaction. A self-sustaining series of nuclear reactions in which neutrons produced by fission cause more fission. Essential to the functioning of nuclear reactors and weapons.

Chemical separation. A process for extracting uranium and plutonium from dissolved spent nuclear fuel and irradiated targets. The fission products that are left behind are high-level waste. Chemical separation is also known as reprocessing.

Cladding. The outer layer of metal around the nuclear fuel or target element. Department of Energy nuclear fuels generally have aluminum or zirconium cladding.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Enacted in 1980, this federal law governs the cleanup of hazardous substances. The Act and its amendments created a trust fund, the "Superfund," to finance the investigation and cleanup of abandoned and uncontrolled hazardous waste sites.

Coolant. A fluid that is used to remove and dissipate heat. Many nuclear reactor types are distinguished by the type of coolant that is used (e.g., liquid metal cooled, boiling water).

Criticality. The conditions necessary for a sustained nuclear chain reaction .

Decay (radioactive). Spontaneous disintegration of the nucleus of an unstable atom that results in the emission of particles and energy.

Decay product. An isotope that results from the decay of an unstable atom.

Decommissioning. Retirement of a nuclear facility, including decontamination and/or dismantlement.

Decontamination. Removal of radioactive or hazardous material through a chemical or mechanical process.

De minimis level. An amount small enough to be of no concern.

Department of Energy (DOE). The cabinet-level U.S. Government agency responsible for nuclear weapons production, energy research and the cleanup of hazardous and radioactive waste at its sites. It was created from the Energy Research and Development Administration and other Federal Government functions in 1977.

Deuterium. A naturally occurring isotope of hydrogen that is twice as heavy as ordinary hydrogen. It is most often found in the form of heavy water .

Disposition. Reuse, recycling, sale, transfer, storage, or disposal of materials.

Fissile. Capable of being split by a low-energy neutron. The most common fissile isotopes are uranium-235 and plutonium -239.

Fission. The splitting of a nucleus of a heavy atom such as plutonium or uranium usually caused by absorption of a neutron . Large amounts of energy and one or more neutrons are released when an atom fissions.

Fission products. The large variety of smaller atoms left over from fission of uranium or plutonium. Most of these atoms are radioactive and decay into other isotopes. There are more than 200 isotopes of 35 elements in this category. Most of the fission products in the U.S. are in spent nuclear fuel and high-level waste .

Fuel (nuclear). Natural or enriched uranium that sustains the fission chain reaction in a nuclear reactor. Also refers to the entire fuel element, including structural materials such as cladding .

Fuel element. Nuclear reactor fuel including both the fissile and structural materials; typically in the shape of a long cylinder or a bundle of rods or plates.

Fusion. The process whereby the nuclei of lighter elements, especially the isotopes of hydrogen (deuterium and tritium ) combine to form the nucleus of a heavier element accompanied by the release of substantial amounts of energy.

Gammaradiation. High-energy electro-magnetic radiation emitted in the radioactive decay of many radionuclides similar to X-rays. Highly penetrating but can be blocked by dense materials such as lead, concrete, or water.

Gaseous diffusion. The most common process used to enrich uranium in the United States.

Geologic repository. A system that is intended to be used for, or may be used for, the disposal of radioactive wastes in excavated geologic media. A geologic repository includes: (1) the geologic repository operations area, and (2) the portion of the geologic setting that provides isolation of the radioactive waste.

Half-life. The time it takes for one half of any given number of unstable atoms to decay. Each isotope has its own characteristic half-life, ranging from small fractions of a second to billions of years.

Heavy metals. Metallic elements with high atomic weights (e.g., mercury, chromium, cadmium, arsenic, and lead) that can damage living things at low concentrations and tend to accumulate in the food chain. Uranium, thorium, and plutonium are also heavy metals.

Heavy water. Water that contains deuterium in the place of hydrogen atoms. Used in the Savannah River Site production reactors.

High-level waste. Highly radioactive material resulting from the reprocessing of spent nuclear fuel, including liquid waste produced directly in reprocessing and any solid material derived from such liquid waste that contains fission products in sufficient concentrations; and, other highly radioactive material that the Nuclear Regulatory Commission, consistent with existing law, determines by rule requires permanent isolation. Inert gas. A gas that does not react chemically with other substances: helium, neon, argon, xenon, and radon.

In situ. In place.

Ionizing radiation. Radiation that is capable of breaking apart molecules or atoms. The splitting or decay of unstable atoms typically emits ionizing radiation.

Irradiate. To expose to ionizing radiation, usually in a nuclear reactor. Targets are irradiated to produce isotopes .

Isotopes. Different forms of the same chemical element that differ only by the number of neutrons in their nucleus. Most elements have more than one naturally occurring isotope. Many more isotopes have been produced in nuclear reactors and scientific laboratories.

Lithium. The lightest metal and the third lightest element. Lithium has two naturally occurring isotopes, lithium-6 and lithium-7. Lithium-6 targets are irradiated to manufacture tritium .

Low-level waste. Any radioactive waste that is not spent fuel, high-level, or transuranic waste .

Materials in inventory. Materials that are not currently in use (i.e., have not been used during the last year and are not expected to be used within the coming year) and have not been designated as waste or set aside by the Nuclear Weapons Council for national defense purposes. For nuclear materials, 'not currently in use' is synonymous with 'inactive' per DOE Order 5660.1B.

Mixed waste. Waste that contains both hazardous waste and source, special nuclear, or byproduct material subject to the Atomic Energy Act of 1954 .

National Environmental Policy Act (NEPA). A law that requires federal agencies to include in their decisionmaking processes appropriate and careful consideration of all potential environmental effects of proposed actions, analyses of the alternatives, and measures to avoid or minimize adverse effects of a proposed action. These analyses are presented in either an environmental assessment (EA) or in an environmental impact statement (EIS).

Neutralizing. The process of combining an acid with a caustic substance to reduce or eliminate the acidity or causticity.

Neutron. A massive, uncharged particle in the nucleus of an atom.

No radioactivity added policy. A Department of Energy policy forbidding the release of materials originating in radiological control areas unless they are proven to be uncontaminated.

Non-proliferation. Efforts to prevent or slow the spread of nuclear weapons and the materials and technologies used to produce them.

Nuclear reactor. A device that sustains a controlled nuclear fission chain reaction .

Nuclear weapons complex. The chain of foundries, uranium enrichment plants, reactors, chemical separation plants, factories, laboratories, assembly plants, and test sites that produced nuclear weapons. There were 16 major facilities in the U.S. nuclear weapons complex, located in 12 states.

Nucleus. The group of protons and neutrons at the center of an atom that determines its identity and chemical and nuclear properties.

Pit. The central core of a nuclear weapon consisting of a fissile materials surrounded by a sealed metal shell.

Plutonium. A man-made fissile element. Pure plutonium is a silvery metal that is heavier than lead. Material rich in the plutonium-239 isotope is preferred for manufacturing nuclear weapons, although almost any plutonium can be used.

Plutonium residues. Material left over from the processing of plutonium that contains too much plutonium to be disposed of as transuranic waste .

Production reactor. A nuclear reactor that is designed to produce man-made isotopes. Tritium and plutonium are made in production reactors. The United States has 14 such reactors: 9 at the Hanford Site and 5 at the Savannah River Site. Some research reactors are used to produce isotopes .

Radiation. Energy transferred through space or other media in the form of particles or waves.

Radioactive. Of, caused by, or exhibiting radioactivity .

Radioactivity. The spontaneous emission of radiation from the nucleus of an atom. Radionuclides lose particles and energy through this process of radioactive decay.

Radionuclide. A radioactive species of an atom. Tritium and uranium 235 are examples of radionuclides.

Radiological control area. An area containing or contaminated by radionuclides , to which access is controlled.

Record of Decision (ROD). The final determination of the preferred alternative that follows the consideration of public comment. RODs apply to both CERCLA and NEPA .

Reprocessing. Synonymous with chemical separation .

Research reactor. A class of nuclear reactors used to do research in nuclear physics, reactor materials and design, and nuclear medicine. Some research reactors also produce isotopes for industrial and medical use.

Resource Conservation and Recovery Act (RCRA). A federal law enacted in 1976 to address the treatment, storage, and disposal of solid and hazardous waste.

Sealed source. A small package of radioactive materials used as a portable source of radiation packaged to minimize possibility of dispersion of radioactive contents.

Shielding. Material such as lead, concrete, or water used to block or absorb radiation. Often placed between sources of radiation and people or the environment.

Spent nuclear fuel. Fuel elements and targets that have been irradiated in a nuclear reactor .

Stakeholder. Anyone interested in, or affected by, Department of Energy activities.

Superfund. A term commonly used to refer to the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) .

Target. Material placed in a nuclear reactor to be bombarded with neutrons. This is done to produce new, man-made radioactive materials. Targets of uranium-238 are used to make plutonium, and targets of lithium are used to make tritium .

Transuranic elements. All elements beyond uranium on the periodic table. All of the transuranic elements are manmade.

Transuranic waste. Waste contaminated with uranium-233 or transuranic elements having half-lives of over 20 years in concentrations more than 1 ten-millionth of a curie per gram of waste.

Tritium. The heaviest isotope of the element hydrogen. Tritium is three times heavier than hydrogen. Tritium is used to boost the explosive power of most modern nuclear weapons. It is produced in production reactors and has a half-life of over 12 years.

Uranium. The basic material for nuclear technology. It is a slightly radioactive naturally occurring heavy metal that is more dense than lead and 40 times more common than silver. The most common isotopes are uranium-235 and uranium-238.

Uranium enrichment. The process of separating the isotopes of uranium from each other done in the U.S. using the gaseous diffusion process.

Vitrification. A process that stabilizes nuclear waste by mixing it with molten glass. The glass is poured into metal canisters, where it hardens into logs. Plants for vitrifying high-level waste have been built in the United States at West Valley, NY and the Savannah River Site.

Volumetrically contaminated. Describes a material that has radioactive contamination throughout its volume as opposed to only on it surface.

Weapons-grade uranium. Uranium made up of over 90 percent of the fissile uranium-235 isotope.