Glossary of Nuclear Terms

Atom	the basic component of all matter, the smallest part of an element. Atoms are made up of protons, neutrons and electrons.
Background Radiation	the radiation present in the natural environment, including cosmic rays and other radiation from elements around and within the bodies of humans and animals.
Boron	a chemical element that absorbs neutrons, thus controlling or stopping a nuclear chain reaction.
Capacity	the amount of electric power a generating unit can produce.
Chain Reaction	a reaction that causes itself to repeat; the process by which atomic fission becomes self sustaining.
Condenser	a device used in power plants to extract heat from steam.
Containment Building	houses the reactor, pressurizer, reactor coolant pumps, steam generator and other equipment or piping containing reactor coolant. The containment building is an airtight structure made of steel-reinforced concrete. The base slab is approximately 9 feet thick; the vertical walls are 3 3/4 feet thick; and the dome is 3 feet thick.
Control Rod	a device that absorbs neutrons. When inserted into the nuclear fuel, the rods stop the fission process, which shuts down the reactor.
Control Room	the operation center of a nuclear power plant where the entire plant can be monitored and controlled.
Coolant	a fluid, usually water, circulated through the core of a nuclear power reactor to remove and transfer heat energy.
Cooling Tower	a large, tapered, hollow structure over a football field in height, open at each end. Water pumped midway up the tower falls through the open air to cool for reuse. A natural or mechanical draft moves extracted heat from the water upwards and pulls cooler air into the tower at its base.
Core	the central part of a nuclear reactor that contains the fuel assemblies and control rod assemblies. Nuclear fission takes place and heat is generated within the core.
Curie	the basic unit used to describe the strength of radioactivity in a sample of material.
Decommissioning	the process of closing down a nuclear reactor after its useful life has come to an end.
Decontamination	the removal of radioactive material.
Dose	the amount of radiation that a person has received, measured in millirems.
Dosimeter	a device which can be worn and used to measure the radiation a person receives over a period of time.
Fission	the nuclear process in which a heavy atom, such as uranium, splits into fragments.
Fuel Assemblies	a group of fuel rods. There are 157 fuel assemblies in the reactor vessel.
Fuel Pellets	thimble-sized uranium oxide pellets. A modern reactor core may contain up to 10 million pellets.
Fuel Rods	long, hollow tubes of zirconium metal that contain stacks of fuel pellets. There are 264 fuel rods in each fuel assembly.
Generator	device that converts the mechanical energy of the turbine into electrical energy.
Half-Life	the time required for half the atoms of a radioactive substance to disintegrate or the length of time it takes for a radioactive substance to lose one-half of its radioactivity. Radioactive isotopes have half-lives ranging from split seconds to thousands of years.
Kilowatt	a unit of electric energy equal to 1,000 watts.
Kilowatt-Hour	a unit of energy consumption that equals 1,000 watts used for one hour. For example, ten 100-watt light bulbs burned for one hour use one kilowatt-hour of electricity.
Megawatt	a unit of energy equal to 1,000 kilowatts (1 million watts).
Millirem	a measurement of the biological effects of different types of radiation equaling 1/1000th of a REM.
Moderator	a material used in a nuclear reactor to slow neutrons.
Monitored Retrievable Storage	a temporary (40 years) collection and storage facility for spent fuel rods until a permanent waste repository is available.
Neutron	a particle in the nucleus of an atom.
Nuclear Reactor	a device in which a chain reaction can be initiated, maintained and controlled.
Nuclear Regulatory Commission (NRC)	the federal government agency that regulates the nuclear power industry.
Nucleus	the central part of an atom.
Pressurized Water Reactor	a reactor in which water, heated by nuclear energy is kept at high pressure to prevent the water from boiling. Steam is then generated in a secondary loop.
Pressurizer	a high-strength tank containing steam and water used to control the pressure of the reactor coolant, or primary loop.
Radiation	energy released in the form of tiny particles or waves. Neutron radiation occurs when an atom splits. 1. Alpha radiation travels only a few inches in the air. It can be stopped by a sheet of paper. 2. Beta radiation, discharged from the nucleus of an atom, can be stopped by a thin sheet of metal. 3. Gamma radiation is caused by electromagnetic waves discharged from the nucleus of an unstable atom. It is basically the same as X-rays and can be stopped with lead or concrete.
Radioactivity	the property of an element to emit energy through disintegration of the nuclei of its atoms.
Reactor Core	the central portion of a nuclear reactor containing nuclear fuel, water and control mechanism as well as supporting structure.
Reactor Vessel	the steel pressure vessel that holds the fuel elements in a reactor.
REM (Roentgen Equivalent Man)	common unit for measuring human radiation doses, usually in millirems (1,000 millirems = 1 rem).
Shielding	material, such as lead or concrete, used around a nuclear reactor to prevent the escape of radiation and to protect workers and equipment.
Spent Fuel	is used nuclear fuel awaiting disposal.
Uranium	a radioactive element found in natural ores, the heaviest natural element. Uranium is the basic fuel of a nuclear reactor.