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Nuclear Terminology

In our communication efforts at Westinghouse, we endeavor to clarify terms unique to the nuclear power industry. Sometimes, though, it may be convenient to have a glossary. Here are a few terms and some links that may help you.

Boiling Water Reactor (BWR) — A nuclear reactor in which water is boiled in the reactor vessel; the resulting steam drives a turbine to generate electricity

Cladding — Tubing, usually an alloy of zirconium, which encapsulates nuclear fuel pellets in a reactor core

Coolant — A fluid, usually water, used to cool a nuclear reactor and transfer heat energy. The water also moderates, or slows down, the fission of neutrons

Criticality — The condition at which a nuclear reactor is just capable of sustaining a chain reaction

Enriched Fuel — Uranium that has been modified by increasing the concentration of the fissionable isotope U-235

Fuel Cycle — The sequence of steps involved in supplying, using, and disposing of the fuel used in nuclear reactors

Half-life — The time during which any radioactive substance will lose one-half of its radioactivity

Megawatt — A measure of electrical power equal to one million watts

Pressurized Water Reactor (PWR) — 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

Spent Fuel — Nuclear fuel, containing fission products, which can no longer economically sustain a chain reaction

Some terms commonly encountered in describing PWR technology that may be of use include:

Fuel Rod/ Fuel Assembly — A cylindrical rod, 12 to 14 feet in length, made up of fuel pellets containing enriched uranium in cladding. Fuel rods are bundled into fuel assemblies

Core — The central heat-producing part of a nuclear reactor which contains the fuel assemblies

Control Rod — A device in the core of a reactor which absorbs neutrons, and is used to control the rate of fission and to stop the chain reaction

Primary Loop — A closed system which provides cooling water to the reactor and transfers heat to the secondary loop

Reactor Coolant Pump — A piece of equipment designed to move the coolant through the primary loop so that the heat generated in the core can be transferred to the steam generator

Reactor Vessel — A cylindrical steel vessel that contains the core, control rods, coolant, and the structures that support the core

Secondary Loop — A system of piping that carries non-radioactive water, which then absorbs heat through steam generator tubes, is boiled and, as steam, is used to spin the turbines

Steam Generator — A piece of equipment within which heat is generated from the primary loop to the secondary loop without the water of the two systems actually touching

Pressurizer — A high-strength tank containing steam and water used to control the pressure of the reactor coolant in the primary loop

Containment Building — Houses the reactor, pressurizer, reactor coolant pumps, steam generators, and other equipment or piping containing reactor coolant.

These terms, and many others, can be found in a Nuclear Energy Glossary available from Westinghouse.

There is also a comprehensive glossary of nuclear terms available through the United States Nuclear Regulatory Commission Web site.

For more general information on the nuclear power industry, please refer to the Nuclear Energy Institute Web site.

Westinghouse Electric Company