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Nuclear glossary

More material still to be added. Email any questions on definitions to Dr. Gonzo. They will be addressed on this page soon.

The NRC keeps a comprehensive glossary online, many of the definitions here were culled from it. For our purposes definitions included have context within the nuclear emergencies database. Where ever possible the definition is linked to its source.

Annuciator: alarm panels usually located along the top of the main control board to alert the operators to potential equipment problems or unusual conditions.

Alert:If an alert is declared, events are in process or have occurred which involve an actual or potential substantial degradation in the level of safety of the plant. Any releases of radioactive material from the plant are expected to be limited to a small fraction of the Environmental Protection Agency (EPA) protective action guides (PAGs).

Busbar: In electric utility operations, a busbar is a conductor that serves as a common connection for two or more circuits. It may be in the form of metal bars or high-tension cables.

Control Rod: A rod, plate, or tube containing a material such as hafnium, boron, etc., used to control the power of a nuclear reactor. By absorbing neutrons, a control rod prevents the neutrons from causing further fissions.

Drywell: The containment structure enclosing a boiling water reactor vessel and its recirculation system. The drywell provides both a pressure suppression system and a fission product barrier under accident conditions.

Emergency Classification: An Emergency Classification is a set of plant conditions which indicate a level of risk to the public. Both nuclear power plants and research and test reactors use the four emergency classifications listed below in order of increasing severity. The vast majority of events reported to the NRC are routine in nature and do not require activation of our incident response program.

Emergency Core Cooling Systems (ECCS): Reactor system components (pumps, valves, heat exchangers, tanks, and piping) that are specifically designed to remove residual heat from the reactor fuel rods should the normal core cooling system (reactor coolant system) fail.

General Emergency: A general emergency involves actual or imminent substantial core damage or melting of reactor fuel with the potential for loss of containment integrity. Radioactive releases during a general emergency can reasonably be expected to exceed the EPA PAGs for more than the immediate site area.

Reactor Coolant System (RCS): The system used to remove energy from the reactor core and transfer that energy either directly or indirectly to the steam turbine.

Scram: The sudden shutting down of a nuclear reactor, usually by rapid insertion of control rods, either automatically or manually by the reactor operator. May also be called a reactor trip. It is actually an acronym for “safety control rod axe man,” the worker assigned to insert the emergency rod on the first reactor (the Chicago Pile) in the U.S.

Site Area Emergency: A site area emergency involves events in process or which have occurred that result in actual or likely major failures of plant functions needed for protection of the public. Any releases of radioactive material are not expected to exceed the EPA Protective Action Guidlines (PAGs) except near the site boundary.

Spent Fuel Pool: An underwater storage and cooling facility for spent (used) fuel elements that have been removed from a reactor.

Turbine: A rotary engine made with a series of curved vanes on a rotating shaft, usually turned by water or steam. Turbines are considered the most economical means to turn large electrical generators.

Trip (reactor): A term that is used by pressurized water reactors for a reactor scram (see Scram).

Unusual Event: Under this category, events are in process or have occurred which indicate potential degradation in the level of safety of the plant. No release of radioactive material requiring offsite response or monitoring is expected unless further degradation occurs.

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