Nuclear Terms

Operations at Callaway Energy Center 
Background radiation
Radiation that is constantly present in the environment and is emitted from a variety of natural and artificial sources. The average American receives radiation exposure of about 620 millirem (mrem) annually, according to the National Council on Radiation Protection and Measurements.

Chain reaction

The continuous splitting of uranium atoms. This process is controlled in the reactor.


The metal (a zirconium alloy) surrounding the uranium fuel, acting as a barrier between the fuel and the water in the reactor coolant system.


Radioactive material, where it is not desired.

Control rods

Metal rods placed between the fuel rods to absorb neutrons and control the fission process. When inserted into the reactor core, the reactor quickly shuts down.

Control Room

The center from which the nuclear plant is operated, monitored and controlled. Operators licensed by the U.S. Nuclear Regulatory Commission are on duty at all times.


The central part of a nuclear reactor containing the fuel assemblies.


The removal of radioactive material.

Emergency Core Cooling System

An important back-up safety system for a nuclear power plant. It provides cooling water for the reactor if the primary cooling system is not operating.

Emergency Planning Zone (EPZ)

The area around a nuclear power plant for which plans are developed for public protection in the event of a nuclear accident. The zone covers approximately a 10-mile radius from the facility. View a map of the Callaway Energy Center Emergency Plant Zone.

Federal Emergency Management Agency (FEMA)

An agency of the federal government charged with establishing policy for and coordinating all civil emergency planning and assistance functions for other federal agencies.


The splitting of an atom into two or more new atoms. When a uranium atom splits in the reactor, two new atoms, neutrons and heat are produced.

Fuel rod

A cylindrical rod, 12 feet long, containing uranium fuel pellets.

Ingestion Exposure Pathway EPZ

The area within a 50-mile radius of the Callaway Energy Center in which people may be indirectly exposed to radiation by eating or drinking contaminated food, milk and water, if radioactive material was released in a nuclear emergency.

Millirem (mrem)

Unit used to measure radiation dosage (1/1000 of a REM). REM stands for Roentgen Equivalent Man, a measure of radiation that indicates potential impact on the human body.

Nuclear Regulatory Commission (NRC)

Agency of the federal government responsible for regulating and inspecting nuclear plants.

Plume Exposure Pathway EPZ

The area within a 10-mile radius of the Callaway Energy Center in which people may be directly exposed to radiation if radioactive material was released in a nuclear emergency.

Primary coolant

Water which passes through the reactor vessel, picking up heat from the nuclear fuel.


The property possessed by some elements which enables them to give off energy in the form of particles or waves.


The large steel vessel in a nuclear power plant containing fuel assemblies, primary coolant and other equipment. The fissioning (or splitting) of atoms is controlled within the reactor.

Reception and Care Centers

Centers providing food and shelter to residents of evacuated areas in the event of a nuclear emergency. The centers are operated by the State of Missouri with assistance from the American Red Cross.


Process of reducing environmental radiation to normally acceptable levels following a nuclear emergency.


Temporary return under controlled conditions, into a restricted, contaminated area with the 10-mile EPZ following a nuclear emergency.


See "millirem."


Comprises the various materials within a nuclear power plant, preventing radiation from escaping into the environment. Shielding can be steel, lead, concrete or water.
State Emergency Management Agency (SEMA)

Missouri state government agency responsible for development and implementation of procedures to protect the public during natural or other emergency conditions.


Specific geographical areas within the EPZ, used in providing protective action recommendations to the public.

Used Fuel

High-level radioactive waste from nuclear power plants, also known as spent fuel.
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