Nuclear Energy Education Resource Hub

Chain reaction — a nuclear reaction that initiates a series of subsequent reactions.

Cold shutdown — when the cooling-water temperature in the reactor is below the boiling point and the pressure is reduced to atmospheric pressure.

Coolant — a fluid, usually water, used to cool a nuclear reactor and transfer heat energy. 

Containment — the steel and concrete structure, along with the various components, that surround and isolate the reactor. 

Contamination — the presence of unsealed sources of radioactive material in a place where it is not desired.

Control rods — movable rods used to slow down or stop a nuclear chain reaction. 

Core — the central part of a nuclear reactor that contains the fuel assemblies.

Curie — the basic unit used to describe the strength of radioactivity in a sample of material.

Dosimeter — a device that can be worn and used to measure the radiation a person receives over a period of time.

Emergency Core Cooling System — an emergency system designed to return coolant to the reactor core if coolant is lost.

Emergency Planning Zone (EPZ) — the 10-mile area around the plant. This area is required to have special emergency plans.  

Fission — the splitting or breaking apart of atoms into two or more new atoms. The process releases energy and produces heat. 

Fuel assemblies — a group of fuel rods.

Fuel pellets — pencil eraser-sized uranium oxide pellets. A reactor core may contain millions of pellets.

Fuel rods — long, hollow tubes of zirconium metal that contain stacks of fuel pellets.

Half-life — the length of time it takes for a radioactive substance to lose one-half of its radioactivity.

Millirem — a unit used to measure radiation dose.

Nuclear Regulatory Commission (NRC) — the government agency that regulates the nuclear power industry.

Plume — something such as smoke, steam or water that rises into the air in a tall, thin shape.

Radiation — energy released in the form of tiny particles or electromagnetic waves. Radiation is also emitted when you have a medical x-ray.

Reactor core — the central portion of a nuclear reactor containing nuclear fuel, water and the control mechanism, as well as the supporting structure.

Reactor trip (SCRAM) — refers to the insertion of control rods into the fuel core of the reactor, stopping the fission process.

Reactor vessel — the thick steel vessel that contains the fuel, control rods and coolant. 

Roentgen Equivalent Man (REM) — common unit used for measuring human radiation doses, usually in millirem (1,000 millirem = 1 rem).

Shielding — any material, such as lead or concrete, used around a nuclear reactor to protect workers and equipment.

Spent fuel — Nuclear reactor fuel that has been used to the extent that it can no longer effectively sustain a chain reaction.

Uranium — a radioactive element found in natural ores. Uranium is the basic fuel of a nuclear reactor.