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Nuclear Power Frequently Asked Questions


Nuclear Glossary

Here are a few commonly used words in the nuclear industry. Visit the NRC website for additional words and phrases. 


The smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core called a nucleus, which contains protons and neutrons. Electrons revolve in orbits in the region surrounding the nucleus.

Atomic Energy

Energy produced in the form of heat during the fission process in a nuclear reactor. When released in sufficient and controlled quantity, this heat energy may be used to produce steam to run a conventional turbine generator to produce electrical power. Atomic energy is more correctly called nuclear energy.

Background Radiation

Radiation in the environment from cosmic rays and radioactive material that naturally exists in soil, water and air. The amount of radiation a person gets is measured in millirems, and the average person receives about 360 millirems of radiation each year — about 80 % from natural sources and the rest from manmade sources.

Boiling Water Reactor (BWR)

A kind of commercial power reactor Duke Energy operates. The water flows upward through the core, where it is heated by fission and allowed to boil in the reactor vessel. The resulting steam then drives turbines, which activate generators to produce electrical power.

Capacity Factor

A measure of reliability, reflecting the amount of electricity a generating unit provides versus how much it could provide if operating at all times.

Combined Construction and Operating License (COL)

A license issued by the NRC authorizing a licensee to construct and operate a nuclear power plant at a specific site in accordance with established laws and regulations. A COL is valid for 40 years, with the possibility of a 20-year renewal.

Containment Building

The structure housing the nuclear reactor, pressurizer, reactor coolant pumps, steam generators and other associated piping and equipment. It is an airtight structure, steel-lined, with heavily reinforced concrete walls several feet thick. It is designed to withstand tremendous physical forces.

Control Rods

Rods made of material that absorbs neutrons. When inserted into the nuclear fuel, the rods stop the fission process, thereby shutting down the reactor.

Cooling Tower

A heat exchanger designed to aid in the cooling of water that was used to cool exhaust steam leaving the turbines of a power plant. Cooling towers transfer exhaust heat into the air, instead of into a body of water.


The central portion of a nuclear reactor, which contains the fuel assemblies, moderator, neutron poisons, control rods and support structures. The reactor core is where fission takes place.


The splitting of the atom, which releases tremendous amounts of heat energy.

Fuel Rod

A long, slender, zirconium metal tube containing pellets of fissionable material, which provides fuel for nuclear reactors. Fuel rods are assembled into bundles called fuel assemblies, which are loaded individually into the reactor core.

Pressurized Water Reactor (PWR)

The kind of commercial power reactor Duke Energy operates. The reactor heats water in a closed system that then transfers its heat to another closed system in the steam generators to produce steam for a turbine generator.


Particles and/or energy given off by unstable atoms as they undergo radioactive decay to stability.


A cylindrical, steel vessel that contains the core, control rods, coolant and structures that support the core.

Steam Generator

A large heat exchanger. In a pressurized water reactor, it’s the large steel tank where steam is produced. It is located inside the containment building.

Turbine Generator

A structure housing the steam turbine, electric generator and much of the feedwater system.


A critical element used in nuclear power reactors because of the ability of its atoms to undergo fission when it absorbs neutrons.