Glossary of Terms

(Other industry terms can be found at the bottom of the page)

ANS American Nuclear Society

Actinide An element with atomic number of 89 (actinium) to 103. Usually applied to those above uranium – 93 up (also called transuranics). Actinides are radioactive and typically have long half-lives. They are therefore significant in wastes arising from nuclear fission, e.g. used fuel. They are fissionable in a fast reactor.  Minor actinides are americium, curium and neptunium.

BOP Balance of Plant

Base load That part of electricity demand, which is continuous, and does not vary over a 24-hour period. Approximately equivalent to the minimum daily load.

Boiling water reactor (BWR) A common type of light water reactor (LWR), where water is allowed to boil in the core thus generating steam directly in the reactor vessel; the resulting steam drives a turbine to generate electricity.

CRADA Cooperative Research and Development Agreement

Chemical Recombination Following an ionization event, the positively and negatively charged ion pairs may or may not realign themselves to form the same chemical substance they formed before ionization. Thus, chemical recombination could change the chemical composition of the material bombarded by ionizing radiation.

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

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; 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.

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.

Combined License An NRC-issued license that authorizes a licensee to construct and (with certain specified conditions) 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). For additional detail, see Combined License Applications.

Condensor A large heat exchanger designed to cool exhaust steam from a turbine below the boiling point so that it can be returned to the heat source as water. In a pressurized-water reactor, the water is returned to the steam generator. In a boiling-water reactor, it returns to the reactor core. The heat removed from the steam by the condenser is transferred to a circulating water system and is exhausted to the environment, either through a cooling tower or directly into a body of water.

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

DARPA Defense Advanced Research Projects Agency

DCD Design Certification Document

Design Certification Certification and approval by the NRC of a standard nuclear power plant design independent of a specific site or an application to construct or operate a plant. A design certification is valid for 15 years from the date of issuance but can be renewed for an additional 10 to 15 years. For additional information, see the Backgrounder on New Nuclear Plant Designs and Design Certification Applications for New Reactors.

DOD Department of Defense (U.S.)

DOE Department of Energy (U.S.)

EPR Enhanced Power Reactor

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.

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.

G4M Gen4 Module

GW Gigawatt

GWh Gigawatt hour

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

IAEA International Atomic Energy Agency

KWh Kilowatt hour

LANL Los Alamos National Laboratory

LBE Lead Bismuth Eutectic

LWR Light Water Reactor

MA Marketing Agent

MPR Mini power reactor

MWe Megawatts electric

MWt Megawatts thermal

Megawatt (MW) A measure of electrical power equal to one million watts

NEA Nuclear Energy Agency

NEI Nuclear Energy Institute

NPP Nuclear Power Plant

NRC/U.S. NRC United States Nuclear Regulatory Commission

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

Pressurized Water Reactor (PWR) -A common nuclear power reactor design in which very pure water is heated to a very high temperature by fission, kept under high pressure (to prevent it from boiling), and converted to steam by a steam generator (rather than by boiling, as in a boiling-water reactor). The resulting steam is used to drive turbines, which activate generators to produce electrical power. A pressurized-water reactor (PWR) essentially operates like a pressure cooker, where a lid is tightly placed over a pot of heated water, causing the pressure inside to increase as the temperature increases (because the steam cannot escape) but keeping the water from boiling at the usual 212°F (100°C). About two-thirds of the operating nuclear reactor power plants in the United States are PWRs. For additional detail, see Pressurized Water Reactors (PWRs).

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.

SMR Small medium reactor

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.

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

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.

UN Fuel Uranium Nitride

Additional Glossary Resources