Nuclear reactor

A device that initiates and controls a sustained nuclear reaction, typically fission, to produce heat or neutron radiation.

Nuclear fission: The splitting of an atomic nucleus into lighter nuclei, releasing energy and often additional neutrons. Fission releases the heat and neutrons that sustain most power reactors.
Criticality (nuclear engineering): The condition in which each fission generation produces, on average, one further fission generation. A reactor operates near this balance to keep its chain reaction steady.
Nuclear power plant: A facility that uses one or more nuclear reactors to generate electricity. Power plants use reactor heat to drive turbines and produce electricity.
Pressurized water reactor: A reactor design that keeps water under high pressure to prevent boiling in the core. It is the most widely deployed commercial power-reactor design.
Neutron moderator: A material that slows neutrons through collisions without usually absorbing them. Slower neutrons make fission more likely in many reactor fuels.
Neutron cross section: A measure of the probability that a neutron will interact with a particular nucleus. Cross sections determine how fuel, moderators, and absorbers affect reactor behavior.
Research reactor: A nuclear reactor primarily designed to provide neutrons for research, training, or isotope production. Research reactors prioritize neutron flux and experimental access over electricity generation.
Boiling water reactor: A reactor design in which water boils in the core and the resulting steam drives a turbine. It contrasts with pressurized-water designs by sending core-generated steam directly to the turbine.
Nuclear reactor core: The region of a reactor containing nuclear fuel and the materials that support the chain reaction. The core is where the controlled chain reaction takes place.
Nuclear fuel: Material containing fissile or fertile nuclides that can support energy production in a nuclear reactor. Fuel composition sets the reactor's energy source and neutron economy.

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