Reactor

A reactor is a device or system in which a controlled transformation takes place, most commonly a chemical reaction or a nuclear fission process. Reactors are designed to manage reaction rates, heat generation, and safety, and they are used in power generation, manufacturing, and research.

In a nuclear reactor, fissile material sustains a fission chain reaction that releases heat, which is typically converted to electricity. The core contains fuel assemblies, moderators to slow neutrons, and control rods to adjust reactivity. Coolant removes heat and provides radiation shielding. Containment structures limit releases in accidents. Designs include light-water reactors (pressurized and boiling) and heavy-water reactors; fast reactors use a different neutron spectrum and no moderator. Safety systems, proper siting, and regulatory oversight govern operation and decommissioning.

In chemical and biochemical applications, reactors are vessels or systems that convert reactants into products under controlled conditions. Batch reactors operate in discrete runs; continuous stirred-tank reactors and plug-flow reactors are common for steady production. Key concerns include reaction kinetics, heat transfer, mass transfer, catalysis, and mixing. Bioreactors use living organisms or enzymes to produce pharmaceuticals, fuels, or food ingredients, with emphasis on sterility, oxygen transfer, and shear control.

Other uses include plasma and materials-processing reactors, as well as research devices used in physics experiments. The term is also used metaphorically to describe components in software and systems engineering that process inputs to outputs. Across disciplines, reactor design balances efficiency, safety, and cost while complying with regulatory standards.