Nuclear reactor

A nuclear reactor is a complex physical facility in which controlled nuclear reactions, generally involving criticality (nuclear), take place for a variety of purposes. These purposes may include heat generation for electrical generation, marine propulsion, or heating industrial plants; the preparation of radioactive isotopes for use in nuclear medicine, industrial testing, or creating controlled sources of radiation; production of nuclear materials such as plutonium or tritium; or making materials temporarily radioactive for procedures such as neutron activation analysis. While there can be some overlap of functions, larger reactors tend to be optimized for a single purpose; part of the design failures causing the Chernobyl Disaster were that the reactor tried to be equally effective for electric power and plutonium generation.

Cooling

Reactors of any appreciable size are liquid- or gas-cooled. The most common liquid coolant is highly purified water, or "light water" to differentiate it from heavy water. Heavy water cooling, which plays a part in moderation, has specific applications in reactors that produce plutonium or tritium. For some power producing reactors, there has been continuing experimentation with liquid sodium, which has advantages for heat transfer.

Surveillance

Reactors designated as being for peaceful purposes are under the inspection of the International Atomic Energy Agency, which makes physical inspections, and also installs unmanned but tamperproof seals on certain reactor components, as well as on-site cameras and other instrumentation.

Soviet plutonium-producing reactors released ₈₅krypton, detectable by air sampling.