Editing Magnox (section)

{{Short description|Type of nuclear reactor}}
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{{Use dmy dates|date=January 2020}}
[[Image:Magnox reactor schematic.svg|thumb|350px|Schematic diagram of a magnox nuclear reactor showing gas flow. The heat exchanger is outside the concrete radiation shielding. This represents an early Magnox design with a cylindrical, steel, pressure vessel.]]

'''Magnox''' is a type of [[nuclear reactor|nuclear power / production reactor]] that was designed to run on [[natural uranium]] with [[graphite-moderated reactor|graphite as the moderator]] and [[carbon dioxide]] gas as the [[heat exchanger|heat exchange]] coolant. It belongs to the wider class of [[gas-cooled reactor]]s. The name comes from the [[magnesium]]-[[aluminium]] [[Magnox (alloy)|alloy]] (called '''mag'''nesium '''n'''on-'''ox'''idising), used to clad the [[fuel rod]]s inside the reactor. Like most other [[Generation I reactor|generation I nuclear reactors]], the magnox was designed with the dual purpose of producing [[electrical power]] and [[plutonium-239]] for the [[Nuclear weapons and the United Kingdom|nascent nuclear weapons programme in Britain]]. The name refers specifically to the United Kingdom design but is sometimes used generically to refer to any similar reactor.

As with other plutonium-producing reactors, conserving [[neutron]]s is a key element of the design. In magnox, the [[Neutron moderator|neutrons are moderated]] in large blocks of [[graphite]]. The efficiency of graphite as a moderator allows the magnox to run using natural uranium fuel, in contrast with the more common commercial [[light-water reactor]] which requires slightly [[enriched uranium]]. Graphite oxidizes readily in air, so the core is cooled with CO<sub>2</sub>, which is then pumped into a [[heat exchanger]] to generate [[steam]] to drive conventional [[steam turbine]] equipment for power production. The core is open on one end, so fuel elements can be added or removed while the reactor is still running.

The [[Dual-use technology|dual-use]] capability of the magnox design led to the UK building up a large stockpile of [[Reactor-grade plutonium#Classification by isotopic composition|fuel-grade]] (reactor-grade) plutonium, with the aid of the [[B205|B205 reprocessing facility]]. The low-to-interim [[burnup]] feature of the reactor design would become responsible for changes to US regulatory classifications after the US–UK [[Reactor-grade plutonium#.22Reactor-grade.22 plutonium nuclear tests|reactor-grade plutonium detonation test]] of the 1960s. Despite improvements to the design in later decades as electricity generation became the primary operational aim, magnox reactors were never capable of competing with the higher efficiency and higher fuel [[burnup]] of [[pressurised water reactor]]s.

In total, only a few dozen reactors of this type were constructed, most of them in the UK from the 1950s to the 1970s, with very few exported to other countries. The first magnox reactor to come online was [[Sellafield#Calder Hall nuclear power station|Calder Hall]] (at the [[Sellafield]] site) in 1956, frequently regarded as the world's first commercial nuclear power station,<ref name=pathe-2011>{{cite AV media |url=https://www.britishpathe.com/programmes/day-that-shook-the-world/episode/asc/playlist/39 |title=A Day That Shook the World : First Nuclear Power Station 1956 |last=Humphrys |first=John |publisher=British Pathe |year=2011 |access-date=2 January 2023}}</ref> while the last in Britain to shut down was Reactor 1 in [[Wylfa Nuclear Power Station|Wylfa]] (on [[Anglesey]]) in 2015. {{As of|2016}}, [[North Korea]] remains the only operator to continue using magnox style reactors, at the [[Yongbyon Nuclear Scientific Research Center]]. The magnox design was superseded by the [[advanced gas-cooled reactor]], which is similarly cooled but includes changes to improve its economic performance.