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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 teep o nuclear pouer/production reactor that was designed tae run on natural uranium with graphite as the moderator an caurbon dioxide gas as the heat exchange coolant. It belongs tae the wider class o gas cooled reactors. The name magnox comes from the magnesium-alumeenium alloy used tae clad the fuel rods inside the reactor. Like a nummer o other "Generation I nuclear reactors", the Magnox was designed with the dual purpose o producin electric pouer and plutonium-239 for the nascent nuclear wappens programme in Breetain. The name refers specifically tae the Unitit Kinrick design but is sometimes used generically tae refer tae any similar reactor.

Like other plutonium-producin reactors, conservin neutrons is a key element o the design. In Magnox, the neutrons are moderated in large blocks o graphite. The efficiency o graphite as a moderator allows the Magnox tae run usin natural uranium fuel, in contrast tae the more common commercial light watter reactor which requires slightly enriched uranium. Graphite oxidizes readily in air, so the core is cooled bi caurbon dioxide (CO2), which is then pumped in tae a heat exchanger tae generate steam tae drive conventional steam turbine equipment for pouer production.

The "dual use" capability o the Magnox design led tae the UK buildin up a large stockpile o fuel grade/"reactor grade" plutonium, with the aid of the B205 reprocessin facility. The Low-to-interim burnup feature o the reactor design would become responsible for changes to US regulatory classifications after the US-UK "Reactor-grade" plutonium detonation test o the 1960s. Despite improvin its electricity generating capabilities in later decades, marked bi the transition to electric-power becomin the primary operational aim, Magnox reactors were never capable of consistently generating high efficiency/high fuel "burn-ups" due to the handicap of its design an natural uranium heritage, compared with pressurized watter reactors, the most widespread power reactor design.

In total, only a few dozen reactors o this teep were constructed, most o them in the Unitit Kinrick from the 1950s tae the 1970s, with very few exported tae other kintras. The first Magnox reactor tae come online was Calder Hall (at the Sellafield site) in 1956, frequently regarded as the "first commercial-scale electricity producing reactor in the world", while the last in Breetain tae shut down was Reactor 1 at Wylfa Nuclear Pouer Station in 2015. North Korea remains the only operator tae continue usin Magnox style reactors as o 2016, at the Yongbyon Nuclear Scientific Research Center. The Magnox design was superseded by the Advanced Gas-cuiled Reactor, which is similarly cuiled but includes a nummer o changes tae improve its economic performance.