Editing Magnox (section)

===Windscale===
{{main|Sellafield}}
The UK's first full-scale [[nuclear reactor]] was the [[Windscale Piles|Windscale Pile]] in [[Sellafield]]. The pile was designed for the production of [[plutonium-239]] which was bred in multi-week reactions taking place in [[natural uranium]] fuel. Under normal conditions, natural uranium does not absorb enough of its own emitted "fast" [[neutron]]s to maintain a [[chain reaction]]. To improve the fuel's sensitivity to neutrons, a [[neutron moderator]] is used, in this case highly purified [[graphite]].<ref name=WNN>{{cite web |url=http://www.world-nuclear-news.org/WR_First_look_at_Windscale_pile_2108081.html |website=World Nuclear News |date= 21 August 2008 |title= First look at damaged Windscale pile}}</ref><ref name=WISE>{{cite web |title= Windscale Pile problems |date=27 June 2000 |url=https://www.wiseinternational.org/nuclear-monitor/532/windscale-pile-problems }}</ref>

The reactors consisted of a huge cube of this material (the "pile") made up of many smaller blocks and drilled through horizontally to make a large number of ''fuel channels''. Uranium fuel was placed in aluminium canisters and pushed into the channels in the front, pushing previous fuel canisters through the channel and out the back of the reactor where they fell into a pool of water. The system was designed to work at low temperatures and power levels and was air-cooled with the help of large fans.<ref name=WNN/><ref name=WISE/>

Graphite is flammable and presents a serious safety risk. This was demonstrated{{Dubious|Talk:Magnox#Windscale_fire|date=October 2023}} on 10 October 1957 when Unit 1 of the now two-unit site caught fire. The reactor burned for three days, and massive contamination was only avoided due to the addition of filtering systems that had previously been derided as unnecessary "[[John Cockcroft#Cockcroft's Folly|follies]]".<ref>{{cite web |title=Windscale Piles: Cockcroft's Follies avoided nuclear disaster |first= Duncan |last=Leatherdale |url=https://www.bbc.com/news/uk-england-cumbria-29803990 |website=BBC News |date=4 November 2014}}</ref>