Magnox Reactors

Magnox technology was developed in the UK in the 1940s and 1950s and has remained almost exclusively in the UK; although reactors were sold to Italy and Tokai Mura in Japan. The Magnox reactor utilises natural uranium and as such does not require enrichment services - a real selling point to the UK in the 1940s and 50s.

The fuel for Magnox reactors is natural uranium metal encased in a Magnesium Non Oxidising (Magnox) alloy. These elements are stacked in a graphite core and cooled by carbon dioxide gas at 20 bar pressure (290 psi). The graphite acts as the moderator, and the carbon dioxide gas as the coolant. The heat from the fission reaction is removed by the carbon dioxide gas, circulated by large fans around the core; passing through giant boilers. Pure water enters these boilers and is turned into steam.

This steam is passed to the turbine, whose windmill like blades rotate when the steam hits them. In the UK, the turbine turns at 3000 revolutions per minute (the blades spin so quickly that the tips travel at twice the speed of sound). In France, turbines spin at 1500 rpm, and at 1800 rpm in North America. Click here to find out why. Once the steam has passed through the turbines it is drawn into a condenser below the turbine which is held under vacuum. In the condenser are thousands of small tubes, inside which flows cool lake, river or sea water. The vacuum and cooling tubes condense the steam back to water whereupon it is purified and pumped back to the boilers using large feed pumps.

The spinning turbine is coupled to a large electromagnet which spins inside a large coil of copper wire. As Michael Faraday discovered in the 1800s, this produces electricity which is fed out from the station and along transmission lines to homes, schools and industry.

The world's first commercial nuclear power station at Calder Hall was a four unit Magnox power station, which is now being decommissioned. Click here to see a video of the cooling towers being demolished (note this is an external website). 22 Magnox reactors were built in the UK across 10 stations. Currently, only 2 stations are in operation at Oldbury in the South West and Wylfa in North Wales, operated by Magnox North (click here to visit their website), the remainder being decommissioned.

Left: A cutaway model of one of Chapelcross' Magnox Reactors. Photograph taken at the Science Museum, London.