The eleven Magnox nuclear power stations have provided a significant proportion of the electricity generated in the UK over the past 40 years, with magnesium alloys being used exclusively as a canning material in the core of the gas cooled, graphite moderated reactors.
The reactors contain fuel elements that consist of bars of uranium contained within finned magnesium cans. A controlled chain reaction involves naturally occurring U235 atoms undergoing spontaneous fission, giving rise to neutrons which themselves trigger the fission of other U235 atoms. Carbon dioxide gas flows through the channels, extracting heat from the fuel elements and passing it on to the steam generating plant.
With natural uranium as a fuel, it is essential to select a canning material that does not readily absorb neutrons. The choice of magnesium over other materials was based upon the following advantages:
- Small tendency to absorb neutrons
- Magnesium does not alloy with uranium
- Adequate resistance to carbon dioxide at service temperatures of 450°C - 500°C
- Good thermal conductivity
- Good creep ductility properties
- Excellent machining characteristics
- Lightweight for ease of handling
The unique properties required from a canning material required extensive research to develop a suitable range of magnesium alloys. Magnesium Elektron played a central role in the development of the canning alloys and today supplies extruded bar, strip and semi-fabricated components in the alloys AL80, ZR55, MN80 and MN150.