Magnox Reactors

Magnox reactors are pressurised, carbon dioxide-cooled, graphite-moderated reactors using natural uranium (i.e. not enriched) as fuel and magnox alloy as fuel cladding. Boron-steel control rods were used.

On power fuelling was an economically essential part of the design, to maximise power station availability by eliminating refuelling downtime. This was particularly important for Magnox as the unenriched fuel had a low burn-up, requiring more frequent changes of fuel than most enriched uranium reactors.

Early reactors have steel pressure vessels, while later units (Oldbury and Wylfa) are of reinforced concrete; some are cylindrical in design, but most are spherical.

Technical Features:

Steam Quality: There is very little difference in the steam conditions between the American light water reactor and the European gas cooled reactors. Both produced saturated steam at approximately the same temperature and pressure.
In gas cooled and pressurized water reactors, the steam systems were separate, non-radioactive systems, a feature that was a good selling point to customers concerned about the unknown dangers of radioactive contamination.



1. there was a view that gas reactors would eventually provide better steam conditions as material knowledge improved and as inert gas coolants like helium became more available.


2. Construction Costs:The Magnox reactors had low maximum fuel temperatures and low coolant heat transfer capability thereby were several times larger than a LWR with the same power output.


3. Magnox reactors required construction of large, high purity graphite structures with tight tolerances and very large, high quality pressure vessels. Being very large to transport were built at site.


4. LWR imposed different constraints. The reactor internals were also carefully manufactured components with tight tolerances, but were small enough to be produced in a factory for later transport . The pressure vessel that enclosed the reactor internals was a challenging component and required a large investment in specialized manufacturing equipment, but the final product was small enough to be transported provided there were rail or water routes available. So the manufacturers were interested in a large no of deals to get back their investment.


5. The fuel used in the Magnox reactors was natural uranium metal clad with Magnox alloy. Initially maximum burn-up obtainable was about 3000 MWD/ Te of heavy metal, but it improved to about 6000 MWD/ Te ton . In 1960, the cost per kilogram of Natural uranium $18.00.


6. The fuel for the light water reactors was uranium oxide with a U-235 concentration of 3 percent clad with either stainless steel or zirconium alloy. At first, the maximum burn-up for this fuel was about 5000 MW days per ton, but it improved to about 25,000 MW days per ton within a few years. In 1962, the cost per kilogram of 3 percent enriched uranium hexafluoride (the direct product of the enrichment plants) was listed by the AEC as $254.00.


7. Disposal Costs: The natural uranium reactors produced a larger volume of high/medium level waste because of larger reactors with lower burn-up fuel . This tended to raise the cost estimates for decommissioning those reactors. This factor was countered by longer plant life estimates based on the lower stresses and lower neutron irradiation of the pressure vessel. The waste volume could also be reduced by fuel material and moderator recycling.


8. Large PWR have a significant cost disadvantage compared to gas cooled reactors as the pressure vessels are more highly contaminated and normally had to be cut up before disposal. The barges and rail lines that delivered the vessel were frequently at their capacity limits in moving an empty vessel, there is little space or weigh capacity left for adding the shielding.


9. Gas cooled vessels will also have to be dismantled, but it is far easier to cut a steel wall that is <> vessels.