NNC Magnox

The 300 MW(e) plant, proposed by the National Nuclear Corp, (NNC), UK, Incorporates a natural uranium magnox reactor. The design is based upon that used for two magnox reactors at the Oldbury Station which have given continuous satisfactory service to the CEGB since they were commissioned in 1967. During 1980-81 the station achieved a load factor of 90.2 and the availability is now 90%. 

With the Magnox reactor, the spent fuel leaving the reactor is of low value and there is no need for re-processing. On-site fuel storage is also cheap. A substantial fraction of local supply and manufacture in the construction can be foreseen, as the reactor incorporates no strategic materials and does not call for particularly sophisticated engineering techniques either at the manufacturer s works or on the site. 

The plant is designed for on-load refuelling. Increasing the aluminium concentration in the uranium fuel rod to reduce the rate of swelling has permitted longer irradiation. An average discharge burnup of 5300 MWd/t without any limit on residence time in the reactor core is now achieved. 

One significant feature of the reference plant which has now been proposed to be changed is the replacement of mild steel with 9% Cr, steel for the superheater and re-heater tubes and boiler casings. This will enable the operating temperature to be raised from 365°C to 400°C, resulting in an increase in unit electrical output from 208 MW to 300 MW. 

The reactor has a pre-stressed concrete pressure vessel and several attractive safety features as well as other features to facilitate easier and quicker maintenance  

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