Magnox stations generate a number of waste streams characteristic of their type.

‘Mobile’ wastes comprise mainly resins used for pond and waste water treatment; sludges from backwashing of filters, especially those used in the pond water clean-up plant and composed largely of hydrides of magnesium and aluminium, and tritiated desiccants from the coolant treatment plant.

Solid wastes include activated components (e. g. flux-flattening bars, fuel grabs, control rod assemblies); fuel element debris (FED) from the removal of fuel splitters or lugs; and in some reactors graphite sleeves or struts forming part of each fuel element. At some sites, the solid waste vaults contain a very heterogeneous mix of components giving major challenges to processing and packaging.

On many sites, the pond may have become heavily contaminated with fuel corrosion products due to extended storage of fuel or poor control of pond water chemistry. This can result in fission product/fissile contamination of components in contact with the pond water, including skips, FED and filtration plant.

Waste disposal of intermediate level wastes (ILW) in the UK is mostly through encapsulation in cementitious grout in stainless steel packages, for eventual despatch to an ILW repository. The lack of a currently available ILW repository has led to the construction of on-site stores for ILW packages. Low level wastes (LLW) are sent from site to the UK’s Low Level Waste Repository although other options are being explored, including controlled landfill for lower activity LLW, recycling and smelting of contaminated steels and on-site disposal by burial of LLW.

At Dungeness A, FED, which comprises mostly Magnox material, has been dissolved in carbonic acid and routed to a liquid effluent stream that, after a clean-up, is discharged to the sea. The Magnox itself is a low specific activity material, although higher activity components (such as Nimonic springs) and particulates (e. g. pond sludge containing fuel particles) may be associated with it and require separation. Similar dissolution plants are being considered at other sites.

In the UK, the current philosophy for decommissioning Magnox reactors is to defer final demolition:

• remove the fuel

• decommission plant outside the bioshield, and empty waste vaults

• put the reactor into a period of care and maintenance

• demolish the remaining structures

The advantage of the long period of care and maintenance is that shorter-lived radionuclides (such as the strong gamma emitter Co-60, half-life 5.27 years) will have largely decayed, until external dose rates are dominated by much longer — lived nuclides such as Nb-94 and Ag-108. After 100 years the activity level of Co-60 will have dropped by a factor of a million, enabling manned working in the reactor core. There is little benefit to radiation protection from further delay to final decommissioning.

In France, more rapid programmes for Magnox decommissioning are being considered, using remote dismantling in air or in a water-flooded reactor.