In the UK, the preferred method for handling discharged fuel has been to store it underwater in fuel cooling ponds. The reactivity of the cladding requires an elevated pH to prevent corrosion, and the usual method is to dose with sodium hydroxide to a pH of around 11. Reduction of corrosion and removal of decay heat requires cooling plant, with typical operating temperatures of around 13 °C.

Many early Magnox reactor sites had open-air cooling ponds. This led to problems of control of pond conditions, and admission of debris in the form of atmospheric dust and bird guano. High winds at coastal sites led to foaming of the water surface and airborne activity being released from the pond to the surrounding land. As a consequence, the ponds were eventually all roofed.

The ponds were equipped with clean-up plant to remove particulate and dissolved activity. Typical plant comprised sand pressure filters for removal of solids (magnesium and aluminium hydroxides and the, fission product strontium) and ion exchange beds for removal of (principally) caesium isotopes.

Chapelcross Power Station did not chemically dose its ponds, but relied on corrosion of the fuel cladding to raise the pH. It was unique in that each of its two ponds was emptied for cleaning on a two-yearly cycle, and radio-caesium levels were controlled by pumping water through in-pond enclosed skips filled with zeolite.

In later years, several fuel storage ponds were equipped with in-pond IONSIV units. These comprised a pumped ion exchange resin cartridge with an extremely high degree of affinity for caesium, equipped with a pre-filter to remove particulate and a post-filter to prevent highly active resin fines being returned to the pond. These have been very successful in controlling water activity levels.

Fuel storage was in open-topped boxes (skips), designed to fit into transport flasks to enable the fuel to be removed to the Sellafield reprocessing plant. (Hinkley Point A had a unique design of storage skip, necessitating transfer to a transport skip). Other than at Hunterston A, which used aluminium skips, all skips were made of painted mild steel.

UK Magnox ponds were equipped with machinery for removing splitters or lugs from the fuel, enabling a higher density of packing in the transport skips. A variety of designs of desplittering or delugging machine were used, some more successfully than others. Desplittering machines fell into two categories: ram-and-die, in which the fuel element was forced through a die thereby removing splitters or lugs, and designs in which jaws closed around the fuel element, severing the bands holding the splitter cage assemblies, which then sprang off. The latter designs were by-and-large good at avoiding fuel damage; however, the ram-and-die machines frequently damaged the end fittings of fuel elements, leading to exposure of fuel or breaking of the fuel element. Later designs of ram — and-die machine used a split die, which opened as the end fitting passed, thereby reducing the potential for damage.

Fuel element debris (FED), comprising splitter cages or lugs, frequently with end fittings containing Nimonic springs and occasionally fuel fragments, was removed for storage in FED vaults. The Nimonic springs in particular were highly active, each containing Co-60 at GBq levels, resulting in handling challenges for the stored FED.

Difficulties in desplittering, and transport issues, led to large backlogs of fuel in some Magnox ponds. As a consequence, extensive fuel corrosion was an issue at many sites, with the ponds becoming highly contaminated, and access to the pond environment requiring respiratory protection.

Wylfa Power Station was unique in the UK in having dry fuel storage facilities. Discharged fuel was initially stored in large carousels cooled under a CO2 atmosphere, before being moved to a longer term air-cooled store in skips similar to those used in ponds. Problems of fuel corrosion under water were thereby avoided, along with the much reduced need for water treatment plant and reduced arisings of mobile wastes (sludges and resins).