Sellafield is the site of Britain's worst nuclear accident. A blaze in 1957 in the reactor of Pile 1 released a massive plume of radioactive caesium, iodine and polonium that spread across Britain and northern Europe.
Up to 200 cases of cancer - including thyroid and breast cancer and also leukaemia - may have been triggered by the fire's emissions, according to estimates which were published by epidemiologists led by Professor Richard Wakeford, of Manchester University, two years ago.
The fire occurred when graphite rods used to control reactions in the nuclear plant's core caught fire. For two days, the core blazed out of control. At one point workers used sledgehammers to try to knock the damaged, highly radioactive fuel rods out of the reactor before eventually managing to extinguish the blaze.
After the fire the government placed a six-week ban on consumption of milk from cows grazing within 200 miles of Windscale (as Sellafield was then known). However, the weather carried nuclear contamination far beyond that boundary.
The reactor was left in such a dangerous state of intense radioactivity that it has lain undisturbed ever since and is still considered too dangerous to decommission. As a result, Pile 1 is destined to be one of the last sites to be cleaned up during the decommissioning of Sellafield. "The plant was a primitive piece of equipment," says Wakeford. "We should never forget that." However, its companion reactor, Pile 2, is now being successfully dismantled and its radioactive parts rendered safe.
This has not been the only major accident to occur at the site. On 19 April 2005, 83,000 litres of radioactive waste was found to have leaked from Sellafield's Thorp reprocessing plant. No radiation entered the environment and no one was injured, it is believed. In addition, during the early years of its operation, radioactive waste from its reprocessing centres was diluted and discharged by pipeline into the Irish Sea. It is thought that around 200 kg of plutonium was deposited in the marine sediments as a result of these releases, triggering furious complaints from the Irish government at the time.
In 1983, British Nuclear Fuels Limited, or BNFL, which was then the operator of the Sellafield plant, was fined £10,000 after radioactive discharges containing ruthenium and rhodium 106 were found to have contaminated a beach near the power station.
The plant - which was originally expected to make profits of around £500m for Sellafield's operators - is now expected to make losses of up to £1bn and has been earmarked for closure by the year 2010.