Four other workers were also involved, and one was feared to have absorbed the potentially lethal element, which provides a nuclear weapon's explosive core.
But managers at the Berkshire site are trying to draw a veil over the accident, which happened during a stocktaking procedure that is carried out almost daily. "The circumstances are a matter for an internal inquiry which is now under way," said a spokesman for the AWE.
The incident looks set to reopen criticism of safety precautions at the site, which handles the assembly of the Trident missile nuclear warhead and the dismantling of those from the recently retired Polaris submarine fleet. In October 1994 the Health and Safety Executive (HSE) criticised the AWE's organisation, making 65 recommendations to improve standards, 19 of them "priorities". At the time, the pressure group Greenpeace said the HSE had revealed "some horrifying lapses and lack of safety procedures" at Aldermaston.
The latest incident occurred 10 days ago as five workers were carrying out a stocktaking of radioactive materials in a store at the site. They were wearing protective clothing but not masks. The cause of the contamination is not known, but when the team left the store, radiation detectors picked up the plutonium's presence.
Two people were thought to have breathed in microscopic particles of the highly poisonous material, but tests showed that only one person was affected. The dose absorbed was minuscule, equivalent to a fraction of the annual radiation that workers in the industry are allowed. "It should not have any harmful impact," said Peter Morgan of the HSE.
The incident is worrying because it has shown up flaws inprocedures. A spokesman for the AWE, which has not announced the incident publicly, said that nobody knew how the plutonium had contaminated the store and the workers. "There's no suggestion that anything was dropped or that proper procedures were not followed," he said.
But it has exposed difficulties that the HSE faces in trying to establish responsibility for safety at the plant, which is one of four nuclear research centres in the UK carrying out work for the Ministry of Defence. Because of the military nature of its work, the AWE, which was taken over by a private firm in 1993, is reluctant to reveal any details of its operations, even to the HSE, which has a legal obligation and right to inspect any site with radioactive materials.
"They have been playing a pretty straight bat to all my questions," said an HSE source last week. "I don't think they honestly know how it happened themselves. But the message they're giving me is that it's confidential."Reuse content