Following the discovery of harmful radioactivity on an office chair and beside roadways last month, managers at the plant cordoned off large areas of the site last week after fresh contamination was detected. Radioactivity has now been found in 40 areas of the plant.
The latest "hot" metals - in topsoil and on the seat of a vehicle used to transport materials around the site - were uncovered by scientists conducting an environmental survey of the plant. UK Atomic Energy Authority managers say the metals date from the 1960s. They do not know how they were released and why they lay undetected for so long.
John Baxter, the director of Dounreay, said: "We have contamination and we are not 100 per cent sure why." But "the indications" were that unsafe "past practices" - in particular the storage of nuclear waste in unsealed flasks - were to blame.
Mr Baxter said the harmful particles "should not be present", and he tried to reassure the plant's 1,400 staff. "The contamination is being dug out where it is found, or, if it will take some time to remove, the areas concerned are being barriered off. We are doing everything to make sure that there is no hazard to people on site."
Soil samples from the contaminated areas were being analysed and the site survey would be completed this week. Mr Baxter said it was possible staff had come into contact with the particles in the past 20 years, but he stressed there was no evidence any workers had suffered ill-effects.
The news is the latest embarrassment to managers at the plant. Last month the Government's Committee on the Medical Aspects of Radiation in the Environment and the Radioactive Waste Management Advisory Committee issued a damning joint report on pollution of the beaches near Dounreay.Reuse content