More than a third of the plutonium dumped in the Irish Sea by Sellafield is unaccounted for, according to scientists at Britain's Centre for Environment, Fisheries and Aquaculture Science.
The scientists suggest some of it could be buried in coarse-grained sand in the Irish Sea close to the Cumbrian coastline, where it cannot be detected by scientific surveys, while previously underestimated amounts may have been carried out towards Scotland and Scandinavia by shifting sea currents.
In a study by Dr Peter Kershaw and a group of scientists at CEFAS - which is part of the Ministry of Agriculture, Fisheries and Food - they discovered a "significant shortfall" between detectable amounts of plutonium and americium and the levels of plutonium discharged from the Cumbrian nuclear plant. The study is published in the Journal of Environmental Radioactivity and its findings are reproduced in the New Scientist.
Between 1952 and 1995, after which radioactive dumping was reduced, Sellafield discharged 182 kilograms of plutonium into the Irish Sea. But following Dr Kershaw's audit of the discharged plutonium, he concluded that 36 per cent could not be found and up to 40 per cent of the americium was also unaccounted for.
Dr Kershaw suggests, however, it is unlikely that the missing plutonium and americium could be washed up on the Irish coastline.
He told The Irish Times yesterday that the inability to account for this amount of plutonium was longstanding, but there was no risk to the human population: "It is a source of irritation that we aren't able to account for this. But looking at the longer-term trends of distribution in the Irish Sea, the seabed is moving away from the Cumbrian coast, further north and west and the distribution is being carried north out of the Irish Sea to Scotland and Scandinavia."
Dr Tom O'Flaherty of the Radiological Protection Institute of Ireland said its concerns about dumping plutonium in the Irish Sea were not altered by Dr Kershaw's study.
"We have been basing our studies on the total amount discharged and the fact that this study hasn't been able to find all of that doesn't alter our reports, in which we have expressed our concern about the dumping of plutonium . . . It will reinforce the concerns about Sellafield," Dr O'Flaherty said.
The Green Party MEP for Dublin, Ms Patricia McKenna, said Dr Kershaw's report was further evidence of a dismal safety record.
British Nuclear Fuels, which owns and operates Sellafield, said it was not responsible for the missing plutonium. "To blame us for not being able to find it in the sea is a bit of a nonsense. We don't see any grounds for it causing any concern to the public or knocking us on the head for it."