The main Government adviser on nuclear issues has moved to allay fears that unaccounted-for plutonium at Sellafield could fall into the hands of terrorists.
However, senior officials at the Radiological Protection Institute of Ireland (RPII) have raised serious concerns about the growing discrepancies in accounting procedures which gave rise to yesterday's official report, which found 30 kilogrammes of the material were not accounted for.
Dr Tony Colgan, director of advisory services at the RPII, said the discrepancy arose from the way the plutonium was counted. Estimates are provided from customers of Sellafield about the amount of plutonium contained in fuel which is sent for reprocessing.
The plutonium taken from the reprocessed material is then measured and should be equal to the original estimate.
The International Atomic Energy Agency (IAEA) allows a 1 per cent difference between the two figures.
Dr Colgan said the RPII was satisfied that the Sellafield figures were within this margin, and that it was an accounting issue as opposed to one of material being missing.
There was concern within the RPII about the increasing size of the discrepancy, he said.
The 30kg discrepancy in the latest audit by the Office of Civil Nuclear Security compares with a 19kg discrepancy for 2003.
He said the figures should on average cancel out, and the fact that this was not happening gave rise to concern about the accounting procedures at Sellafield.
"We certainly do feel that the discrepancy is getting higher and higher," Dr Colgan added.
The RPII would be seeking further information from British nuclear authorities on the report.
In a statement yesterday, British Nuclear Fuels Ltd, which operates Sellafield, said no material had been stolen.
"None has been removed from our plants, and there are no security implications of this accounting issue.
"There are also no safety or environmental implications whatsoever. These uncertainties exist in all industrial processes," BNFL said.
The growing discrepancies were raised in the Dáil yesterday by the Green Party leader, Mr Trevor Sargent, who said questions needed to be answered by the Government as to whether Ministers were aware of the issue, which he described as a serious breach of safety and security.
He also called on the Government to "make a stand against having the Euratom treaty as part of the new EU constitutional treaty, given that in effect Irish taxpayers are helping to fund this discredited industry."
Labour's spokesman on nuclear safety, Mr Emmet Stagg, said the revelation that such a large amount of nuclear material could go missing could not merely be discounted as an embarrassment for the British government and its nuclear industry.
"It should act as a jolt to the Irish Government to reactivate their long-standing policy to pursue the closure of Sellafield," he said.