Figures published today are said to show that up to 30kg of plutonium are unaccounted for in an audit of nuclear material stored at the Sellafield site in Cumbria.
However Britain's Department of Trade and Industry has stressed that the material is not missing and that it is not unusual for annual audits to show nuclear material unaccounted for.
The figures have been published in The London Times newspaper.
Nuclear material stored at Sellafield is measured every year under International Atomic Energy Authority guidelines.
While the accounting loss does not mean any material has been stolen or diverted, it is thought such a large discrepancy will be an embarrassment for British Nuclear Fuels - the company which runs Sellafield - and the British government.
The government is about to embark on a lengthy process of making safe decommissioned nuclear sites across Britain.
The matter was raised during the order of business in the Dáil this morning.
Green Party leader Trevor Sargent asked for a special debate on the issue while Fine Gael deputy Fergus O'Dowd said it was enough plutonium to make eight bombs.
