Fianna Fáil's 65th annual Ard-Fheis continues in Dublin today. The Taoiseach Mr Ahern is due to deliver his keynote speech to the conference later this evening.
Last night Mr Ahern demanded the British government close down the Sellafield nuclear power plant in Cumbria.
He said the risk of terrorism at the site is "unacceptably increased" with the announcement of the new Mox fuel operation.
Mr Ahern has accused the British Prime Minister Mr Tony Blair of burying the announcement while world attention was diverted by the terrorism crisis.
Opening the ard-fheis, he described the plant as the biggest threat to Ireland's environment. He said it was being "kept on a life support machine" by the British taxpayer.
Mr Ahern's address to the party conference came the day after an article in New Scientist magazine warned a terrorist strike on Sellafield could release 44 times more radioactive material than the disaster at Chernobyl.
"We are appalled by the decision to proceed with the new Mox plant," Mr Ahern told delegates at Citywest in Dublin.
"It has all the hallmarks of a bad news story hastily released in the midst of a momentous international crisis in the hope that most people will be distracted. It poses a significant additional and totally unacceptable threat to our environment and to our national security.
"In the context of the heightened threat from terrorism the existing risks from Sellafield are unacceptably increased.
"The opening of the Mox plant would mean that the Irish Sea is used as a highway for the transport of highly dangerous nuclear fuel to and from nuclear plants around the world. And this is in addition to the existing and equally unacceptable activities of Sellafield."
To rapturous applause he added: "The position of Fianna Fáil is clear and uncompromising. We demand that Sellafield is shut."
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