The Government said yesterday it had been assured that ships carrying weapons-grade plutonium will not pass through Irish territorial waters.
A batch of radioactive cargo, taken from the warheads of US missiles, is in transit from the US port of Charleston to Cherbourg in France on ships owned by British Nuclear Fuels.
A spokeswoman for the Department of the Environment said it had been told by agencies responsible for the shipment that the ships would not pass through Irish waters.
However, the Green Party leader, Mr Trevor Sargent, said the same ships transported Japanese nuclear fuel through Irish waters two years ago, and called on the Government to send naval vessels to monitor the ships' movements.
"The potential dangers this nuclear flotilla poses to Ireland should not be underestimated. Fire on a plutonium shipment would result in a radioactive cloud, hundreds of square kilometres large, in a matter of hours. An accident could lead to plutonium fallout in Ireland," Mr Sargent said.
The cargo of 140 kilogrammes of plutonium oxide will travel around 1,000 kilometres over land to the Cadarache nuclear complex, near Aix en Provence. It will then be fabricated into nuclear reactor fuel before being shipped back to the US next year.
A Greenpeace ship, meanwhile, has arrived at Cherbourg ahead of the arrival of the plutonium shipment. It is supporting a group of boats and ships which has called itself the Atlantic Nuclear-Free Flotilla which will demonstrate again the shipment.
Mr Shaun Burnie of Greenpeace International said transport of the nuclear material posed an unacceptable risk to people and the environment, especially given that there were less environmentally-threatening options available. Greenpeace said the plutonium should be mixed with highly radioactive waste, solidified and stored.
"This technically feasible option, opposed by the plutonium industry, would be quicker, minimise transport, cost less and be far more secure," Mr Burnie said.
Mr Sargent, meanwhile, said he would ask Green Party councillors to call on their local authorities to become nuclear-free zones.
"This will send a strong message to the Government that Irish people are opposed to nuclear proliferation and the nuclear industry," he said.
