The Greenpeace ship, the Rainbow Warrior, has left Dublin with five other vessels to protest at the arrival of nuclear cargo ships this weekend in the Irish Sea.
The plutonium mixed oxide fuel, or MOX, is being returned to Sellafield after a British Nuclear Fuels client in Japan refused to take the material when it emerged that safety records had been falsified.
Greenpeace estimates that two nuclear cargo ships, carrying five tons of MOX, will enter the Irish Sea this weekend.
The activists have dismissed suggestions that their plan amounts to tokenism.
The British government has been supportive of its nuclear industry which has been under severe financial pressure over the past months.
Greenpeace claims that public pressure could lead to a change, just as the French were forced to abandon nuclear testing in the South Pacific after a long campaign:
British Nuclear Fuels has long maintained that the transportation of nuclear material by sea is safe. It will point to the fact that the material left Sellafield, went to Japan and back without incident.
The only problem encountered was when a protestor in a floatable dinghy tried to get in front of the ships.
A cat and mouse game will now get underway as Greenpeace attempts to locate the ships entering the Irish Sea this weekend and bring their protest to the attention of the world's media.
