Sea trials will soon be conducted to establish whether it is a realistic option to transport highly radioactive material from Dounreay to Sellafield
But Dounreay Site Restoration Ltd (DSRL), the consortium in charge of the £1.6 billion decommissioning of the Caithness plant, insists no decision has been taken on whether to take 26 tonnes of material south by rail or by ship.
Concerns have been raised about such a dangerous cargo being taken through the Pentland Firth and down through the Minch and passed the Argyll islands to the giant nuclear plant in Cumbria.
Dounreay accumulated more than 100 tonnes of nuclear fuel and material when the decision was taken in 1998 to close down and clean up the site.
A few tonnes belonged to foreign reactor operators and most of this has now been returned by road, air and sea over the last decade.
The remainder belongs to the Nuclear Decommissioning Authority quango which wants the spent fuel to be managed at Sellafield.
But 26 tonnes are made of so-called 'Dounreay exotics' , highly radioactive fuels, some of which include highly enriched uranium.
Dr Richard Dixon, Director of Friends of the Earth Scotland said: "The proposal to use ships sounds like a ploy to get this problem out of people's minds rather than the safest option."
A DSRL spokeswoman said "The sea trial has not been conducted yet. It is planned for later on in the year. There has no decision to take the material by sea. The Dounreay Stakeholder Group was informed in March that trials of a sea route would be carried out. If successful, this will give the option of two routes."