Radioactive material could be moved from Dounreay in Caithness to Sellafield in Cumbria by rail at a cost of £30m, according to a new report.
The Nuclear Decommissioning Authority (NDA) said there was a "clear and compelling" case to deal with the breeder material at Sellafield.
Dounreay is being demolished at a cost of £2.6bn.
Dounreay Site Restoration Limited (DSRL) said the first of 44 tonnes of fuel could be moved in early 2012.
In the report, the NDA said managing the material at Sellafield, rather than dealing with it at Dounreay, was its preferred option.
The authority has estimated the cost of preparing it for transportation by rail at £30m.
It would cost about a further £30m to mix the breeder with a fuel at Sellafield.
Dounreay does not have the means of reprocessing the breeder material and the process of immobilising and disposing of it in Caithness would cost about £65m, the NDA has reported.
The material was used in a nuclear power experiment at Dounreay later abandoned following the discovery of oil and gas in the North Sea.
It provided a means of converting uranium to plutonium for the generation of electricity.
In its report, the NDA said: "The breeder material is not classified as a fuel, as it does not take part in the nuclear 'core' reaction and is not converted into fission products but neither is it waste.
"This is why, to avoid confusion, it is referred to as 'material'."
"The breeder material is radioactive, but much less so than fuel since it does not contain large amounts of fission products, and it has also been cooled since 1977."