Almost half the stock of nuclear fuel left over at Dounreay from its research role in the last century is to begin leaving the site next summer.
Forty-four tonnes of breeder material from the Dounreay Fast Reactor will be moved by rail from Caithness to Cumbria over a 4-5 year period.
The material is to be reprocessed at the Sellafield nuclear site to recover fuel that could be used to generate electricity in the future.
The announcement was made today by the Nuclear Decommissioning Authority, which inherited the material after the research programme ceased.
A "preferred option paper" published by the NDA in July generated responses from 12 organisations and individuals. The NDA's response to these comments is also published today.
DSRL will work closely with train operator DRS, Sellafield Sites Ltd and the Civil Nuclear Constabulary to secure the safe delivery of the breeder material to Cumbria, following today's announcement.
"We've moved out the foreign nuclear fuel over the past 10 years and this decision lets us now start returning the UK fuel," said Alex Anderson, head of fuel and waste at site closure contractor DSRL. "It is the beginning of the end for nuclear transports in the Highlands."
Dounreay's other materials containing plutonium, such as unirradiated mixed oxide fuel, are currently the subject of an NDA assessment into potential future management routes. One of the options includes transportation to and management at Sellafield. NDA is expected to publish a paper on this subject early in 2012.