A worker inside the new breeder containment building
One of the largest engineering projects at a former nuclear research complex in Caithness is close to completion.
The new facility is being built to handle breeder elements removed from Dounreay's experimental fast reactor.
When it was in use, the reactor exposed uranium to neutrons turning it into plutonium for fuel. The term breeder was given to this process.
Scottish Environment Secretary Richard Lochhead is due to visit Dounreay and meet staff later on Wednesday.
While original structures on the site are being demolished, new ones such as the breeder containment building are having to be constructed to deal with highly radioactive materials.
Almost 1,000 breeder elements, each made up of 14 cylindrical containers of natural uranium wrapped in stainless steel cladding, will have to be removed from the fast reactor which is housed in Dounreay's iconic sphere.
DOUNREAY FACT FILE
The Dounreay Fast Reactor was shut down in 1977
£50m has been invested in removing and process the breeder left inside
The overall decommissioning project will take decades to complete at an estimated cost of £2.9bn
Once transferred to the containment building, the elements will be cut up, washed, examined and packaged so it can treated as waste or re-usable material.
The new plant has reinforced concrete walls to shield workers from radiation while this work is carried out.
Ahead of his visit, Mr Lochhead said: "Decommissioning of Dounreay is incredibly significant for this part of Scotland, representing both past activities and the challenges for the future.
"The Scottish Government is committed to moving away from nuclear power and towards increasing our renewable energy capacity.
"Dounreay's experience in technology development and the skills of its workforce have the potential to be at the forefront of the Scottish renewables revolution."