Work is progressing on taking apart one of the "highest hazards" in the UK civil nuclear industry.
The Dounreay Fast Reactor (DFR) is housed inside the dome at Dounreay, near Thurso in Caithness.
The DFR is being dismantled as part of work to decommission the wider experimental nuclear power complex.
Workers have just completed the removal of one of hundreds of concrete blocks from one of two pits that were used to shield against radiation in the DFR.
Resembling swimming pools and called ponds, the 6m (19.8ft) deep pits were once filled with water and protected people working in the DFR from radiation emitted from spent fuel.
There are about 180 concrete blocks in each pond to be removed.
Because of risk from radioactive contamination, workers have to wear protective clothing while cutting out the blocks and then packaging them for storage as waste.
Project manager Suzanne Griffiths said: "Decommissioning of the ponds is technically challenging.
"While each block is only around one metre square, it is extremely heavy and the process of cutting it is complex.
"The team has worked exceptionally well together and applied lateral thinking, deploying new techniques to allow the concrete liner to be removed in preparation for final demolition."
The metal Dome structure will also eventually be demolished.