Work has begun on cleaning up a radioactive spillage that closed a treatment plant at the Dounreay Nuclear site in Caithness.
Radioactive liquid on the sealed drum
The spillage, which happened in September, has set back decommissioning of Dounreay by about a year.
Despite an alarm sounding, radioactive liquid was poured over a sealed drum in the site's cementation plant.
It has taken months to devise a hi-tech clean up solution because the operation was too hazardous for humans.
The cementation plant is the area where intermediate level waste from the reprocessing of nuclear fuel rods is mixed with cement and stored in drums.
The facility was shut down after the lid of one drum was sealed when a batch of the liquid was released.
Norman Harrison: "A wake-up call"
Officials said nobody had been harmed or exposed to radioactive waste as a result of the problem.
No formal disciplinary action was taken against any member of the workforce.
The authority said the spill was "contained within the cell", but admitted it was a "setback" to the 30-year decommissioning programme.
The bulk of the waste has now been contained using remote control equipment, but the £1m recovery operation will not be complete until the autumn.
Dounreay management described the spillage as a wake-up call and said safety procedures had been reviewed and lessons learned.
Site director Norman Harrison said he wanted to get to the bottom of the incident, identify where shortfalls were and then enact a recovery plan.
"We were concerned and disappointed that it happened. It did show there was not an even approach to safety across the site," he said.
"Some areas of the site were demonstrating a world-class performance and so it was actually a wake-up call for us."
Lorraine Mann, of Scotland Against Nuclear Dumping, said the incident illustrated that Dounreay's safety risks were not in the past.
She added: "They still have significant safety challenges that the site has to address and until that's done there can be no confidence that this clean-up is going to be the last."
Dounreay, which is run by the United Kingdom Atomic Energy Authority, was used as Britain's centre of fast reactor research and development from 1955 until 1994.