By Steven McKenzie
Highlands and Islands reporter, BBC Scotland news website
Dounreay was a fast reactor research site
Equipment and techniques used in the decommissioning of a Scottish nuclear power research complex have attracted international interest.
A patent has been applied for a pump and camera used to drain the final dregs of hazardous liquid from a reactor at Dounreay in Caithness.
It could potentially be used in the clean-up of French sites.
Scandinavians have also been watching closely how a deep shaft containing toxic waste has been isolated.
About 900 tonnes of sodium which once flowed in the circuits of Dounreay's Prototype Fast Reactor (PFR) were pumped out.
However, a 1ft-long pump and 9"-long camera to help operators guide it to harder to reach sections was designed and built to retrieve five tonnes that remained in the bottom of the reactor vessel.
It was developed at t3UK, a facility at Janetstown on the outskirts of Thurso.
Staff with the UK Atomic Energy Agency Authority (UKAEA), the main contractor carrying out the clean-up for the Nuclear Decommissioning Authority (NDA), said the invention had attracted interest from the French nuclear sector.
Billy Husband, senior project manager at PFR, said his team was very pleased with the device.
He said: "The pump and camera had to go down 18m into the vessel to suck the sodium out.
"The sodium was at 200C, but the camera was only good at 60C so we had to cool it down with nitrogen gas.
"It took a very complex design to do that and we have applied for a patent for the technology we have basically invented."
Mr Husband added: "It was a very complex path to put it down into the reactor because of the innards of the reactor itself.
"The major lesson we've probably learnt, if we build fast reactors again in this country, is to put a tap at the bottom of the reactor to drain the sodium out because that would have made life so much simpler for us."
Meanwhile, close to the rocky coastline below the main site, tests were poised to begin on a cement grout barrier around a 65m deep shaft.
It was used to dump radioactive material between 1959 and 1977, when it was sealed off after an explosion.
To stop ground water seeping through minute cracks in the rock around the shaft, engineers have sunk about 200 boreholes to a depth of 80m, before injecting a fine grout at high pressure into the holes.
John Whitfield, project engineer on the shaft isolation project, said the technique could be used in the construction of a nuclear waste repository in Finland.
Swedish tunnel builders have also been watching the operation with interest.
Mr Whitfield said: "We are trying to drastically reduce the amount of water getting through the cracks in rock around the shaft so that when the waste is taken out the amount of water that flows in will be much, much smaller.
"Grouting generally is used throughout the civil engineering industry, but this sort of grouting - because of the very fine cracks and use of very fine cement around a nuclear shaft - is unique."