Robot submarines are to be used to sweep particles of plutonium and other radioactive materials from the seabed near one of Britain's biggest nuclear plants in one of the most delicate clean-up operations ever in this country.
Each submersible will be fitted with a Geiger counter and will crisscross the sea floor to pinpoint every deadly speck close to Dounreay on Scotland's north coast before lifting each particle and returning it to land for safe storage.
Two kilometres of beach outside the Dounreay nuclear plant have been closed since 1983, and fishing banned, when it was found old fuel rod fragments were being accidentally pumped into the sea. The cause was traced and corrected but particles - including plutonium specks, each capable of killing a person if swallowed - are still being washed on to this bleakly beautiful stretch of sand and cliff on mainland Britain's northern edge.
The UK Atomic Energy Authority (UKAEA), owners of Dounreay, was eventually fined £140,000 at Wick Sheriff Court last year for 'very grave errors' that led to the beach's contamination. The authority's safety director, Dr John Crofts, admitted the release represented 'an unacceptable legacy.'
The seabed clean-up, which will take years to complete, is only one part of the major operation to close down Dounreay. For 40 years, test reactors - part of Britain's fast breeder reactor construction programme - operated there but the technology turned out to be messy. Fast breeders use liquid metal coolants and their contaminated remnants still await removal. 'At the time, engineers were only interested in building reactors. No one thought how we might dismantle them,' said Colin Punler, Dounreay's communication manager. 'This was at the birth of Britain's nuclear industry.'
Although the UKAEA kept no precise accounts for building and running Dounreay, it is known to have cost several billion pounds. Now a further £2.5 billion will be spent returning the site to its pre-nuclear condition, leaving only a vault, covered with grass, to hold low-level nuclear waste while high-level waste will probably be shipped to a central UK nuclear store yet to be approved. 'An immense amount of money was spent here,' admitted Steve Beckitt, a senior Dounreay project manager.
'However, this was a world-beating nuclear facility. We built the first fast breeder reactor to generate electricity for a national grid. We were pushing the limits of technology and have gained immense experience and expertise that could still be invaluable to Britain.'
Fast-breeder reactors were conceived in the Fifties when uranium - the nuclear industry's raw material - was scarce. At the same time, the US was being uncooperative in sharing nuclear expertise, despite Britain's role in developing the atom bomb. So UK nuclear chiefs set up a fast breeder programme to ensure fuel independence and stationed it in remote Caithness - because they feared their first test reactor might explode. They even encased it in a giant sphere of steel, known as Fred the Golf Ball - Fred standing for Fast Reactor Experiment in Dounreay - to contain any blast.
This 60-metre metal ball still dominates the site and might even be retained as a key landmark or possibly a visitor centre, according to Scottish Heritage. 'Unfortunately, the sphere still contains about 50 tonnes of highly radioactive liquid metal coolant,' said Simon Middlemas, Dounreay's site director. 'That will take an awful lot of cleaning before people can walk inside.'
In the end, Dounreay was doomed because uranium was discovered in significant quantities in Australia and Canada, making standard reactors relatively cheap to run. In 1994, the government ordered closure along with a full-scale clean-up, to be completed by 2025.
Today, Dounreay bristles with armed police. The storage of vast amounts of uranium and plutonium, extracted from old fuel elements, has raised fears of attacks by terrorists. Security checks and vehicle inspections are routine - along with the constant clip-clop sound of Dounreay's fissile warning system. 'It's maddening but it tells you things are safe,' said Punler. 'If it speeds up, you know something is wrong and you run.'
At the same time, engineers labour away - behind thick lead sheeting - with robot arms, stripping down fuel elements and cleaning contaminated equipment. The work is painstaking and will take years before each building is stripped of radioactive fragments and demolished. Dounreay will then be razed.
In its heyday, the place provided work for thousands of scientists whose children made Caithness an educational hotspot, with local schools finding university places for pupils at a rate topped only by Oxford and Cambridge. Now local leaders fear a return to days when farming and fishing were the main occupations, although there are plans to use Dounreay's engineering expertise to create a new energy industry: tidal power. 'The waters here have some of the world's fastest currents and would make an ideal tidal power centre,' said Middlemas. 'We want to redirect our talent to devices like these.' Thus Dounreay, home of Britain's most advanced nuclear site, could find itself being turned into a centre for renewable energy research - an irony not lost on staff or locals.