On a typically desolate and windswept industrial park, some miles from the Sellafield complex, scientists are working on a prototype robot capable of extracting the damaged fuel rods and isotope cartridges.

The targets are in a fragile condition with some reduced to ash on their graphite boats. Many remain jammed after the hurried attempts to force them through the narrow fuel channels at the height of the fire.

The pile project team estimates that, altogether, 9,000 cartridges remain inside about 400 channels. This represents 15 tonnes of radioactive fuel and 1.7 tonnes of isotopes, making up about 8,500 separate items – each a threat to life and limb.

For the past year the UKAEA team along with specialists from SA Robotics and Amec have been perfecting a remote-control robot, called the fuel channel retrieval tool, with rotating arms to scour, scratch, push, pull or grip the material.

The plan is to cut a 5ft-square hole in the concrete pile cap and lower the machine from a carbon-fibre arm so that it faces the discharge wall, the space where the spent fuel rods were designed to be ejected, and fall into a water duct below.

Dick Sexton, an American seconded to head the pile project from the US company CH2M Hill, apologises as the prototype laboriously retrieves a fuel rod from a mocked-up section of the graphite core. “I know, it is kind of like watching paint dry,” he jokes. “We need a variety of scoops, fingers and slots because the material we need to recover is such a hotchpotch.”

Elsewhere on the industrial floor other clanking, whirring machines show how the radioactive material will be separated into various sizes, stored in drums with an internal helix design and filled with a polymer material.

“While we say this is innovative,” Mr Sexton said. “We try to use tried and tested technology.”

For many years it was feared that aggressive decommissioning could spark a fresh fire, prompting the remaining fuel to go “critical” or produce a graphite dust explosion. There was, for some time, so little knowledge of what was inside the core that one theory suggested it was simply a large hole.

Costs and delays increased as complex schemes were devised to keep the material stable. These included submerging the entire core under water, or inside a bubble of gas such as argon.

It was only after a “safety case” in June 2006 concluded that such dramatic scenarios were no longer credible that the technicians pressed ahead with a more conventional decommissioning process. Further intrusive surveys of the damage have confirmed the diagnosis. “It took a while for science to catch up with what was in the reactor and what the hazards were,” Mr Sexton said.

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