£20m Swiss army knife will harvest nuclear material 19 July 2011

It's been dubbed the most sophisticated Swiss army knife ever built – a 16-piece tool designed to reach deep inside one of Britain's earliest atomic experiments and harvest the nuclear material.

Measuring 40ft in length, each of its 16 tool-bits has been designed to withstand the harsh operating conditions inside the Dounreay Fast Reactor, which shut down in 1977 after almost 20 years of experiments and is now being decommissioned.

The custom-built retrieval arm will spend three years inside the reactor vessel, cutting free 977 metal rods standing vertically in a hexagonal rack around the near-empty core.

Each rod will be cut free from its mounting and transferred to a waiting basket, ready to be lifted through the roof of the reactor and returned to the outside world after 50 years.

French engineers designed and built the tool – at a cost of £20 million – which has now been moved into position above the reactor, ready to descend into the vessel below.

"The reactor was a one-off design and so is the tool we need to take out the breeder rods," comments Alex Potts, engineer in charge of the project at Dounreay Site Restoration.

"It's too toxic in there for anyone to do the job manually – the radiation levels are still very high and the residual traces of liquid metal coolant add to the hazard. So we need a tool capable of doing the job by remote control. It's a pretty sophisticated version of a Swiss army knife."

Each detachable tool-bit cost £100,000, weighs 37—93kg and covers the range of equipment needed to retrieve the metal rods – grabs, manipulators, milling and cutting equipment.

Up to three tool-bits will be in use at any one time and can be replaced by another three, carried in a tool box, without needing to remove the tool itself from the reactor. The rest of the tool-bits will be stored above the reactor, ready to be swapped during service and maintenance breaks.

Radiation-proof cameras and spotlights will guide operators working around the clock in a control room 20 feet above, in the hall of the containment sphere.

The operation is expected to take three years to remove the 977 rods from the breeder zone around the core and the single remaining fuel pin stuck in the core.

Brian Tinham

Related Companies
Dounreay Site Restoration Ltd

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