£20m for upgraded ‘Swiss army knife’ to clean up DFR
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IT has been dubbed the most sophisticated Swiss army knife ever built.
The 16-piece tool is designed to reach deep inside one of Britain’s earliest atomic experiments and harvest the nuclear material that once promised to revolutionise how the nation generated its electricity.
Measuring 40ft in length, each of its tool-bits has been designed to withstand the harsh operating conditions inside Dounreay Fast Reactor.
The reactor shut down in 1977 after almost 20 years of experiments and its decommissioning is allowing energy bosses to reap the last of the plutonium and uranium from its unique "breeder" zone.
A custom-built retrieval arm will spend three years inside the reactor vessel, carefully 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 needed to do the job safely at a cost of £20 million. It has now been moved into position above the reactor, ready to descend into the darkness of the reactor vessel below.
"The reactor was a one-off design and so is the tool we need to take out the breeder rods," said Alex Potts, the Dounreay Site Restoration Ltd engineer in charge of the project.
"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 the team came up with."
Each detachable tool-bit cost £100,000, weighs between 37kg and 93kg and covers the range of equipment needed to retrieve the metal rods – grabs, manipulators, milling and cutting.
Up to three tool-bits will be in use at any one time and can be replaced by another three carried in a special toolbox without needing to remove the tool itself from the depths of reactor. The rest of the tool-bits will be stored above the reactor, ready to be swapped during service and maintenance breaks.
Special radiation-proof cameras and spotlights will guide operators working around the clock in a control room 20 feet above in the sphere.
It is expected to take three years to remove the rods from the breeder zone and the single remaining fuel pin stuck in the core.
An animation showing how the tool will work can be viewed on the Dounreay website – www.dounreay.com
Some 2000 rods surrounded the core when the reactor operated between 1959 and 1977. Over half were removed after it shutdown but 977 were left in place. Some had become jammed and a shortage of storage space at the site delayed their removal.
Now, with the site being razed to the ground, the rods need to be removed before the rest of the reactor can be dismantled safely.
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