Shredding machinery that can cut steel and other waste recovered from the Dounreay shaft and silo has gone on trial at a test facility in Caithness, northern Scotland.

Austrian firm Untha, based in Salzburg, was chosen to supply a specialist shredding machine after worldwide suppliers were asked to demonstrate their plant.

Dounreay’s controversial waste shaft and silo contain hazardous mixed waste, and there is limited knowledge of its composition.

The actual mechanical process to be used on the shaft and silo waste will be operated remotely inside heavily-shielded cells to protect workers from the radiological and chemical hazards.

The shredder is now commissioned and ready to cut its way through steel drums, iron bars and other materials at the nearby ‘T3UK’ test centre.

Other machinery will be installed there over the next 12 months to create a mock-up of the whole process line that will receive the waste from the shaft and silo.

The line will demonstrate and prove the process, from the grabbing of waste inside the shaft and silo through its shredding, cleansing, and eventual encapsulation in cement inside steel storage drums.

Geoff Moore, Dounreay project manager with the concept design team, said: “We are going to use mechanical equipment already proven in other fields to process the waste. The Untha shredder is in use worldwide in the waste industry.

“We’ve installed it at ‘T3UK’ and over the next 12 months we will mock up the rest of the process using proven equipment from other suppliers. We think the Untha machine will be able to shred 90% of the waste in the shaft and silo.

“Based on the records that were kept at the time, we think there were something like 14,000 containers sent to the shaft and silo. These need to be shredded when we bring them back to the surface so the waste can be sorted and treated properly.

“The shredder will rip through things like drums, metal wrappers, scaffolding poles, pipes, plastic and wood. Master-slave manipulators on the process line will pick out the things that cant be shredded, such as lead bricks.

“We are planning to use other proven machines to size-reduce material which cannot be shredded.

“We will feed the trial shredder with iron bars, paper, wood, and 200-litre drums containing steel from local scrap metal merchants at ‘T3UK’. The shredder has four circular rows of teeth that shred waste into pieces that can be returned to the local merchants.”

The retrieval plant and waste treatment line is scheduled for construction at Dounreay between 2012 and 2016.