Preparations for Dounreay waste retrieval

24 September 2009

The UK is preparing to remove and package more than 1500 tonnes of radioactive waste from its fast reactor experiments at Dounreay that has been buried in two underground vaults for up to 50 years.


Dounreay Site Restoration Ltd (DSRL), which is managing the project, said that tests are currently underway in the UK, Germany and the USA to develop the heavily-shielded plant that will sift and package the intermediate-level radioactive waste (ILW) once it is brought back to the surface.


Work is expected to begin later in 2009 on a scheme design for the robotic machinery that will descend up to 65 metres below the surface to recover the waste from the vaults. Detailed designs will be ready by 2012, when construction companies worldwide are expected to bid for the contract to build the major plant needed to empty the two separate vaults.


Steve Efemey, project manager at DSRL, said, "We're on course to start construction in 2013, with the first waste due to come to the surface in 2017."


The older of the two facilities is an unlined shaft, 65 metres deep. It was first used in 1958. A second vault - a 750 cubic metre concrete box set just beneath the surface and known as the wet silo - was used from 1971.


Since 1988, when the UK government decided to clean out both facilities, work has been completed on the first phases of their decommissioning. These included a £27 million ($44 million) hydro-geological project that wrapped the entire shaft with grout to divert the flow of groundwater, demolition of disused headworks and other redundant buildings, and ongoing ground services preparation costing £6 million ($10 million).


Ten miles from Dounreay, at the T3UK industrial test site run by JGC, heavy plant is being assembled from around the world to create a full-scale mock-up of the waste processing line. The remotely-operated line includes cranes, grabs, power washing, feed conveyors, metal shredding, rotary screens, a trommel to separate solid and liquids, water decontamination, sludge treatment and drum filling. In Germany and the USA, tests are being conducted on an X-ray system to scan and characterise each piece of waste.


At Dounreay, the assembled process line will be housed near the top of the shaft and silo in sealed cells to protect operators from the radiological and chemical dangers in the waste emerging from underground.


Waste retrieved from the shaft and silo will be segregated, characterised and conditioned in containers of cement for above-ground storage pending a national management strategy for ILW.


Waste minimisation is an important factor in the project. Five years ago, the estimated number of 500-litre ILW drums needed to contain the debris after processing was 9300. Today, it is less than 2000.


"We've looked across every industry using similar plant, such as waste water, mining and aviation security, and assembled a process where virtually every part is proven already in other fields," said Efemey.


Innovation in the hydraulic isolation of the shaft eliminated £200 million ($325 million) in future water treatment costs, DSRL said. In addition, the adoption of process plant tried and tested by other industries has kept the cost of this current phase of the project to less than £1.5 million ($2.4 million) a year.


The project team is in the final stages of the approval process for tendering the scheme design contract for the waste retrieval system.


The total estimated cost of decommissioning the shaft and silo, excluding the cost of managing the recovered waste in the longer term, is approximately £290 million ($470 million). The project is scheduled to be completed in 2025.


The Dounreay site was the home to two fast reactors plus a materials test reactor, and associated fuel cycle facilities