Workers are drilling through the concrete that surrounds Dounreay’s uranium fuel reprocessing plant to let demolition robots move inside and begin dismantling it.
Clean-up bosses have turned to specialist demolition firm Brokk to supply the remotely-operated equipment that can work inside cells and a pond where radiation levels are still too high for human access.
The robots – mounted on tracks like a construction excavator and powered by electricity – have been fitted with specially-designed tools.
They will go inside the cells and pond to cut up and package the vessels and pipes where more than 10,000 spent fuel elements were dissolved and reprocessed before the plant shut down in 1996.
The internal process plant vessels and pipes have been washed through with aggressive cleaning fluids but a legacy of contamination and radiation from almost 40 years of operation means some of the cells are still too radioactive for people to work in.
The walls and ceilings of these cells and pond structures are made from reinforced concrete several feet in thickness. These provide environmental containment and protection from the internal radiation.
Additional containment made from stainless steel and glass-reinforced plastic has been erected around the outside of the “high active cell north” wall.
Inside the temporary containment, a team wearing protective suits and respirators is using diamond-tipped core drills to penetrate the walls to within 50 millimetres of the cell on the other side.
They are core drilling in a carefully designed pattern to weaken the wall sufficiently and form an opening to let the first of the robots punch its way into the cells by the end of the year. The drilling will also weaken internal walls between the cells.
A similar penetration and entry will be made from the south side of the cell structure and the pond .
The robot tools and equipment have been trialled and operators trained. Commissioning of the remote control viewing and operation system will be completed before the robots enter the cells and pond structures.
Once inside, the three-tonne robots will use an array of shears, grapples and crushers to strip out the chemical plant.
Each part of the dismantled chemical works will be cut up into pieces less than 400mm long, flattened and segregated in a dedicated waste processing structure where a platform-mounted robot will consign each item as low or intermediate-level waste after radation checks.
Low level waste items will be packaged into specially-designed waste containers and monitored in a new lead-lined assay system. Drums of intermediate-level waste will be consigned for storage, allowing the entire facility to be demolished in 2010.
“The hazards will vary between cells,” explained decommissioning project manager Graham Carle.
“Some cells will be contaminated, which carries a risk inhalation or ingestion. In other areas, it will be direct exposure to radiation."
The coring is being carried out by a team from specialist contractor Clyde Valley Drilling Ltd, working alongside specialist advisors from Dounreay Site Restoration Ltd.
The approach to decommissioning has been designed and managed by DSRL with a combined implementation team of DSRL and contractor support. Other contractors include Morson International, G & A Barnie, JGC, D Gow, MTDS, Doosan Babcock and Johnson Controls.
DSRL, a subsidiary of UKAEA, is contracted by the Nuclear Decommissioning Authority to manage the clean-up and closure of Dounreay.