As the decommissioning of Dounreay’s dome continues apace the legacies from the past are being stripped out of the redundant facility.
The storage ponds were built in 1956 to safely house fuel and breeder elements after their removal from the reactor. In the earlier stages of this key decommissioning work, pond racks and sludge were removed and preliminary in situ water treatment was performed to lower the contamination levels. The water is now being removed, with 20% of the pond water already treated to date via the bespoke water treatment plant installed, commissioned and optimised for the project.
Project manager Mark Aitken said: “The team has worked hard and put in the extra effort to ensure that the water is treated to well below the discharge parameters. They’ve done a good job all round.”
The pond facility is an above ground-level reinforced concrete structure, which consists of two reinforced concrete tanks separated by a concrete wall with a sluice gate located in the separation wall. There is an inner pond liner consisting of a composite layer of bitumen and concrete which is approximately 300mm thick.
As part of DSRL’s site hazard reduction DFR decommissioning teams aim to empty both ponds within the next couple of years. Some of the project’s highlights are detailed below:
• Following successful subsurface radiological surveys data has been analysed to identify the hazards and pressure washing trials have demonstrated no significant loose contamination on the walls.
• The pond walls are being washed with a high pressure power washer that was designed, manufactured and tested by DSRL and its contractor Mowat Technical Design Services.
• A remotely operated telescopic mast with trolley and rail system was designed to be mounted onto the existing transporter, with the capability to permit washing of all wall surfaces within the pond by rotating through 360°.
• Pressure washer operations are deployed below the water surface to help prevent airborne activity. Power washing is undertaken in horizontal bands 500mm deep prior to lowering the pond water level.
• The mast has also been designed to take an airless sprayer lance for sealing the concrete walls for an extended period of care and maintenance, if required.
• Continuous radiological monitoring is carried out to ensure a safe working environment.