Three and a half years after the Calder hall cooling towers came down, the Sellafield site skyline has changed yet again with the construction of a new 122 metre high concrete ventilation discharge stack.
The completion of the civil construction work on the new stack is major milestone achieved for the Separation Area Ventilation (SAV) Project.
Sellafield Limited Project Manager Cliff Roberts said: “The new discharge stack will, when operational, allow further decommissioning work to commence on legacy plants and aerial discharge stacks that are nearing the end of their operational life.
” We constructed the 122 metre high concrete stack windshield using a continuous ‘slip forming’ process, which was a 24/7 operation and took just 34 days to reach its full height.”
The continuous ‘slip forming’ process is essentially a circular concrete shutter housed on a rig, which is used as the working platform for the construction teams. The rig is continuously raised up via a hydraulic jacking system.
The stack is supported by a ring of 12 reinforced concrete piles, each of which is 1.2 metres in diameter and 38 metres deep, with each pile socketed 3 metres into the bedrock. On top of the working piles sits the pile cap, which is a reinforced concrete raft made up of 60 tonnes of reinforcement steel bar and 450 cubic metres concrete.
The SAV project – a major Design & Build – comprises of a new two storey ventilation plant room housing various ventilation equipment; a ventilation discharge monitoring plant room and a series of new steel support structures which carry ventilation ductwork from existing donor plants through to the monitoring plant room and up to the new discharge stack.
Construction of the new SAV facility commenced in early 2010. One of the first jobs was to install a new electrical substation. Work then commenced on the ventilation stack foundations which were completed in November 2010. The next milestone was the construction of the plant room steelwork which was completed two months ahead of schedule in January 2011, comprising a total of 350 tonnes of steel.
The design and construction of the new stack was undertaken by Doosan Babcock and their specialist sub-contractors Kier Construction, Bachy Solentanche and Bierrum International.
Mark Newby, Sellafield Ltd Sub Project Manager said: “Like all major construction projects the stack has had a number of challenges to overcome. However we’ve had some excellent teams working on the design, approvals process and construction to enable us to complete this phase of construction ahead of schedule.”