Separation Area Ventilation Project
Background
Two of the historical stacks within the Separation Area of the Sellafield site (the pile chimney and stack associated with the Primary Separation Plant) are nearing the end of their effective operational lives and are scheduled for demolition.
These stacks currently discharge aerial effluent from a number of plants on the site which will continue to operate well beyond the demolition of the stacks.
There is a requirement therefore to produce a new discharge capability for aerial effluents from the Separation Area which will replace the two ageing stacks and provide a long term facility for future decommissioning.
Challenge
The project has faced a number of challenges commencing with identifying a suitable site to locate the new facility within the congested confines around the various donor plants. As these donor plants are owned and operated by a number of business units, considerable stakeholder management has been essential to negotiate outages to modify the existing ventilation ductwork and to minimise the impact on their plant operations. Routing of the new ductwork through the congested site has also been a challenge.
Solution
The new discharge facility will comprise a 120 metre high stack with associated plant room, monitoring room and substation. The three storey plant room will house the fans, additional filtration and the control room.
The facility will be constructed away from the main processing areas of the site with new ductwork runs and pipebridges to connect to the various donor plants.
Achievements and progress to date:
In advance of the main construction work, a contract was awarded to Amec to prepare each of the ventilation streams for diversion to the new plant. This involved shutting down each vent stream and replacing a section of ductwork with a tee piece. Due to the complex interactions between plants on Sellafield, significant co-ordination was required to arrange a suitable outage. By the end of 2009, six of the seven planned tie-ins have been completed.
A second enabling contract was also awarded to Amec to strengthen existing foundations and construct new ones within the main processing part of the site in readiness for the later construction of new pipebridges. This work was completed in 2009.
The main contract to complete the detail design and to construct the plant was awarded to Doosan Babcock in November 2008. They have since awarded sub-contracts to Kier Construction, Balfour Kilpatrick, Jacobs Engineering, Bierrum International, Shepley Engineers and Senior Hargreaves.
Construction of the new SAV facility commenced in early 2010 with the installation of the new 11kV electrical substation. The substation is primarily to provide the electrical power for the SAV Plant room, but has been designed such that it forms part of the Sellafield Site Electrical Infrastructure.
November saw the achievement of another major milestone for the project, with the completion of the ventilation stack foundations. The foundations consist of a ring of 12 augured piles each 1200mm in diameter x 38m deep, with each pile socketed 3m into the bedrock. In addition to the 12 working piles, there were 4 x 25m deep piles constructed to support the pile testing plant and equipment. One of these working piles was tested under a compressive and tensile load, with each test carried out over a 24hour period.
On top of the working piles sits the pile cap. This is a 15.7m diameter and 2.2m deep reinforced concrete raft. This is made up of 60te of reinforcement steel bar and 450m3 concrete. The concrete was poured in a single day utilising on site and off site batching plants.
The focus is now on the site set up in preparation for the commencement of slip forming the ventilation stack concrete windshield. Construction work is scheduled to commencement in January 2011 and is expected to take approximately 35 days to reach its full height of 122m.
Construction work on the stack monitoring room foundations is also nearing completion. This is a 15.2m x 15.4m x 1.1m thick reinforced concrete raft foundation. The monitoring room steel superstructure design is currently going through the design approval process. Construction of this will commence once the Ventilation Stack Concrete Windshield has been completed.
As part of the SAV project, there is a requirement to install approximately 3500m of ducting ranging in size from 800mm diameter to 1800mm diameter with the longest duct run of approximately 1Km. In order to support this duct work, the project has to install a series of new pipebridge structures from the donor plants to the new SAV plant room.
The construction of pipebridge foundations commenced during September 2010 with 11 completed to date, consisting of 710m3 of concrete and 17te of steel re-bar cages. The pipebridge structures and ventilation duct tie-ins are in the latter stages of design, with construction scheduled to begin in February 2011.
Completed Substation Foundation
An artists impression of the new SAV facility
The structure of the SAV
