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 to support 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.
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 2010 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 24 hour 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.
August 2011 saw the successful completion of the ventilation stack concrete windshield. The stack was constructed using a continuous slipforming process. This is essentially a circular concrete shutter housed on the slipforming rig, which was used as the working platform. The rig was continuously raised via a hydraulic jacking system. The slip forming construction of the windsheild was a 24/7 operation that took 34 days to reach its full height of 122m.
Following on from the successful completion of the concrete windshield the top 17 (out of 19) steel support floors and access ladders have now been installed within the stack.
The floors were fabricated off site, assembled at ground level in the base of the stack and then winched into position. Once there, the floors were secured to the concrete windshield. The remaining two floors will be installed once the ventilation duct work and Plenum chamber installation is complete.
With the support floors in place, the installation of ventilation duct (flues) could commence. There are 6 flues in total to be installed, all of varying diameters. Each flue section was winched up via strand jacks positioned on the stack roof to a height where by the next flue section could be attached.
This process was repeated for each flue system until the entire duct was secured to the underside of the roof at 120m. To date all 6 flue systems have been installed and secured from the roof down to 23m level. Preparations are underway to receive the cell vent Plenum Chamber. This will be installed in a similar method as the 6 duct flues above.
Construction work on the stack monitoring room foundations has also been safely completed. This is a 15.2m x 15.4m x 1.1m thick reinforced concrete raft foundation. The monitoring room steel superstructure has been completed and this enabled the construction of the Ventilation Stack Concrete Windshield to commence.
With the superstructure and concrete floor complete the external roof and wall cladding works could commence. This works were completed in November 2011.
The SAV plant room building structure is predominantly complete with north and south window installation, external doors and construction opening remaining in order to complete the external envelope of the building. This is to progress over the coming months.
The internal Civil Structural & Architectural works continues with the partitioning and painting of equipment rooms progressing to support installation of plant and equipment, again this is forecast to be complete by the end of the financial year.
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 steel work and pipe bridge erection has been completed up to the monitoring room. This has been the second stage of construction for the pipe bridge structure. This second phase has been followed by duct installation, low active drain installation and then finally electrical ancillaires.
This pipe bridge section has been constructed in two specific phases, these have been termed - the north and south sections. The north section consists of 11 off towers with 10 pipe bridge sections installed between the towers. The length of this pipe bridge is a total length of 125m. The south section consists of 5 off towers and 3 pipe bridge sections. The length of this pipe bridge is a total length of 50.2m.
The new 125m long pipe bridge consists of: 250 tonnes of structural steel, 30 tonnes of steel re-enforcement in the foundations, 800m3 of concrete and 750m of stainless steel ventilation duct work ranging from 800mm to 1800mm diameter
Steel work erection for the first lift of steel work has been completed and the final steel work installation is due to commence within the coming periods once scaffolding operations have been completed.
The project has encountered issues within this area of work with respect to sub surface ground conditions, 9 out of 13 foundation modifications have been completed with 1 in progress and final design imminent on the remaining 3 foundations.
July 2011 saw the Monitoring Super structure steelwork complete, involving 80te of steelwork in the construction process. Since completion of the plant room steelwork, the cladding has been installed to the building structure, making it watertight and allowing the installation of the Heating Ventilation and Air Conditioning (HVAC) plant and equipment to commence.
January 2012 saw the achievement of another major milestone to the project, with the completion of the Duct/Fan installation in Fan room 1, which is located in the SAV plant room. This was achieved 17 days ahead of schedule.
The electrical power distribution containment has also been installed to support cable installation. The project have installed the switch gear within the switch rooms and started the power distribution cable installation with cables pulled between the substation and plant room. The project will be progressing electrical installation over the coming months with electrical equipment being released from the supply chain to support the construction programme.
Installation continues with the ductwork within Filter rooms 1 & 2. The main header sections are again predominantly complete and the filter units have been delivered to site to allow them to be installed and site measures to be undertaken to complete installations. The project again will proceed to install the auxiliary systems following completion of the main process ductwork.
Ductwork manufacture continues inline with the construction programme. The manufacture of the CE&I panels is progressing well with 41 panels approved for manufacture, of these, 8 have been shipped to site and 14 are in storage awaiting completion of the rooms.
The new SAV Facility
Fan Room 1 Installation Complete
The structure of the SAV
