Framing the end state

23 July 2019



Six major new framework contracts mean the Dounreay fast breeder and reprocessing site in Scotland is well on its way to being an empty brownfield site, Corrina Thomson reports.


ONE OF THE WORLD’S MOST complex decommissioning projects has taken another step forward with the award of six major framework contracts worth up to £400 million at Scotland’s most northerly nuclear site.

Dismantling of the experimental 1950s Dounreay fast breeder and reprocessing site on the windswept north coast has been progressing over many decades but the new framework leads the way to a brownfield site, regarded as the ‘interim end state’.

Tasks such as dealing with the site’s mixed waste shaft, silo, and pits are now in the picture. Waste from these old facilities must be retrieved, sorted, appropriately packaged and consigned correctly. Then, the structures themselves must be either dismantled or, in the case of the underground shaft, left in a manner that meets current environmental standards.

While many buildings on site have been non- operational for a long time, it is only in the last ten to fifteen years, since the creation of the Nuclear Decommissioning Authority (NDA) and its focus on dismantling, that progress has been made on taking Dounreay apart.

Major work has already been done to dismantle the old nuclear site, including liquid metal coolant removal and destruction and progressive removal of breeder fuel elements from the site’s spherical fast reactor building, demolishing contaminated buildings in the fuel cycle area, exporting nuclear material and packaging wastes.

To facilitate decommissioning, new structures and facilities have been built. This includes a new ventilation system for the fuel cycle area, which replaces the contaminated legacy system dating from site construction a half-century ago.

Construction of the site from the 1950s onwards and its day-to-day operation were focussed on liquid metal-cooled fast reactors and reprocessing. This has left a complex radioactive waste legacy with numerous engineering challenges for those taking the site apart in the present day. Decommissioning was not considered when buildings were constructed, nor when site experiments were being carried out, nor during disposal of the resulting waste.

Employment

The six new framework contracts are good news for decommissioning this complex site and good for the supply chain but a reminder for the local community that employment levels enjoyed during site operations and early dismantling will not continue.

Caithness, the county where Dounreay is sited, is projected to lose 21 per cent of its population within the next 20 years. This dramatic projected depopulation is directly related to the end of decommissioning work at Dounreay and the knock-on effect that will have on other jobs and services in the community. There are around 1000 staff at Dounreay and contractor numbers fluctuate, sometimes up to another 1000 people.

Dounreay Site Restoration Ltd (DSRL) is owned by Cavendish Dounreay Partnership Ltd, which comprises Cavendish Nuclear, CH2M Hill and AECOM. The site’s annual planned expenditure for 2019/20 is £185 million and decommissioning is carried out on behalf of the NDA.

The six framework contracts are initially for up to four years with a possible three-year extension. The companies will compete for distinct packages of work.

Dounreay managing director Martin Moore said: “Six framework contracts have been awarded which bring together the capabilities of at least 28 companies and their supply chains to contribute to deliver of major projects in the years ahead.

“We are looking forward to working with these organisations, which range from small businesses in our local area to some of the industry’s largest players, to drive our hazard reduction programme and make progress towards the site’s interim end state.”

Stephen Adamson, Dounreay’s head of commercial services, said: “This agreement will deliver real and visible signs of progress towards achieving our mission. It is about forming long-term partnerships so that the successful companies can work alongside our own Dounreay staff, ensuring a first-class team combining the best site skills and experience with the wider industry knowledge and innovation that the supply chain can offer.”

Bidders also had to consider a positive impact on the local community such as plans to support science, technology, engineering and maths subjects and development of small and medium-sized enterprises.

A spokesperson for DSRL confirmed that only one local firm, JGC Engineering & Technical Services, is part of the new framework. Others are satellites of larger companies.

The work involved to bring the site to its interim end state includes: construction of a transit flask facility; the shaft and silo waste retrieval facilities; a waste pits retrieval temporary building and facility to repackage waste; demolition of all redundant buildings; land remediation; landscaping; dismantling of three nuclear reactors and continuation of ancillary infrastructure decommissioning works.

Origins

The three reactors at Dounreay are the Dounreay Materials Test Reactor, the 14MWe Dounreay Fast Reactor (DFR) with its famous containment sphere, and the larger 234MWe Prototype Fast Reactor (PFR). In 1962, DFR was the first fast reactor in the world to supply electricity to the grid.

A neighbouring onshore Ministry of Defence submarine reactor site, Vulcan, does not form part of the NDA’s decommissioning responsibilities. Vulcan is the home of the Dounreay Submarine Prototype 1 and the Shore Test Facility PWRs.

A key part of the decommissioning of DFR is the breeder fuel removal project. When the reactor shut down in 1977 many of the fuel elements were burst and stuck in the core. A plan is now being developed to remove these elements and transport them to Sellafield in England at a timescale set out in the Magnox Operating Programme. The elements currently number just under 1000 and work is in progress using a bespoke tool made locally.

The Fuel Cycle Area must also be dismantled. It was originally the home of reprocessing plants, fuel examination buildings and a fuel fabrication plant. It is also used to store wastes in various forms including liquors produced during reprocessing. It is in the FCA that a new ventilation system has been constructed so that ventilation meets modern standards while the site is decommissioned.

While some parts of Dounreay, such as the DFR sphere and the waste shaft, are well known, there are many lesser aspects to end state decommissioning that are rarely noticed. The site’s radioactive laundry also has to be taken apart and also the PIE facility — once used for post-irradiation examination of fuel. Since its inception in the 1950s, Dounreay has been home to some of the UK Atomic Energy Authority’s imaginative nomenclature as well as scientific processes, such as the PUMA plutonium moderated assembly and Panther plutonium nitrate thermal reactor in the former criticality test facility.

When the interim end state (shown in the computer- generated image) is reached, the site will be a field with a smaller fenced area containing a waste store and personnel building. The waste shaft will be a concrete plinth on the coastline.

The shaft

The 70m-deep waste shaft became notorious in the UK as a symbol of poor nuclear waste management after it exploded in 1977. The explosion was due to liquid metal, used as coolant at the site, reacting with water.

Originally blasted out to remove rock excavated to create an undersea passage for radioactive effluent pipes and a chamber, it was later plugged and used for disposal of unusual shapes and sizes of mixed radioactive and other waste from Dounreay, Vulcan and the Harwell nuclear site in England. The contents of the shaft are estimated and will only be known accurately once retrieval takes place.  

Following the explosion, disposals were halted. A decade ago the shaft underwent hydraulic isolation from the environment by injecting grout into boreholes in the bedrock around it. At that time, the plug was also grouted. This grout helps to stop further contamination of the bedrock, particularly on the seaward side where ground and seawater has flowed back and forth in the strong tides.

Apart from helping to isolate its estimated 739m3 of radioactive waste from the environment, this grouting also means that when waste is removed, Dounreay will not have the problem of large volumes of contaminated water that would be produced as the waste is removed and water runs in. Figures suggest that the volume of contaminated water will be reduced from 350m3 per day to 13m3 per day. 

The shaft waste comprises an estimated 645m3 of solid waste and 93m3 of sludge. It includes metallic reactor components, metallic fuel element debris and cladding; equipment and tools; plastics from bag “posting” operations and wrappings on undrummed components and gaiters; and metallic components from plant decommissioning and refurbishment work. Small items include manipulator jaws and tools. A previous report on the site’s waste shaft noted there was anecdotal evidence that the old Panther rig was disposed of in the shaft.

The shaft waste is also expected to contain 23 sea disposal drums from Harwell that contained mostly strontium titanate but also other radioactive waste. These drums may no longer be intact, having been in the shaft since 1974, and may not be fully immobilised inside.

Among the other potentially challenging wastes could be unreacted liquid metal coolant, gas cylinders, and borated glass which might cause assay problems. Previous studies suggested there could be kilogrammes of fissile material in the shaft from breeder waste and other sources.

A spokesperson for DSRL outlined the shaft decommissioning process, saying: “We expect to construct new facilities over the shaft and silo to enable the waste to be removed using a remotely-operated process. 

“The waste would then be characterised, repackaged and cemented inside stainless steel drums for long-term storage on site. When all of the waste is removed, the shaft and silo would be cleaned and then backfilled and capped with concrete.”

The new shaft retrieval building is to be 16m high with a 2382m2 footprint and will be made of concrete with a structural steel frame including an overhead crane and gantries. It will include a HEPA air filtration unit and an emissions stack.

End state landscape

Documents detailing the landscape of the interim end state show the management of areas of the remaining contaminated land and how surface water runoff will be dealt with. The plans also show that the brownfield site will contain a waste store and possible store extension, and an office building.

There will also be a heritage viewing area where visitors can see local historic monuments: Dounreay castle and a chambered cairn, as well as the area where the reactors and fuel cycle area used to be. Where once stood three reactors and reprocessing plants, there will be cycle paths, a wetland wildlife area, a waste store and a low-level waste disposal site.  


Organisations appointed to DSRL’s decommissioning services framework: 

Aecom E&C UK — MW Hargreaves; Kier Infrastructure and Overseas; Morson Projects; NIS; NSG Environmental; Squibb Group; Westinghouse Electrical Company UK

Dounreay Decommissioning Framework Alliance — Cavendish Nuclear; BAM Nuttall; KDC Contractors; JGC Engineering and Technical Services

Dounreay Wood Alliance — Wood; Aquila Nuclear Engineering; GD Energy Services; Orano Projects

Jacobs UK — Atkins

Nuclear Decommissioning Ltd — James Fisher Nuclear; REACT Engineering; Shepley Engineers; WYG Engineering; JBV Demolition; RPS Consulting Services

Nuvia — Graham Construction; Oxford Technologies; Thompson of Prudhoe

A representation of the Dounreay site in future (Photo Credit: DSRL/NDA)
A current view of the DFR sphere (Photo Credit: DSRL/NDA)
Nuclear material being moved to Sellafield from Caithness by train (Photo Credit: DSRL/NDA)
A historic image of sphere construction (Photo Credit: DSRL/NDA)


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