The Magnox transformation18 February 2020
Valerie Drake, former magnox waste strategy & permissioning manager, discusses the scope for cost reductions at UK magnox and research reactor sites.
FACED WITH A GROWING BILL to clear away the legacy of radioactive waste from the country’s first generation of nuclear power plant, the UK government posed industry a question. Could the cost be lowered without reducing the standards of protection for the public and environment?
Magnox and Research Sites Restoration Limited, the two site licence companies responsible for 12 legacy plants, had already shaved costs from their programme.
Cavendish Fluor Partnership, a transatlantic joint venture that managed the sites from September 2014 to August 2019, looked at their plans and concluded there was scope for more.
The group challenged historical assumptions. Did it really need so many separate facilities to store the higher-activity waste until a national facility was ready? Could it reduce costs without lowering standards by introducing more cost effective shielded containers and consolidating those at fewer storage locations using a standard design? Could divers be deployed to speed up pond clearance following removal of the fuel? Was there a better balance between decontamination and disposal?
The answer was yes. Applying techniques and innovation learned by industry in the UK and the USA, and using an organisational delivery model to allow for repeatable solutions to waste problems (a programmised approach), the Cavendish Fluor Partnership came up with a new plan that offered lower costs and quicker results.
The Cavendish Fluor Partnership took over the leadership of the two site licence companies and their 12 sites in 2014 under a contract with the Nuclear Decommissioning Authority, merging the two companies to create a single operating model. The existing plan was overwritten, new outcomes set and working practices re-aligned to deliver the savings.
Plans for 11 interim storage facilities for higher activity waste at each site have been replaced by seven regional stores, all of which have been completed.
The rate of low-level waste production increased four-fold as accelerated decommissioning set in, yet the proportion being sent to the UK’s dedicated low level waste repository (LLWR), for burial reduced dramatically. Between April and September 2018, the company had a diversion rate of 97% for metallic low level waste (LLW), combustible LLW and very low-level waste sent away from the repository.
Decommissioning of all sites is now on course to reach the end-state or start of their care and maintenance phase (C&M). In 2018, Bradwell in Essex became the first nuclear site in the UK to be placed in care and maintenance, providing valuable learning for the other sites.
Bradwell — pathfinder
The Bradwell site in Essex was a pathfinder for the rest of the Magnox fleet.
It was chosen in 2009 for accelerated decommissioning, which would be delivered using a range of technologies. These included different waste packages made of ductile cast iron, store design, and waste dissolution plant, which were intended to be developed and used at the other sites.
The Cavendish Fluor Partnership, which steered the project, was working towards delivering the site into a passively safe and secure state known as care and maintenance (C&M) by a forecast date in 2019. The site successfully achieved its long-term care and maintenance conditions in November 2018, when it became the first UK site to reach this stage of decommissioning.
In order to successfully achieve this accelerated closure, 240 tonnes of intermediate level waste and fuel element debris (FED) had to be dealt with. When the Cavendish Fluor Partnership initially took over the contract dissolution was the strategy for this metallic waste. Dissolution negated FED storage on-site and, in theory, this was a good idea. However, the technology was novel and in order to achieve the C&M date, a parallel strategy was required.
The Cavendish Fluor Partnership pursued direct disposal to LLWR. It was able to demonstrate that the preparation work, involving the removal of the highly radioactive springs, reduced the activity sufficiently to enable the waste to be considered as LLW. Approximately half of the total FED was disposed of in this manner, which resulted in significant savings. The 18 FED vaults were deplanted and a total area of 972m2 was decontaminated — equivalent to five tennis courts.
The greatest visual impact at Bradwell was recladding the twin reactor buildings to leave them in a safe, weather- proof and seismically secure condition until their final clearance towards the end of the century.
Bradwell’s interim storage facility housing intermediate level waste will also be used to store similar arisings from Dungeness A and Sizewell A, which is now responsible for the care and maintenance regime at Bradwell. Conditioned waste is already being received from Dungeness into the store.
Technical innovation has been key to yielding reductions in waste management costs without compromising radiological safety and environmental compliance.
The Cavendish Fluor Partnership worked with the Magnox teams, developing a “lead and learn” approach that allowed new techniques to be rolled out across the estate after successful demonstration.
The use of ductile cast iron containers for disposal of high volumes of ILW was re-evaluated and replaced with lower-cost self-shielded 6m3 concrete boxes and a modular encapsulation plant.
This approach also allowed a simplified approach to the treatment of FED at the other Magnox sites, moving from a high-cost chemical dissolution process to the simpler technology of encapsulation in cement, or grouting.
The principal challenges faced and overcome when implementing the revised waste management strategy were:
- integrating the 6m3 box with existing retrieval equipment, store designs and new encapsulation requirements;
- inter-site transport of packaged waste, including transport licences, letters of compliance, planning permissions and stakeholder engagement to achieve storage consolidation; and
- integration and sequencing with the overall work programmes and existing processes.
Defuelling and pond clearance
In September 2019, the Magnox estate became completely clear of nuclear fuel, less than four years after the last of the stations ceased generating electricity. Moving the fuel to Sellafield in Cumbria eliminates 99% of the radiological hazard at the other sites. Fuel removal and transportation is a routine practice in the UK. But the age of the Magnox stations and ensuring their infrastructure remained fit-for- purpose for the last operation demanded high levels of engineering and safety professionalism.
A separate programme to remove research nuclear material from Harwell to Sellafield is at 60% of completion. Some flask components had to be re-manufactured and new transport licences obtained along the way. When complete, the remaining ILW from research sites at Harwell and Winfrith will be consolidated at Harwell, pending its ultimate removal to a geological disposal facility.
Prior to transportation the fuel is stored in ponds and the empty ponds have presented their own challenges to the decommissioning teams. Empty fuel skips, ion exchange units and a build-up of sludges and other high-dose debris on the pond floor had to be removed. For the first time, divers carried out the removal of the pond furniture, including underwater cutting of the emptied skips — an innovation that proved hugely successful.
The same team completed the work at all the sites, to maximise efficiencies and reduce overall durations. As of August 2019, eight legacy spent fuel cooling ponds have been completed or are near to completion.
Clearing the vaults
At Berkeley in Gloucestershire a series of modules are being assembled to process and package the waste remaining in its vaults. Approximately 1700m3 of radioactive waste arising from reactor and fuel management operations were deposited here during operation.
Over 100 ductile cast iron containers have now been filled with waste retrieved from the vaults. The system uses Cavendish Nuclear designed waste modules to retrieve sort and assay the waste. Work is now in progress to install an industrial shredder to deal with some of the more difficult containerised waste. Due to the very high volume of waste, work is also in hand to introduce the 6m3 waste package instead of ductile cast iron containers.
Since starting work on the sites in 2014, the Cavendish Fluor Partnership and the Magnox Ltd team have implemented a wide range of new initiatives and strategies that are delivering, and will continue to deliver, significant benefits to the Magnox estate and the UK taxpayer.
The number of successes delivered, in such a short amount of time, has been nothing short of transformational and all delivered whilst ensuring a very high safety and environmental performance throughout. The partnership set out to achieve some challenging waste management strategies to save taxpayers’ money and the building blocks not only help Magnox but will also move the industry forward.
Main Image: The Bradwell site in Essex, pictured in August 2019 (photo courtesy Magnox Ltd)
Author information: Valerie Drake is Waste strategy director at Cavendish Nuclear