Their task was to build a picture of the waste inside, which had long since been consigned to vaults beyond the reach of the human eye.
The findings would be used to refine the design of the plant to deal with the material. But the results did not underpin the plan, in fact they undermined it. And, in the process, they turned the decommissioning of the Magnox Swarf Storage Silo (MSSS) on its head.
This pioneering research work had yielded a revolutionary scientific breakthrough, which has been hailed as one of the most important moments in Sellafield’s history. Alan Parry, Sellafield Ltd’s head of strategy for MSSS, explains why. “I began working on this in earnest in April 2014, but the seed of the idea goes back a lot further,” he says.
“The Silos Direct Encapsulation Plant (SDP), a complex treatment and encapsulation plant, had long been the preferred option for dealing with the intermediate level waste in MSSS. However, because of the uncertainties about the nature and state of the waste within the silos, the design had been based on ultra-conservative assumptions. The research work was commissioned in order to fill in some of the blanks; to give us the information we required to underpin the approach. However, the more we discovered about the material, particularly its reactivity when taken out of water and into air, the more it became obvious that our assumptions had been overly pessimistic. This gave us the opportunity to think radically about the best solution to dealing with this waste.”
The findings were the result of experiments carried out laboratories at Springfields, near Preston, peer reviewed by academic institutions. And these were bolstered by a parallel human research project, with former workers at the silo asked to recall their memories about what exactly was tipped into the building in the days when record keeping was not the priority it is today. The findings emerged at an opportune time. In February 2014, the G6 group had been formed. This is a collective made up of the organisations with a major stake in the decommissioning of Sellafield, it includes: the Department of Energy and Climate Change; the Nuclear Decommissioning Authority; Sellafield Ltd, the Office for Nuclear Regulation; the Shareholder Executive; and the Environment Agency. Its purpose is to remove barriers – perceived or otherwise – to the accelerated clean-up of the site’s high hazard facilities. And solutions to the clean-up of MSSS were soon on its agenda.
“The SDP project was one of the first issues raised by the G6,” recalls Alan. “The project was coming out of the procurement cycle and it was clear that it was not going to be available until later than we required it. This could have the potential hold up the number one priority task of the MSSS programme – removing the waste. Through the G6 we were able to look at the strategy and ask: ‘Might there be another way of doing it?’ We were able to take a holistic approach and ask ourselves what should be the primary focus of the programme? SDP was all about creating a disposable product; a heavily engineered solution that treated and encapsulated the waste in a form that would be acceptable for disposal in a geological disposal facility.”
“However, we began to think that the emphasis was wrong; that what we should really be pursuing is accelerated risk reduction – emptying the silo in the quickest time possible. The SDP approach meant we had to execute a phased approach to waste retrievals, with pauses in between, thus slowing down that risk reduction. So we looked at a simplified approach, essentially a one-step solution – retrieving the waste, placing it ‘raw’ into containment, and transferring to interim storage. The containers would be grouted at a later stage before finally being consigned to a geological disposal facility. The removal of SDP, and its complex treatment and encapsulation processes, would in theory accelerate retrievals and de-risk the programme. As added bonus, it would have the potential to save hundreds of millions of pounds, although this was never the focus, merely a fortunate by-product.
“We had identified some feasibility, it looked good, but at that time it was not underpinned. From August this year, the work became about context – could we make this work in the Sellafield environment? We worked on that and took it through a review process. We calculated the benefits and discovered that because we could get after the waste earlier – without the need for discrete phases – we could empty the silo four years earlier and ensure far more predictability.”
So far so good, but how would the company responsible for acceptability of waste products for the geological disposal – Radioactive Waste Management Ltd (RWM) – react to a move away from a heavily engineered waste product to a raw waste option?
“RWM were fantastic and understood straight away what we were trying to do,” adds Alan. “We worked with them to apply what we call the ‘decommissioning mind set’ and work out whether we had the balance right between the future needs of the geological disposal facility and reducing risk at Sellafield. They immediately saw that an insistence on an engineered waste product actually increased risk because it slowed down the emptying of the silo and introduced complexity – and thus unpredictability – into the programme. They did a formal assessment of the raw waste product and ultimately gave us a letter of acceptance to say they saw no reason why they could not accept the packages with some simple finishing steps like grouting prior to consignment.”
Approval by ONR was also secured and the alternative approach was recommended by the Sellafield Ltd and NDA boards. The final step was taken in October 2015 when the Government gave the green light to turn off the SDP project, allowing Sellafield Ltd to pursue the alternative approach full throttle.
“I’m immensely proud of what everyone involved in this has achieved,” says Alan. “Not many opportunities come along at Sellafield where you can reduce costs as well as reducing risk and hazard at the same time. One of the most exciting things about the new approach is that we’re no longer foreclosing future opportunities for managing the waste. If something like Thorium research comes to maturity, we haven’t packaged this waste away beyond reach. We can retrieve if an alternative approach becomes available. The switch to alternative approach has been described by the NDA as a “paradigm shift” and by Sellafield Ltd’s managing director as a “pivotal moment in the site’s history.”
So what is the lasting legacy of this work?
“I think what we’ve done is provide a new blueprint for problem solving at Sellafield,” says Alan. “We have unpicked arguments that have been around for decades, by using research and experiments to remove uncertainty. We haven’t invented anything magical here, but I think we have pointed the way to a new way of thinking about Sellafield.”