After more than twenty years of preparation, a landmark moment has been reached in the ongoing Sellafield radioactive waste removal project.
Seventy tonnes of waste have now been taken out of the site’s most hazardous building, the Magnox Swarf Storage Silo (MSSS), and placed into safe storage. This milestone marks a significant advance in one of the UK’s most complex nuclear clean-up challenges.
The work began in 2022, following decades of planning to tackle a structure that was never designed to be emptied. When the silo was first built in the 1960s, the focus was solely on storing waste materials from nuclear reprocessing. At that time, no-one considered how the contents would eventually be retrieved. The building, constructed more than sixty years ago, was originally used for the underwater storage of Magnox fuel cladding – or “swarf” – stripped from used nuclear fuel rods. Its 22 deep compartments, each large enough to hold six double-decker buses, were gradually filled with thousands of cubic metres of waste until 1991, when the site stopped routinely receiving new material.
Sellafield’s head of legacy silos, Phil Reeve, described the removal of waste as a moment of real progress. “It’s a big moment to see it successfully deployed in an active environment for the first time,” he said, referring to the latest retrieval equipment.
“It allows us to crack on with confidence.” The retrieval process has already created a 7-metre crater in the centre of the waste pile, which now needs careful management to prevent the surrounding material from collapsing inward.
To deal with this, engineers at Sellafield have developed a unique piece of equipment that resembles a garden rake. Weighing 1.4 tonnes, it uses stainless steel arms to pull waste from the edges toward the centre, levelling the crater and making the next stage of Sellafield radioactive waste removal safer and more efficient.
Because no exit route was designed when the silo was first constructed, engineers had to retrofit one. This involved assembling massive Silo Emptying Plant (SEP) machines on top of the silo’s compartments. These machines act like industrial “lucky grabbers”, using hydraulic claws to lift the submerged waste into shielded containers. Each SEP machine weighs around 400 tonnes and measures over 13 metres long. They move on rails across the silo’s roof, locking into position above compartments to extract and contain the waste.
The first of these machines began retrieving material in April 2022, while the second was completed in 2023 and is expected to begin active operations this year. A third SEP machine is already being prepared for installation, with all three due to work simultaneously in the coming decade. Together, they will empty the silo section by section, beginning with the oldest compartments. Even with this advanced machinery, the full Sellafield radioactive waste removal process is expected to take around 25 years.
The waste is being transferred into shielded containers known as transfer packages, which are then moved to a new interim storage site, the Box Encapsulation Plant. This modern facility, due to open in 2027, will safely house the retrieved material in robust cemented boxes. It will also handle the transport of contaminated equipment to the Silo Maintenance Facility, where the retrieval tools will be serviced and maintained.
The contents of the MSSS are exceptionally hazardous because of the materials involved. The Magnox cladding is made primarily of magnesium, which can ignite easily when exposed to air. To prevent fires, the waste has been stored underwater, but this has created further complications. The interaction between the metal and water generates hydrogen, requiring continuous ventilation to keep the gas levels safe. Over time, radioactive material has also leached into the water, creating a hazardous “liquor” that must be carefully managed.
This liquor has leaked on rare occasions, including a self-sealing leak first detected in the 1970s that briefly resumed in 2019. Although the leaking material is now far less radioactive, its presence underscores the urgency of the retrieval programme. For over a decade, teams have been removing liquor from some areas of the facility, replacing it with clean water to dilute the radioactive content. This has already halved radiation levels in parts of the silo, improving conditions for ongoing operations.
Major upgrades to the structure have also taken place to support the Sellafield radioactive waste removal mission. These include the construction of a seismic restraint tower in 2012 to strengthen the building, new nitrogen systems installed in 2018 to reduce fire risk, and extensive overhauls of electrical systems. Each of these steps has made the process safer and more controlled.
Although seventy tonnes of waste have now been removed, around 10,000 tonnes remain inside the silo. The timeline ahead is long: the second SEP machine is set to join operations in 2025, the third by 2030, and major waste removal milestones are expected throughout the 2040s. By 2050, Sellafield aims to have removed 95% of the silo’s waste, marking the near completion of one of the most challenging decommissioning projects in the world.
This latest achievement is not just a milestone for Sellafield radioactive waste removal but a symbol of the UK’s ongoing commitment to dealing safely with its nuclear legacy.
