According to Sellafield Ltd., the Magnox Swarf Storage Silo, which contains intermediate-level fuel cladding swarf waste arising from reprocessing Magnox reactor fuel, is the site’s most hazardous building and the company’s primary decommissioning priority.
Background: Standing in the oldest part of the Sellafield site, the Magnox Swarf Storage Silo has stored nuclear waste for the last 60 years in water-filled chambers (silos). The building was originally constructed as six silos in the 1960s. As the silos became full, more were added between the 1960s and 1983, totaling 22 compartments. The Magnox Swarf Storage Silo stopped receiving fuel cladding waste in 2000.
The silos, however, were not built with decommissioning in mind, making retrieval of the waste difficult. Sellafield Ltd. has been emptying waste from the silos using the first waste retrieval machine since April 2022.
The machines: Sellafield Ltd. said that the second waste retrieval machine was fully built inside the Magnox Swarf Storage Silo, with the final piece of equipment—the main control cubicle—being lifted into the silo and fixed into position in February.
The silo emptying machines are far bigger than any of the entry points into the silo and so must be lifted in in 22 different modules and then assembled inside the legacy building—like ships in a bottle.
All three machines were originally designed and manufactured in Wolverhampton, England, by Ansaldo NES, and all are now under the control of Sellafield Ltd. and i3 Decommissioning Partners, the U.K.’s decommissioning delivery partnership framework partner.
Weighing 360 tons and comprising of around 13,500 working parts, the design, manufacture, and assembly of the first machine started more than 20 years ago. According to the company, it will take another three years of preparation and commissioning work inside the silo before the machine can start retrieving waste.
“It’s a big task involving lots of different skills: fitters, riggers, electricians, and all the people behind the project too,” said Gary Kershaw, part of the i3 engineering team that assembled the second machine. “At any given time during assembly there’ll be roughly a dozen people in our team working on site and half a dozen people at the off-site locations. Everyone knows just how important getting this right is.”
Claw game: The machines work by lowering a claw grabber into the silo, lifting waste debris back up and placing it into a stainless steel container (skip), which is gradually filled and then sent to a separate interim waste storage facility in more robust overpack containers. With no control over what waste the grabber picks up, the machine operates much like an arcade claw game. It is a “lucky dip” arrangement with every grab, Sellafield Ltd. said.
Emptying the large, individual silos using the machines has been compared to “emptying a dust bin with a teaspoon.”
