Sellafield is deploying remotely operated mini submarines explore radioactive sludge in a spent fuel pond to aid the complex remediation process.
The submarines are being used to explore, survey and carry out remote operations at the bottom of Sellafield’s First Generation Magnox Storage Pond (FGMSP), which the site operator described as one of the biggest decommissioning challenges there.
The 1950s’ pond handled 27,000t of nuclear fuel over its lifetime and it is estimated that there is up to 1,500m3 of radioactive sludge within, equivalent to more than half an Olympic swimming pool.
The pond has thick reinforced concrete walls, however, it was built with no roof and is open to the elements, so sludge, made up of algae, corrosion products and wind-blown material has accumulated and is now radioactive.
“We’ve taken technology used in the hazardous deep sea conditions and applied it at Sellafield in our own hazardous nuclear fuel storage ponds,” said Sellafield FGMSP head Martin Leafe. “The mini submarines can explore, survey and carry out remote operations at the bottom of the pond, while the workers remain safe and dry outside the pond.
“We are building up our knowledge of the radioactive sludge characteristics to help develop equipment for bulk sludge retrievals, which will have to cope with sludge up to one-metre-deep in places. The greater our understanding of the sludge the more opportunities we will have to accelerate decommissioning of this priority project.
“Significant savings will be made using mini submarines rather then designing and building complex bespoke equipment which was our original plan. We now have the ability to clear space in this hugely congested storage pond to help with the recovery of nuclear fuel, contaminated waste and radioactive sludge as part of our work to empty this legacy facility.”
FGMSP manager Dave Skilbeck added: “We are extending our Remotely Operated Vehicle (ROV) capability all the time to help empty this historic nuclear pond. Our experienced pilots can ‘fly’ the machines within the pond to survey the fuel and sludge, take sludge samples for analysis, and pick up and consolidate nuclear fuel into fuel containers for export out of the pond.
”Our latest success has been attaching an eductor to the ROV which has proved that we can lift the sludge from the bottom of the pond. The eductor device is like a powerful jet pump that creates a negative pressure differential that draws the sludge up through a thick hose.
“We need about 50m3 of sludge to commission and test the new Sludge Processing Plant later this year and we’ve now proved the technology to get the job done. We can safely get the radioactive sludge off the bottom of the pond whilst leaving behind the water which is a significant step forward.”
Radioactive sludge to a depth of 300mm was successfully removed from a small area of the pond floor right down to the concrete base slab.
Further trials are now being carried out to capture and temporarily store the sludge, before it is turned into a consistency suitable to start pumping it across to the new Sludge Processing Plant at the end of 2014.