Clearing sludge from Sellafield’s oldest pond

A new machine that sucks up sludge is helping to safely decommission the world’s largest open air nuclear fuel storage pond. 

The Sellafield sludge retrieval project has taken nine years of work, requiring significant engineering on the 60-year-old plant, as well as the design of bespoke equipment to operate in an underwater, radioactive environment.

The Pile Fuel Storage Pond (PFSP) poses one of Sellafield’s most challenging decommissioning projects and an accelerated programme of work is underway.

The machine, known as the Sludge Retrieval Hood, was designed and built to suck up radioactive sludge from the pond floor. The PFSP contains more than 15,000 cubic metres of radioactive water, more than 300 cubic metres of sludge, various nuclear wastes and legacy spent nuclear fuel.

Radiation levels mean that the Sludge Retrieval Hood has to be deployed and operated remotely at the bottom of the six-metre deep pond, where it sucks up some 25 cubic metres of material per hour. The sludge is then transferred into the Sludge Corral, where it will be stored pending treatment through the Local Sludge Treatment Plant, currently undergoing inactive commissioning.

The project is also cleaning sludge from open-topped metal skips stored in the pond. There were around 180 skips and 24 have now been emptied, cleaned and exported to create space.

Steve Cottam, Head of PFSP Programme Acceleration, said:

“Decommissioning the PFSP has been hampered by the layer of sludge on the pond floor and in the metal skips. We’ve had to come up with an innovative solution to remove this radioactive sludge to allow the pond to be emptied.

“It is quite exciting to see the plant make the transition into full-blown retrieval operations. Getting to this stage has, however, been a series of challenges. Equipment was initially designed based on existing drawings and plant records, but we quite often discovered that conditions were not as expected, and sometimes had to make last-minute modifications to equipment. Even now we still find unexpected things!” 

The PFSP, built in 1948, was the very first nuclear fuel storage pond at Sellafield and sludge, in the form of algae, corrosion products and wind-blown material, has been accumulating ever since.  It was built to store nuclear fuel and isotopes from the Windscale Reactors that produced nuclear materials for the defence industry.

Sludge retrieval operations commenced in 2008, when water lances were deployed in the bays to flush the sludge into the main pond. However it is only now that a machine has been developed to move sludge from the main pond itself. 

Kevin Newland, PFSP Technical Manager, added:

“Decommissioning the PFSP is a unique piece of work. Because the pond is open air, we have to proceed with the utmost caution as there is no building to contain any radioactive contamination. We need to prevent any radioactive materials being released into the environment and so we’re looking for new and innovative techniques to successfully complete the project.”

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