The 10-month decommissioning operation is being carried out by management and operations contractor Magnox for site-owner the Nuclear Decommissioning Authority.

Pond clean-outs have traditionally used remotely operated equipment to lift the radioactive metal skips used to store thousands of used nuclear fuel-rods clear of the water.

This exposes the waste to air before the skips cane be cut up, decontaminated, stored and eventually disposed of, a process that incurs potential radiation-dose risks for the workers.

Magnox says that by using divers to carry out the work under water – which, along with their protective suits, is said to act as a radiation barrier – the skips can be cut up more safely and awkward areas accessed more easily.

This makes the process safer, faster and more productive, says the contractor, which claims that it also has a lower environmental impact.

The nuclear dive-team tackled their first UK operation in 2016 at Kent’s Dungeness A Site, which also closed at the end of 2006. During more than 250 dives there, new ideas emerged, says Magnox, including the use of lightweight plastic platforms for divers to stand on while exploring uncharted areas of the pond floor.

The fuel from Dungeness was removed and transported to Sellafield for reprocessing, and the lessons learned there are now being applied at Sizewell A’s pond, says Magnox.

The first dive has just taken place to survey the pond floor, transfer sludge into a purpose-built tank, set up cutting equipment and start work on the first of 35 skips classified as containing “intermediate level” radioactive waste.

“The scale of work to be delivered by the divers is huge,” said Programme Manager Steve Franks. “Although we only have one pond to decommission, the inventory of the ponds is larger than at Dungeness A, but we will still be looking to speed up the work wherever it is safe to do so.”

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