Office for Nuclear Regulation

Divers enter legacy pond at Sellafield

29 March, 2023

Underwater divers have successfully entered a nuclear pond at Sellafield and completed 14 dives to remove waste from a longstanding storage facility in a milestone achievement at the site.

The Office for Nuclear Regulation (ONR) granted permission to Sellafield Ltd for underwater divers to access the Pile Fuel Storage Pond (PFSP) following a rigorous series of assessments and appraisals of the work in Cumbria.

The use of divers replicates a well-established technique previously carried out internationally and at other UK nuclear sites during their decommissioning phase.

The PFSP was commissioned for operation in the 1950s for the receipt and storage of fuel and isotopes from the Windscale Piles. It is one of oldest and most hazardous facilities on the Sellafield site, containing spent fuel, sludge, radioactive and contaminated solids, intermediate level waste and low-level waste, pond water and contaminated concrete.

While significant progress has been made in removing historic waste from the facility with more than 75% of the waste safely taken out so far, divers are needed to help extract the remaining inventory.

Removing the remaining material from the pond and placing it into modern safe storage is a strategic priority for Sellafield and a key regulatory priority for ONR.

Underwater divers at a nuclear pond at Sellafield.

After a detailed assessment of the safety case by ONR inspectors from a range of different specialisms including fault studies, radiation protection, human factors and conventional health and safety, ONR issued a licence instrument granting Sellafield Ltd permission to pilot the use of divers in bays 11 and 12 of the pond.

During the last ten years, Sellafield Ltd has undertaken significant clearance work inside these two bays using a range of techniques including remotely-operated vehicles and workers deploying long reach tooling from the edge of the bays.

Good progress has been made, but these established clearing techniques have gradually delivered diminishing returns. This is because of the many integral structures attached to the floor of the pond complicate the recovery of the remaining sludge, debris and fuel and hinder easy access to the radioactive material.

Alan Wylie, ONR’s Superintending Inspector, said: “Due to the work that has been completed in bays 11 and 12 during the last decade to remove significant amounts of the waste, and because of the isolation of these two bays from the rest of the pond, this area presented the lowest risk in which to pilot the use of divers.

“Our specialist inspectors assessed Sellafield Ltd’s safety submission and were satisfied that the risks to divers entering the pond had been demonstrated to be as low as reasonably practicable and that Sellafield Ltd had taken suitable and sufficient measures to reduce risk.

Underwater divers at a nuclear pond at Sellafield.“As such we were satisfied that it was safe for divers to enter and work in the pond.

“The use of divers has allowed Sellafield Ltd to make progress with retrieving the remaining material from bays 11 and 12, which existing retrieval techniques are no longer able to do.

“Our inspectors will continue to monitor the retrievals work from this facility as part of our inspection activities on the site.”

Diving in nuclear ponds is a widely accepted and mature technique for waste removal and is a recommended procedure from the International Atomic Energy Authority’s (IAEA) guide to pond decommissioning.

The technique has been successfully used in the clean-up of other sites across the UK including Dungeness A in Kent, and more recently at Sizewell A in Suffolk.