Taking the plunge with Sizewell A pond clearance

Scuba divers have started working in the former fuel storage pond of the Sizewell A Magnox nuclear power plant in the UK. They will use lessons learned from underwater work previously carried out to remove radioactive waste from the ponds at the Dungeness A plant.

Scuba divers have started working in the former fuel storage pond of the Sizewell A Magnox nuclear power plant in the UK. They will use lessons learned from underwater work previously carried out to remove radioactive waste from the ponds at the Dungeness A plant.

A diver performs work within the Sizewell A storage pond (Image: Magnox)

A team of 12 divers supplied by US contractor Underwater Construction Corporation (UCC) recently performed the first dive at the Sizewell A pond. The main focus of that dive was to survey the pond floor, transfer sludge into a purpose-built tank, set up cutting equipment and size-reducing the first of 35 skips that were once used to store used nuclear fuel at the site. These skips - which will be packaged for disposal - are classified as intermediate-level radioactive waste.

Pond clean-out conventionally takes place using remotely operated equipment to lift the whole skips clear of the water, exposing them to air, where they are carefully cut up before decontamination, storage and eventual disposal. This process is slow with potential radiation dose risks for workers.

By working under water, the divers can cut up the skips more safely and access awkward areas more easily, making the whole process safer, faster and more productive. The water acts as shielding, reducing doses accrued by the team of divers, who wear full protective suits.

This approach was commissioned by Magnox at the Dungeness A site, with UCC performing a total of 265 dives in two ponds from late 2016 to 2017. During that time, the team of divers cut up empty fuel storage skips and retrieved other pieces of submerged equipment.

A number of innovations emerged during the work at Dungeness A, including the use of lightweight plastic platforms for divers to stand on when exploring uncharted areas of the pond floor.

The lessons learned at the Dungeness A pond are being put into practice at Sizewell A as part of a decommissioning project expected to take some ten months to complete.

Sizewell A's two 210 MWe Magnox gas-cooled reactors operated from 1966 until 2006. Defuelling began in 2009, with fuel removed from the reactors placed in the site's used fuel storage ponds before being packaged in transport containers for shipment to the Sellafield complex for reprocessing. The final flask of fuel was shipped to Sellafield in August 2014. Sizewell A was declared completely fuel free in February 2015. The decommissioning milestone marked the removal of 99% of the radioactive hazard from the former Magnox nuclear power station.

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

Magnox Ltd, owned by Cavendish Fluor Partnership, is the management and operations contractor responsible for managing the UK's former Magnox nuclear power plants on behalf of the country's Nuclear Decommissioning Authority (NDA).

Geoff Suitor, head of the Magnox programme for the NDA, said: "Magnox's implementation of innovative approaches, such as the use of divers to handle radioactive waste in ponds, contributes to real progress in reducing risks and hazards at the Magnox sites. Together, we are successfully cleaning up and making safe the UK's earliest nuclear sites on behalf of communities and the environment."

Researched and written
by World Nuclear News