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How sonar and gaming technology is helping the decommissioning of Sellafield’s legacy nuclear waste storage ponds

24 May 2017

A particularly difficult job at the Sellafield site has just been completed - mapping the magazine transfer bay, one of the most congested legacy areas of the First Generation Magnox Storage Pond. This article, originally published in Sellafield Magazine, looks at the some of the challenges facing the team trying to identify the contents of the pond and the technology used to complete the task and prepare it for emptying and decommissioning.

The First Generation Magnox Storage Pond: Image - Sellafield Ltd
The First Generation Magnox Storage Pond: Image - Sellafield Ltd

The First Generation Magnox Storage Pond (FGMSP) at Sellafield is one of the site’s four Legacy Pond and Silo facilities. The Magnox Storage and Decanning Facility was constructed during the 1950s and 1960s as part of the UK’s expanding nuclear programme. Its role was to receive and store irradiated fuel from the UK’s first generation Magnox reactors, and to remove the fuel cladding prior to the fuel being processed.

In 1974, a long reprocessing shutdown at Sellafield caused fuel to be stored underwater in the storage pond for longer periods than normal. This resulted in the Magnox fuel corroding in the pond, which in turn gave rise to increased radiation levels and poor underwater viewing. This slowed the rate of decanning, leading to increased residence times and further fuel corrosion.

The plant continued to operate until its replacement, the Fuel Handling Plant at Sellafield, was commissioned in 1986. The final fuel was received into the First Generation Magnox Storage Pond in 1992.

The FGMSP was constructed as an open-air pond. Over the years, it has accumulated significant quantities of waste materials, sludges from corrosion of fuel cladding, fuel fragments and other debris which has blown into the pond.

Its nuclear fuel, sludge, intermediate level wastes and water each need to be safely removed and processed through separate routes.

A particular problem in the pond was the clutter caused by blocked or faulty fuel magazines which were suspended above the floor. The tangle of material meant the area became inaccessible by remotely operated vehicles, so that originally the only way of seeing what was inside was by peering in from above with torches.

Specialist sonar has fundamentally changed this situation, but identifying the different types of structures and sludges in the pond is still not easy. Steve Lainson, Managing Director of sonar equipment designer and operator Fortis Remote Technology, takes up the story.

“It is literally like chasing shadows,” says Lainson. “Each time the sonar picks up something solid it means there’s a blind spot or ‘shadow’ behind that point which we have to map from a different angle. There was so much material in there that it took more than three times the normal number of sonar scans to survey the area. Add in the challenge of working in an area where access is restricted by radiation levels and it was the hardest job we’ve ever done.”

Sonar shows a more complete picture of the wastes in the storage pond
Sonar shows a more complete picture of the wastes in the storage pond

Considering other jobs by Fortis could be looking for faults in an oil rig’s structure deep in the North Sea, that gives an idea of the achievement at Sellafield.

The company has built up an international business from its rural base in Broughton, Cumbria. In 2007 Fortis successfully applied for an R&D grant from the Nuclear Decommissioning Authority to use variable frequency sonar equipment to help characterise sludge in nuclear facilities. That grant allowed the company to build on the capability and intelligence offered by the more basic sonar equipment it had been using before. This has not only brought benefits to the UK nuclear industry, it is also helping abroad. Fortis is now working alongside Cockermouth-based Createc on mapping reactors 1 and 2 at Fukushima. It is currently carrying out feasibility studies and modelling work before conducting the actual surveys at the Japanese facility later in 2017.

“Working with our technology partners Createc and Marine Electronics we’re taking sonar technology to new places for nuclear applications,” says Lainson. “We are currently developing sonar mapping so that it will not only tell us that there’s something there, it will also tell us what it’s made of. Our next generation sonar probes will be able to ‘feel’ the environment so they can tell the difference between, for example, sludge or concrete or steel. For nuclear applications the sonar data will be overlaid with the gamma radiation value of the target area too.”

More precise information and modelling on the nature of the challenge should also help remove much of the uncertainty about a job, meaning Sellafield will have more accurate and realistic estimates of what the work is likely to cost.

The information captured in the sonar mapping of the magazine transfer bay in the FGMSP is being used in new ways, thanks to technology pioneered in the gaming world. To fully explore the 3D map created by the sonar probes, those responsible for cleaning up the legacy pond will be wearing virtual reality headsets to build an accurate idea of the pond’s contents. The basic virtual reality equipment is now available off the shelf for about £1,000 and Sellafield robotics and autonomous systems expert Dr Paul Mort says the nuclear industry is now enjoying the benefits of products created for the gaming sector.

“Twenty years ago we looked at buying laser capture systems similar to the ones you now put on top of the console or television to play certain games. They cost around £25,000. Now you can get far more powerful and sophisticated versions for your home for around £80. The mass market is having massive benefits for us. Many families have teenagers using joypads to interact with 3D games. This development has helped us ‘humanise’ information and processes which could be really dry and boring if presented in just words or diagrams. It helps us get more value out of our data.

Mort says affordable, off-the-shelf gaming technology could also help the nuclear industry open its doors to more small to medium sized enterprises. “If we can use this technology to illustrate an area which needs to be cleaned up, then it could remove the need to walk around the facility to scope out a job. That means new people with new ideas could start to help us. More precise information and modelling on the nature of the challenge could also help remove a lot of the uncertainty, meaning we’d have more accurate and realistic estimations of what the work is likely to cost. This technology could potentially narrow down our cost predictions to the tune of billions of pounds and help drive out risk.”

Sonar technology has advanced hugely in recent years. Now sonic probes fire millions of pulses which shape incredibly detailed 3D images in a ‘point cloud’. The mapping of the magazine transfer bay in the First Generation Magnox Storage Pond comprised around 24 million of these ‘points’.

Now that there is a better understanding of exactly what is in the pond, the team can plan far more effectively on how to empty and decommission the bay, building on the work carried out to bring the adjoining Magazine Maintenance Facility back into service in February 2016. The facility can now receive the blocked magazines from the bay so the team can work on dislodging the fuel bars and getting the waste out.

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