Taking a deep dive into the problem of nuclear waste

In December 2022 Josh Everett, a diver from the specialist US nuclear diving team Underwater Construction Corporation Ltd, became the first person in more than 60 years to descend a ladder and set to work in one of the most unique workplaces in the world. The last time anyone entered Sellafield’s Pile Fuel Storage Pond (PFSP) was in 1958, when records show a maintenance operator and health physics monitor carried out a dive into the newly constructed pond to repair a broken winch.

In December underwater divers successfully completed 14 dives to remove waste from a longstanding storage facility. The dives take years of preparation with facilities created to successfully replicate the legacy ponds, although contamination and visibility in the pools are unable to be measured, leading to the specialist teams having to navigate a whole new operation.

Ryan Crellin, a senior project manager at Sellafield Ltd, says: “We try and replicate the environment off site as closely as we can do so that the divers can experience what they’ll actually encounter on site. Obviously there are a few things that we can’t replicate around visibility and the contamination and how they deal with that, but certainly the infrastructure and how they enter and exit the water we try to replicate that as closely as possible. The company that we partnered with have been diving in nuclear ponds since the 1970s in America, the UK has dived previously in magnox sites. Where this is a significant step on is that the levels of contamination and the tasks that they’re carrying out are kind of world leading and world firsts. This job because of the hazardous nature of it and it being a complex and novel piece of work for Sellafield required full permission from our regulators, the ONR and the Health and Safety Executive dive specialist team. What comes with that is a huge amount of internal governance to make sure that we’re carrying out the right action at the right time in a safe and effective manner.”

The Pile Fuel Storage Pond is one of the oldest buildings on the Sellafield site and was constructed in the 1940s to support the operation of the Windscale Piles; the first nuclear reactors to be built at Sellafield. The 100m long outdoor pond was used for the cooling, storage, and de-canning of spent fuel from the reactors as part of the UK’s post-war atomic weapons programme. Operations ceased in the 1960s and in the years that followed sludges formed from the decaying nuclear fuel, algae and other debris. 

The dive was needed to get into the parts of the legacy ponds that machines are unable to reach, making sure that for the first time in 60 years people were able to see within all the ‘nooks and crannies’. “Humans are much more dexterous than the machines that we deploy so we look to divers to be able to get into those fine areas and nooks and crannies of the pond floor and really into some of those more complex features that machines really struggle to access,” says Ryan.

The specialist teams and Sellafield Ltd employ dive supervisors to control the divers whilst in the water; the water is a key tool in combatting radiation. Jeremy Swoyer, a diver and dive supervisor at Underwater Construction Corporation Ltd, explains: “The dive supervisor basically controls the diver as if they were a tool that you were using in the water so that they are able to think and conduct the task as they see fit with the guidance of the dive supervisor. So it’s kind of just receiving the feedback and then directing the diver into how they’re going to complete their next task. If you were working in air and you walk through a door and there was a higher dose rate on the other side of the door that could give you a substantial dose, you’re taking quite a bit from it.

“When we are in the water if we move closer to something, we get a real time reading and all you have to do is slightly move away and the dose drops off so we can be within a short distance of something that could be up to a sievert or multiple sievert (a unit that measures the amount of radiation), and we could pick up with our CV reachers, put it in a bucket and take care of it.”

Carl Carruthers, SL head of programme delivery for Legacy Ponds, says: “The PFSP diver project has been five years in the planning and has been a huge success. The team are used to diving in toxic and hazardous environments all over the world, including inside nuclear reactor vessels, but this is a first for us. Safety has been our priority throughout, and the divers are monitored and communicating with the dive supervisor at all times. Their work has helped us make real progress in cleaning up the pond and our site mission to deal with the nuclear legacy and create a clean and safe environment for future generations.”

Once all of the waste materials have been removed from the pond the water will then be removed, ready for final demolition of the building. Current plans estimate the decommissioning work will cost around £212m and will be completed by 2039, an achievement almost a century in the making.

David Redpath, NDA director of performance improvement at Sellafield, added: “The success of the PFSP diver project is an important decommissioning milestone for Sellafield and a really positive example of sharing learning to overcome common challenges on sites across the NDA group. It’s a testament to the skill and expertise of both Sellafield and the diving team and demonstrates how we are utilising innovative techniques to ensure the UK’s legacy nuclear waste is dealt with safely and securely.”