Workers have started removing used nuclear fuel from the reactors at the UK’s Hunterston B NPP in Scotland, EDF Energy said. The station stopped generating electricity in January. Since then the workforce has been carrying out a statutory outage to ensure the two units are ready for defuelling.

Hunterston B plant comprises two 490 MWe advanced gas-cooled reactors (AGRs) – reactors 3 and 4. Reactor 3 began operating in 1976 with an original lifespan of 25 years. However, its operating life was extended to more than 45 years. Reactor 4 started up in 1977 and was taken offline with reactor 3 in January.

Defuelling will entail removing more than 300 channels of fuel from each of the reactors. The fuel channels will be stripped and processed then taken to the on-site fuel storage pond to cool before being packaged into used fuel flasks and transported by rail to Sellafield in Cumbria. The first fuel stringer, a 10 metre long assembly of fuel pins and other component parts, has been removed from reactor 3 and dispatched to Sellafield. The empty fuel plug unit has been returned to the reactor.

Over the next three years the station will send around 350 of these flasks to the facility in Cumbria for processing and safe storage. "To achieve this three-year target, an average of three flasks will need to be processed a week,” said EDF Energy Managing Director of Generation Matt Sykes. Defuelling will remove 99% of the nuclear material from the site before it is handed over to the Nuclear Decommissioning Authority (NDA) for its Magnox subsidiary to carry on with decommissioning.

The site is the first of the UK’s Advanced Gas-cooled Reactor (AGR) stations to reach this milestone and EDF Energy has made clear its commitment to an agreement with the UK Government to defuel all seven AGRs. These include Torness and Hunterston B in Scotland, Dungeness B in Kent, Hartlepool in Teesside, Heysham 1 and 2 in Lancashire and Hinkley Point B in Somerset. These are all scheduled to reach the end of their operational lives this decade.

Originally, EDF had been responsible for decommissioning the AGR stations. However, in June 2021, the UK government and EDF agreed that EDF will aim to shorten the time it takes to remove the fuel from the plants as they come offline, and would then transfer ownership of the stations to NDA. EDF said it hopes to take up to five years to completely defuel at each site, although Dungeness B will take longer "due to its unique design and requirement for extra preparation time".

Station Director, Joe Struthers, said: “Since January, we’ve been working hard to get the site ready for this next step. The team has carried out thousands of pieces of work as part of the outage, hundreds of documents have been updated and we’ve secured a new safety case from the regulator to allow defueling to start. We are absolutely focused on delivering defuelling safely and cost-effectively and I am delighted it is now underway.”

Image: Defueling is officially underway at Hunterston B