Trawsfynydd Decommissioning
Gwynedd, Wales, UK · Operations 1965-1991, Decommissioning ongoing (reactor height reduction 2025-2029) · £70m (Costain contract for reactor height reduction), part of overall Magnox Ltd decommissioning budget
The judgement call
Account-gated at launchTrawsfynydd was chosen as a lead site for a Rolling Programme of Decommissioning, aiming to guide future dismantling efforts. - A major contract was awarded to Costain for the partial removal and height reduction of the reactor buildings, a significant visual change to the landscape. - Milestone reached in retrieving legacy material, demonstrating progress in hazard reduction.
Key engineering challenges
Decommissioning the UK's first inland civil nuclear power station, located within a National Park. - Reducing the height of the iconic reactor buildings while managing radioactive materials. - Retrieving and processing legacy radioactive material for long-term storage. - Adapting decommissioning strategies to a unique inland site with environmental sensitivities.
Project facts
- Client / owner
- Magnox Ltd (subsidiary of Nuclear Decommissioning Authority), Nuclear Restoration Services
- Lead contractor
- Costain (for reactor height reduction)
- Lead designers
- AtkinsRéalis (Reactor Dismantling Design and Integration Support)
- Project type
- decommissioning
- Scale
- Two Magnox reactors, 54m high reactor buildings reduced in height, ~2,300 tonnes of legacy material retrieved
- Disciplines
- nuclear; civil; structural; mechanical; electrical; waste management; remote handling
- Standards & frameworks
- ONR
Sources: ONR: Trawsfynydd (https://www.onr.org.uk/our-work/what-we-regulate/sellafield-decommissioning-fuel-and-waste/sites/trawsfynydd) - World Nuclear News: Decommissioning milestone reached at Trawsfynydd (https://www.world-nuclear-news.org/articles/decommissioning-milestone-reached-at-trawsfynydd) - GOV.UK: Major decommissioning contract awarded at Trawsfynydd site (https://www.gov.uk/government/news/major-decommissioning-contract-awarded-at-trawsfynydd-site) - AtkinsRéalis: Trawsfynydd Reactor Dismantling – Design and Integration Support (https://www.atkinsrealis.com/en/projects/reactor-dismantling-design-integration) - Costain: Costain selected for complex nuclear decommissioning contract in North Wales (https://www.costain.com/media/press-releases/2025/costain-selected-for-complex-nuclear-decommissioning-contract-in-north-wales/) - LinkedIn: Costain wins £70m contract for Trawsfynydd site decommissioning (https://www.linkedin.com/posts/nuclear-restoration-services_trawsfynydd-decommissioningprogress-nuclearrestoration-activity-7381244426615947264-vWd0)