Costain begins next phase of Trawsfynydd nuclear decommissioning
Costain takes over reactor building work at Trawsfynydd, launching a four‑year, £70m programme that will cut structures from 54m to 25m and boost local jobs.
The handover of the former Trawsfynydd nuclear power station’s reactor building area to Costain marks the start of the next phase of a four‑year decommissioning programme.
Nuclear Restoration Services transferred control to the contractor after a joint review confirmed that plans and arrangements were progressing as expected.
The £70 million contract, awarded in October 2025, tasks Costain’s in‑house engineering team with partially demolishing and stabilising the two Magnox reactor buildings.
Work will see the towers’ height reduced from roughly 54 metres to 25 metres, a key step before later stages of dismantlement.
Early on‑site activity includes a mobile crane delivering scaffolding, hoists and electrical infrastructure, with larger crawler cranes slated to arrive later this year.
Two tower cranes are scheduled for installation inside the reactor buildings in early 2027 to facilitate the height‑reduction works.
At peak activity the project is expected to employ more than 100 people, drawing on local labour and supply‑chain firms.
Costain has highlighted opportunities for apprenticeships and training, aiming to develop skills that remain in the region after the site closes.
Trawsfynydd, a Magnox‑design station commissioned in the 1960s, has been under decommissioning since 1991 and is one of six former UK reactor sites currently being dismantled.
The site is also under consideration for possible future nuclear development, adding strategic importance to the current work.
Costain previously delivered enabling works at Trawsfynydd, including the installation of new capping roofs on the reactor buildings.
The contractor is concurrently working with Nuclear Restoration Services on a separate six‑year decommissioning programme that spans 11 locations across the United Kingdom.
“Reaching this milestone reflects years of planning, preparation and collaboration for our dedicated workforce and supply chain partners.”
NRS describes Trawsfynydd as a “lead and learn” site, noting that experience gained here will inform future decommissioning programmes elsewhere.