The UK Office for Nuclear Regulation (ONR) has permissioned EDF’s post-defueling safety case (PDSC) for the Hunterston B site in North Ayrshire, Scotland. This is the first such permission to be granted across EDF’s Advanced Gas-Cooled Reactor (AGR) fleet and constitutes a significant milestone at Hunterston B as it progresses to the next phase of its lifecycle.
Hunterston B comprises two 490 MWe AGRs – Reactors 3 and 4. Reactor 3 began operation in February 1976 and was expected to run for 25 years. However, its operating lifespan was increased to more than 45 years and it closed in November 2021. Reactor 4, started up in March 1977 and was shut down in January 2023.
In a further significant development, ONR also approved a revision to the site’s emergency plan in recognition of the significantly-reduced hazard at the North Ayrshire site in Scotland. This comes after EDF completed the defueling of both reactors in April, transferred all nuclear fuel off-site, and completed comprehensive fuel-free verification activities.
Defueling took two years and 10 months involving removal of 4,880 used fuel elements which were processed and packaged into almost 350 large, specially engineered, flasks. The fuel was transported by rail from Hunterston B to Sellafield, in Cumbria, for long-term storage.
In 2026, the nuclear site licence for Hunterston B will be transferred from EDF Energy to Nuclear Restoration Services (NRS), a subsidiary of the Nuclear Decommissioning Authority (NDA) after which NRS will dismantle and demolish the plant and buildings.
Tom Eagleton, ONR Superintending Inspector, said: “Our specialist inspectors have conducted a thorough assessment of the safety case, and we are satisfied that it meets the high regulatory standards expected. As an enabling regulator, we are committed to working with EDF and Nuclear Restoration Services, who will assume operational responsibility for the site in 2026, in progressing the vital decommissioning work safely.”
He added: “This will enable EDF to progress these essential activities. Additionally, the extensive work undertaken in recent years to defuel Hunterston B has significantly reduced the nuclear hazard on the site, and we are therefore satisfied that it is appropriate for the emergency plan to be updated accordingly.”
During the next 15 years, the site will undergo decommissioning activities to prepare it for a prolonged period of care and maintenance for approximately 85 years before final site clearance work takes place. ONR will maintain appropriate regulatory oversight of the site and will continue to conduct regular inspections to ensure all work is carried out safely and in accordance with regulatory requirements.
