Hunterston B, in North Ayrshire, started generating electricity in 1976 and at peak operation made enough electricity to power almost 2 million homes a year. Since it started generating, Hunterston B has produced enough low carbon electricity to power every home in Scotland for 31 years. The last of the station’s two reactors stopped generating electricity on 7 January 2022 when the station moved into the next phase of its operating life – decommissioning.
In 2014, the first crack related to the aging of the graphite was identified in Reactor 4 at Hunterston B. Over the next eight years regular inspections allowed close monitoring of the progression of graphite cracking at the site.
During graphite inspections in March 2018 we identified a slightly higher rate of cracking than expected and kept the reactor offline for more than two years to allow us the time to carry out additional inspections, modelling and analysis and present a safety case, based on new evidence, to the regulator for assessment.
In October 2018 we also decided to carry out graphite inspections on Reactor 4. The results showed that the graphite was ageing as expected but we kept the unit offline while we refreshed the safety case. In August 2019, the ONR gave approval for the unit to return to service for a period of around 4 months, allowing it to reach almost the same power output as Reactor 3. Approval for a further run of 6 months was granted before another round of graphite inspections.
We received approval from the independent regulator, the ONR, to bring Reactor 3 at Hunterston B back online in August 2020. This followed a major, two-year inspection and investment programme to prove that the station can respond safely to a range of earthquake scenarios, far worse than the UK has ever experienced or expects to occur.
The safety case the reactors operated under for the final 12 months of their generating lives showed they could operate and shutdown in all circumstances. This included a 1 in 10,000 year earthquake, larger than the UK as ever experienced.
The work carried out to support the final seismic graphite case for Hunterston B is being used to support safety cases at the other AGR stations around the UK.
All of our work on graphite at Hunterston B has shown a cautionary approach and commitment to nuclear safety that we will adopt across the rest of the AGR fleet as graphite ageing develops.
For all the latest information on Hunterston B, you can visit the station news page.