Hunterston B, in North Ayrshire, started generating electricity in 1976 and when both units are operating is capable of making enough electricity to power almost 2 million homes a year. Since it started generating, Hunterston B has produced enough low carbon electricity to power the whole of Scotland for eight years. The station will move into the next phase of its operating life by January 2022 at the latest. At this point the reactors will stop generating electricity and we will start to remove all the fuel in a process called “defuelling”.
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.
We first identified cracking related to the age of the graphite in 2014 and regular inspections have allowed close monitoring of its progression since then.
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.
This safety case shows the reactor can operate and shutdown in all circumstances. This includes a 1 in 10,000 year earthquake, larger than the UK as ever experienced.
We plan to operate the reactor for six months before carrying out further inspections and, subject to regulatory approval, a final six month run of generation.
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. As agreed, it was taken back offline in December, following a safe, continuous operating run. In September 2020, the ONR approved a new safety case and Reactor 4 was safely returned to service. We also plan to run the Reactor 4 for two six months runs with inspection and assessment in the middle before the station moves into defuelling; subject to regulatory approval.
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.