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. The station will move into the next phase of its operating life by 2023. At this point the reactors will stop generating electricity and we will start to remove all the fuel in a process called “defuelling”.
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.
Reactor 3 has been offline since March 2018, when we identified a slightly higher rate of cracking than expected. Since then we have carried out three additional rounds of inspection, the most extensive on this type of reactor, and used these results along with other updated analysis and modelling to prepare a safety case that 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. The industry regulator, the ONR, is now considering the safety case that would allow operation for six months.
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 the same power output as reactor 3. As agreed, it was taken back offline in December, following a safe, continuous operating run. We have submitted a new safety case to the regulator for its assessment.
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.