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. We expect it to generate low carbon electricity until 2023.
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 an extensive inspection programme 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, even an earthquake larger than the UK as ever experienced. The industry regulator, the ONR, is now considering a 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 make electricity for a period of around four months. Since returning to service, the reactor has operated safely and efficiently. We are now approaching the end of the four month operational period and intend to take the unit back offline in December to carry out more graphite inspections.
We have carried out significant modelling and analysis work to predict the future state of the graphite cores at Hunterston B and we are bringing all of this work together to produce a further safety case which will take the reactors through to the end of generation.
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.