EDF Energy has delayed restart of a reactor at its Hunterston B nuclear plant – possibly until the end of 2018 – because it found new cracks in the graphite blocks that form the reactor core.

Graphite cracking is an increasing problem as the UK’s AGR reactors age and EDF Energy has spent over £100 million on a research programme to understand its progress. But inspections revealed that new cracks were arising faster than expected. EDF Energy said that although the reactor could gain permission to restart from the Office for Nuclear Regulation, it will remain offline while the company assesses long-term implications.

If the unit returns to service before the end of 2018, as expected, it will reduce 2018 nuclear output forecast by up to 3TWh. The cost of that outage will be felt by Centrica as well as EDF Energy, as Centrica retains a 20% stake in EDF’s AGR fleet, although that stake has been up for sale since last year. Analysts Agency Partners estimated the shutdown would cut Centrica earnings by £22 million. 

The issue could also affect three other reactors in EDF Energy’s fleet that are of the same design: a second reactor at Hunterston B and two reactors at Hinkley Point B. All four have Capacity Market contracts for the winter of 2018/19. All date back to the late 1970s and are currently expected to remain in operation until 2023.