An ONR spokesman said: “We are currently assessing the safety case submitted by EDF after a planned outage identified a number of cracks in the graphite blocks that make up reactor three’s core.

“Before we grant permission to EDF to restart reactor three we will require that an adequate safety case justifying further operation has been made. ONR has to formally permission the restart of the reactor.”

The ONR still has a number of weeks to carry out its assessment before it can report on the safety of the structure.


An EDF spokeswoman said: “As part of the normal ageing process we expect to see defects occurring in some of the graphite blocks that make up the reactor core of our plants.

“This phenomenon is understood and is recognised in our operational safety cases which are agreed with the nuclear safety regulator. We have prepared well for this; we have a £100 million graphite research programme.

“Hunterston B remains safe to operate and will be back online once the current outage is completed. We will, as normal, consult with our regulators before returning the reactor to service.”