BBC News cited experts as saying that the root cracks identified in two of the 6,000 graphite bricks in one of two Hunterston B reactors are of more serious nature than earlier fractures.

EDF Hunterston-B station director Colin Weir told BBC News that the crack was discovered during a periodic shutdown, which began in August.

Commissioned in 1976, the Hunterston-B nuclear reactor was scheduled to be closed in 2016, but EDF intends to extend its operations until 2023 and beyond.

Weir said: "Every time we take the reactor out of service for planned maintenance we inspect the graphite core which is made up of around 6,000 bricks.

"During the current Hunterston outage we found two bricks with a new crack which is what we predicted during Hunterston B’s lifetime as a result of extensive research and modelling.

"It will not affect the operation of this reactor and we also expect that a few additional cracks will occur during the next period of operation.

"The small number of cracked bricks found during routine inspection is in line with our expectations, the findings have no safety implications and are well within any limits for safe operation agreed with our regulator."