The 480-megawatt (MW) reactor in Scotland had been expected to come back on line on Aug 5, but that has been pushed back to Aug. 30.

The reactor has been offline since October, when routine inspections found cracks in the graphite core of the reactor. This is now the 10th delay to its restart date.

EDF said in a community stakeholder notice that on the one hand regulations require it to give an estimated start date for the reactor, while on the other, it does not know "with certainty" how long the review will last.

"To support time for the ONR assessment, we have declared 30 August 2019 for Reactor 4, a slight adjustment to the previously declared date of 5 August," it said, referring to Hunterston B-8.

Neighbouring reactor Hunterston B-7 has been down since March 2018 for the same reason and is not expected to come back online until the beginning of October.

EDF Energy operates all 15 active nuclear reactors in Britain, which have a combined capacity of 9 gigawatts (GW).

(Reporting by Lefteris Karagiannopoulos and Sabina Zawadzki, editing by Nerijus Adomaitis, David Evans, Kirsten Donovan)