A nuclear reactor at Hunterston could be offline until the end of the year after root cracks were discovered in its core.
EDF Energy said they had been in discussion with the Office for Nuclear Regulation (ONR) to agree the return to service of Reactor 3 at Hunterston B following the completion of a recent inspection programme.
The inspections confirmed the expected presence of new keyway root cracks in the reactor core and also identified these happening at a slightly higher rate than modelled.
EDF Energy has said that, while Hunterston B Reactor 3 could return to operation from the current outage, it will remain offline while the company works with the regulator to ensure that the longer term safety case reflects the findings of the recent inspections.
The operation of other reactors is not affected.
A spokesperson for the energy giant said: "We have been working over many years to fully understand and prepare for these late life changes to the reactor core and regular inspections at all our plants have provided a clear understanding of how the reactor cores age.
"The longer term safety case will build on work already completed and EDF Energy expects that this will demonstrate that there are large safety margins both now and for the projected reactor lifetime.
"Over £100m has been spent on the graphite research programme which benefits from the expertise of our own team of specialists as well as academics at several leading U.K. universities.
"During this time EDF Energy may take the opportunity to carry out additional planned routine maintenance. We expect the unit to return to service before the end of 2018. This will result in a reduction in 2018 nuclear output forecast of up to 3TWh."
When cracks were first discovered in 2015, only three were found, but that number has now increased to 39.
The BBC reported that the additional cracks are 'life limiting as they sit in channels were the control rods which suppress the nuclear reaction slide into the core'.
EDF have permission now to return the reactor to use, but the energy giant have taken the decision to keep it closed up possibly up until the end of the year in order to spend time investigating the issue.
First Minister Nicola Sturgeon said she would seek 'further assurance' on safety from EDF Energy, after questions were raised at the Scottish Parliament by Cunninghame North MSP Kenneth Gibson.
Mr Gibson said: "I am deeply concerned at the news that EDF Energy has had to keep Reactor 3 at Hunterston B out of action for repairs until the end of 2018, as a precaution, after expected new keyway root cracks in the reactor core were found to be happening at a slightly faster rate than expected.
"I asked the First Minister, who was due to meet with EDF Energy's Chief Executive, to seek assurances that safety will remain EDF’s number 1 priority and that, once repairs are completed fully, Hunterston B will continue to operate at least until its planned closure in 2023 and prior to the commencement of decommissioning.
"I have also written to ask about the Scottish Government's efforts regarding contingencies being put in place to replace the jobs if the plant closes early."
Drew Cochrane, who sits on the Hunterston site stakeholders group, said: "Having listened intently to experts from the Office of the Nuclear Regulator at the Hunterston Stakeholders Group meeting and having had an on site tour and demonstration of the Hunterston B reactors the reality is that there are 6000 bricks and 3000 fuel bricks.
"There are a small number of cracks which have been discovered which are the size of the head of a ballpoint pen. The experts say that there would have to be 350 cracked bricks to be a serious situation. 
"There is no doomsday scenario, we don't need to built nuclear bunkers and, personally, I hope Hunterston B continues providing electricity beyond 2023 which isn't far away."
A Green MSP is challenging the Scottish Government to give the community a say in any decision to extend the plant’s lifetime. 
Ross Greer says the lack of public consultation has been unacceptable, while highlighting that European law says all ageing nuclear power stations should have an environmental impact assessment.
Ross Greer MSP said: “This is obviously of major safety and economic concern to the local community."
Donald Urquhart, deputy chief nuclear inspector at the Office for Nuclear Regulation, said: "We welcome the decision by EDF to delay the return to service of reactor 3 at Hunterston B pending further assessment of the significance of the most recently identified keyway root cracks.
"I view EDF's decision as responsible, conservative, and made in the best interest of public safety."