Cracks have been found in bricks that make up the core of one of the two reactors at the Hunterston B nuclear power station in North Ayrshire.

EDF Energy said that two cracked bricks were found during a planned maintenance inspection of 6,000 that make up the reactor's graphite core.

The operator said that the cracks were predicted and did not pose any safety risks.

Colin Weir, station director at Hunterston B, 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."

The nuclear power station began operating in 1976 and was originally scheduled to be shut-down in 2011 but this was extended to 2016.

EDF Energy later said a technical and economic evaluation of the plant confirmed it could operate until 2023.

WWF Scotland director Lang Banks said: "News of yet more cracks in the country's ageing fleet of nuclear power stations underscores why we're right to be taking steps to harness cleaner, safer forms of energy.

"These cracks are a sign that we can expect these nuclear facilities to become increasingly unreliable in the future.

"As Scotland continues to grow its renewables capacity we can look forward to a day when we can switch off nuclear power for good."

Scottish Conservative energy spokesman Murdo Fraser said: "There's absolutely no suggestion of these cracks causing any safety or health issue, that's been made absolutely clear by the owners.

"Any scaremongering to the contrary is unacceptable.

"But this issue does demonstrate that this is a power station approaching the end of its working life, having made an important contribution.

"Nuclear energy is an important asset for Scotland and that's why the Scottish Government has to drop its opposition to new power stations."

Green MSP Patrick Harvie said: "We should not be alarmist about the Hunterston news but should re-double our commitment to forge ahead with the different renewable technologies which will serve Scotland far better in the long-term.

"Decisions about lifetime extensions to our ageing nuclear plants must no longer be made behind closed doors by the industry and ministers, but must instead involve a much greater degree of public consultation.

"That's why it's important that the Scottish Government drops its opposition to carrying out a full environmental impact assessment of any extension."

A Scottish Government spokesman said: "The Office for Nuclear Regulation have provided an assurance that there are no immediate safety implications affecting Hunterston-B and that it is safe to continue generating electricity

"At the same time, this development does illustrate that Scotland's nuclear facilities have a limited lifespan and we need to put in place longer-term energy alternatives.

"That is why Scottish Government is opposed to the building of new nuclear capacity in Scotland, as it would divert billions of pounds away from renewable alternatives where Scotland has a key competitive advantage.

"However, subject to strict safety considerations, extending the operating life of Scotland's existing nuclear stations can help to maintain security of supply while the transition to renewables and cleaner thermal generation takes place."