Electricity generation from the Hunterston B nuclear power station could fall by 40% this year after cracks were discovered in one of the reactors.

Colin Weir, station director at the North Ayrshire power plant, said the reduction in output came after the "right and appropriate" decision was taken to put one of the reactors offline after a "slight increase" in the number of defects.

A planned inspection of the graphite bricks that make up the core of Reactor 3 in March uncovered new "keyway root cracks".

These were found to be developing at a slightly higher rate than anticipated, operator EDF Energy revealed.

The reactor had been expected to restart a few weeks after it was taken offline, but that has now been delayed.

Bosses at the site, which opened in 1976, now expect the reactor to return to service before the end of the year.

Mr Weir told BBC Radio Scotland's Good Morning Scotland programme that, "because of the slight increase" in cracks found in Reactor 3, "it is right for us to take the time to review these findings and do some more assessments and potentially do some more inspections of the core".

He added: "Obviously this year we will be reduced in output - it will be around a 40% reduction in our planned output for this year - taking this decision, the right and appropriate safe decision to have the unit off while we do this assessment."

But he insisted that the plant, which is scheduled to remain in operation until 2023, is still safe.

"Our safety margins are way beyond where we are just now," Mr Weir said.

"This is a far distance from any safety margins."