PICTURES showing cracks in the core of a nuclear reactor at Hunterston B Power Station have been released.
Reactor three has not been used to generate electricity since the cracks were found at the site in North Ayrshire, Scotland, in March 2018.
EDF3 Pictures taken inside reactor three's core show hairline cracks just a couple of millimetres wide on 370 graphite bricks. The dark vertical lines in this image are two such cracks
3 Reactor three at Hunterston B in Ayrshire has not produced electricity since the cracks were first found a year ago – but the number of fractures forming is rising faster than expected
Around 370 hairline fractures have been discovered in the graphite bricks inside the reactor — which is about one in every ten bricks in the core.
EDF Energy, which owns and operates the power station, says it does intend to seek permission to restart from the Office of Nuclear Regulation (ONR).
The firm first has to demonstrate that it can still shut down the reactor in all circumstances.
Graphite bricks make vertical channels inside the reactor where nuclear fuel is housed.
Alongside them are thinner channels where control rods can be lowered into position to counteract the nuclear reaction.
Modelling and tests have been carried out to make sure an earthquake wouldn't distort the control channels and prevent the power station being shut down.
Station Director Colin Weir told the BBC: "Nuclear safety is our overriding priority and reactor three has been off for the year so that we can do further inspections.
It has got a huge safety margin before we are anywhere near a cliff edge.
Colin Weir, Hunterston B Station Director
"We have to demonstrate that the reactor will always shut down and that it will shut down in an extreme seismic event."
An inspection found reactor three had gone over the operational limit of 350 cracks permitted for the latest period of operation.
Now EDF plans to ask the regulator for permission to restart with a new operational limit of 700 cracks.
The energy firm will not state what it believes to be an unsafe operational limit, but it does accept that cracking is "life-limiting" for the reactor.
Weir added: "We have demonstrated our operational allowance, we've demonstrated our safety allowance. This cliff edge is still to be demonstrated. It has got a huge safety margin before we are anywhere near a cliff edge."
The two reactors at Hunterston B provide a base-load of electricity large enough to power 1.8 million homes.
It has advanced gas-cooled reactors (AGR) like those used in Torness, Hartlepool, and Hinkley Point B.
The industry expects all of them to be decomissioned in time because of the cracking.
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Nuclear expert Prof Neil Hyatt from Sheffield University said: "The structural integrity of the graphite core has always been known to be the ultimate limiting factor to the lifetime of these reactors. So, ultimately there may come a point in time where those reactors have to come offline and are not able to restart."
Hunterston B is scheduled to continue producing electricity until 2023.
If it were decommissioned early because of the cracks, and other AGC reactors were too, then serious energy problems could arise.
3 The core of the reactor is made up of 3,000 graphite bricks and cracks have been found in one in every ten of them