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Nuclear experts have warned against re-opening a 43-year-old Scottish nuclear reactor riddled with cracks over fears of a meltdown.

Hunterston B nuclear power plant was shut down last year after it was found that Reactor 3 had almost 400 cracks in it - exceeding the operational limit.

EDF, which own the plant in Ardrossan, Ayrshire, are pushing to return the reactor to service at the end of June and July and want to extend the operational limit of crack allowed from 350 to 700.

However, the plans to reopen the plant have sparked fears it could lead to a nuclear meltdown similar to the 1986 Chernoybl disaster .

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Experts have warned that in the very worst case the hot graphite core could become exposed to air and ignite leading to radioactive contamination and evacuation of a large area of Scotland's central belt – including Glasgow and Edinburgh.

According to Dr Ian Fairlie, an independent consultant on radioactivity in the environment, and Dr David Toke, Reader in Energy Policy at the University of Aberdeen, the two reactors definitely should not be restarted.

Speaking about the cracks in the barrels, they warned: "This is a serious matter because if an untoward incident were to occur – for example an earth tremor, gas excursion, steam surge, sudden outage, or sudden depressurisation, the barrels could become dislodged and/or misaligned.

"These events could in turn lead to large emissions of radioactive gases.

(Image: PA) (Image: Bloomberg via Getty Images)

“Further, if hot spots were to occur and if nuclear fuel were to react with the graphite moderator they could lead to explosions inside the reactor core.

"In the very worst case the hot graphite core could become exposed to air and ignite leading to radioactive contamination of large areas of central Scotland, including the metropolitan areas of Glasgow and Edinburgh."

A planned inspection of the graphite bricks that make up the core of reactor three in March last year uncovered new "keyway root cracks".

Around 370 hairline fractures were found, which the BBC reports equates to about one in every 10 bricks in the reactor core.

EDF Energy said these have now grown to an average of 2mm wide.

(Image: Getty Images) (Image: Getty Images)

The operational limit was 350 cracks but the inspection found this had been exceeded.

Cracks to the graphite blocks is known to occur but legislation is in place to ensure they do not threaten the structural integrity of the reactor.

EDF is now hoping to prove it is safe to use and would stand up to the most stringent tests and wants the ONR to increase the upper operational limit to 700 cracks.

The reactors have been closed since October 2018, but EDF Energy said yesterday it was confident its Hunterston B nuclear plant would eventually reopen.

Station Director Colin Weir said: "Nuclear safety is our overriding priority and reactor three has been off for the year so that we can do further inspections.

(Image: Getty Images)

"We've carried out one of our biggest ever inspection campaigns on reactor three, we've renewed our modelling, we've done experiments and tests and we've analysed all the data from this to produce our safety case that we will submit to the ONR.

"We have to demonstrate that the reactor will always shut down and that it will shut down in an extreme seismic event."

Tests and modelling have been undertaken to ensure that an earthquake would not distort the control channels and prevent the power station being shut down, the BBC reports.

EDF Energy said a £100 million million pound, 5-year research process had been undertaken into issues surrounding the lifetime of its plants.

An EDF spokesperson added: “Market rules mean we would immediately have to announce if this extensive research had altered our expectations about the closure of our power stations."

(Image: Neil Murphy / Daily Mirror)

She was responding to a report by the Energy & Climate Intelligence Unit (ECIU), a non-profit organisation, published on Friday, which said Britain’s climate target could be in jeopardy if the plant does not re-open and if the six other nuclear plants in Britain, with the same Advanced Gas-cooled Reactor (AGR) design, were also forced to close early.

“If this happens it is unlikely that the lights will go out, but it could make hitting our carbon targets more challenging,” said Jonathan Marshall author of the ECIU report.

The ECIU report said the government should launch fresh support for new renewable projects, to ensure any gap in nuclear generation is filled by low-carbon sources instead of gas plants.

EDF Energy said the scenario outlined in the report was unrealistic.

The plant, which is more than 40 years old, can generate enough electricity to power more than 1.7 million homes, and is one of Britain’s eight nuclear plants which provide around 20 percent of the country’s electricity.

What caused the explosion at Chernobyl?

Chernobyl was considered a state-of-the-art nuclear power plant – a triumph of USSR engineering.

The station was built nine miles north-west of Chernobyl with the city of Pripyat constructed at around the same time, exclusively as a place for those who worked at the power plant to live.

In September 1981 Reactor 1 suffered a partial meltdown - but the damage was minor and the accident was not made public until several years later.

In the spring of 1986 Reactor 4 had recently come online and had begun producing power, however a series of tests still needed to be performed.

The night shift had very limited time to prepare for and carry out the experiment and operators were unaware of the reactor flaws due to, among other things, the myriad of bureaucracy in the communist state.

And Anatoly Dyatlov, the deputy chief engineer, chose to override safety protocols, such as starting the test when the reactor was generating a low amount of power - something that made it temperamental and hard to control.

Despite the protests of some operators the test went ahead with almost none of the control rods inserted.

Soon after the power levels began to spike.

Alexander Akimov called for fail-safe button (AZ-5) to be pushed, inserting all the control rods to shut down the reactor.

But the boron rods, designed to stop the reaction, had graphite tips.

These displaced water in the lower parts of the core, leading to more steam and more reactivity.

After just two seconds the chain reaction began to increase at an unstoppable speed.

The reactor was destroying itself, parts reaching more than 3,000C.

There was a series of steam explosions. These events exposed the graphite moderator of the reactor to air, causing it to ignite and explode.