NUCLEAR experts have warned of a Chernobyl-like “catastrophic accident” after more than 350 cracks were discovered in the power reactor at the Hunterston plant in North Ayrshire.

This breaches the Government’s agreed safety limit and has prompted calls for a permanent shutdown.

Hunterston’s operator, EDF Energy, insist the reactor is safe.

Reactor three at Hunterston B nuclear power station originally started generating electricity in 1976, and is the oldest in the UK.

It was closed in March this year to allow inspectors to probe for cracks.

The reactor was initially due to restart on March 30, but the date has been repeatedly postponed as more cracks have been found.

EDF is now hoping for permission from the UK government’s Office for Nuclear Regulation (ONR) to fire up the reactor on 18 December.

It follows a long-running investigation by the Ferret website. In April they revealed that new cracks had been discovered in the reactor, but at the time neither EDF nor the ONR would say how many.

In May, EDF said that 39 cracks had been found and they were “happening at a slightly higher rate than modelled”.

But yesterday, the website reported that more than 350 cracks had been discovered.

According to ONR, 350 is the “operational limit” in the safety case that determines whether or not the reactor is allowed to operate.

EDF has told the local Hunterston Site Stakeholder Group that it was likely to propose to the ONR that reactor three in future be permitted to run with up to 1000 cracks.

The cracks are produced by intense radiation bombarding the graphite blocks that make up the reactors.

Dr Ian Fairlie, a consultant on radiation in the environment and former member of the three-person secretariat to Britain’s Committee Examining the Radiation Risks of Internal Emitters, told the Ferret: “If other safety systems failed at the same time, there could be a catastrophic accident – such as occurred at Chernobyl in 1986 in the former USSR.”

He added: “EDF does not have a good handle on the ageing mechanisms inside the reactor. This means that reactor three should definitely not be restarted.”

An EDF spokesperson responded: “We have carried out the most extensive inspection programme on an advanced gas-cooled reactor station to date at Hunterston B.

“During the most recent inspection of reactor three we examined around a quarter of the core. As expected we identified a number of new cracks. This number exceeded the operational limit of the existing safety case but was significantly mitigated by the cracks being much narrower than modelled in the safety case.”

“The most recent results support the work we are doing on the long-term safety case and underline our confidence that the normal operations at the station are unaffected and that there would be safe shutdown in the event of a one in 10,000 year earthquake. We are preparing to present a safety case for return to service of reactor three to the regulator, ONR, for their assessment.

“We have also carried out similar inspections on reactor four and the case for return to service for that unit is currently with the ONR for review.”

The Scottish Government said that they were “aware of the situation at Hunterston B”.