Running an ageing nuclear reactor at Hunterston in North Ayrshire for another year could cause cracks in its core to rise by 65 per cent to nearly a thousand, according to the plant’s operators.
But that won’t breach the reactor’s operating limit for cracks because the limit has been increased fourfold by the power company EDF Energy – and agreed by the UK Office for Nuclear Regulation (ONR).
Campaigners describe the rising number of cracks as “alarming” and “reckless”, criticising EDF and ONR for “continuously moving the safety goalposts”. They accuse ONR of becoming “EDF’s pet poodle” rather than the public’s safety watchdog.
The French multinational, EDF, counter-attacks campaigners for “scaremongering” and defends ONR as “the world’s strongest regulator”. ONR says that EDF has shown that the reactor can tolerate more cracks “because of improvements in the analysis methods”.
Technical reports released by ONR also reveal that a credible earthquake could trigger “overloads” and 500 more cracks, further eroding safety margins.
ONR describes some of EDF’s safety analysis as “inherently subjective”, and suggests that its methodology for demonstrating that the reactor is safe is “approaching its limit of viability”.
In August ONR gave the company permission to restart the reactor for six months after being closed for two and a half years. But it still has to decide whether to allow a second six months’ operation, as EDF wants.
Reactor three at Hunterston B nuclear power station started generating electricity in 1976 and is the oldest of its kind in the UK. There are 13 other similar reactors at six sites across Scotland and England, including reactor four at Hunterston and two reactors at Torness in East Lothian.
What happens at reactor three is likely to be repeated at the other reactors. It was closed down on 9 March 2018 with an estimated 377 cracks in its graphite core caused by prolonged bombardment by intense radiation.
According to ONR, spreading cracks could potentially distort the core and prevent control rods from being inserted to shut it down safely. There was a risk that the reactor could overheat and cause a “large offsite release” of radioactivity, it said.
On 27 August 2020 – the day ONR said reactor three could restart for six months – EDF announced that it wanted to run the reactor for another year. The company also said that it would then close the reactor down for good “no later than 7 January 2022” – 15 months earlier than previously planned.
On 24 September ONR gave permission to restart reactor four at Hunterston, which had an estimated 209 cracks, for another six months. EDF also wants to run that for another year, and then close it down permanently.
ONR has now released four detailed technical reports underlying its decision to allow reactor three to operate for six months. One assessing the “structural integrity” of the graphite core revealed that EDF had made new “pessimistic” estimates of the number of cracks.
The new estimates put the number of cracks in August 2020 at 570, and predicted that this could rise to 781 after six months operation and 943 after a year. That would not exceed the “currently established damage tolerance level” of 1,331 cracks, the company said.
But the ONR report disclosed that EDF had scrapped its previous “operational allowance” of just 350 cracks, which caused the reactor’s prolonged shutdown. Instead the company argued that it was now safe to run the reactor with approaching four times as many cracks.
The ONR accepted EDF’s argument, saying that the “robustness” of the company’s methodology had not been undermined by the new tolerance level. But ONR said it would need new arguments to justify a second six months.
According to ONR’s report, EDF has also done fresh analysis of “in-event cracking” to assess the damage that could be done by an earthquake. This predicted that “overloads” from the kind of major earthquake expected once every ten thousand years could result in 500 additional cracks.
In addition ONR re-examined the risks that multiplying cracks could cause sections of the graphite core to break off and fall into the reactor. The Ferret reported in October 2019 that 58 fragments and pieces of debris had been found in Hunterston’s two reactors.
The danger is that debris could block cooling channels and cause fuel cladding to melt. EDF’s estimate of the likelihood of debris “migrating to safety significant locations” was “inherently subjective”, ONR said.
ONR’s report concluded by warning that EDF’s argument that the reactor could keep being operated safely was becoming stretched. The current safety case methodology “is reaching a limit of viability due to the conservatisms embedded within it,” ONR said.
To justify a second six months of operation EDF would have to “identify the major conservatisms and uncertainties and seek to quantify their combined effect on the damage tolerance assessment,” ONR recommended.
The 50-strong group of nuclear-free local authorities (NFLA) in the UK described Hunterston as a “litmus test” for ONR. During the Covid-19 pandemic there had been “little need” to restart the reactors, it argued.
“To hear the cracks could approach nearly a thousand if a full 12 months of operation is approved is not just alarming, but well above previously accepted safety limits,” said NFLA Scotland convener and Glasgow SNP councillor, Feargal Dalton.
“NFLA was flabbergasted that ONR gave approval for the reactors to restart again and has a growing sense that it will continue to acquiesce to EDF’s demands.”
The Green MSP for the west of Scotland, Ross Greer, argued that efforts should have been put into planning a “just transition” for Hunterston workers rather than extending the station’s lifetime. “This is utterly reckless behaviour by a global energy giant trying to maximise its profits, whatever the cost,” he said.
“Nuclear power stations shouldn’t be allowed to rewrite their safety rules every time their reactors exceed the limits they themselves had previously set.”
The Campaign for Nuclear Disarmament (CND) accused ONR of “continuously moving the safety goalposts” on the acceptable number of cracks. “Essentially ONR is allowing EDF to do whatever it wants to do and finding reasons to do so,” said CND UK vice-president, Dr Ian Fairlie.
“Instead of being a nuclear watchdog, ONR is fast becoming EDF’s pet poodle. It is placing the people living in the central belt of Scotland at risk of a serious nuclear accident.”
Scottish CND has launched a “virtual mass demonstration” under the hashtag #ShutDownHunterstonNow, claiming that nuclear power has “entanglements” with nuclear weapons. More than 100,000 people live within 20 kilometres of Hunterston, it pointed out.
Edinburgh-based nuclear consultant and critic, Pete Roche, thought ONR’s position was “exasperating”. He questioned the point of a nuclear watchdog “with no teeth”.
He said: “It looks as though ONR agrees with critics that restarting these reactors is a risky business, but they are not prepared to say no to EDF.”
The Office for Nuclear Regulation stressed that it was independent, and that its sole priority was the safety of workers, residents and the wider public. “We will only allow nuclear facilities to operate if we are satisfied that they are safe to do so,” an ONR spokesperson said.
“In reaching our decisions, we have applied stringent national and international safety standards, have scrutinised the safety justification for the operation of both reactors for this next period of operation, and have sought further evidence from EDF as we felt necessary.”
ONR was “satisfied that the nature of the cracking observed in reactor three will not prevent the reactor from operating safely or impede its ability to be shut down safely.”
It had always been intended by EDF, and understood by ONR, that the “currently established damage tolerance level” could be increased to justify the safety of allowing more cracks, the ONR spokesperson told The Ferret.
“An increase in the tolerance level has been possible because of improvements in the analysis methods. We are satisfied that the detailed safety case demonstrates that the reactor can operate safely for this period of operation, after which it will be shut down and the core re-examined.”
In order to win a second six months of operation EDF would have to make a new safety case which would be subject to detail scrutiny, ONR added. “If we are not satisfied that it can operate safely for a further period, we will not allow it to do so.”
EDF Energy said it did not expect to have much in common with groups that were totally opposed to nuclear power. “However, it is disappointing to see the usual scaremongering about a low carbon energy source that has been essential in limiting carbon emissions for over 40 years and which has generated a lot of prosperity in Ayrshire and beyond,” added a company spokesperson.
“EDF presented its safety case to the ONR following more than two years of thorough inspections, modelling and collaboration with universities and specialist companies. The technical queries received from the ONR showed robust, independent challenge that reinforce its reputation as the world’s strongest nuclear regulator.”
EDF accused its opponents of showing “a complete lack of understanding of how safety cases work and how they develop based on new evidence and risk assessment, not just, in this case, a count of cracks present.”
The company spokesperson added: “We absolutely stand by the detailed evidence which shows the reactor would be able to shut down safely, even after a seismic event far larger than the UK has ever experienced.
“Neither EDF or the independent regulator, the ONR, would ever give permission for any reactor to be returned to service if there were doubts about the safety of workers or the public.”
Cover image thanks to EDF Energy. This story was published in tandem with the Sunday National.