One of the two cracked reactors at Hunterston B nuclear power station in North Ayrshire has been given permission to reopen – but only for four months.

The UK Office for Nuclear Regulation (ONR) is allowing EDF Energy to restart reactor four, which has an estimated 209 cracks in its graphite core. It was shut down on 2 October 2018.

ONR has accepted EDF’s argument that it’s safe to relax the limit for the permitted number of cracks. The “operational allowance” for cracks per reactor is being doubled from 350 to 700.

But ONR stressed that after four months EDF would again have to prove that it was safe to carry on running the reactor. “The longer term condition of the reactor remains uncertain,” ONR said.

Reactor three at Hunterston, which has an estimated 377 cracks in its graphite core, remains closed. It has been shut down since 9 March 2018, and ONR said the safety case for reopening it will be assessed “in due course”.

Campaigners have previously argued that the reactors should remain closed to prevent the risk of a “catastrophic” nuclear accident spreading radioactivity over Glasgow and Edinburgh. They expressed disappointment that reactor four was being allowed to restart.

Probes into four safety incidents at Hunterston nuclear plant

EDF has repeatedly postponed scheduled dates for restarting both ageing reactors at Hunterston, as reported by The Ferret. The reactors started generating electricity in 1976 and were originally due to close in 2006, but EDF wants to keep them both going until at least 2023.

ONR said that its team of specialist inspectors had completed an “extensive assessment” of the safety case submitted by EDF Energy. This focussed on “whether the cracking observed in the reactor graphite core will compromise its fundamental nuclear safety requirements.”

A statement from ONR said: “ONR is satisfied that reactor four is safe to operate for the next period and can be safely shut down in all foreseeable circumstances, including that of a significant seismic event. The core would be able to fulfil its fundamental safety requirements.”

The safety requirements included the “unimpeded insertion of control rods and unimpeded movement of fuel” and “ensuring that gas flow will remain adequate to ensure cooling of the fuel and core.”

According to ONR’s deputy chief inspector, Donald Urquhart, experts had been examining the safety implications of the cracks for years. “EDF Energy has completed an extensive programme of work to analyse the condition of the graphite cores at Hunterston B and other reactors in the UK to increase their knowledge and provide sufficient evidence to ensure safe operation,” he said.

“I have met with many of our interested stakeholders during the course of our assessment and I recognise that this is an emotive issue, but let me reassure you – it is ONR’s statutory role to examine the evidence objectively and make our decisions based on that. Nuclear safety remains our utmost priority and we would only allow a reactor to re-start with clear evidence that it remains safe for workers and the public.”

The longer term condition of the reactor remains uncertain and the licensee will need to justify safe operation. Donald Urquhart, Office for Nuclear Regulation

Urquhart emphasised that permission to operate was only for a limited period. “The longer term condition of the reactor remains uncertain and the licensee will need to justify safe operation beyond this period,” he added.

“ONR will continue to engage with EDF Energy to ensure all operations are only carried out with a detailed and underpinned safety case.”

Dr Ian Fairlie, a radiation consultant to the 50-strong nuclear-free group of local authorities (NFLA) said: “The reactors at Hunterston are among the oldest in Europe and are well past their sell-by dates.

“It is a pity that reactor four has been granted this four month lease of life to see if any more cracks appear. The precautionary principle should have been applied here especially as Scotland does not need the electricity from these reactors.”

NFLA Scotland convener and Glasgow SNP councillor, Feargal Dalton, also expressed disappointment. “It remains of real concern that reactors of their age, and with the levels of keyway route cracking as they have, should resume even time-limited operation,” he said.

“NFLA is particularly concerned that the ONR have accepted from EDF the possibility of up to 700 keyway root cracks on the reactors and still allow their operation. NFLA remains of the view that the age and the level of cracks should see these reactors be closed for practical safety reasons.”

He added: “NFLA will carefully consider the suite of justification documents from the ONR on how it came to this decision, and will actively engage with senior ONR inspectors over the next few months.”

According to the Green MSP for the west of Scotland, Ross Greer, there was “nothing reassuring” about the restart approval for communities around Hunterston. “The ONR themselves have detailed four previous notable safety incidents,” he said.

“These include lost cooling for a reactor, the failure of a shutdown pump and smoke from a control room panel. EDF have said these individual incidents are minor, but together with the 350 cracks in the reactors, they paint the picture of an ageing relic being pushed beyond its already repeatedly extended lifespan.”

Closure urged after 350 cracks found in nuclear reactor

EDF welcomed ONR’s decision. “The safety case for reactor four has been subject to extensive scrutiny and testing by our own internal independent nuclear assurance, the Nuclear Safety Committee – a body of independent industry experts – and by the ONR themselves,” said a company spokesperson.

“Since the decision was made to take both reactors offline last year, we have completed the most extensive investigation of the reactor core that has ever been undertaken. This has provided us with valuable knowledge about condition of the graphite core.”

The spokesperson added: “As part of this programme we have worked with the University of Bristol to confirm our understanding of how the core would react in the event of a major earthquake, of a magnitude never experienced in the UK.

“We have demonstrated that even in the most extreme conditions our reactors operate within large safety margins. In particular, all control rods would operate as they are designed to do and will safely shutdown the reactor in all circumstances.

“This has been agreed with the nuclear regulator, ONR, a statutory independent body which is representative of an industry whose regulatory regime is one of the most stringent and respected in the world.”

This story was updated at 14.45, 15.10 and 16.38 on 20 August 2019 to include comments from Dr Ian Fairlie, councillor Feargal Dalton and Ross Greer MSP. Photo thanks to David Autumns.

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