At present (May 2020), the two EdF reactors at the Hunterston Nuclear Station (R3 and R4) on the shore of the Firth of Clyde in Scotland have been shut for about 2 years for safety reasons – pending review by the Office for Nuclear Regulation (ONR). Both reactors are 44 years old, ie well past their original closure date of 2006. Already the ONR has extended their lifetimes – twice. They are scheduled to close permanently in 2023.
EdF is pressing ONR to permit both their Hunterston reactors to restart in June 2020.
The main safety issue (of several) is the extent of cracking in the graphite cores of the two reactors. For example, according to the ONR, EDF inspections in R3 have found cracks in several hundred graphite bricks and these were causing other nearby graphite bricks to crack. Inspections have showed bricks with one or two full-height cracks and additional partial-height cracks. ONR has warned of the potential for bricks to crack into three or more vertical parts and become multiply-cracked bricks which increased the risk of the nuclear fuel snagging. Brick cracking was also found to generate graphite debris which could inhibit cooling of reactor fuel. Reactor 4 is also affected but not to the same extent.
Meetings between ONR and NGOs
In 2018 2019 and 2020, representatives of concerned groups including myself have had three long meetings with ONR representatives about EDF’s proposed restarting of the reactors at Hunterston B.
Graphite cracking, including keyway root cracking (KRC), featured prominently during these discussions. KRC involves fissures in important keying slots in the graphite cores of the reactors. They result in the graphite bricks (~1 meter in diameter and about 1 meter in height) splitting into two halves.
I am not a nuclear engineer but my late colleague and friend, John Large, was one. When he worked at CEGB in the 1970s as a nuclear designer he designed and helped build the early AGRs. Before his untimely death in 2018, John and I had been in daily contact about the dangers of reactors 3 and 4 at Hunterston B.
He was clearly worried about the reactors and was adamant that they should be shut permanently: partly because of keyway root cracking but also for other reasons especially graphite mass loss. See http://largeassociates.com/wp/wp-content/uploads/2019/03/R3154-Graphite-FINAL-28-06-06.pdf
He stated on several occasions that the dilapidated Hunterston B reactors were “knackered” and must be shut permanently. He wanted us both to go up to Scotland to give public talks on the matter and we’d been planning to do so when he passed away suddenly. John’s sad death is a great loss to his family and to the environmental movement.
EdF’s policy is to keep the AGRs running – no matter what
EDF in Paris has apparently decreed the British AGRs must stay open – with the tacit support of the UK Government Department for Business Energy and Industrial Strategy – BEIS. The Hunterston B reactors are the oldest AGR reactors – another 12 ageing AGRs will also have to close over the next decade.
As part of its policy, EDF is spending £millions each year funding specialist academics at the University of Manchester (Professor Marsden and his teams) to keep studying AGR graphite problems in a clearly orchestrated effort to keep these old reactors going.
Many people may assume that these reactors are needed for the electricity they generate, but this is incorrect. They have been closed for two winters without any electricity supply problems. Indeed Scotland has a glut of electricity and would be better off without the Hunterston reactors.
What causes AGR graphite cracking?
The teams of specialist academics at University of Manchester don’t know the full answer. None of their models accurately predicts the observed cracking rates. Indeed the models have underestimated the extent of the cracking. Although ramping the reactors up and down might appear to be a cause, ONR seems to think it is more due to burnup hours. Eg at the end of 2019, ONR allowed R4 to restart for 4 months to catch up with the burnup hours that R3 (which had many more cracks) had operated. In my view, allowing a less damaged reactor to operate so that it has the same operating hours as its more damaged sister reactor is clearly not precautionary and is worrying.
One could go into more detail about graphite cracking, but the science gets increasingly abstruse and argumentative. No sooner has one discredited an EDF technical point than myriad others pop up. One sometimes feels like one is peering down a KRC rabbit hole….. as in Alice in Wonderland. It seems this is now less a scientific issue than a political one.
If one adopts the principled standpoint that public safety is of paramount importance, then the Hunterston B reactors should be closed permanently. At the very least, this would observe the precautionary principle which has apparently been absent during ONR – EDF discussions.
However recent indications suggest that ONR may be giving EDF the green light to restart the 2 reactors in June – even during the current Covid-19 epidemic.
In other words, the twin political pressures from EDF in Paris and BEIS in London may have prevailed. But it is the people of central Scotland who will have to run the risks if anything were to go wrong. Let’s cross our fingers and hope it doesn’t.