Restarting Hunterston’s Ageing Nuclear Reactors – Ongoing Correspondence with EDF

Hunterston B by David Autumns
Hunterston B, Ayrshire, Scotland photo by David Autumns
Hunterston A by David Autumns
Hunterston A, Ayrshire, Scotland photo by David Autumns

Members of Radiation Free Lakeland, have been inspired by the example set by David Autumns to write individual letters to EDF the French electric utility company, (largely owned by the French state) asking EDF to completely scrap the restarting of their ageing nuclear reactors at Hunterston B.   There should be widespread anti-nuclear protests in the streets  given the enormity of what could happen as a result of restarting these nuclear reactors which have hundreds of cracks in their radioactively hammered graphite cores.    But who is talking about this?  Who is opposing it?  Who cares a stuff about the potential radioactive fall out?

Here is some of the correspondence – get a cup of tea and prepare for toe curling patronising greenwash from the most dangerous industry on earth.

“Dear Mr Autumns,
Further to our CEO Simone Rossi’s response to your letter, I would like to deal with some of the more technical points you raised.
If you’ll allow me, I want to repeat Simone’s point that we would never allow Hunterston B, or any of our other reactors, to operate if we had any doubts over their safety. Nuclear safety drives everything we do. This means we work within very large safety margins and our approach to safety means that we would shut down long before anything which would affect the reactor’s safe operation. We are also subject to extremely rigorous and independent scrutiny by the Office for Nuclear Regulation who would not allow us to operate our sites if they had any concerns over safety.
Since we took the decision to take reactor 3 at Hunterston out of service last year we have completed the most extensive inspection of a graphite core that we have ever done. We have inspected over a third of the bricks in the core and, for the first time, completed an inspection of the channels used by the control rods used to regulate or shut down the reactor. The inspections showed that the level of cracking in the bricks was higher than we predicted in our modelling, but the rate of expansion in existing cracks was smaller than predicted. There was no degradation in the control rod channels.
The design of the reactor core means that all the fuel bricks are held securely together through a keying system with bricks interlocking with each other. This means that although a brick may have cracks that run the length of it, during normal operating conditions it will not be able to move or cause a distortion that could hamper the insertion of a control rod in an emergency situation.
As a responsible operator we need to be sure that this would also be the case in the most extreme scenarios. We have worked with the University of Bristol to model the impact of an earthquake on the site, building a ¼ sized model of a reactor core and subjecting it to a number of different strength seismic events. We have proved that even in the event of an earthquake of a magnitude not seen in the UK before that we would be able to control the reactor and that all control rods would operate as they are supposed to do.
As well as Bristol University, we have been working with leading consultancies and expert academics at universities across the UK including Strathclyde, Glasgow, Manchester, Oxford, Sussex, Nottingham and Durham as well as with leading UK companies such as AMEC Foster Wheeler, W S Atkins and Fraser-Nash. We have also invested over 1000 person years into this research and invested over £125m in the programme.
I note your concerns about deterioration of the graphite. The neutron irradiation and radiolytic oxidation of the graphite were known at the design process. The shrinkage is exactly as predicted, the loss of mass within expectation, and the cracking has been long anticipated and we have thoroughly prepared for it, even though its consequences are negligible. Our safety assessments show conclusively that the reactors will operate and shutdown as designed in all situations.
Only 12 control rods are needed to shut the reactor down. Out of the 81 control rods in each reactor 12 of them are ‘super articulated’ which allows them to be inserted fully into the core even in the hugely unlikely possibility of an earthquake causing distortion. Some commentators have painted a picture of control rods not being able to be inserted but this is extremely misleading.
Independent expert modelling shows that even in the event of an earthquake with a force higher than anything in our history that the distortion in the reactor core would be around 15 mm with many other channels distorting by less than 10mm. The design of the reactor means that we would need to see distortion of over 60mm to produce contact between most control rods and the graphite bricks, for the articulated control rods this goes up to over 100mm giving us significant safety margins.
As I said at the outset of the letter, nuclear safety is paramount. So while we are completely confident that the systems I have outlined above would mean that we can maintain control of the reactor in the most extreme of conditions, we do have a back-up system at our disposal and can inject nitrogen gas into the reactor and this will immediately shut down the unit.
You write about your fears of a ‘fuel element melt’. This can’t happen in the AGRs. Our reactors are designed to fail safe. There are multiple layers of safety systems constantly monitoring every aspect of operation, so any deviation from the clearly-defined operating margins results in the reactor shutting itself down instantly.
I wanted to deal with some of the inaccuracies in the HBO Chernobyl drama. It’s important to point out that such a scenario could not happen here for a number of reasons. Yes the reactor core of seven of our 8 UK nuclear stations is made of graphite, but that’s where the similarity ends. Chernobyl was a boiling water reactor with a flawed core design and it was ‘unforgiving’ for the operators. These conditions provoked a dangerous operating state. The operators were unaware of this and did not know the test could bring the reactor to an explosive state.
The UK reactors were designed with defence in depth. All nuclear power stations in the UK, unlike those in the Soviet Union at that time, must have engineered automatic controls and protection systems. Our Advanced Gas-cooled Reactors are designed so that the ‘runaway’ reaction that happened isn’t technically feasible. The Soviet era politics also allowed operators to override safety systems with an unauthorised plant manoeuvre – our UK regulation system and safety culture is a further check on the deliberate non-compliance with safety culture shown at Chernobyl.
The work at Hunterston B is providing greater understanding of how graphite ages which we can apply to the safety cases of the other younger AGRs at the appropriate time, avoiding further lengthy down-time in the future.
Finally, we will perform regular and frequent inspections so that we remain confident that the Hunterston reactors continue to operate with the large margins we have demonstrated and agreed with the independent nuclear regulator.
I hope that I have been able to respond to all your concerns but as Simone has suggested you would be welcome to visit one of our nuclear sites where you can take a tour of the station and talk with the people who operate the plant. You will find the links to the visitor centres and your nearest station here.
Andy Goddard
Chief Technical Officer
Nuclear Generation
EDF Energy Generation”
A further reply from David…

“Dear Mr Goddard

First may I thank you for putting back the restart of Hunterston B Reactor 3 to the 31st October and Reactor 4 to the 22nd July

This begs the question why? The Reactors are clearly not as bullet proof and reliably safe as your email might have suggested.

Having surveyed 1/3 of the graphite core this leaves you with 2/3’s of the core of which you are unaware of it’s state. Is it at all possible that any of the cracked graphite might fall down the holes. now or in the future, and block a control rod channel that even one of the super-articulated variety might not be able to descend to shut down the Reactor? Is it possible, despite your reassurances, that a crack in a graphite brick might cause an offset between the bricks such that the cooling carbon dioxide is impeded causing Uranium fuel rods to melt?

Are you suggesting that graphite monitoring on the later AGR’s will be abandoned and their shutdown be based entirely on models based on the results of Hunterston B’s degregation?

You say that Hunterston B was designed with defence in depth. Has the boron bead system in place in later AGR’s been retrofitted to the Hunterston B reactors? This is still a first generation design without secondary containment present. Just concrete under 600psi held together with pre-stressed cables. Stressed cables that have been in place since before 1976 – the same design as the now closed Oldbury.

Are you still having the stator winding issues with the cooling gas circulators at Hunterston B or have these been replaced recently?

Could you comment on Dungeness B’s outage and it’s progress?

Calling an AGR “advanced” really is a misnomer, given the timescale of it’s design. It’s the incremental improvement of having the boilers within the biological screen over the Magnox design meaning the workers and local population have to suffer less so called “Shine”. Having those boilers alongside the core however opens us up to more risk of a water/steam leakage into the reactor core and it’s consequences. The issue at Heysham 1 with the boiler mounting spline… is there any possibility of this failure mode, or one like it, occurring in any of the other aged Reactors?

As the Reactors are now functioning outside of their design spec are you, unlike the operators at Chernobyl, fully aware of how your Reactors might react?

I ask you and your Colleagues at EDF to turn off Hunterston B for good. Please.


David Autumns”



4 thoughts on “Restarting Hunterston’s Ageing Nuclear Reactors – Ongoing Correspondence with EDF

  1. Martyn Lowe

    This is a wonderful example of how the Nukiller industry does not think things through.

    in the middle iof this letter it is stated that; ‘ we have been working with leading consultancies and expert academics at universities’ which is followed on by stating ‘ We have also invested over 1000 person years into this research and invested over £125m in the programme.’

    That £123Million is tax free of course.

    He also states that: ‘Independent expert modelling shows that even in the event of an earthquake with a force higher than anything in our history ‘.

    There is reference to which of the following it might of been.

    Yet in his letter we also read: ‘The inspections showed that the level of cracking in the bricks was higher than we predicted in our modelling.’

    That’s pre earthquake.

    From which I can only conclude that EDF are consulting the Wrong Kind of Experts.

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