22 Nov 18
Hunterston B - Graphite

Community update

Letter to Hunterston SSG - 22 November 2018

Dear SSG Member,

As a member of our community, I believe it is important to keep you updated on any developments at Hunterston B Power Station.

You may be aware of some media coverage today about the recent graphite inspections at Hunterston B. This coverage was prompted by an article on a website called The Ferret which I would like to address.

I have written and spoken to you many times about the effects of graphite aging, what it will do to the reactor core and the circumstances in which this may pose a challenge to control rod entry. None of this has changed.

As you will recall, the information about the number of cracks and where they placed the reactor in relation to the existing safety case was disclosed in public at the SSG meeting in June 2018. A full discussion which was include in the minutes took place. A full discussion took place during which my colleague Dr Roddy Angus, as well as Stuart Fannin from the ONR, answered a number of questions which appear to have been raised again in the course of this coverage.

Hunterston B remains safe to operate. Nothing in the extensive research and modelling we have carried out suggests impacts of the type outlined in the story on The Ferret. As you know, the cracking only poses a potential challenge to the entry of the control rods in an extreme and highly unlikely earthquake scenario and even then we have back-up systems which include super-articulated control rods (designed to bypass distortions) and nitrogen plant which operates within seconds to shut-down the affected unit.

Again, you will have heard me say this before, but nuclear safety is our overriding priority. This has been publically questioned but it is exactly why we are taking the approach we have.

This priority is why we have carried out the most extensive inspection programme on an AGR station to date at Hunterston B. We have inspected around a quarter of the core of Reactor 3 and a tenth of the core of Reactor 4.

It is also why we have set out a clear strategy for moving forward with revised safety cases for the units based on the modelling we have developed with leading academics and consultants over the past decade.

There has been good progress on this strategy. This includes enhancements to the seismic modelling using a more representative model of the reactor building. Using this improved model significant additional safety margins are demonstrated. The safety assessments show that, even in an extreme, highly unlikely earthquake, the core will behave as designed with no challenge to control rod entry.

The safety case demonstrating safe operation for the next period of generation for Reactor 3 is now being subject to robust internal assessment including with our independent experts. Once this process is completed, the safety case will be submitted to Office for Nuclear Regulation. To enable the teams to complete this work we have extended the time available for this assessment. We welcome the robust regulatory environment in which we operate and are working very closely with the nuclear regulator to achieve our shared objective of ensuring nuclear safety.

We also decided to carry out graphite core inspections at Hunterston Reactor 4. The outage started on 2 October and we inspected 34 channels, more than a tenth of the core. Again, the number of cracks is in line with our predictions, with narrower than modelled crack opening and no significant core distortion. The case for return to service of Reactor 4 is now with the ONR for external assessment.

I hope this information is useful to you as a member of the Site Stakeholder Group.

Should you wish to ask any questions please feel free to ring the Station on 01294 826000 and ask for our Communications Officer, Nikki Thomson.

Colin Weir

Station Director