19 Nov 15

Hunterston B update

Planned maintenance has been taking place on one of the two nuclear reactors at the Hunterston B nuclear power station in North Ayrshire.

As part of routine inspections, engineers looked at part of the reactor’s graphite core. Three graphite bricks were found to be cracked. This is known as keyway root cracking and was predicted to start happening at this point in the station’s lifetime. It does not affect the operation of the reactor and the findings have no safety implications and are well within any limits for safe operation. Inspections on the station’s other reactor found similar results in October 2014.

EDF Energy is publicising these findings as part of its commitment to openness and transparency. Further inspections will look at more of the graphite core and if any additional cracks are found, EDF Energy will share this information.

Station director Colin Weir said, “Nuclear safety drives everything we do. This means we work within very large safety margins. This applies to graphite bricks too.  The level of cracking which is considered reasonable is far below anything which would affect the reactor’s safe operation.

“It is accepted by our regulators and materials experts that cracks will occur in some of the bricks and that the core will lose some of its mass as part of the normal ageing process.

“The observations were anticipated and are in line with our understanding, so our view of the best estimate lifetime planning date of 2023 has not changed.”


The graphite core of the reactor is made up of around 6,000 graphite bricks (3,000 of these are the graphite bricks containing fuel channels) which are all connected together. The structure is designed to contain many redundant bricks meaning a very large number of bricks would have to crack before there were any significant safety concerns.

Over time, graphite slowly loses weight as part of the normal ageing process. This is a well-known phenomenon which was fully considered as part of the stations’ design and is factored into safety limits approved by the independent regulator, the Office for Nuclear Regulation (ONR).

Graphite ageing is one area used to determine the lifespan of an AGR nuclear power station. Greater understanding of the ageing process by sampling and modelling can lead to them operating safely for longer, giving the UK secure and reliable low-carbon electricity.

EDF Energy would always take a nuclear power station out of service long before an issue became unsafe, regardless of commercial considerations.

The Office for Nuclear Regulation has produced some helpful background on graphite here http://www.onr.org.uk/civil-nuclear-reactors/graphite-core-of-agrs.htm

EDF Energy in Scotland

In Scotland EDF Energy operates Hunterston B in North Ayrshire and Torness in East Lothian which employ over 1,000 staff and around 500 contracting partners across the two power stations. EDF Energy employs a further 200 office based staff in East Kilbride.  As well as generating enough power to serve some 4 million homes the company also provides gas and electricity to over 80,000 Scottish customers with around half of those opting for one of the company’s Blue+ products which are backed by low-carbon generation. We operate two windfarms in the Scottish Borders and make sure we buy enough electricity generated from a low-carbon nuclear source to match every unit of electricity we estimate our Blue customers use. EDF Energy is proud to power up some of the largest organisations in the UK, including supplying almost all public sector bodies in Scotland with after being awarded Scotland’s largest electricity supply contract by annual volume from April 2013. Following a landmark agreement with Network Rail the company also provides nuclear-backed Blue energy to power up the UKs electric rail network, covering most of the south east of England and the main lines from London to Edinburgh and Glasgow, as well as the Merseyrail network around Liverpool and the Glasgow suburban network.