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 the reactor’s graphite core which is made up of around 6,000 graphite bricks. This is the second graphite core inspection EDF Energy has carried out this year and follows an inspection of one of the reactors at Hinkley Point B in February.
The inspection monitored the two graphite bricks which were found to have cracks during an inspection in October 2014. As expected, there has been no significant increase in the cracking of the two bricks. As the reactor continues to operate further cracks are expected to occur due to the ageing of the graphite. During this inspection we identified two additional cracked bricks as a result of keyway root cracking. This is in line with our expectations at this stage of the reactor life, there are no safety implications and it does not affect the operation of the reactor.
EDF Energy is publicising these findings as part of its commitment to openness and transparency.
Station director Colin Weir said, “EDF Energy’s extensive graphite research programme has allowed us to develop a model of how our reactor cores will age. Each time there is an outage at one of our stations it allows us to add to this research and confirm that the reactors are ageing as we would expect.
“We know that during the life of a nuclear reactor the core will lose some of its mass and that cracks will appear in some of its bricks. This is part of the normal aging process and is accepted by our regulator. The results of the recent inspection were in line with our expectations and do not have an effect on the lifetime planning date of 2023.
Nuclear safety is our overriding priority. The safety margins we work to are very large and the level of cracking which we consider reasonable is far below anything which would affect the reactor’s safe operation.”
For more information on the graphite inspections on this reactor at Hunterston B power station, visit: http://media.edfenergy.com/r/758/hunterston_b_update.
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.
Safety limits approved by the ONR do not define a boundary between plant being safe or unsafe. Beyond these limits, there is a wide margin before the plant would be deemed to pose an unacceptable safety risk. In the highly unlikely event of a safety issue arising, the most extreme effect would be the reactor safely shutting down and being put out of service.
EDF Energy would always take a nuclear power station out of service long before this moment was possible, 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.