08.03.2019_No48 / News in Brief

EDF Energy Releases Video Footage Of Hunterston B-1 Graphite Cracks

Unplanned Events & Incidents

8 Mar (NucNet): EDF Energy has released video footage of inspections that show cracks in graphite bricks in the reactor core of the Hunterston B-1 nuclear power plant in Scotland.

The Hunterston B nuclear power station in Scotland. Photo courtesy EDF Energy.

In a letter to local community groups EDF Energy’s acting station director for Hunterston, Roddy Angus, said the videos are representative examples of the kind of “keyway root cracking” that has been discovered during inspections.

He said the footage, from 2017, shows that the cracks are around 1mm when first observed and they are opening very slowly.

“The average crack size is currently approximately 2mm and we have demonstrated in our safety cases that cracks up to a width of 10mm on the inside of the fuel channel and 18mm on the outside of the fuel channel are acceptable.”

EDF Energy said the reactor cores of all 14 advanced gas-cooled reactors (AGRs) in the UK are made up of graphite bricks. Channels run through these bricks for nuclear fuel, and also for control rods which can stop the nuclear reaction if needed. This graphite was always expected to change over time. How it ages is one factor which will determine how long the UK’s AGRs will operate.

“Since March 2018 we have been been carrying out the most extensive graphite investigation programme ever undertaken which has told us a lot about the condition of the graphite cores in both Hunterston reactors,” EDF Energy said.

Hunterston B has two AGRs. Hunterston B-1 began commercial operation in February 1976 and Hunterston B-2 in March 1977

The graphite core of both units is made up of around 6,000 graphite bricks – 3,000 of which contain fuel channels – which are all connected. 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.

In March 2018 Hunterston B-1 came offline to carry out routine inspections of the graphite core. The inspections confirmed the expected presence of new keyway root cracks in the core and also identified them as happening at a slightly higher rate than modelled.

In May 2018, EDF Energy decided that Hunterston B-1 would remain offline to enable the company to work with the regulator to ensure the plant’s safety.

More details: https://bit.ly/2J2Ftur

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David Dalton

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