Fresh cracks found in Hunterston B reactor core

Fresh cracks have been found in the core of reactor 3 at the Hunterston B nuclear power station in Scotland, EDF Energy has revealed.

The plant operator said, while the reactor could be put back into operation immediately following a planned outage for inspections, it will remain offline for the time being to allow further discussions with the Office of Nuclear Regulation (ONR) to ensure its long-term safety.

The advanced gas-cooled reactor (AGR) is expected to be returned to service by the end of 2018. EDF Energy said the extended outage, which is projected to cut output by up to 3TWh, may be used as an opportunity to carry out additional routine maintenance. The firm said the operation of the other reactors in its nuclear fleet will not be affected.

The faults were found in the interlocking graphite bricks into which fuel and controls rods are inserted. The bricks act as a moderator, slowing down the neutrons that are produced from fission reactions so they can be absorbed by the nuclear fuel and stimulate further reactions. They also contain the channels through which the coolant – carbon dioxide – is pumped.

EDF Energy said inspections confirmed the presence of new “keyway root cracks”, which form as the bricks lose weight and become more brittle due to irradiation. Whilst this was expected to happen as the reactor grows old, the inspections found the cracks are emerging at a faster rate than previously predicted.

“We have been working over many years to fully understand and prepare for these late life changes to the reactor core and regular inspections at all our plants have provided a clear understanding of how the reactor cores age,” the firm said in a statement.

“The longer-term safety case will build on work already completed and EDF Energy expects that this will demonstrate that there are large safety margins both now and for the projected reactor lifetime.”

Priors inspections have uncovered similar cracks in both reactors at Hunterston B. In October 2016, the ONR was revealed to have ordered EDF Energy to modify the reactor shutdown process to introduce new super-articulated control rods that can more easily bend down the channels in the graphite bricks if they become warped.

Hunterston B was commissioned in 1976 and was originally due to close in 2011. However, the life of the plant has been extended twice, initially to 2016 and later to 2023.

EDF Energy currently operates 14 advanced gas-cooled reactors in the UK at seven different power stations: Hunterston B, Dungeness B, Hinkley Point B, Hartlepool, Torness and Heysham 1 and 2. All are scheduled to close by the end of the next decade.