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ONR gives permission for Reactor 4 at Hunterston B to return to service

The Office for Nuclear Regulation (ONR) has today provided EDF Energy Nuclear Generation Ltd (EDF NGL) with permission for Reactor 4 at Hunterston B power station to return to service for a limited period of operation.

The permission is for operation up to a total of 16.25 terawatt days, which is approximately six months operation.

ONR’s assessment focussed on whether cracking observed in the graphite bricks that form the reactor core of Reactor 4 could compromise its fundamental nuclear safety requirements. These are:

  • unimpeded insertion of control rods and unimpeded movement of fuel;
  • ensuring that gas flow will be maintained to ensure cooling of the fuel and core; and
  • that appropriate moderation (slowing neutrons to sustain the nuclear chain reaction) and thermal inertia (reducing the speed of temperature changes) are maintained.

Following extensive examination of the safety justification and underpinning evidence, and engagement with EDF in technical discussions to ensure that all significant issues have been addressed, specialist ONR inspectors have concluded that an adequate safety justification for a limited period of operation had been provided.

ONR is satisfied that Reactor 4 is able to operate safely and can be safely shutdown (including in a significant seismic event) as required.

Donald Urquhart, ONR Deputy Chief Inspector, said: “In reaching this decision, ONR’s team of independent expert inspectors are committed to ensuring the safety of site workers, local residents and the wider public.

“We have scrutinised the safety justification and supporting evidence for this next period of operation in great detail, and I am satisfied that the high standards of nuclear safety that we expect have been demonstrated. We will only allow nuclear facilities to operate if we are satisfied that they are safe to do so.”

More information about the technical assessments that underpin this decision can be found in the Project Assessment Report.