The UK's Office for Nuclear Regulation (ONR) has today provided EDF with permission for Reactors 3 and 4 at the Hinkley Point B power station in Somerset, England, to return to service for a limited period of operation. This follows ONR's assessment of whether cracking observed in the graphite bricks that form the reactor core could compromise the key nuclear safety requirements.

Reactor 4 and Reactor 3 were taken offline on 21 February and 8 June 2020, respectively, for a series of planned inspections of the graphite core. The company plans to run Hinkley’s two reactors for six months, "pause" for further inspections and, subject to ONR approval, generate power for a second six-month period. It is expected that the 12 months of operation will generate 8 TWh of electricity.

ONR said the three key nuclear safety requirements were: the graphite core will not impede control rod entry, thereby ensuring that the reactors can be safely shutdown and held down, both under normal conditions and during or following fault conditions including seismic events; fuel and core component cooling remains adequate both under normal operating conditions and during or following fault conditions including seismic events; and fuel handling risks due to graphite core cracking remain acceptable.

Permission for Reactor 3 will allow it to operate to a core utilisation of 17.55 terawatt days, while permission for Reactor 4 is to operate to a core utilisation of 17.3 terawatt days, which equates to two periods of approximately six months operation for each reactor. Graphite core inspections will take place between each period of operation.

ONR said it was satisfied that the Hinkley Point B Reactors 3 and 4 are safe to operate for these specified periods, and that they can be safely shut down, including in a significant seismic event, if required.

Donald Urquhart, ONR's executive director of operations and deputy chief inspector, said: "Our team of specialist inspectors have thoroughly assessed and scrutinised the evidence provided by EDF. I am satisfied that this evidence demonstrates that Reactors 3 and 4 at Hinkley Point B are able to not only operate safely, but to be shut down safely under both normal and abnormal conditions, as may be necessary."

EDF said the results of the inspections were "well within" its expectations. Detailed analysis by specialist EDF teams had revealed the graphite was "in exactly the condition" the company had forecast, EDF said. Last autumn the ONR’s Chief Inspector noted the number of cracks in one of the reactors’ graphite was "lower than expected", the company added.

EDF has invested GBP3 million (USD4 million) over the past year upgrading the Hinkley Point B plant while detailed assessments have been completed on the graphite in the nuclear reactors.

Peter Evans, station director of Hinkley Point B, said: "Our core purpose at Hinkley Point B is helping Britain achieve net zero and we have been doing this since long before the term net zero arrived. The approval to restart power generation, which has come after many months of physical works and technical assessments of our site, plant and nuclear reactors, is really positive news.

"When I look back at the last 12 months it is incredible to think we have delivered a major inspection and maintenance programme and a thorough justification to restart the nuclear reactors, all as we grappled with a pandemic which has fundamentally changed the way we work. But we've done the work, proved our case and I’m thrilled that we can get back online and once again do what we do best."

Hinkley Point B is one of the UK's seven nuclear Advanced Gas-cooled Reactors (AGRs), which have provided around 20% of the country’s power supply over the last four decades. Hinkley Point B started operations in 1976 and, in 2012, the estimated end of its generation was extended to 2023, with a +/- 2 years proviso. Since then it has been "the most productive" UK nuclear power plant, EDF said, generating enough electricity to meet the needs of every home in the UK for three years, and helping to avoid the emission of more than 100 million tonnes of CO2.

Last November EDF announced that Hinkley Point B would operate no later than July 2022 before moving into the defuelling phase.

EDF is building two EPRs at Hinkley Point C and developing plans for a replica plant at Sizewell C, in Suffolk.