EDF Energy said this week March that it has extended outages at the two reactors at its Hunterston B plant in Scotland while the Office for Nuclear Regulation assessed their safety cases. Hunterston B-8 (reactor 4) is now expected to restart on 30 April, a month later than previously announced. Hunterston B-7 (reactor 3) is scheduled to restart on 29 June, instead of the previous date of 30 April.
The two AGR units were taken offline after significant cracks were discovered in March and October 2018. In November 2015, EDF Energy had said cracks found in three of the graphite bricks in reactor 3 and two bricks in reactor 4 had no safety implications. However, in May 2018 EDF admitted the cracks were expanding more quickly than anticipated and in December extended the outages by several weeks, for further work.
The two units at Hunterston B started operating in 1976 and 1977. They were originally scheduled to shut in 2011, but their operating lives were extended to 2016. After a technical and economic evaluation of the plant, EDF later confirmed it could operate until 2023. In March 2018, Hunterston B 3&4 were taken offline to carry out inspections of the graphite core. These confirmed the presence of cracks and showed these were growing more quickly than had been modelled. Since then, EDF Energy has conducted more inspections and said it has improved its modelling on how the reactors would operate in normal conditions and in a highly unlikely earthquake.