The two units at Hunterston B started operating in 1976 and 1977. They were originally scheduled to shut in 2011, but their operating life was extended to 2016. After a technical and economic evaluation of the plant, EDF later confirmed it could operate until 2023. The graphite core of each AGR reactor includes around 6000 graphite bricks, 3000 of which are the graphite bricks containing fuel channels. The core 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, EDF Energy said in 2015.