[en] The UK’s fleet of fourteen graphite moderated Advanced Gas-cooled Reactors (AGR) are the only power producing nuclear reactors in the world that have a graphite moderated core cooled by carbon dioxide gas operating at > 500◦C. The graphite core cannot be replaced and during its lifetime it is subject to the combined ageing and degradation effects of irradiation and oxidation. The UK has a long history and experience of operating graphite moderated cores. Early development reactors in the 1950’s were succeeded by the commercial power producing Magnox design. The UK operated 11 Magnox stations; the first began generation in 1956 and the last ceased operation in 2015. The UK’s second generation reactors, the AGR, first started generation in 1976 and are all still in operation today. The early developmental reactors had air-cooled graphite cores operating at low temperatures which presented problems in terms of Wigner energy build-up. The lack of understanding in the UK of this aspect of irradiated graphite behaviour resulted in a reactor fire in one of the piles situated at Windscale. The UK government’s response following an inquiry into this nuclear accident was the formation in 1959 of an independent UK nuclear safety regulator. This regulatory body is now known as the Office for Nuclear Regulation and is responsible for enforcing relevant legislation across all UK nuclear licensed sites.