Provision of Provision of a Graphite Technical Advisory Committee (GTAC) and Research in the Area of Nuclear Graphite Structural Integrity for the Office for Nuclear Regulation

BACKGROUND TO THE PROJECT The four remaining graphite moderated Advanced Gas Cooled Reactor (AGR) power stations represent a technology unique to the UK. Together they account for the large majority of the electricity generated by nuclear power within the UK. The AGRs commenced operation between 1978 and 1988 and are now experiencing ageing and obsolescence issues. The licensee, EDF Energy Nuclear Generation Limited (EDF), wishes to operate the reactors for as long as they are safe and economic to run. As well as dealing with the physical ageing, there is a need for continuity of knowledge and experience that is faced both by ONR and the licensee. The use of graphite as a moderator and carbon dioxide as a coolant has led to two significant technical issues that potentially challenge the essential safety functions of the core. These issues are graphite dimensional change and graphite oxidation. The former leads to cracking of the graphite moderator bricks, which could ultimately challenge the maintenance of adequate core geometry, and the latter leads to graphite weight loss. Both these phenomena lead to diverse and complex challenges including the implications of graphite brick cracking on safety functions and core moderation. Limits on these phenomena are defined and set in safety cases produced by the licensee and assessed by ONR. There is a limited pool of expertise in these graphite ageing mechanisms and given the uniqueness of the problem to the UK AGRs, EDF dominate research activities on this subject. For ONR to sustain an informed and independent view on these matters, ONR has for the last 20 years maintained a pool of experts independent to EDF, who's views can be consulted on significant technical matters regarding graphite ageing phenomena. o Over the course of the existing contracts the work performed has included the provision of specific advice, generally by the carrying out of specific analysis, according to a programme of work agreed with ONR inspect