AGR (Advanced Gas cooled Reactor). General Presentation of the British Nuclear Fleet

Gas-cooled reactors, moderated with graphite and natural uranium metal, enabled Great Britain and France to build the first nuclear power plants for electricity generation (MAGNOX and UNGG systems). When the availability of enriched uranium became clear, France turned to pressurized water reactors, while Great Britain pursued the gas-cooled solution. To do so, it drew on feedback from MAGNOX reactors (CO ₂ coolant reactors, with natural uranium metal fuel, graphite moderator) by developing a specific pathway: that of the AGR (Advanced Gas cooled Reactor). The new direction involved the use of slightly enriched fuel and the switch from metallic fuel to steel-clad rod oxide fuel, a choice that enabled the implementation of a high-temperature thermal cycle with an efficiency of 42% and an increase in the reject irradiation rate to 44 GWj/t. By opting for a specific reactor associated with the oxide fuel cycle, future developments towards the gas- or sodium-cooled fast neutron reactors currently under study remained open. This fuel solution also enables irradiated fuel to be stored in pools over long periods, unlike MAGNOX fuel.

After a brief historical review of the introduction of AGRs, this article presents the main features of this technology: general architecture, concrete vessel, core, graphite structure, neutronics, fuel management, cooling circuits, overall design. A comparison with MAGNOX reactors and a brief analysis of the advantages and special features of AGRs are also provided. By 2023, this technology, which is the main component of the UK nuclear fleet (14 out of 15 reactors), will be operated by an EDF subsidiary.