Advanced Gas-cuiled Reactor
The Advanced Gas-cuiled Reactor (AGR) is a teep o nuclear reactor designed an operated in the Unitit Kinrick. These are the second generation o Breetish gas-cuiled reactors, usin graphite as the neutron moderator an caurbon dioxide as coolant. They have been the backbone o the UK's nuclear generation fleet since the 1980s.
The AGR was developed from the Magnox reactor, the UK's first-generation reactor design. The first Magnox reactors had been optimised for generating plutonium and, for this reason, they incorporated a nummer o features that are not necessarily the best for economic performance. Primary among these requirements was the Magnox's ability to run on natural uranium, which demanded the use o a cuilant wi a low neutron cross section, in this case caurbon dioxide (CO2), and an efficient neutron moderator, graphite. Magnox also ran relatively cool compared tae other power-producing designs, which made it less efficient in extracting pouer from the reactor core.
The AGR retained the Magnox's graphite moderator an CO2 cuilant but increased its operatin temperature tae improve efficiency o steam production. The characteristics o the steam it produced were deliberately identical to those from a coal-fired plant, allowin the same steam turbines an generation equipment tae be used. Durin the initial design stages, it was necessary tae switch the tubin enclosing the fuel pellets from beryllium to stainless steel. Steel has a higher cross section and this change demanded the switch tae enriched uranium fuel tae maintain criticality. As part o this change, the new design had higher burnup o 18,000 MWt-days per tonne o fuel, requirin less frequent refuelling.
The first prototype AGR became operational in 1962 but the first commercial AGR did not come online until 1976. A total o fourteen AGR reactors at six sites were built between 1976 an 1988. All o these are configured wi two reactors in a single building. Each reactor has a design thermal pouer output o 1,500 MWt driving a 660 MWe turbine-alternator set. The various AGR stations produce outputs in the range 555 MWe tae 670 MWe though some run at lower than design output due tae operational restrictions.