Editing Advanced gas-cooled reactor (section)

{{short description|Type of nuclear reactor}}
[[File:Torness Power Station - geograph.org.uk - 1777307.jpg|thumb|AGR power station at [[Torness nuclear power station|Torness]]]]
The '''advanced gas-cooled reactor''' ('''AGR''') is a type of [[nuclear reactor]] designed and operated in the United Kingdom. These are the [[generation II reactor|second generation]] of British [[gas-cooled reactor]]s, using [[Nuclear graphite|graphite]] as the [[neutron moderator]] and [[carbon dioxide]] as coolant. They have been the backbone of the UK's [[nuclear power generation]] fleet since the 1980s.

The AGR was developed from the [[Magnox]] reactor, the UK's first-generation reactor design. The first Magnox design had been optimised for generating [[plutonium]],<ref name="GilbertKahn2007">{{cite book|last1=Gilbert|first1=Richard J.|last2=Kahn|first2=Edward P.|title=International Comparisons of Electricity Regulation|url=https://books.google.com/books?id=AeAEJ91dlAIC|access-date=6 October 2017|date=18 January 2007|publisher=Cambridge University Press|isbn=9780521030779|page=47}}</ref> and for this reason it had features that were not the most economic for power generation. Primary among these was the requirement to run on [[natural uranium]], which required a coolant with a low [[neutron cross section]], in this case [[carbon dioxide]], and an efficient [[neutron moderator]], [[graphite]]. The Magnox design also ran relatively cool gas temperatures compared to other power-producing designs, which resulted in less efficient steam conditions.

The AGR design retained the Magnox's graphite moderator and carbon dioxide coolant but increased the cooling gas operating temperature to improve steam conditions. These were made identical to those  of a coal fired plant, allowing the same design of turbines and generation equipment to be used. During the initial design stages it was found necessary to switch the fuel cladding from [[beryllium]] to [[stainless steel]]. However, steel has a higher [[neutron cross section]] and this change required the use of [[enriched uranium]] fuel to compensate. This change resulted in a higher [[burnup]] of 18,000 [[MWt|MW<sub>t</sub>]]-days per tonne of fuel, enabling less frequent refuelling.

The prototype AGR became operational at [[Windscale]] in 1962,<ref>[http://www.sellafieldsites.com/what-we-do/featured-projects/wagr History of Windscale's Advanced Gas-cooled Reactor] {{webarchive|url=https://web.archive.org/web/20111001192111/http://www.sellafieldsites.com/what-we-do/featured-projects/wagr |date=1 October 2011 }}, Sellafield Ltd.</ref> but the first commercial AGR did not come on-line until 1976. A total of fourteen AGR reactors at six sites were built between 1976 and 1988. All of these are configured with two reactors in a single building, and each reactor has a design thermal power output of 1,500 MW<sub>t</sub> driving a 660 [[MWe|MW<sub>e</sub>]] turbine-alternator set. The various AGR stations produce outputs in the range 555 MWe to 670 MWe though some run at lower than design output due to operational restrictions.<ref name=predec-20160217>{{cite web |url=https://www.oecd-nea.org/rwm/wpdd/predec2016/docs/S-1-1___ppt__BRYERS__.pdf |title=Preparation for future defuelling and decommissioning works on EDF Energy's UK fleet of Advanced Gas Cooled Reactors |author=John Bryers, Simon Ashmead |publisher=OECD Nuclear Energy Agency |work=PREDEC 2016 |date=17 February 2016 |access-date=18 August 2017}}</ref>