Advanced gas-cooled reactor
Encyclopedia
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
. These are the second generation
Generation II reactor
A generation II reactor is a design classification for a nuclear reactor, and refers to the class of commercial reactors built up to the end of the 1990s...
of British gas-cooled reactors, using graphite
Nuclear Graphite
Nuclear graphite is any grade of graphite, usually electro-graphite, specifically manufactured for use as a moderator or reflector within nuclear reactors...
as the neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
as coolant. The AGR was developed from the Magnox
Magnox
Magnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
reactor, operating at a higher gas temperature for improved thermal efficiency, requiring stainless steel fuel cladding to withstand the higher temperature. Because the stainless steel fuel cladding has a higher neutron capture cross section than Magnox fuel cans, enriched uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
fuel is needed, with the benefit of higher "burn ups" of 18,000 MWt-days per tonne of fuel, requiring less frequent refuelling. The first prototype AGR became operational in 1962 but the first commercial AGR did not come on line until 1976.
All AGR power stations are configured with two reactors in a single building. Each reactor has a design thermal power output of 1,500 MWt driving a 660 MWe
MWE
MWE may refer to:*Manufacturer's Weight Empty*McDermott Will & Emery*Midwest Express, an airline*Merowe Airport - IATA code*Multiword expressionMWe may refer to:*Megawatt electrical...
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. http://www-pub.iaea.org/MTCD/publications/PDF/cnpp2004/CNPP_Webpage/pages/..%5Ccountryprofiles%5CUnitedKingdom%5CUnitedKingdom2003.htm
AGR design
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...
temperatures do not vary too much from those seen in a Magnox
Magnox
Magnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
station. The superheater outlet temperature and pressure were designed to be 2,485 psia (170bar) and 543°C.
The fuel is uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...
pellets, enriched to 2.5-3.5%, in stainless steel tubes. The original design concept of the AGR was to use a beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
based cladding. When this proved unsuitable, the enrichment level of the fuel was raised to allow for the higher neutron capture losses of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
cladding. This significantly increased the cost of the power produced by an AGR. The carbon dioxide coolant circulates through the core, reaching 640°C (1,184°F) and a pressure of around 40 bar (580 psi), and then passes through boiler (steam generator) assemblies outside the core but still within the steel lined, reinforced concrete pressure vessel. Control rods penetrate the graphite moderator and a secondary system involves injecting nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
into the coolant to hold the reactor down. A tertiary shutdown system which operates by injecting boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
balls into the reactor has been proposed 'as retrofit to satisfy the Nuclear Installations Inspectorate’s concerns about core integrity and core restraint integrity'.
The AGR was designed to have a high thermal efficiency (electricity generated/heat generated ratio) of about 41%, which is better than modern pressurized water reactor
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...
s which have a typical thermal efficiency of 34%. This is due to the higher coolant outlet temperature of about 640 °C (1,184°F) practical with gas cooling, compared to about 325 °C (617°F) for PWRs.
However the reactor core has to be larger for the same power output, and the fuel burnup ratio at discharge is lower so the fuel is used less efficiently, countering the thermal efficiency advantage
http://www.royalsoc.ac.uk/downloaddoc.asp?id=1221.
Like the Magnox, CANDU and RBMK
RBMK
RBMK is an initialism for the Russian reaktor bolshoy moshchnosti kanalniy which means "High Power Channel-type Reactor", and describes a class of graphite-moderated nuclear power reactor which was built in the Soviet Union. The RBMK reactor was the type involved in the Chernobyl disaster...
reactors, and in contrast to the light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...
s, AGRs are designed to be refuelled without being shut down first. This on-load refuelling was an important part of the economic case for choosing the AGR over other reactor types, and in 1965 allowed the CEGB
CEGB
The Central Electricity Generating Board was the cornerstone of the British electricity industry for almost 40 years; from 1957, to privatisation in the 1990s....
and the government to claim that the AGR would produce electricity cheaper than the best coal fired power stations. However fuel assembly vibration problems arose during on-load refuelling at full power, so in 1988 full power refuelling was suspended until the mid-1990s, when further trials led to a fuel rod becoming stuck in a reactor core. Only refuelling at part load or when shut down is now undertaken at AGRs. http://www.greenpeace.org/raw/content/international/press/reports/nuclearreactorhazards.pdf#page=31
The AGR was intended to be a superior British alternative to American light water reactor designs. It was promoted as a development of the operationally (if not economically) successful Magnox design, and was chosen from a plethora of competing British alternatives - the helium cooled High Temperature Reactor (HTR)
Very high temperature reactor
The Very High Temperature Reactor , or High Temperature Gas-cooled Reactor , is a Generation IV reactor concept that uses a graphite-moderated nuclear reactor with a once-through uranium fuel cycle. The VHTR is a type of High Temperature Reactor that can conceptually have an outlet temperature of...
, the Steam Generating Heavy Water Reactor (SGHWR) and the Fast Breeder Reactor (FBR) - as well as the American light water pressurised and boiling water reactors (PWR and BWR) and Canadian CANDU designs. The CEGB conducted a detailed economic appraisal of the competing designs and concluded that the AGR proposed for Dungeness B would generate the cheapest electricity, cheaper than any of the rival designs and the best coal fired stations.
There were great hopes for the AGR design. An ambitious construction programme of five twin reactor stations, Dungeness B, Hinkley Point B, Hunterston B, Hartlepool and Heysham was quickly rolled out, and export orders were eagerly anticipated. However, the AGR design proved to be over complex and difficult to construct on site. Notoriously bad labour relations at the time added to the problems. The lead station, Dungeness B was ordered in 1965 with a target completion date of 1970. After problems with nearly every aspect of the reactor design it finally began generating electricity in 1983, 13 years late. The follow on stations all experienced similar problems and delays. The financing cost of the capital expended, and the cost of providing replacement electricity during the delays, were enormous, totally invalidating the pre-construction economic case.
The small-scale prototype AGR at the Sellafield
Sellafield
Sellafield is a nuclear reprocessing site, close to the village of Seascale on the coast of the Irish Sea in Cumbria, England. The site is served by Sellafield railway station. Sellafield is an off-shoot from the original nuclear reactor site at Windscale which is currently undergoing...
(Windscale) site is in the process of being decommissioned. This project is also a study of what is required to decommission a nuclear reactor safely.
Current AGR reactors
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, owned and operated by EDF Energy
EDF Energy
EDF Energy is an integrated energy company in the United Kingdom, with operations spanning electricity generation and the sale of gas and electricity to homes and businesses throughout the United Kingdom...
:
| AGR Power Station | Net MWe | Construction started | Connected to grid | Commercial operation | Accounting closure date |
|---|---|---|---|---|---|
| Dungeness B | 1110 | 1965 | 1983 | 1985 | 2018 |
| Hartlepool | 1210 | 1968 | 1983 | 1989 | 2019 |
| Heysham 1 | 1150 | 1970 | 1983 | 1989 | 2019 |
| Heysham 2 | 1250 | 1980 | 1988 | 1989 | 2023 |
| Hinkley Point B Hinkley Point B nuclear power station Hinkley Point B is a nuclear power station near Bridgwater, Somerset, on the Bristol Channel coast of south west England.-History:The construction of Hinkley Point B, which was undertaken by a consortium known as The Nuclear Power Group , started in 1967. The reactors were supplied by TNPG and the... |
1220 | 1967 | 1976 | 1976 | 2016 |
| Hunterston B Hunterston B nuclear power station Hunterston B Power Station is a nuclear power station in North Ayrshire, Scotland. It is located about 9 km south of Largs and about 4 km north-west of West Kilbride. It is operated by EDF Energy... |
1190 | 1967 | 1976 | 1976 | 2016 |
| Torness Torness nuclear power station Torness nuclear power station was the last of the United Kingdom's second generation nuclear power plants to be commissioned. Construction of this facility began in 1980 for the then South of Scotland Electricity Board and it was commissioned in 1988... |
1250 | 1980 | 1988 | 1988 | 2023 |
In 2005 British Energy announced a 10-year life extension at Dungeness B, that will see the station continue operating until 2018, and in 2007 announced a 5-year life extension of Hinkley Point B and Hunterston B until 2016. Life extensions at other AGRs will be considered at least three years before their scheduled closure dates.
Since 2006 Hinkley Point B and Hunterston B have been restricted to about 70% of normal MWe output because of boiler-related problems requiring that they operate at reduced boiler temperatures. This output restriction is likely to remain until closure.
In 2006 AGRs made the news when documents were obtained under the Freedom of Information Act 2000
Freedom of Information Act 2000
The Freedom of Information Act 2000 is an Act of Parliament of the Parliament of the United Kingdom that creates a public "right of access" to information held by public authorities. It is the implementation of freedom of information legislation in the United Kingdom on a national level...
by The Guardian
The Guardian
The Guardian, formerly known as The Manchester Guardian , is a British national daily newspaper in the Berliner format...
who claimed that British Energy
British Energy
British Energy was the UK's largest electricity generation company by volume, before being taken over by Électricité de France in 2009. British Energy operated eight former UK state-owned nuclear power stations and one coal fired power station....
were unaware of the extent of the cracking of graphite bricks in the cores of their reactors. It was also claimed that British Energy did not know why the cracking had occurred and that they were unable to monitor the cores without first shutting down the reactors. British Energy later issued a statement confirming that cracking of graphite bricks is a known symptom of extensive neutron bombardment and that they were working on a solution to the monitoring problem. Also, they stated that the reactors were examined every three years as part of "statutory outages". http://news.bbc.co.uk/1/hi/uk/5149650.stm
On 17 December 2010, EDF Energy announced a 5 year life extension for both Heysham 1 and Hartlepool to enable further generation until 2019.
External links
- Advanced gas-cooled reactors - IAEA conference paper, September 1980
- Project WAGR - decommissioning the Windscale AGR
- AGR estimated closure dates, House of LordsHouse of LordsThe House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....
HansardHansardHansard is the name of the printed transcripts of parliamentary debates in the Westminster system of government. It is named after Thomas Curson Hansard, an early printer and publisher of these transcripts.-Origins:...
column WA232, 24 Feb 2005 - Review of Graphite core issues at Hinkley Point B and other AGRs, Large & Associates (Consulting Engineers) for GreenpeaceGreenpeaceGreenpeace is a non-governmental environmental organization with offices in over forty countries and with an international coordinating body in Amsterdam, The Netherlands...
- British Energy's bifurcation blues, Nuclear Engineering International, 22 November 2006
- Account of visiting Torness AGR, Charlie Stross