UNGG reactor
Encyclopedia
The UNGG is an obsolete design of nuclear power reactor developed by France. It was graphite
moderated
, cooled by carbon dioxide
, and fueled with natural uranium
metal.
It was developed independently of and in parallel to the British Magnox
design, and to meet similar requirements. The main difference between the two designs is that UNGG used a horizontal fuel rod orientation, rather than the vertical orientation used in the Magnox reactor. The fuel cladding material was magnesium
-zirconium
alloy in the UNGG, as opposed to magnesium-aluminium
in Magnox. As both claddings react with water, they can be stored in a spent fuel pool
for short times only, making short-term reprocessing
of the fuel essential, and requiring heavily shielded facilities for this.
The UNGG and the Magnox are the two main types of GCR
. A UNGG reactor is often referred to simply as a GCR in English documents, or sometimes loosely as a Magnox.
The first generation of French nuclear power stations were UNGGs, as was Vandellos
unit 1 in Spain
. Of ten units built, all were shut down by end 1994, most for economic reasons due to staffing costs. The largest was Bugey 1 with a net electrical output of 540 MW.
The earlier units, at Chinon and Marcoule, had heat exchangers outside the main pressure vessel; Later units (Saint-Laurent, Bugey and Vandellos) moved these heat exchangers to inside the pressure vessel.
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
moderated
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....
, cooled by carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, and fueled with natural 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...
metal.
It was developed independently of and in parallel to the British 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...
design, and to meet similar requirements. The main difference between the two designs is that UNGG used a horizontal fuel rod orientation, rather than the vertical orientation used in the Magnox reactor. The fuel cladding material was magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
-zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
alloy in the UNGG, as opposed to magnesium-aluminium
Magnox (alloy)
Magnox is an alloy—mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium metal fuel with a non-oxidising covering to contain fission products in nuclear reactors....
in Magnox. As both claddings react with water, they can be stored in a spent fuel pool
Spent fuel pool
Spent fuel pools are storage pools for spent fuel from nuclear reactors. They are typically 40 or more feet deep, with the bottom 14 feet equipped with storage racks designed to hold fuel assemblies removed from the reactor. A reactor's pool is specially designed for the reactor in which the...
for short times only, making short-term reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
of the fuel essential, and requiring heavily shielded facilities for this.
The UNGG and the Magnox are the two main types of GCR
Gas Cooled Reactor
A gas-cooled reactor is a nuclear reactor that uses graphite as a neutron moderator and carbon dioxide as coolant...
. A UNGG reactor is often referred to simply as a GCR in English documents, or sometimes loosely as a Magnox.
The first generation of French nuclear power stations were UNGGs, as was Vandellos
Vandellòs
*Vandellòs town*Vandellòs i l'Hospitalet de l'Infant municipality*Vandellòs Nuclear Power Plant...
unit 1 in Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
. Of ten units built, all were shut down by end 1994, most for economic reasons due to staffing costs. The largest was Bugey 1 with a net electrical output of 540 MW.
Units
- G1, G2 and G3 at MarcouleMarcouleMarcoule Nuclear Site is a nuclear plant in the Chusclan and Codolet communes, near Bagnols-sur-Cèze in the Gard department of France, which is in the touristic, wine and agricultural Côtes-du-Rhône region...
. G1 was the first UNGG to go critical, in 1956. - Chinon Nuclear Power PlantChinon Nuclear Power PlantThe Chinon Nuclear Power Plant is near the town of Avoine in the French Indre et Loire département, on the Loire river . The power station has seven reactors, of which three are now closed....
A1, A2, and A3 in Indre-et-LoireIndre-et-LoireIndre-et-Loire is a department in west-central France named after the Indre and the Loire rivers.-History:Indre-et-Loire is one of the original 83 départements created during the French Revolution on 4 March 1790...
. - Saint-Laurent Nuclear Power PlantSaint-Laurent Nuclear Power PlantThe Saint-Laurent Nuclear Power Station is located in the commune of Saint-Laurent-Nouan in Loir-et-Cher on the Loire River – 28 km downstream from Blois and 30 km upstream from Orléans....
A1 and A2 in Loir-et-CherLoir-et-CherLoir-et-Cher is a département in north-central France named after the rivers Loir and Cher.-History:Loir-et-Cher is one of the original 83 departments created during the French Revolution on 4 March 1790. It was created from parts of the former provinces of Orléanais and...
, operated from 1969 and 1971 to April 1990 and June 1992. - Reactor 1 at Bugey Nuclear Power PlantBugey Nuclear Power PlantThe Bugey Nuclear Power Station is located in Bugey in the Saint-Vulbas commune , about 30 km from the Swiss border. The site occupies 100 hectares. It is on the edge of the Rhône River, from where it gets its cooling water, and is about 30 km upstream from Lyon...
in AinAinAin is a department named after the Ain River on the eastern edge of France. Being part of the region Rhône-Alpes and bordered by the rivers Saône and Rhône, the department of Ain enjoys a privileged geographic situation...
, the last UNGG built in France, first criticality 1972, closed May 1994. - Vandellòs Nuclear Power PlantVandellòs Nuclear Power PlantThe Vandellòs Nuclear Power Plant is a nuclear power station in Vandellòs located close to the Coll de Balaguer pass in Catalonia, Spain....
Unit 1 in SpainSpainSpain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, the only UNGG built outside France, closed July 1990.
The earlier units, at Chinon and Marcoule, had heat exchangers outside the main pressure vessel; Later units (Saint-Laurent, Bugey and Vandellos) moved these heat exchangers to inside the pressure vessel.