UNGG reactor

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Two UNGG reactors at Saint-Laurent Nuclear Power Plant A1 A2 saint laurent.JPG
Two UNGG reactors at Saint-Laurent Nuclear Power Plant
Schematic of a UNGG reactors HD.15.075 (11839817825).jpg
Schematic of a UNGG reactors
Cross section of UNGG fuel, showing internal cooling path Section cartouche combustible UNGG Bugey.png
Cross section of UNGG fuel, showing internal cooling path

The UNGG (Uranium Naturel Graphite Gaz) is an obsolete nuclear power reactor design developed in France. It was graphite moderated, cooled by carbon dioxide, and fueled with natural uranium metal. 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.

Graphite allotrope of carbon, mineral, substance

Graphite is a crystalline form of the element carbon with its atoms arranged in a hexagonal structure. It occurs naturally in this form and is the most stable form of carbon under standard conditions. Under high pressures and temperatures it converts to diamond. Graphite is used in pencils and lubricants. Its high conductivity makes it useful in electronic products such as electrodes, batteries, and solar panels.

Neutron moderator medium that reduces the speed of fast neutrons, turning them into thermal neutrons that can sustain nuclear chain reactions; e.g. water, graphite, heavy water, beryllium

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 or a similar fissile nuclide.

Carbon dioxide chemical compound

Carbon dioxide is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas. The current concentration is about 0.04% (410 ppm) by volume, having risen from pre-industrial levels of 280 ppm. Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, ice caps, glaciers and seawater. It is present in deposits of petroleum and natural gas. Carbon dioxide is odorless at normally encountered concentrations. However, at high concentrations, it has a sharp and acidic odor.


The UNGG and the Magnox are the two main types of gas cooled reactor (GCR). A UNGG reactor is often referred to simply as a GCR in English documents, or sometimes loosely as a Magnox. It was developed independently of and in parallel to the British Magnox design, and to meet similar requirements of simultaneous production of electric power and plutonium. The first UNGG reactors at Marcoule used horizontal fuel channels and a concrete containment structure. Chinon A1 used vertical fuel channels, as did the British Magnox reactors, and a steel pressure-vessel. [1]

Magnox obsolete type of nuclear power reactor

Magnox is a type of nuclear power/production reactor that was designed to run on natural uranium with graphite as the moderator and carbon dioxide gas as the heat exchange coolant. It belongs to the wider class of gas cooled reactors. The name comes from the magnesium-aluminium alloy used to clad the fuel rods inside the reactor. Like most other "Generation I nuclear reactors", the Magnox was designed with the dual purpose of producing electrical power and plutonium-239 for the nascent nuclear weapons program in Britain. The name refers specifically to the United Kingdom design but is sometimes used generically to refer to any similar reactor.

Chinon Nuclear Power Plant

The 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.

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.

Magnesium Chemical element with atomic number 12

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Zirconium Chemical element with atomic number 40

Zirconium is a chemical element with the symbol Zr and atomic number 40. The name zirconium is taken from the name of the mineral zircon, the most important source of zirconium. It is a lustrous, grey-white, strong transition metal that closely resembles hafnium and, to a lesser extent, titanium. Zirconium is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. Zirconium forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, three of which are stable. Zirconium compounds have no known biological role.

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. Magnox is short for Magnesium non-oxidising. This material has the advantage of a low neutron capture cross section, but has two major disadvantages:

The programme was a succession of units, with changes to the design increasing power output. In the experimental phase they were built by the Commissariat à l'Énergie Atomique (CEA), and later by Électricité de France (EDF). [1] The largest UNGG reactor build was Bugey 1 with a net electrical output of 540 MW.

Électricité de France French electric utility company

Électricité de France S.A. is a French electric utility company, largely owned by the French state. Headquartered in Paris, with €71.2 billion in revenues in 2016, EDF operates a diverse portfolio of 120+ gigawatts of generation capacity in Europe, South America, North America, Asia, the Middle East and Africa.


Indre-et-Loire Department of France in Centre-Val de Loire

Indre-et-Loire is a department in west-central France named after the Indre River and Loire River. In 2016, it had a population of 606,223. Sometimes referred to as Touraine, the name of the historic region, it nowadays is part of the Centre-Val de Loire region. Its prefecture is Tours and subprefectures are Chinon and Loches. Indre-et-Loire is a touristic destination for its numerous monuments that are part of the Châteaux of the Loire Valley.

Saint-Laurent Nuclear Power Plant Nuclear power stations in France

The Saint-Laurent Nuclear Power Station is located in the commune of Saint-Laurent-Nouan in Loir-et-Cher on the Loire – 28 km upstream from Blois and 30 km downstream from Orléans.

Loir-et-Cher Department of France

Loir-et-Cher is a department in the Centre-Val de Loire region, France. Its name is originated from two rivers which cross it, the Loir on the North and the Cher on the South. Its prefecture is Blois. The INSEE and La Poste gave it the number 41.

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.

See also

Nuclear power in France

Nuclear power is a major source of energy in France, with a 40% share of energy consumption in 2015. Nuclear power is the largest source of electricity in the country, with a generation of 379.1 TWh, or 71.6% of the country's total production of 519.4 TWh, the highest percentage in the world.

Vandellòs I Nuclear Accident

Vandellòs I Nuclear Accident was a fire that caused an interruption of the cooling system in the nuclear reactor of Vandellòs, Catalonia (Spain) on 19 October 1989.

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Light-water reactor type of nuclear reactor uses normal water

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Chapelcross nuclear power station

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Gas-cooled fast reactor

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  1. 1 2 Ten Years of Nuclear Power (PDF) (Report). UKAEA. 1966. Retrieved 15 January 2015.