The UNGG (''Uranium Naturel Graphite Gaz'') is an obsolete nuclear power reactor design developed in France. It was

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

moderated, cooled by

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

, and fueled with

natural uranium Natural uranium (NU or Unat) is uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes from ura ...

metal. The first generation of French nuclear power stations were UNGGs, as was Vandellos unit 1 in Spain. Of the ten units built, all were shut down by the end of 1994, most for economic reasons due to staffing costs. A UNGG reactor is often simply referred to as an ''GCR'' in English documents.

Design

The UNGG is along with the Magnox the main type of gas cooled reactor (GCR). It was developed independently of and parallel to the British Magnox design, both to meet similar requirements of simultaneous production of electric power and plutonium. Although the French and the British models both used natural uranium and the same moderator and coolant, there were differences in design. In France, each next built reactor had a different design. The first UNGG reactors at Marcoule used horizontal fuel channels and a concrete containment structure.

Chinon Chinon () is a Communes of France, commune in the Indre-et-Loire Departments of France, department, Centre-Val de Loire, France. The traditional province around Chinon, Touraine, became a favorite resort of French kings and their nobles beginn ...

A1 used vertical fuel channels and a steel pressure-vessel. The fuel cladding material was a

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...

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 Spent fuel pools (SFP) are storage pools (or "ponds" in the United Kingdom) for spent fuel from nuclear reactors. They are typically 40 or more feet (12 m) deep, with the bottom 14 feet (4.3 m) equipped with storage racks designed to hold ...

only for short periods of time, making short-term reprocessing of fuel essential, which requires heavily shielded facilities. 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 The French Alternative Energies and Atomic Energy Commission, or CEA ( French: Commissariat à l'énergie atomique et aux énergies alternatives), is a French public government-funded research organisation in the areas of energy, defense and sec ...

(CEA), and later by

Électricité de France Électricité de France SA (; ), commonly known as EDF, is a French multinational corporation, multinational electric utility company owned by the government of France. Headquartered in Paris, with €139.7 billion in sales in 2023, EDF ope ...

(EDF).''Ten Years of Nuclear Power''
IAEA bulletin Vol. 6, no. 3, 1964
Via
/ref> The largest UNGG reactor built was Bugey 1 with a net electrical output of 540 MW.

Units

* G1, G2 and G3 at Marcoule. G1 was the first UNGG; a prototype for military use. G1 had a net output of 2 MWe and became critical in 1956.''Marcoule G1''
INSC * Chinon Nuclear Power Plant A1, A2, and A3 in

Indre-et-Loire Indre-et-Loire () is a department in west-central France named after the Indre River and Loire River. In 2019, it had a population of 610,079.Saint-Laurent Nuclear Power Plant A1 and A2 in

Loir-et-Cher Loir-et-Cher (, ) is a Departments of France, department in the Centre-Val de Loire Regions of France, region of France. It is named after two rivers which run through it, the Loir in its northern part and the Cher (river), Cher in its southern p ...

, operated from 1969 and 1971 to April 1990 and June 1992. * Reactor 1 at Bugey Nuclear Power Plant in Ain, the last UNGG built in France, first criticality 1972, closed in May 1994. * Vandellòs Nuclear Power Plant Unit 1 in Spain, the only UNGG built outside France, closed in 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.

References

French activities on gas cooled reactors
D Bastien, IAEA-TECDOC—899, pp:51-53, 30 Oct - 2 Nov 1995
Twenty-nine years of French experience in operating gas-cooled reactors
D Bastien, IWGGCR—19, pp:113-119 21-23 Sep 198
Better copy archived
{{Nuclear power in France Graphite moderated reactors Nuclear power reactor types

Design

Units

See also

References