UNGG reactor

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The UNGG (Uranium Naturel Graphite Gaz) 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 the fuel cladding material, which was magnesium-zirconium alloy in the UNGG, as opposed to magnesium-aluminium in the Magnox reactor. Both claddings react with water, 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 are now shut down.

[edit] Units

G1, G2 and G3 at Marcoule. G1 was the first UNGG to go critical, in 1956.
Chinon A1, A2, and A3 in Indre-et-Loire.
Saint-Laurent Nuclear Power Plant A1 and A2 in Loir-et-Cher.
Bugey Nuclear Power Plant 1 in Ain, the last UNGG built in France, first criticality 1972.
Vandellòs Nuclear Power Plant 1 in Spain, the only UNGG built outside of France.

The earlier units, at Chinon and Marcoule, had heat exchangers outside the main pressure vessel; Later units (Saint-Laurent, Bugeye and Vandellos) moved these heat exchangers to inside the pressure vessel.