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From Wikipedia, the free encyclopedia

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 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. 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.


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.

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