UNGG reactor

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Two UNGG reactors at Saint-Laurent Nuclear Power Plant
Cross section of UNGG fuel, showing internal cooling path

The UNGG (Uranium Naturel Graphite Gaz) is an obsolete nuclear power reactor design developed by 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.

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. 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 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.

Units[edit]

Chinon Nuclear Power Plant with three UNGG reactors

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.

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