COMURHEX II: meeting tomorrow’s challenges
"Rapport environnemental Chalon Saint-Marcel 2007" [FR]
Two distinct industrial processes
There are 2 industrial uranium enrichment processes currently in use: gaseous diffusion and centrifugation. Although the first is currently more common, the second provides better performance.
The differences in chemical properties are very slight between uranium isotopes; the only effective means of separating them is to use the difference in mass between the 2 isotopes (uranium-238 and uranium-235). The uranium-235 isotope is actually lighter than the uranium-238 isotope.
This is the principle currently used in the only 2 enrichment processes used in the world on an industrial scale: gaseous diffusion and centrifugation.
How does it work?
- All the molecules in a gas are in movement, striking the wall of the container in which they are confined.
- The lighter molecules are the fastest, thus statistically they will strike the wall more often.
- If this wall is porous, the lighter molecules will come through it more frequently than the heavier molecules.
- The isotopes are thus separated, and this separation yields enrichment.
Using this principle, enrichment is carried out in successive stages: gaseous UF6 is pushed by a compressor through a cascade of diffusers containing porous diffusion barriers. The gas is enriched in uranium-235 hexafluoride at each passage (1,400 in all).
AREVA conducts uranium enrichment by gaseous diffusion at the Georges Besse plant, located at the Tricastin nuclear site between Drôme and Vaucluse (France).
This enrichment process is currently the most widely used in the world.
A transition at Tricastin: diffusion to centrifugation
The Georges Besse plant, in Tricastin, enriches the uranium necessary for the operation of more than one hundred reactors, i.e. 25% of the world’s park.Why and how is enrichment performed? All about site technology, logistics, and environmental protection.
How does it work?
- Gaseous UF6 is introduced into a cylinder turning at very high speed in a vacuum in an air-tight chamber.
- Under the effect of the centrifugal force, the heavier molecules are sent to the edge of the tube.
- The gas enriched in the lighter uranium-235 isotope in the center of the tube rises. The gas richer in heavier uranium-238 descends.
- The enriched and depleted products are recovered at the 2 ends of the tube, the top and bottom.
Centrifugation is the highest performance technology available today. It offers better guarantees in terms of energy savings, controlling environmental impact and also competitiveness. It is already used in many countries around the world.
The agreement found between URENCO and its shareholders in 2003 and completed in July 2006 enables AREVA to access use of centrifugation technology. This process has been in use since 2009 in the Georges Besse II plant in Tricastin, France, which is scheduled for full production capacity in 2016.
