How is the enrichment of uranium achieved?

The enrichment of uranium, specifically the increase of the proportion of Uranium-235 isotopes relative to Uranium-238, is primarily achieved through processes such as gas diffusion or ultracentrifugation. These methods capitalize on the slight mass difference between the isotopes to separate them effectively.

In gas diffusion, uranium hexafluoride gas is passed through porous membranes where the lighter Uranium-235 can migrate more readily than the heavier Uranium-238. This process can be repeated in multiple stages to progressively increase the concentration of Uranium-235.

Ultracentrifugation employs rapid spinning of uranium hexafluoride within a rotating cylinder. The centrifugal force exerts a greater influence on the heavier Uranium-238, thus allowing the lighter Uranium-235 to accumulate at the top of the centrifuge, facilitating a separation process.

Both of these techniques are essential in enriching uranium because they exploit the physical properties of the isotopes rather than chemical methods or simple physical separations, which would not achieve the required enrichment levels effectively. Consequently, this makes the described processes the standard methods used in uranium enrichment for nuclear fuel.