Uranium enrichment is the process of increasing the concentration of the uranium-235 isotope, which is needed for nuclear fuel or weapons. Natural uranium contains about 0.7% uranium-235, with the rest mostly uranium-238. To be used in most nuclear reactors, uranium needs to be enriched to about 3% to 5% uranium-235. Here's how uranium enrichment is typically done:

1. Conversion to Uranium Hexafluoride (UF6): Natural uranium oxide is chemically converted into uranium hexafluoride (UF6), a compound that becomes a gas at relatively low temperatures. This gaseous form is necessary for the enrichment process.
2. Enrichment Using Gas Centrifuges: The UF6 gas is fed into centrifuges, which are rapidly spinning tubes. Because uranium-235 is slightly lighter than uranium-238, the spinning creates a centrifugal force that separates the isotopes by mass. Uranium-238 collects closer to the walls of the centrifuge, while uranium-235 collects nearer the center.
3. Cascade of Centrifuges: The slightly enriched uranium-235 is continuously cycled through many centrifuges arranged in series and parallel (called cascades) until the desired concentration of uranium-235 is reached (typically 3-5%).
4. After Enrichment: The enriched UF6 gas is then compressed, cooled, and converted into solid form for use in nuclear fuel fabrication.

There is also a laser enrichment technology in development that uses lasers to selectively increase uranium-235 concentration, but gas centrifuge enrichment is the main commercial process currently in use. This process significantly increases the fissile component in uranium for reactor fuel or other applications, while depleted uranium (lower U-235) is a byproduct. This method is energy-efficient compared to older processes like gaseous diffusion, requiring only a small fraction of the electricity.