Laser isotope separation is being developed as a potentially more energy-efficient method of uranium enrichment.

The majority of nuclear reactors require fuel containing enriched uranium, typically with a concentration of 3—5% of the fissile isotope ²³⁵U, compared with about 0.7% in natural uranium. Enrichment is a physical process rather than a chemical one because the two principal uranium isotopes have virtually identical chemical properties and differ only slightly in mass. The capacity of an enrichment facility is expressed in Separative Work Units (SWU), a measure of the effort required to separate uranium into streams with different concentrations of ²³⁵U. The amount of separative work required depends on the quantity and enrichment of the product as well as the concentration of ²³⁵U remaining in the depleted uranium, known as the tails.

In the past, gaseous diffusion enrichment was used on a large scale in France, the USA and Russia. Today, this technology has been almost entirely replaced by much more energy-efficient gas centrifuges. Centrifuge enrichment is used not only in these countries but also in the United Kingdom, the Netherlands, Germany, Japan and several other countries around the world.

Gas centrifuges became an important enrichment technology during the second half of the 20th century and today dominate commercial uranium enrichment. A centrifuge consists of a tall, narrow rotor spinning at very high speed. Typical European centrifuge rotors are about 3—5 metres high and 20 cm in diameter and rotate at speeds of 50,000—70,000 revolutions per minute. Gaseous uranium hexafluoride is fed into the centrifuge, where molecules containing the heavier ²³⁸U isotope become slightly more concentrated towards the outer wall, while molecules containing the lighter ²³⁵U isotope become relatively more concentrated nearer the centre.

The slightly enriched and depleted gas streams are continuously withdrawn from the centrifuge. Because each centrifuge produces only a small increase in enrichment, large numbers of centrifuges are connected in cascades, with stages arranged in series and parallel. Typically, around 10—20 stages may be sufficient to reach the required enrichment, compared with a thousand or more stages in the gaseous diffusion process.

One method of laser isotope separation is based on the selective ionisation of ²³⁵U atoms using a precisely tuned laser.

Laser Excitation

Laser isotope separation has been investigated since the 1970s as a potentially more efficient method of uranium enrichment. Several different processes have been developed, using precisely tuned lasers to selectively affect molecules or atoms containing a particular uranium isotope. One technology still under development is SILEX (Separation of Isotopes by Laser Excitation), which uses uranium hexafluoride (UF₆) as its feed material.

SILEX has not yet been deployed commercially for uranium enrichment. Global Laser Enrichment is currently developing the technology in the United States and operates a test facility. In 2025, the company submitted an application to the US Nuclear Regulatory Commission to construct and operate a commercial laser enrichment facility in Paducah, Kentucky.