What exactly is a uranium centrifuge?

Uranium is an element that bears a resemblance to iron. Just like iron, uranium ore is extracted from the earth and refined to obtain pure uranium. After processing, the result is uranium oxide. This uranium oxide contains two varieties (or isotopes) of uranium: U-235 and U-238. U-235 is the isotope you need to either create a bomb or to fuel a nuclear power plant. However, uranium ore typically contains around 99% U-238. Therefore, the U-235 must be separated from the U-238, a process known as enrichment, where centrifuges play a key role.

U-235 has a slightly lighter mass compared to U-238. By taking advantage of this difference, it becomes possible to separate the two isotopes. The initial step in this process involves reacting uranium with hydrofluoric acid, an exceptionally strong acid. After a series of steps, the outcome is the creation of uranium hexafluoride gas.

Once the uranium is in a gaseous state, it becomes easier to handle. The gas is then introduced into a centrifuge and spun at high speeds. The centrifuge generates a force that is thousands of times stronger than gravity. Since U-238 atoms are marginally heavier than U-235 atoms, they are pushed outward toward the centrifuge's walls, while the U-235 atoms remain near the center.

Although the difference in concentration is minimal, when you extract the gas from the center of the centrifuge, it contains slightly more U-235 than before. If you repeat this process with the extracted gas in another centrifuge, you achieve further concentration. Over thousands of repetitions, this process can produce a gas enriched significantly with U-235. At a uranium enrichment plant, this is achieved by linking thousands of centrifuges in extended cascades.

At the final stage of the centrifuge chain, uranium hexafluoride gas is produced with a higher concentration of U-235 atoms.

The production of the centrifuges themselves is a significant technological feat. They must rotate at incredibly high speeds — up to 100,000 rpm. To achieve this velocity, the centrifuges must meet the following criteria:

Meeting all of these specifications has historically been beyond the capability of most nations. However, the development of affordable, highly accurate, computer-controlled machining tools has eased this challenge. This explains why more countries have started to enrich uranium in recent years.

To convert uranium hexafluoride gas back into uranium metal, calcium is added. The calcium interacts with the fluoride, forming a salt, while leaving behind pure uranium metal. This enriched U-235 metal can then be used either to create a nuclear weapon or to fuel a nuclear reactor.