The uses of enriched uranium

Times 12th May 2018 Uranium is mined and then processed as nuclear fuel for military or civilian purposes. The ore is ground up and chemically treated to yield “yellowcake”, a coarse powder of uranium oxide. Converted into purified fuel rods, it can be used in pressurised heavy water reactors.

For other uses, the uranium oxide is converted into uranium hexafluoride gas so that it can be enriched. The enrichment process increases the percentage of a particular isotope, uranium-235, which makes up 0.7 per cent of natural uranium. The rest is uranium-238. The commonest method of enrichment is isotope separation by gas centrifuge. Centrifuges rotate at high speed, separating the isotopes by weight and sending the heavier uranium-238 to the outside of the cylinder while the lighter 235 collects at the centre.

The slightly enriched stream is extracted and fed into the next centrifuge, where the process is repeated, enriching it further. Most nuclear power reactors use uranium that has been enriched to a composition of between 3 and 5 per cent uranium-235. Anything up to 20 per cent uranium-235 is called low-enriched uranium. Uranium enriched to between 12 and 19.75 per cent is used in the production of medical isotopes in research reactors.

Uranium enriched above 20 per cent is called highly enriched uranium, while 20 per cent is the lowest theoretical threshold for weapons-grade uranium. Most weapons use uranium that is 90 per cent enriched. The first stages
require more centrifuges due to the volume of uranium. The process gets easier as purity increases, making the leap from low to high-enrichment easier than the leap from natural uranium to low-enriched. Once the 20 per cent threshold is breached, weapons grade is within reach.
https://www.thetimes.co.uk/edition/world/iran-saudi-arabia-uranium-from-ore-to-weapons-grade-mf0jdqr86