Uranium Enrichment
The Technical Pathway to Nuclear Weapons
Natural uranium contains approximately 0.7% of the fissile isotope Uranium-235 (U-235). Enrichment increases the proportion of U-235 through isotope separation, typically via gas centrifuges. Low-enriched uranium (LEU, up to 5% U-235) is used in civilian nuclear power reactors. Highly enriched uranium (HEU, above 20%) has both civilian research and weapons-related applications. Weapons-grade uranium requires enrichment to approximately 90% U-235. The jump from 60% (Iran's current level) to 90% (weapons-grade) is technically achievable in a relatively short "breakout time," estimated at weeks to months depending on available centrifuge capacity. The IAEA's discovery of 440.9 kg of 60%-enriched uranium is significant because this material could be further enriched to weapons grade.
- Natural uranium: ~0.7% U-235
- LEU (reactor grade): 3-5% U-235
- HEU threshold: above 20% U-235
- Weapons-grade: ~90% U-235
- 60% enriched uranium → 90% weapons-grade: a short technical step; represents an imminent proliferation risk
- Critical mass for a uranium bomb: approximately 50 kg of weapons-grade uranium (depending on design)
● Tracked since February 27, 2026 · last seen June 26, 2026 · updates as the daily brief publishes