Trump’s failure to get control of the 60% U235 enriched uranium leaves Iran a very fast and easy path to get to 90% and a bomb. I think we need to assume they already did it.

Step-by-Step: Enrichment from 60% to 90%

1. Feedstock The process starts with uranium hexafluoride (UF₆) enriched to 60% U-235. Iran reportedly had around 400 kg, according to the NYT reporting cited by Faytuks.
2. Centrifuge Cascades To raise the enrichment from 60% to 90%, you’d need:
   • Fewer centrifuges than earlier stages.
   • Possibly 1–2 cascades of ~160–200 IR-6 machines could do the job in 2–3 weeks, depending on efficiency and operational runtime.
3. Product Output Assuming no material losses, you could produce around 25–35 kg of 90% enriched uranium—enough for at least one nuclear weapon, depending on the design and engineering.
4. Technical Considerations
   • The SWU cost for this enrichment step is modest: ~25–30 SWU per kg of 90% product.
   • The tails assay (waste enrichment level) would likely be adjusted to optimize throughput and limit material loss—typically ~10–20% in this phase.

Strategic Implication

This is precisely why 60% stockpiles set off alarm bells: once a country has this material, the technical and time barrier to weapons-grade material shrinks dramatically.

Key Points:

• The SWU requirement for this enrichment step is ~25–30 per kg of 90% U-235.
• Enrichment is most SWU-efficient at higher levels; fewer centrifuges are needed per unit gain.
• Tails assay (leftover enrichment) is typically high in this final stage to reduce loss of valuable U-235, which is why most of the original 400 kg ends up in the tails.
• The timeline is short: a few weeks or less, assuming operational centrifuge cascades.