"Highly enriched uranium (HEU) is anything enriched above 20% and weapon-grade uranium is commonly considered to have been enriched above 90% U-235. However, some research reactors use 90% enriched U-235 to produce medical isotopes, so there are civilian applications for this fuel too."

https://armscontrolcenter.org/uranium-enrichment-for-peace-or-for-weapons/

[–] CanadaPlus@lemmy.sdf.org 2 points 4 hours ago* (last edited 4 hours ago)

I stand corrected. It's less clear which ones definitely need it, exactly. Wikipedia mentions that even Tc-99m generator designs can use low-enriched uranium. You don't need large quantities in that case, either, since a little radioisotope goes a long way and there's only so many people that need treatment.