"As such all uranium isotopes form UF6. " Not quite, Zog. For...

"As such all uranium isotopes form UF6. "
Not quite, Zog. For enrichment, the uranium isotopes have to be in the form of gaseous UF6. But for fuel bundles, the enriched UF6 gas is converted to UO2 (a granular solid material), before being packed into pellets and then fuel rods. So although the DU from the enrichment process (i.e. Paducah tails) is still UF6, the nuclear waste and its derivatives from a reactor is in a solid form (UO2, UO2F2, etc). To perform laser isotope separation on the waste, the solid uranium has to be converted back to gaseous UF6 again. Difficult, but doable.