Moosey - I realize that reuse of RepU is somewhat of an "article...

Moosey - I realize that reuse of RepU is somewhat of an "article of faith" for you but at the end of the day you need to be practical. The article you attach (thank you) shows that re-use of UNF for HALEU (with above 7% ²³⁵U) is worth re-using; that's why used HEU (used EBR-II fuel originally at 67% ²³⁵U - metal) and removed (for re-processing in their ARC) when they burned down to 65% ²³⁵U (see HERE); this is currently being recovered/re-used by Idaho NL (see HERE) to produce (recovered) HALEU. They are doing this by downblending and is viable due to its very high remnant ²³⁵U content (e.g 65%). For spent HALEU (from a fast reactor - e.g Natrium) the ²³⁵U content is about 9.1% (see HERE - table 2.1) and ²³⁶U (1.8%) and may well be viable to re-use in a Light Water Reactor (LWR) by down blending (or using the Russian REMIX technology). What none of them suggest is re-enriching. For RepU from a LWR the ²³⁵U content is about 0,78% (²³⁶U content 0.58% - see table 2.1 from above reference) - frankly it's not worth re-enriching due to the low ²³⁵U content and the presence of the ²³⁶U nuclear poisons and the difficulty (and expense) of re-processing. In economic terms I have heard expert say that the natural uranium price would need to be in the US300/lb ballpark to make RepU viable as a fuel (it may be done to reduce the HL waste volume and/or to extract the Pu) for weapons or MoX fuel.

Regarding the ability to separate out the 236U using laser please note from my previous post that the difference the 238UF6 and 235UF6 v3 wavelength is only 0.018 microns (²³⁵UF₆ - 15.916 micron ²³⁸UF⁶ - 15.934 microns = 0.016 microns) - this implies that the difference in v3 wavelength from ²³⁵UF₆ to ²³⁶UF₆ is only 0.006 microns. This implies that their separation band overlap an thus separation would be inefficient. The possible reason for why it may work for ²⁸Si is possibly that the v3 frequency separation for Si (actually we use Halosilane (SiF₂H₂) as feedstock - see HERE) is greater than for UF6, the mass ratio (for separation) of low atomic numbers are better and we afford to (and do) waste both the ²⁹Si and ³⁰Si by "skimming".(i.e biasing the v3 frequency toward the higher atomic number isotopes). One thing is for certain is that reprocessing/separation of RepU (for Silex/GLE) is a very distant prospect.