Moosey I must say you have a very healthy "imagination" - as you...

Moosey I must say you have a very healthy "imagination" - as you may be aware reprocessing UNF actually results in more nuclear waste although the reagents involved in processing the UNF are not HL waste but mid level waste. (the higher actinides remain HL waste - albeit reduced in volume from the original HL waste spent fuel) You may be aware that the US is currently having all sought on difficulty processing (or disposing) of the Hanford waste (see HERE). The Hanford process was largely for separating the plutonium rather than reducing waste. As you have previously pointed out an electrochemical (pyroprocessing) process was used with the EBR-II (see HERE & HERE) which basically separates (in a process similar to the production of Aluminum) which separates the fission products (~30 years half life) which (as you say) have been though 10 half lives in 300 years and thus substantially diminished in radio activity (but still need special handling). The higher actinides (including plutonium - not weapons usable plutonium) can be further irradiated in a fast reactor (the Natrium is a fast reactor but as I understanding not suitable for irradiating higher actinide wastes). After separating these we are not just left with RepU (reprocessed uranium) we also have the molten salt electrolyte which now contains radio active elements which needs to be disposed of along with the the electrodes (also radio active) - it's not simple.

The fuel used in the EBR II was a metallic HEU (enriched to 67% ²³⁵U - see HERE) this is not the fuel intended for the Natrium which is metallic HALEU (enriched to 16.7% ²³⁵U by weight). Light water reactors generally use enrichment levels of below 5% ²³⁵U and burn them down to about 0.5% to 1% ²³⁵U (see table below - reference is HERE



The problem is that the ²³⁵U assay of RepU is about the same as NUF (.71% ²³⁵U) - RepUF₆ prices need to be below the price NUF₆ to make re-enrichment worthwhile. RepUF₆ (due to the presence of even number isotopes - particularly ²³⁶U) is also of lower quality than NUF6 so actually the price need to be substantially lower. As I understand it your issue is that the Silex process would avoid enriching these undesirable even uranium isotopes and thus make re-use of RepU viable - I'm not so sure:

1. The v3 frequency for ²³⁵UF₆ is precisely 15.916 μm - for ²³⁸UF₆ it is 15.931 μm (see HERE) - this implies to me that the v3 frequency for ²³⁶UF₆ is 15.916 + (15.931-15.916)/3 = 15.921 μm - frankly (based upon the fact that for zero spin silicon ²⁸Si) we remove the ²⁹Si but we also remove the ³⁰Si) that our current technology is sufficiently precis to not also concentrate (enrich) the adjacent isotope (in the case of RepU ²³⁶UF₆). Preserving the precis nature of the V3 wavelength is critical to our technology but thankfully for NUF6 this difference is 0.015 μm not .005 μm (NB note that for LIS Technology they are using the v3/3 harmonic and for them their isotopic difference are .005 μm for NUF₆ but for RepUF₆ (for removing ²³⁶UF₆) it would only be .005/3 μm). Frankly I doubt if our separator (worse for LIS Tech separator) would have the required selectivity.

2. RepUF₆ is also more radio active than NUF₆) - it would need special handling and dedicated apparatus - IMO simply not worth it.

3. You would struggle to sell re-enriched RepU fuel to fabricators (and utilities) who would need to give is "special" handling.

4. IMO cheaper to extract uranium from seawater (if/when uranium mined supplies run down) than re-use RepU - use of plutonium makes more sense.