Um... Not to discourage you from looking for interesting solutions, but Kovarex refining can be done without any automation at all, just clever belts and inserters positioning. Here is my slap-dash solution with manual loading:

Factorio - Kovarex Enrichment Setup.png


To add prioritized fuel ...

When some part of the Factory is idle (and it's happens, as it's difficult to balance everything and this balance shifts almost constantly) it consumes idle-mode power. For example all Assembling Machines (1 to 3) have idle mode power equal 1/30 of the active mode power (75+2.5 kW / 150+5 kW / 375 ...