Nuclear Fuel needs Rocket Fuel as on of its Inputs but you can research Nuclear Fuel before you can research Rocket Fuel.
Rocket Fuel is reached in Rocket silo while Nuclear fuel can be got from Kovarex enrichment process.
Not sure if this is a bug or a feature
Nuclear Fuel can be researched before Rocket Fuel
Re: Nuclear Fuel can be researched before Rocket Fuel
Not a bug. Nuclear fuel takes 1500 each of 5 science packs (it doesn't need military or space, but you should be able to produce military packs well before you can research it). Rocket fuel takes 1000 each of 6 science packs (everything but space). So you could easily have rocket fuel before Kovarex enrichment. Which one you get first is just a matter of which one you choose first. Also see viewtopic.php?f=23&t=55416#p325814 . The devs have consistently taken the stance that being able to research something you can't make because you haven't researched one of it's ingredients yet is also NaB.
Re: Nuclear Fuel can be researched before Rocket Fuel
[Koub] Not a bug indeed (Zavian nailed it). Moved to Not a bug.
Koub - Please consider English is not my native language.