TL;DR
Rename the nuclear fuel item (to something else more unique, I would suggest Kovarex fuel) to reduce ambiguity with the nuclear fuel category of items.What ?
The term "nuclear fuel" currently refers to 2 things in Factorio:1) A category of items that can be burned in a nuclear reactor to produce heat
2) Rocket fuel enriched with U235 for use in entities that accept burnable fuel
Somewhat confusingly at first glance, an entity that consumes nuclear fuel (1) cannot consume nuclear fuel (2). I would suggest renaming nuclear fuel (2) to Kovarex fuel, since it is unlocked by the Kovarex enrichment process research, and the name would be unique both within Factorio and probably the rest of the world outside of the game. I think something like "enriched rocket fuel" could also work.