Nuclear Furnace with nuclear fuel makes smelting much faster;
the mod adds special "burnt extractor inserter" for removing "used up uranium fuel cell" from this furnace.
You have a specific set of items the burnt extractor can remove and no way for other mod developers to add their own used-up-..name..-fuel-cell. Could you change the control to have a remote for adding new stuff? Or maybe just make it so the extractor works with all items in the burnt slot? Another limiting factor you've placed on it is that it can only pick up a single item. Is it possible to change that to 1 + entity.force.inserter_stack_size_bonus with a check to count if that number is valid for pick up to prevent (remove from inventory 3 items, then add to inserter hand 3 items...but there was only one item in inventory; so now have two extra items by magic)?
Funny thing, I've actually already rewritten the script for it and stuck it into my own mod. ^_^
I'll update it some time in the next few days.
Do you mind if I change stuff too? Such as adding tiers of nuclear furnaces, research, etc...?