Functions in a data pack seem to not load properly. Other functions are unable to access them and they cannot be accessed by the /function command in-game.
The example provided shows that despite there being the function "pp:hulk/uranium" in the loaded data pack, it will not load in the game. The function "pp:hulk/main" which is intended to activate this function cannot access it either.
Reloading has not worked. I have confirmed that "pp:hulk/uranium" is a .mcfunction file as it should be. However, this may be linked to "pp:hulk/uranium" existing in another directory inside the data pack ("hulk") as I ran into this same problem with another function in an alternate directory.
Your function contains a syntax error. Specifically, you forgot to escape the quotes in the item name. Check the game log next time.