The Physics documentation doesn't tell you that you won't be able to use the uranium, but Fission does say "enables uranium" or something like that. So it isn't completely undocumented. I actually think it's pretty intuitive that you'll need to research fission before being able to build nuclear powered ships etc.
The physics/fission thing is pretty much the same as the scientific method/combustion behavior, except that with oil it's a bit more obvious because you can't build an oil well (although, you can still build a fort to 'get' the oil before it is usable).
The physics/fission thing is pretty much the same as the scientific method/combustion behavior, except that with oil it's a bit more obvious because you can't build an oil well (although, you can still build a fort to 'get' the oil before it is usable).