I had always assumed sorium was the reactor fuel source and it's combustion products were propellant, but that the reaction rate was so low that refueling was practically never required. This is not the case it seems? If sorium is just a reaction mass then I am curious where the in-game reactors draw their power from?
If that was the case you should need fuel to power also weapons, which is my point: why for the shield yes but for weapons not.
I find it obvious that the power of the reactor should come from a source depending on your tech, but I could be wrong easily.
IE a Nuclear Powered reactor it's getting energy from Uranium Bars. Different is when you have an engine that requires fuel to keep working or to generate constantly an impulse. Bear in mind, these are not physics concepts but game mechanics. The whole concept of fuel in space is unknown as fuel will depend on the engine you are building (could be dark matter, a magnetic field or a solar wind) and the gravitational forces that pull you around. KSP gives you a pretty good idea of how flight in space and fuel looks like with our current technology and Avorion simulates the inertia, vacuum of space and the energy as fuel quite well.
For obvious reasons this is not possible in games such as Aurora or Stellaris or they will become tedious and extremely hard.
Finally, in Aurora the fuel source is Sorium and it is universal, and I am more than fine with that.