An actively cooled Reactor/Turbine setup vaporizes a coolant using the heat of the Reactor to generate vapor that can be used to drive the rotors of many Turbines and generate energy.
A coolant is a fluid that, if recognized, can be pumped into the Coolant Fluid Tank of the Reactor using a Fluid Port in input mode.
A vapor is a fluid that is the result of a coolant being vaporized inside a Reactor, and it can be pumped from a Reactor to a Turbine (using Fluid Port) to drive the Turbine rotor and then be condensed back to the original coolant, allowing the cycle to start again.
Only valid coolants and vapors can be used inside a Reactor or a Turbine.
Extreme Reactors register, by default, water as a valid coolant and steam as its resulting vapor.
Other mods or mod packs can add their own fluids or modify/remove the default ones.