Actually we can make nuclear molten salt reactors (working small scale stuff exist for long decades). Since the medium is liquid, it has much better utilization of the fuel, there is no pressurized radioactive water reservoirs (which is the actual issue with current reactors), to stop the reaction, you drain the fuel circulation into a container and you are done, no need to supply water to prevent criticality.
But since those molten salt reactors could not be used to create plutonium for weapons, the current reactor design was chosen during cold war era.
They have some drawbacks, like slow startup times, but the cons it provide are incredible.