Essentially, I'm suggesting a block be added to the reactor that will allow coolant fluid to be pumped into the reactor and automatically filled. Primary reasoning is because fluids such as Gelid Cryotheum can be quite tedius to place for larger reactors.

Only problem is, having different fluids in different parts is more efficient. Maybe have a sort of melting system, where you place the fluids in as blocks (block of resonant ender, maybe add a cryotheum block) and as the reactor heats up it would melt the blocks and replace them with fluids.