We can query the turbine to see how much steam it used last tick but we can't ask the reactor the same question. Would you consider exposing this via lua as well in the next update?

Sounds like a good idea to me. Will do this for 0.3.3.

So, this was already implemented: getEnergyProducedLastTick() returned hot fluid production for active reactors. I've added a getHotFluidProducedLastTick() which only returns non-zero when the reactor is actively cooled, for clarity.

Interesting, I would not have thought to poll a cooled reactor for RF production but thanks for the extra call and clarity!