Edited preface for clarity: This is a suggestion for the base game, though a mod may be able to fill the void.
The yellow box shows what would be a single concrete structure linked to allow the flow/emission of excess steam/water as needed. Thanks go to GotLag's Reactors mod for the graphics.
Each power plant would have two parallel flows passing through them: Steam and water. As the steam goes through the plants, it's converted into electricity and (variably heated) water, with excess being evaporated. Boilers only accept water, not steam.
As described here (motivation), I believe a single entity would unify all aspects of improving steam power--both coal and nuclear--and that it's likely now or never (adding closed-loop later with a 3rd steam generator and new behavior would be hard to justify). If a Mk. 2 steam engine (or turbine that functions exactly the same with a simple increase in power output) were added, it would save some space and time but otherwise be a missed opportunity to improve and diversify steam power while bridging the enormous tech gap between steam engines and nuclear power research/construction.
Coal, nuclear--it doesn't care as long as it gets steam to the turbines and (dynamic amounts of) water to the towers: Assume the boiler chain is outputting steam, despite the old boiler design.
- Inputs: Water, Steam
- Outputs: [More] Water, [less] Steam
- Same electrical priority as solar
- Beginner-friendly design integration (basically a chemical plant that outputs power, and around the same tech level)
- Much more efficient and compact power generation from steam compared to early engines
- Outputs partially preheated water for even greater efficiency
- Accepts steam at the same rate whether generating or evaporating/condensing
- Behavior priorities:
- Turbine (with condensing to water)
- Output excess steam
- Condense steam to water
- Evaporation (once water output flow or temp is at max)
- Overall, gains enough efficiency to be worth the "dumb weight" of wasted excess steam--if scaled appropriately to the base load demand (wasteful if overbuilt, or you let your factory idle without a smart shutoff)
- Turbines slower to ramp up/down, making steam engines (early) and accumulators (later) very useful to handle fluctuations in demand
- "Noteworthy" startup time so turning steam "off" with a pump/valve (or any possible interruption, e.g. nuclear reactor scram) has a cost
- Minimum output, below which turbines in the same network begin to shut down to compensate--see above
- For added complexity, the input temperature of the water source could affect operating parameters. This could be done in many ways with a variety of effects on layout optimization (series vs. parallel turbines, for example)
Burner stage -> Steam stage -> Turbine/Solar stage -> Accumulator stage -> Nuclear steam generation (late game)
It makes for a very fluid (pardon the pun) progression.