The goal is to only consume nuclear fuel when needed. I'm assuming that the base runs off 100% nuke power, but I think it should work fine with solar in the mix as well as that goes first in the energy mix. I don't think it will use coal before nuclear or the other way around, but who burns coal these days?
Note: It's entirely possible that someone posted this exact configuration already. I read a number of posts but didn't read them all (I'm here to play, not to catch up on the reactor design literature ). If you have, let me know and I will give proper credit .
The setup:
Fuel is only inserted when needed, which is if (a) there is no fuel in the reactor and (b) steam is low. (a) is achieved by using the presence of spent fuel in the steel chest as 'memory': after a cycle the spent fuel is inserted in the chest, signalling that the reactor is in standby. The inserter from the steel chest to the provider chest is set to enable on steam < 5k (read from the green wire connected to a steam tank) and read pulse:
I've tested this with a 2 reactor, 16 exchanger, 32 turbine, 16 steam tank setup. Under no load it goes up to just about 25k steam, under medium load it fluctuates between 5k and 10-15k steam, under full load it operates continuously with no steam.
I've only built and tested this in creative mode, not in "the wild", so it's entirely possible that there are some conditions under which it won't work or will not function optimally... please let me know if you see something wrong with the design!
Edit: I've now used it a number of hours in production and haven't seen any real problems. I increased the steam threshold to 10k as a tradeoff of robustness to efficiency with the new slower cooldown/heatup of the heat pipes. Increasing the ratios of steam storage to steam turbines might (currently 1:2 in my setup) also work.