Use regulator to keep ice at steady number, say, 32. Reactor only can eat one ice block per cycle=1 second. So it will work perfectly. Then no need for accurate timing of ice supply.
Nearly-depleted can be be removed by filters. Re-enriched can be removed by same filter, and replaced with isotopes by tick of detector (set to tick on isotopes only, one isotope per one reenriched), or just pumped in, filling any opened space.
It is probably also possible to autoreplace-uranium too, but I have not figured how to do it in a safe way yet. Probably, desync uranium with isotopes, but sync uranium and isotopes separately. Then when uranium will butn out, it will leave nice holes, that you will be able to uranise by timer, or by detecting lack of electricity output, or something.