IRL nuclear reactor fuel doesn't consist of 100% enriched uranium. Any reason why you don't include some 238 in the recipe?
especially since you're so about physics accuracy over game-play in other places.

Enriched uranium is uranium that is mostly U-238 with some higher-than-natural U-235 ratio (LEU ~5-10%, HEU >30%, Weapons grade even higher). So fuel is made from 100% enriched uranium, which still contains mostly U-238. It's all built in and calculated at the centrifuge stage. So you are seeing that physical accuracy built into the recipes. It's there. The depleted uranium isn't purely U-238, either, it just has a higher U-238 ratio than natural uranium ore.

whoops, just realized that HEU isn't pure 235 this morning when I woke up.

No worries. It's a good question. I use a little toy model I built in a librecalc spread sheet to calculate it all. Should be accurate-ish to the second decimal place.

The energy content of a single fuel cell makes building steam storage very difficult, especially for a multi core reactor.