So Iv'e made this breeder, which is a modification to the simple 0-chamber breeder in the OP. What I wanted to do is get some re-enriched U cells fast, so I've added 10 healing cells and some vents, and it appears to keep it stable at 10K heat (4X faster charging), without going to crazy on resources.
Stable breeder is one that stays stable no matter what will hapen with its components. When thorium cell burns out in your reactor, components will melt.
I this it would be much better to use this simple design that stays the same all the time.
Then just keep adding plating and heating cells to get faster breeding. This is the point where no more heating cells can be added and breeder will breed 432 cells in one thorium cycle. After that you can think about adding more cooling to support double or quad thorium cells.