Bug: When the reactor stalls, and the rate of fission drops to 0, the fuel rods act as a heat void
I assume that you are using a modded heat interface as a base for the rods, if so are you using the "Add" mode instead of "Exactly" ?

Suggestion:
Higher Energy Consumption Heat exchangers?

when there is no fission, yes rods dissipate heat. i do think it dissipates too fast.

should lose heat slower and in a more realistic way

Whenever my reactor has no reactivity it slowly gains heat.

Its a rounding error because it produces 800KW of heat (0.8RU) when fully damped

Update out soon which bumps it to 1.2MW, and balances it some more.