Your Breeder isnt bad , but you enrich alot faster at 9k heat (4x as fast) and since your breeder gains heat you either have to manually cool it while it enriches or it will go critical.
I'm sorry, but everything about that statement is wrong. You hear people say "it's going critical!" too much in fiction, when in reality, that means the reactor is functioning perfectly normally. Supercritical is still not much to worry about. Prompt Critical is what you're looking for. When translated into everyday English, it means "The reactor is about to meltdown. Get the hell outta here!" or "Well, fuck it. I'm outta here! Peace! -runs madly in the other direction-", and then there's prompt supercritical, which is entirely impossible for reactors to do.
Just though I would mention it.