Components do only take as much heat as they can take and simply disappear. In case of a Uranium cell, the remaining heat will be applied to a reactor hull.
Exception are the heatswitches, when drawing x heat, they can possibly exceed their maxHeat. Since the melting of heatswitches isn't really an applyable 'intended concept' it doesn't matter, though.
I just found out i was doing things way too complicated, reworking code, fun!
As for more questions:
Basic vents dont have a reactorTransfer rate?
Condensators transfer heat on their own (they take all they can)?