My exposure to GT6 fission reactors is as in-depth as putting down some 2x2 reactor blocks, putting random rods in and out, then banging one of the rods against the block like a caveman and finally moving on to flamethrower some villagers.
On a more serious note, from what I’ve seen on the reactor rework thread those blocks have coolant flowing through them, so I’d assume you pull the hot coolant through a heat exchanger and then pipe that heat either into a boiler for steam or some other heat-accepting machine. Thinking about it, you do make a good point about powering the oven in your kitchen with a nuclear reactor’s heat. NTM has a similar machine that does all of that in a single block but that’s kinda lame.