The tier of the fuel influences the pulses, I believe. If you use Quad uranium with 48 power and Single plutionium with 80 you get this:
Quad U isolated: 48
Single P isolated: 80
Quad U pair: 128
Single P pair: 320
Heat Exchangers are just plain broken, they are completelly bugged. My reactor blew up, had now 90% heat. Put a coolant cell with an exchanger next to it to absorb the heat.
The exchanger filled up with heat, which decreased the reactor's, but didn't dump it in the cell. Right after, my reactor's heat started rising and blew up my exchanger. Meanwhile, the cell remains at 0 heat. Nothing is producing heat, just fix these bugs.