As I played, I noticed that the water in the RBMK Reasim reactor sometimes showed negative values.
In addition, I recommend changing the steam exported from the RBMK Reasim steam outlet to Ultra Dense Steam and adding two machines: RBMK Reasim coolant inlet/hot coolant outlet.

The RBMK ReaSim coolant inlet/outlet you're suggesting sounds close to a RBMK heater column. This can be used by pumping in coolant from the bottom, then using a RBMK Steam Connector to connect the hot coolant acting as an outlet for the steam. As for the UDS output, I think that could be useful as well for controlling the type of steam that is made in ReaSim RBMKs, however at the moment, my knowledge of the fluid system is not advanced enough to add it myself. The negative values are due to the way that ReaSim handles the fluids inside the columns themselves. Normally it doesn't affect gameplay, as it's negative for ~2 ticks.