ExtremeReactors2-1.16.4-2.0.17
ZeroCore2-1.16.4-2.0.16
with default config

This is a 3*3 and 4 blocks tall reinforced reactor

And it shows it produces 286B/t of steam

I've fixed it, thank you for the report. It should be out in the next release

how are you pumping water into the reactor?

You can use pipes. Or, in desperate situations, a bucket on a passive fluid port