Each steam turbine needs 160 steam units to run at 100%, so that's 4 pipes. 18 output faces at 4 per steam turbine means at most 4 steam turbines at 100% and 1 steam turbine at 50%. Last time I checked a Railcraft steam turbine only put out 50EU, so that would mean 1 nuclear reactor could only output 225EU/t maximum via steam?
One nice side effect, is it will output directly into a tank, so you can bypass at least the need for worrying about outputting directly to steam generators. I think (but haven't verified) that it works on the same steam/eu ratio that the turbines do, so a 16 to 5 ratio, i.e. a uranium cell puts out 16 steam per pulse. With a 9x9x8 tank, you could fit a whole lot of pipes to output to the steam turbines then.
Unfortunately a tank won't output directly into a steam turbine, but even without any addons that give you bigger pipes or cobble gold pipes, you can output 21 gold pipes per face of that tank, so assuming you have the reactor taking up one face, that's still 26 turbines. Although I'd hate to actually have to design that mess of pipes and wires. Love to see it, hate to design it. 