I'm kinda new to this type thing, but I built a few nuclear reactors in the simulator including a Mk II and a MkIV.
Mark II:
http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…110010101001010
Mark IV:
http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…1501521s1r11r10