Hey, I'm new to the forum and pretty new to nuclear engineering but a bit of messing around with the planner gave me this:
http://www.talonfiremage.pwp.b…=1k10101001501521s1r11r10
As far as I can tell (though I haven't tested it in-game) it's slightly better than the Mark V in the post. In addition to having 2 more effective EU/t (not much really) it's cheaper to make, and has 8 extra slots for whatever nonsense you want to do. Ice blocks especially will quintuple the effective EU/t.