Sizing reactors for various launchers would get you power generation in various classes, of course. An SLS launched reactor should get you something in the 100kw range. One launched on a Falcon Heavy - probably less than 50kw. A standard EELV? That's trickier, but the old Soviet 'Topaz' reactor only rated about 5kw and back then they only had Soyuz and Proton launchers - as they do now.
Well, I suppose if there is a tele-robotic bulldozer or grader there to cover it with regolith, there's your shielding! Of course, there's the need to get that machine there first.Admittedly, I knew very little about the SAFE-400 and looked it up: Brayton turbines! I hope they'd use silicon-nitride bearings for long life My Google also told me about the HOMER-15 concept which would be very compact at about 215kg and produce about 15kw. That kind of power would easily run a 3 bedroom house, let alone a spacecraft. THIS is the kind of tech that should be funded, but the nuclear bogey-man trumps all, eh?