I didn't think of nuclear subs. It would seem ideal for running a small moonbase. But I don't know how self-contained those reactors are, or how much they weigh. Surely a lot.
There are also the nuclear batteries in some of the longer lived space probes. Those batteries have the major advantage of being very simple - a lump of radioactive material that gets warm - attach a thermocouple and voila! Electricity!
LFTRs can scale down to closet sized, and most of the fuel (Thorium) is stable aside from the ignition uranium plug, but there's a LOT of materials to solve for long service.
There are also the nuclear batteries in some of the longer lived space probes. Those batteries have the major advantage of being very simple - a lump of radioactive material that gets warm - attach a thermocouple and voila! Electricity!