1) Much more efficient:
Allow for continuous refuelling (just load up on pebbles into the hopper, used ones drop out the other side) rather than have to cease operations to replace spent fuel
2) Much safer:
No phase transitions in the coolant, no possibility of meltdown.
I wonder how much development is needed to make liquid-phase reactors useful, e.g. molten salt thorium cycle, or aqueous homogeneous? These seem capable of KW to low Megawatt-scale production, suitable for a small town or industrial plant.
I tried to design a neighborhood nuclear power plant based on aqueous homogeneous reactor[1]; it seemed pretty doable except for needing slightly enriched uranium and chemical engineering for handling fission and decay products. 40KW for a plant that fits on 1/10 acre or so. Good burnup so not much waste.
Another possibility is using decay heat to run small turbines. Short half-life products generate a lot of heat; this will maximize efficiency. Use helium or CO2 for working fluid. These could be used for local base load (what makes up local base load, heheh). The energy density is roughly equivalent to solar power (my hands are waving a little here).
1) Much more efficient: Allow for continuous refuelling (just load up on pebbles into the hopper, used ones drop out the other side) rather than have to cease operations to replace spent fuel
2) Much safer: No phase transitions in the coolant, no possibility of meltdown.