How small?
I don’t know. Small is not mega sized with all sorts of potential problems resulting from size.
A kid down the block had a job tending the reactor on a submarine. That is one version of small.
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LENR fits your requirement of ‘small’, going all the way down to cells that are the size of a D cell battery and hopefully scalable to the MegaWatt range. That’s the true capability, scalability such that we can have a nuke to power our car and a nuke to power our home with very very little radiation to deal with. Decentralized power as small as the gasoline engine with 5000X the energy density of gasoline.