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.
For the record, I worked about 10 years constructing TVA nuclear power plants. I saw the same door to a turbine room replaced five times as a result of constantly changing requirements. TVA developed and began implementation of “smaller” installations that was scrapped.
I recently learned something of note. In recovery from surgery, from her recliner, my wife is traveling the world via You Tube train videos.
The scope of European trains was mostly unknown to me. Railway terminals are huge and very active.
The European trains are all electric. The trains are truly ubiquitous and accommodate different voltages in different countries even.
The need to power them is huge. The green climate change, renewable energy fad simply will not allow the railroads as they presently exist.
When push comes to railroad shove in Europe it seems that small nuclear production will somehow do the job
When thinking of a clean electric high speed train in California, I just laugh.