A friendly reminder that the idea posed by a pioneer of nuclear energy of just dumping big bombs in a hole and harvesting the heat energy with steam/plasma has never been invalidated and remains the most efficiently-simple solution immediately viable
https://en.wikipedia.org/wiki/Project_PACER
If containment is your concern (though underground blast effects are decently understood, and blast chambers could be constructed with still strongly net economic/energy positive) - this does not need to be built around any population centers. At a cost of 1.5% efficiency loss per 1000 km, UHV power lines can direct it from a single write-off location anywhere on earth. That single location can likely be scaled to supply well beyond the total current global energy production.