PARIS (AP) — Small underground nuclear power plants that could be cheaper to build than their behemoth counterparts may herald the future for an energy industry under intense scrutiny since the Fukushima disaster, the incoming head of the Nuclear Energy Agency told The Associated Press.

Size is relative – the modular plants could be about as big as a couple of semi-trailers – easily fitting on the dimensions of coal plants they’re ultimately intended to replace in the U.S. They would have factory-built parts that are slotted together like Lego blocks and hauled by train or truck – making assembly possible anywhere.