Wasn't this number flawed, because it mapped the energy needs 1:1? Like, the efficiency of a heat pump or a battery is vastly better than current motors or burning oil.
I can't find the source, but it was in a video presentation by Kevin Anderson, a senior research fellow at the Tyndall Centre for Climate Change Research.
400 nuclear plants isn't actually that many in terms of numbers, but constructing them is an enormous task.