The external electricity need is an essential security feature of these plants: external power runs the cooling system pumps, as fuel rods have to be cooled even after an emergency shutdown (=no own power available).  The emergency diesel generators are meant to run the cooling system pumps (along with the emergency systems) in case of an external power-down, though they aren't well suited to keep the power plants running, and are often weak links (at least poor maintenance of emergency diesel generators in US plants is widespread).

_{*Lunatic*, n.
One whose delusions are out of fashion.}