I would expect that they would be installed automatically during construction to power systems before the power plant and fuel tank were installed. Then of course they would be useful when overhauling the power plant as the shipyard would just hook to the power umbilical to keep life support, gravity etc working during the overhaul. Naturally search and rescue vessels would want to be able to connect to them as well to power systems if the power plant was down.
So I would assume standard power umbilicals are in fact present already.