Right up there with lifeboats which can't be launched unless the ship is sinking on a perfectly even keel, and heating gas pipelines which freeze up during a blizzard.

Nuclear power needs flowing rivers and spews warm water. Did any design (under construction) improve upon that?

France was able to provide full domestic electrical power inspite of these shut downs, though they had to reduce power exports. Bieng dependent on cool river water shows a significant weakness in nukelear power, and is another reason to discredit claims to bieng a "green" power source or reliable. It should be noted that the European grid stayed up durring the worst of this heat wave, which is a significant achivement that d3monstrates the ability to integrate and distribute power from all of the different(much malligned) power sources.