In THE FLOATING ISLAND, Jules Verne describes such an enterprise. His idea was to bolt together large boxes of plate iron. In the story, an island of several square miles is constructed this way, and a conventional town is built on it.
Verne had unlimited faith in riveted plate iron. The Nautilus goes to the bottom of the sea on the strength of this construction.
Iron has its limitations although it has been used in ships since Jules Verne, think of the titanic sinking just because the iceberg caused a couple of cracks in its brittle hull. There is another natural form of artificial island : floating volcanic tuffa, which with its internal bubbles has a density much less than water.
My vision then is artificial floating, bubble filled, glass islands of SiO2 base material w/tougher borosilicate glass cladding, from a solid density of 2.34 g/cc down to around .5 g/cc. Glass is just about the most expensive common building material because of the HEAT required to convert sand into rough glass. Then still more processing is required to make your basic window pane; it works out to about $50/sf.
Ok then, you propose these floating nuclear plants over the visual horizon of major seacoast cities(a majority of the world’s population lives w/in 30 miles of an ocean beach). They make OODLES of excess heat, why not scoop up seafloor sand as raw material, make a glass furnace and shoot in bubbles as the melt cools : WA-LA : artificial islands by the hundreds, billions.
On 4%-5% of the ocean’s surface you could have a tropical “maui” for every one of 7 billion people : 4 people per 100m x 100m island(city block sized), agriculture above the water line, aquaculture below.
I know, I know, this sounds too visionary but how quickly would the world’s problems disappear if everyone suddenly found themselves on their own “maui” somewhere in the tropics? Where there is no vision, the people perish...