We were still learning about flaws and failure modes of nuclear reactors. Designs kept evolving to try to address these. We never got to the passenger airliner model where we had systematically eliminated nearly every failure mode and could produce this on an assembly line.

> We could have standardized the old reactors too.

Yes, but the potential market for GW-size reactors is fairly limited.

Now, whether the market for any of these SMR reactors is large enough that any of them will be able to see any of these supposed economies of scale is a big question.

Floating nuclear plants next to a city sound like a recipe for disaster

> France is still shutting down its plants because the rivers are too warm in the summer.

That's because French nuclear power plants are designed to be directly cooled by river water instead of using cooling towers.

The biggest nuclear power plant in the US (Palo Verde Generating Station in Arizona) is cooled by evaporating the treated wastewater, in the desert.

You can’t standardize manufacturing of multi billion dollar facilities. Economies of scale just don’t work that way. Even residential housing has the same problem. There’s too much variation in on-site construction.