First U.S. nuclear reactor built from scratch in decades enters commercial operation in Georgia::ATLANTA — A new reactor at a nuclear power plant in Georgia has entered commercial operation, becoming the first new American reactor built from scratch in decades.
This is really only one facet and not even the main driver in cost. MIT did a study a few years ago looking at this (https://news.mit.edu/2020/reasons-nuclear-overruns-1118). Turns out it’s complicated.
In short, in the US, lacked of skilled labor and large scale project management are big drivers also, not just regulations.