I think a lot of the time is spent dealing with local regulatory issues, at least in the US. Non-standard models for nuclear power plants lead to long approval

I think a lot of the time is spent dealing with local regulatory issues, at least in the US. Non-standard models for nuclear power plants lead to long approval times, which have to be more or less restarted each time there is a design change. This is a huge contribution to the time it takes getting a nuclear power plant online. As another commenter pointed out, it's not the same in China, where regulation is far more lax than in the US.