There is also the fact that the "small, cheap" nuclear reactor has never really happened in a commercial context. I have literally heard about those since my childhood and one has actually yet to happen.
The current very large nuclear plants are expensive to build (the ones that have opened on time and on budget are the exception, not the rule).
Most of the recent construction of large nuclear plants is in China, and they're actually doing quite well at building them on time. The ones that are super late and over budget are the exception worldwide; they just make the news more often.
Nuclear plants in SK are on time as well, which is quite impressive since they did not have as much training. I guess just having a good plan is enough.
The regulatory system makes them ESSENTALLY IMPOSSIBLE. Seriously, if people only knew how fucked up the regulatory system is.
Unless you are NASA or DoD you can fuck right of with that stuff.
The regulatory system is HARD LOCKED to one technology. No sane person would invest money in an alternative (unless you are planning on selling it to DoD). The regulatory system had to be changed a huge amount, just for NuScale PWR in a module reactors.
If you wanted for example to build a Molten Salt reactor there is no established regulatory path. Or a small reactor either. There is only tiny research reactors, or fully operational reactors. So you can't even build a small version of your reactor to prove things out. No prototyping for you.
You would basically have to show up with a full design (literally invest 100s of million) then go to the regulator and hand it in. You would also pay them to review and you would literally have to wait years, and potentially decades for them to tell you if your design is good. You would get no early feed-back on what they might consider problems or issues. And there is no criteria what exactly the application needs to look like or how much detail they want and so on. There is no established software that they accept as valid for modeling something like uranium in molten salt. If you are not providing real data its very hard convince them on anything, but of course, you can not actually get real data from anywhere.
That is why essentially no progress has been made. Thankfully in the last 5 years or so, actual progress has been happening and the regulator has admired that there is a problem. The don't have actual solution yet but they are apparently working on improving the situation. That is why, almost all GenIV nuclear startups have converged on Canada. The Canadian regulator after its privatization of CANDU was looking for something to do and they were very open to next generation technology. Their regulatory process is a multi-step process that is technology independent.
It looks like US regulator and the Canada regulator are working together so hopefully Canada can lead the US out of its idiocy.
What you must realize is that the turn against nuclear was hard, on all fronts. Population, Politics, Regulation went totally anti-nuclear and specially for anything that wasn't established. Since Nuclear Commission was abolished, progress has been glacial.
The current very large nuclear plants are expensive to build (the ones that have opened on time and on budget are the exception, not the rule).