The vast majority of nuclear power plants were built before three mile island[1] and the accompanying increases in regulation. The point is, even the supposedly "unsafe" nuclear plants are still vastly safer than most energy sources.

You're correct about the infrastructure needs to construct pressure vessels. That's a large part of why nuclear plants were cheaper when built at scale during the 1960s and 70s. It's a lot easier for heavy industry to recoup the investment of building a heavy press if they have an order of 40 pressure vessels instead of 4.

1. Which, by the way, resulted in no radiation exposures or lasting exclusion zone.