I'm probably going to offend some people when I say this.
Engineering is often done by habit. We've always done things this way, and we know how it works, and unless you can show performance that we simply can't get any other way, we'll keep doing things this way. This is why the rail road steam engines lasted as long as they did.
Regulations get written around these notions. For example, in the 1930s and 1940s, the hottest sparks that were easily available came from magnetos. So they built aircraft engines with them. These magnetos weren't particularly reliable, so they put two plugs in each cylinder and the law mandated two separate ignition systems be available in every aircraft engine. That's still how it is done today in most certified aircraft engine designs, even though we have electronic ignition systems that are offer significantly better performance than a magneto with fixed timing.
In the nuclear industry, there was rapid growth right up to the early 1970's when Three Mile Island nearly melted down. We had a series of things that we knew worked. Modern safety designs were just getting started back then. TMI had many control system problems and they dealt with them poorly.
Those older nuke plant designs were basically set in stone and the industry went into a tail spin. Today, we have very few people who remember how decisions for design on these plants got made and for what reasons. It's not that we do not understand the technologies. It's that the choices that may have been made for less than ideal reasons are fading from memory. People do not remember why things were done the way they got done. So they worship the design and this is enshrined in regulation upon regulation upon regulation. People are deathly afraid to tinker.
Yet that is the only way out of this morass. Thus, we have research reactors that do very small scale stuff, but no larger scale reactors that might consume Thorium fuel, for example.
The nuclear engineers of today are basically caretakers. They maintain these old beasts but rarely change how things are done because almost nobody has a living memory of how things were designed and for what reasons, and even those who do know are not allowed to touch a damned thing. Getting anything done at all involves meeting after meeting after meeting and documentation up the wazoo.
At some point, we need to get past the caretaker stage and get back to actual maintenance and engineering. That is what I hope this generation of nuclear engineers will do.
