We probably still have all the papers and journals and schematics and whatnot. What we don't have, however, is people with the appropriate training to make sense of those things. Without those people - without actual working knowledge of the technology - all that data is useless.
You can figure out what it does rather easily. Figuring out why it was done that way requires a lesson from the school of hard knocks in a lot of cases.
In the case of the nuclear industry those knocks can be rather significant.
We probably still have all the papers and journals and schematics and whatnot. What we don't have, however, is people with the appropriate training to make sense of those things. Without those people - without actual working knowledge of the technology - all that data is useless.