You are shifting your position. You were first claiming they are new and unproven hence they would need a "first" success story. Now they are the same reactors as in the 60s (which i agree to , btw) ? So which is it?
Anyway, the fact that we were able to build reactors in the 60s kinda proves it's possible with 60s tech. With today's tech (and some incremental improvements in the reactor design), you're saying it's harder? How?
There can be other reasons why something that is technically possible and useful is not "popular". But you seem to asume that because it's not popular, it must be difficult, which is a fallacy.