Fukushima was commissioned in 1971. Chernobyl happened in 1986. I would not call the design a "post-Chernobyl" reactor.
I can recommend the section on the wiki page for further reading: https://en.wikipedia.org/wiki/Fukushima_Daiichi_Nuclear_Powe...
> I had even, ignorantly, parroted back
I think this is probably the root cause ;)