If anyone hasn’t seen the amazing HBO series “Chernobyl” I highly recommend it. In it, there is a court scene which has an incredibly lucid explanation of exactly what went wrong. Videos are below, each is about three minutes. If anyone has an interest in this topic it is well worth a watch.
https://www.youtube.com/watch?v=TmIEI4ky-Zc
https://www.youtube.com/watch?v=3azNLCo0wyU
https://www.youtube.com/watch?v=IzbOgvWQhHA
The whole series is well worth a watch too. On one hand are the fumbling, bumbling Soviet bureaucrats, and on the other are the incredibly heroic Russian people. Ripping good yarn. Great acting and all star cast.