Side note: In the movies, everyone runs around screaming because the reactor is "going critical".
In real life... not so much. Critical merely means that it is a "self sustaining reaction". Every fission produces multiple neutrons, one of which will go on to produce another fission.
This is where the reactor makes power. They ALL go critical. Otherwise, they wouldn't make power.
Hey Act - have you heard about the HBO miniseries about Chernobyl? Different kind of nuke, obviously, but I caught a couple of the episodes and it looks like it was a very interesting portrayal of both what happened and how the Soviet system created both the problem and a failure of solutions.
As a Cold War warrior with nuke background, you might like it.