NB in the description what happens when the water was drained off in the surrounding jacket: they dropped out of criticality. Many people talking about “criticality” obviously have no idea of the physics involved in creating and sustaining a critical threshold in a reactor.
BTW - we had an incident similar in result (3 dead) here in the US in the early 60’s. Unlike the incident you’re mentioning, it was a boiling water reactor, not a breeder reactor, the men were killed by mechanical effects of a nuclear mishap, and it resulted in a release of radioactivity.
The men were buried in lead-lined coffins.
http://www.inl.gov/proving-the-principle/
Jump down to “The SL-1 Reactor” if you’re impatient. That’s an example of “prompt criticality.”
BTW - we’re still here. That area of Idaho grows trainloads of wheat .
Just barely. TMI broke out of the reactor vessel at a bottom seal. One of the Control Rod Assembly Tubes was all that kept it from getting to the concrete. Was in a pdf report linked on an early thread.