There were personal heroics but the Soviet response was a catastrophe, it was Sweden that sounded the alarm and the Soviets allowed a May Day parade of children to march through the cloud in Kiev...

"For 36 hours after the explosion, people were given no reliable information about it and left virtually on their own. They never received instructions on how to protect themselves and their children. Radiation levels that according to Soviet laws were supposed to trigger an automatic public warning about the dangers of radiation exposure had already been recorded in the early hours of April 26—but were ignored by one official after another. Finally, people were asked to gather their belongings and wait on the street..." https://www.history.com/news/chernobyl-disaster-coverup

https://www.nationalreview.com/corner/remembering-soviet-res...

> One effort that stands out as "preventing something much worse" is that there was a risk of a potentially larger secondary explosion from steam buildup.

A larger conventional explosion would have been linearly worse, not worse rising to a separate category of problem.

> Also, you can absolutely get a nuclear explosion from a reactor, there is some suggestion that Chernobyl might have been a small one in fact (paper)

This is not what I'm referring to. It's one thing to have a "nuclear explosion" in the sense that the reaction generates enough heat to cause the rapid expansion of gasses which is technically an "explosion".

What I'm referring to is the sort of exponential chain reaction that happens in a nuclear weapon, resulting in something on that scale. You have to design for that on purpose to get it. The density and geometry has to be exactly right.

> you can absolutely get a nuclear explosion from a reactor, there is some suggestion that Chernobyl might have been a small one in fact (paper)

An explosion that's too weak to even blow apart its own assembly doesn't count.