This question already has an answer here:
In the new Chernobyl TV series (https://en.wikipedia.org/wiki/Chernobyl_(miniseries)), in episode 2, there's a reference to the risk of a steam explosion from the molten reactor core entering a water pool. It appears what was referenced here is mentioned here:
In the series it is mentioned that it could trigger a steam explosion of "3 to 5 megaton". That sounds like a really big explosion - I am wondering how that is physically possible because from my (naive) calculations the core would have to be truly massive to contain enough thermal energy to trigger such an explosion? Is this just an exaggeration? In other respects the series appears to be accurate.
Extra question: In the series it is also claimed that such an explosion would release such massive amounts of radioactivity (partly due to other reactors exploding as well) that the whole Eastern Europe and Ukraine etc. would become completely uninhabitable.