How did Chernobyl explode?

Answer 1

One of the reactor faced a sudden power increase which made its core unstable and it exploded, eventually resulting the radioactive fuel exposed to the atmosphere directly and caused a disaster killing many.

Answer 2

I believe you meant to ask "how did Chernobyl radiation spread?"

But if not, then don't read the following

Wind caused radiation from Chernobyl to spread, and possible trade. And since the Soviets did not bother to contain it in time, many other areas were affected/

Answer 3

• Severe operator error.
• Inadequate operator training.
• Engineering/design errors.
• Power surge during attempt to shutdown was immediate cause of the steam explosion.

Going into all the details of these problems is too long for this site. There are several books available that cover the accident and its aftermath in detail.