[Ryzorian]

It's not going to be a nuclear explosion like a Nuclear bomb. There would be a hydrogen explosion that would blow the outer cement structure off. It will have radioactive elements in it yes, but not like a actual thermonuclear weapon. It's called "weapons grade uranium or plutonium" because it takes a certain purity level and a certain amount to make such a huge reaction.

A meltdown can contaimnate a large area but it's a different type of destruction...Radiation posioning is what would result. Not saying that's not seriously bad, just trying to differentiate what they mean by "explosion" here.