Isn't that a little hyperbolic? Sure cancer rates will be elevated wherever the fallout blows but it's not going to end anything.

In terms of severity, Chernobyl was a long way from the worst case.

If the core had melted down to a body of water, the steam flash could have vaporized it & ejected it high into the atmosphere.

That's city-ending, if not quite "continent rendered uninhabitable".