An exposed core melts. It doesn’t explode. That’s why it’s called a meltdown.
http://www.freerepublic.com/focus/f-news/2688397/posts#10
Thanks for posting that link. I see we are at 550C, and the melting point is 2000C. Of course the temperature can already have resulted in some melting in spots. We can’t trivialize the issue, the core could be damaged to a point that makes it produce more heat. However it is very likely that water and boron being injected will keep it subcritical and preclude any further melting. But that also means there will have to be venting.