If there is no water, then fission cannot be sustained (subcritical).
Decay heat is not sufficient to "...melt or burst its way through the pressure vessel" [unlike Chernobyl which became prompt-critical and blew up the fuel (deflagration), setting the graphite moderating rods on fire]
Like TMI, the fuel should be contained within the RPV and within the primary containment. [I haven't seen any reports stating that the earthquake actually broke something open]
There are four fission product barriers; the fuel rods, the RPV, the primary containment, and the secondary contaiment (blew up).
Once the 1st & 4th barriers failed, there are many ways for long lived isotopes to get out of the RPV & primary containment.
The fate of the nuclear industry stands on their success in containing the long lived fission products.
The fact that fuel rods may have been damaged in the spent fuel pool is very very serious threat to the public.