This links to a very interesting and well-developed, detailed discussion of the potential for a second set of explosions to occur at Fukushima.
The author argues that the presence of fission products indicates the cores are critical. The discussion includes diagrams and schematics.
The author of this analysis sees supercriticality as a major threat and explains why in very specific terms.
Based on the discussion of criticality I posted yesterday, I agree that it seems rather obvious that there is some level of criticality occurring with the corium. http://majiasblog.blogspot.com/2011/11/nuclear-chain-reactions-and-forms-of.html#comments
I wondered yesterday whether the level of criticality is sufficient to produce an explosion, but I also noted that even a situation of k=1, where the nuclear chain reaction is insufficient to create an explosion, can result in the production of large amounts of radiation.
A comment made in response to that entry is instructive. Here it is: