We now have TWO confirmed LOCA's and subsequent H2 explosions at the Fukushima complex. To make a big H2 boom, you have to make a lot of H2, which evidently comes from this reaction:

Zr + 2 H2O  -->  ZrO2 + 2 H2

So this means that lots of Zr fuel cladding has turned into zirconia and lots of H2, and that the really hot UO2 fuel pellets (self heating due to daughter products radioactive (via beta emission) decay) are now exposed to hot steam and some nasty "daughters" are puking out of the system via the steam vents.

I thought one known mechanism for hydrogen production was dissociation of cooling/moderator water by neutrons or gamma rays from the nuclear reaction. Can than not possibly produce enough H₂ for the kinds of explosions we've seen without assuming the Zircon alloy fuel cylinders have begun to disintegrate?

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11