Problems at the Japanese nuke plants: Why hydrogen explosions?

As I’m sure most of us are aware by now, there have been a couple of hydrogen explosion at the Fukushima plant.

But why hydrogen? It takes a great deal of energy to split water molecules to obtain elemental hydrogen, so where is this hydrogen coming from? Does this have anything to do with the sea water with which they’ve been trying to cool the reactor cores, and with the salt content of that water? Or do the neutrons crash into the water molecules and break them up?

Saw this explaination in a sister thread.

Most likely the hydrogen is being produced when water reacts with overheated zirconium fuel rod cladding. The oxygen reacts with the zirconium to make zirconium oxide, and the excess hydrogen is released.

Thanks for responding; I forgot to come back here until now.

As a matter of fact I did read that yesterday, after I posted, in a newspaper article about the incident.