There's a LOT of problems with adding water to fuel rods that are already very hot. It will definitely cause oxidation reactions with both the zirconium and uranium (the casing and fuel in the rods). These generate further heat. It could also cause some formation of hydrogen, which causes subsequent explosions. That has already happened several times. And if the rods get VERY hot, the process of hitting them with cold water might even crack the outside casings - releasing pellets of uranium (which would tend to settle by sinking to a lower level).

These are not my thoughts - they came from a buddy at work who was in the nuclear industry. I just talked to him this morning.

BUT with all that being said ... my friend still thinks the best thing is to flood the exposed rods with lots of seawater. And i assume that the Japanese are still working on this option. The trouble is - they are facing one of the biggest challenges in Engineering Emergency Operations in the last decade. Let's see how they handle it.

other Pete