OldFart said: Sorry - looks like I missed this thread. I was a physicist (not nuclear) in my previous life. "Meltdown" if an overloaded word - it can mean many things and as they say the devil is in the details. Anyhow here is good explanation a few days old. Now the situation is more stable with electricity and cooling to the damaged reactors and spent fuel rods restored. Link - http://www.plainenglishnuclear.net/2011/03/yet-another-japan-reactor-post/
"3. Even if the reactor has a meltdown? The media keeps saying we’re headed for a meltdown. Isn’t that a very very bad thing?
Not necessarily. “Meltdown” is a very broad term – it applies to a range of conditions. “Meltdown” is basically any time that the fuel gets hot enough that the cladding (the metal wrapper that holds the fuel in place) gets holes in it. But “meltdown” could mean just one teeny spot on one single fuel pin (the cladding starts to fail at about 2200 degrees F) all the way up to the entire reactor core in a liquid pool on the bottom of the pressure vessel (the fuel itself melts at about 5000 degrees F). The media seems to think it’s that whole-core thing. But that isn’t going to happen."
Though the question still stands on how they're going to be able to continue cooling rods that have reached temperatures exceeding the melting point of malleable metals.
At 212 degree's water turns to steam, which is 1680 times it's original mass.
MontanaTrader said: Inky, there is no way to get liquid nitrogen close enough to the reaction to cool it. The nitrogen or whatever would evaporate, or explode if cooled to quickly. Meaning you can't get nitrogen any where near close enough to the rods to cool the reaction. The nitrogen would just keep evaporating never getting close to the rods.
Note: Eighteen grams of water, a very small amount, pure water expands to 22.4 liters (gas law" mole of any gas is equiv. to 22.4 liters.) So expansion of the cooling material is a big factor. The cooling material evaporates well before it comes close enough to cool a reaction of this nature. Eventually, I believe the reactors will be covered in concrete or some other material like the end result in Russia.
The rods are so hot, they cannot be pick up and separated either. Quite the dilemma, is a core melt down. Every noted scientist in the world is working on this Japan core melt down with no solutions at this time.
I have seen water come in contact with liquid lead, in small amounts the water dances on the surface and does relatively little to cool the lead.
In larger amounts, the water will cause a steam explosion that ejects the melted metal.
Though OF's article does well to state the situation in Japan is under control, I still can't see how water alone will suffice to stem further heat increases when ione reactor is already at 900 F.
I'm not stating they haven't figured it out, but asking what it is their doing.