ARE THREE REACTORS IN NUCLEAR MELTDOWN?

                                    A satellite view of the  Fukushima Dai-ichi nuclear plant

From the Daily Mail.

The Japanese nuclear reactor hit by the tsunami went into 'meltdown' today, as officials admitted that fuel rods appear to be melting inside three damaged reactors. 

There is a risk that molten nuclear fuel can melt through the reactor's safety barriers and cause a serious radiation leak. 

There have already been explosions inside two over-heating reactors at the Fukushima Dai-ichi nuclear plant, and the fuel rods inside a third were partially exposed as engineers desperately fight to keep them cool after the tsunami knocked out systems.

Japanese chief cabinet secretary Yukio Edano said it was 'highly likely' that the fuel rods inside all three stricken reactors are melting.
Some experts class that a partial meltdown of the reactor, but others would only use that term for when molten nuclear fuel melts through a reactor's inner chamber - but not through the outer containment shell.  

As fuel rods melt, they form an extremely hot molten pool at the bottom of the reactor that can melt through even the toughest of containment barriers.

Japan is fighting to avoid a nuclear catastrophe after the tsunami. There was a hydrogen explosion at the reactor in Unit Three of the power station earlier today, in which eleven workers were hurt by the blast that was felt 25 miles away.

It's important to remember that the United States already experienced a nuclear meltdown at Three Mile Island in 1979. Yes the reactor did meltdown as this video discusses. (The part about how the reactor actually melted down begins at 3:40)

It was a core meltdown (about 50%) but it was not the China Syndrome where the molten core breaks through the containment vessel.

We are all just going to have to watch, wait and see.