How Does a Nuclear Meltdown Occur?

You keep hearing conflicting stories of what is going on in Japan.  With the aftershocks subsiding, the attention now turns to the rescue, clean up and the nuclear plant situation.

After more explosions in at least two reactor cores at Japan's Fukushima nuclear power plant - and as the developing crisis is rated at level 6 of seven levels on the International Nuclear Events Scale - attention is turning to just what is happening inside the 40-year-old power plant in north-east Japan.

Here's a video that helps explain what is happening.