I assume everyone has seen the hydrogen explosions that took the roof off the reactor buildings along with upper walls. Those hydrogen explosions and a bit higher than the light towers at the plant. Those were hydrogen pops compared to the explosion that has now cleared the plant.

I assume you did not see the new and fateful explosion that changed everything. This explosion was of the only thing left to explode at reactor 2. It is the containment vessel. IT reaches nearly 8,000 feet in seconds and continues to go higher. After this explosion over 700 workers were evacuated.

It is far more impressive in HD where you can see individual components of the vessel wreakage. But here is a quick low quality view.

http://www.youtube.com/watch?v=T_N-wNFSGyQ