Explosion at Fukushima Daiichi No. 1

The Washington Post reports on an explosion at a Japanese nuclear reactor:

In what may become the most serious nuclear power crisis since the Chernobyl disaster, the explosion followed large tremors at the Fukushima Daiichi No. 1 reactor Saturday afternoon, injuring four workers who were struggling to get the quake-stricken unit under control….

The full extent of the blast remained unclear, but footage on Japanese television showed that the walls of the building housing the reactor crumpled, leaving a skeletal metal frame, according to the Associated Press.

There apparently was already some radioactive release from the reactor, which is about 150 miles north of Tokyo.  We can only hope that the explosion hasn’t made that much, much worse.

UPDATE: video and technical information can be found here.  Apparently, the containment design is obsolete but is still in use by a number of U.S. reactors.