This is an excellent post about why the fuel rods stored at the nuclear reactors in Japan will keep catching fire until they are thoroughly and continuously doused with water. The release dangerous radiation when they burn.
Why hasn't this been done yet?
Radiation levels are too dangerous for workers. Anyone near those reactors will die. Radiation is being released by the cracked reactor vessels (now confirmed) and, worse, by the igniting fuel rods.
Workers remained, giving their lives, but they were pulled out and now it is not clear whether or not any are in the plants now.
The plan was to douse the spent fuel rods that keep igniting from above. However, the roof is only partially blown and it made it difficult to get adequate water in the spent fuel rod pond, particularly at reactor 4, which has most of the rods.
Now the plan is for Japan's police to use water cannons to douse the pools. These police will probably die from their radiation explosure.
Here is what Kyodo news is currently reporting (direct quotes)
Among the six reactors at the Fukushima No. 1 nuclear plant operated by Tokyo Electric Power Co., part of the No. 2 reactor's containment vessel, key to enclosing harmful radioactive substances, suffered damage in the pressure-suppression chamber connected to the vessel following Tuesday's apparent hydrogen explosion.
An estimated 70 percent of the nuclear fuel rods have been damaged at the plant's No. 1 reactor and 33 percent at the No. 2 reactor, Tokyo Electric said Wednesday.
The cores of the No. 1, No. 2 and No. 3 reactors are believed to have partially melted with their cooling functions lost in the wake of Friday's magnitude 9.0 earthquake and tsunami.
The government's Nuclear and Industrial Safety Agency said Wednesday that the water level had dropped in the No. 5 reactor, which was not in service when the killer quake jolted northeastern Japan, posing the risk of overheating. The agency said it will closely monitor data on the reactor to prevent the problems that occurred at other reactors.