"Nuke plants' backups fall way short." Kyodo, Japan Times, Wednesday, April 27.

"Most nuclear reactors in Japan would fail to achieve a stable condition in the event that all regular power sources are lost, even though plant operators have prepared new backup power sources as well as electric generators amid the crisid at the Fukushima No. 1 nuclear plant (Daiichi), according to utility industry sources."
"The possibility of a failure to secure the safety of the reactors is because the backup power sources do not have enough capacity to operate all of the devices needed to keep the reactors cool."

The report goes on the point out the failure of specific plants to have adequate backup.
Some ten firms own Japan's reactors.