What percentage of electrical power in Japan has been disrupted?

Question:

by Daiichi/Fushishima situation. 5 reactors is significant.

What percentage of Japan's electrical needs were supplied by this facility??

Answer:

Note that Western Japan and Eastern Japan run on different power grids. Western Japan is completely unaffected.

Western Japan runs on 100v 60hz but Eastern Japan runs on 100v 50hz. This is due to a long complicated history dating back to the 1880s and Japan never unified it's power grid.

Because of that and due to the low number of power conversion stations, power from Western Japan cannot be sent to Eastern Japan in great numbers to be of any real assistance.