In German media [1] you can read, that it will be quite sure, that the nuclear station will explode an countermines a big zone like Tschnobyl. I would live a zone of minimum 200 km around the reactor Fukushima I.
[1]
Havarie an Japans Akws Fukushima I + II: Kühlung von 6 Reaktoren ausgefallen - taz.de