Just a comment and some thoughts from somebody who is also neither a lawyer nor a legal scholar:

Article 17 of the same law mentioned by Paul J. Scalise, stipulates that in case of a situation described in article 3.1 (that is grave natural disaster or social disturbance) occurs, the state is responsible for compensating for damages. It looks like the government has already started to discuss the exact measures and the scope of compensations to be paid.

http://www.47news.jp/CN/201103/CN2011032001000542.html
http://www.jcp.or.jp/akahata/aik10/2011-03-29/201103290
2_03_1.html

The first of the articles above also argues that TEPCO also will not be able "to escape liability" but it does not explain on what legal grounds it can/will be held liable. Possibly it can be argued that the accident happened because of both the "grave natural disaster"
and TEPCO's negligence. Another possible line of argument that can lead to establishing TEPCO liability would be to argue that the damages sustained by the residents did not result from the accident per se but from TEPCO's failure to deal with it properly.

Yours,
Alexander Bukh
University of Tsukuba