This picture just appeared on Wikipedia, of which I am guessing is the building that may or may not be the one that possibly exploded. Maybe someone more knowledgable than myself can identify what the building is used for. The 2011 Sendai earthquake article says " the outer structure of reactor number 1's containment building had blown off, releasing a large cloud of dust and vapour."

http://en.wikipedia.org/wiki/File:2011-03-12_1800_NHK_S%C5%8...

http://en.wikipedia.org/wiki/2011_Sendai_earthquake_and_tsun...