I've seen a lot of people latch on to this writeup as authoritative, and I'm not sure why. Oehmen may indeed be a "research scientist" at MIT but his specialty is supply-chain risk management, not reactor design (http://web.mit.edu/oehmen/www/). Is there any reason to believe that he's anything more than an interested amateur on this topic?

The post has been moved, and updated by members of MIT's Nuclear Science and Engineering community: http://mitnse.com/2011/03/13/why-i-am-not-worried-about-japa...

Possibly relevant: http://geniusnow.com/2011/03/15/the-strange-case-of-josef-oe...