The very best analysis of the Fukushima incident currently available to civilians. Lengthy but well worth the read, and much more informative than the “sky is falling” rhetoric coming from the media.
It is not entirely clear yet what has happened, but this is the likely scenario: The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside). The problem is that at the high temperatures that the core had reached at this stage, water molecules can “disassociate” into oxygen and hydrogen – an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl. This was never a risk at Fukushima.
— Oehmen, Dr. Joseph. “You can Stop Worrying about a Radiation Disaster in Japan — Here’s Why.” Business Insider, 13 March 2011.
Read the whole thing.