"Worst-case scenario builders consistently underestimate the statistical probability of separate bad things happening simultaneously, as the result of the same underlying causes."

So how is it, despite that sophistication, awareness, and preparedness, that the Fukshima Dai-ichi has nonetheless exceeded worst-case thinking? Here, the story is reminiscent of Three Mile Island and Chernob and the message seems to be the same: Worst-case scenario builders consistently underestimate the statistical probability of separate bad things happening simultaneously, as the result of the same underlying causes. As the TMI accident evolved, the nation was mesmerized by the buildup of hydrogen gas in the reactor vessel (a prospect no member of the general public had ever heard of before), and the danger of its exploding. Subsequent post mortems found, in addition, that a substantial fraction of the reactor core melted during the accident. Had it melted through the bottom of the vessel, vast amount of radioactivity would have found its way into the Susquehanna River and Chesapeake Bay, poisoning their waters permanently, for all practical purposes.

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