"The probability of this occurring is hard to calculate primarily because of the possibility of what are called common-cause accidents, where the loss of offsite power and of onsite power are caused by the same thing. In this case, it was the earthquake and tsunami. So we're in uncharted territory, we're in a land where probability says we shouldn't be. And we're hoping that all of the barriers to release of radioactivity will not fail."

No, this is failure. You knew about common-cause accidents. You should not be

"hoping" that barriers will work, you should know this. A reactor is the most serious life

critical system, that which can affect many lives at once, like a dam or a plane.