Comment Re:already done (Score 3, Informative) 133
External events are considered in US plant design already, this author seems to be a bit ignorant on how the safety case for plants is built. Who cares if we refine the probability of an event is if the plant is already designed to withstand it?
Technically, the Fukushima plant was also already designed to withstand this type of event. It had sufficient backup power systems necessary to continue operating the cooling pumps in the event of a catastrophic disaster of this type.
Where they screwed up was in the redundancy of the backups. This is unfortunately a fairly common failure mode in engineering designs. Say a single diesel generator has a 10% chance of failing to start up if you try to run it during an emergency. People then naively think that if you just put 6 diesel generators into the design, then that reduces the statistical probability of failure to 1 in a million. The chance of all six generators failing is (10%)^6 = 1 in a million.
That's the correct math for generator failures due to independent internal causes. But everything changes when you talk about external causes. Suddenly you have a cause like, oh, say, a tsunmai, which can affect all the generators simultaneously. The failure mode for each generator is no longer independent, and your redundancy does nothing to decrease the odds of a failure. All they had to avoid this effect was put the generators and diesel fuel tanks in different places. But no, the typical Japanese obsession with order and symmetry* mandated that they put all their generators in a row in the same place. And the tsunami took them out and contaminated their fuel all at once. Indeed the two newer Fukushima reactors where the generators and fuel were stored in a different location got through the earthquake and tsunami just fine.
* I rag on the Japanese, but the same thing happened with the Space Shuttle Challenger. They were having problems with poor O-ring seals in the solid rocket boosters. So to reduce the probability of a failure, they just added more O-rings. That worked to stop the independent failures (burn-through due to improper seating of an O-ring in one spot). But when an external factor popped up which caused all O-rings to fail simultaneously (cold weather), the safety of the redundant O-rings was negated.