Japan Nuclear Accident: Worse than Worst, Again

[pokerfan]

"Worst-case scenario builders consistently underestimate the statistical probability of separate bad things happening simultaneously, as the result of the same underlying causes. <...> Actually, ever major nuclear accident has been worse than worst case, and that's a fact every nuclear advocate--this one included--will have to take into account. As we learned in the global financial crisis as well, instrument and devices thought of as separate entities can all "go south" as the result of a single underlying cause, upending estimates of how likely any one failure would be."

http://spectrum.ieee.org/energywise/energy/nuclear/japan-nuclear-accident-worse-than-worst-again">Japan Nuclear Accident: Worse than Worst, Again - IEEE Spectrum

[Demeter]

1. I rest my case

[Tansy_Gold]

5. Ditto. n/t

[Wilms]

2. Sea water drowns a diesel generator and this is what happens.

Talk about failure modes. Seems more like a failure of imagination.

It could turn out that elevating the diesels by 10-15 feet could have averted this situation. And I have little doubt that was suggested...probably by someone who sits alone in the lunchroom.

[roamer65]

3. ...or was fired for being "uncooperative and argumentative" at team meetings.

[Wilms]

4. Precisely. n/t

[Old and In the Way]

7. Could have mounted them on the roof of the containment buildings.

A failure of imagination indeed. You'd think when they were gaming 'worst case scenario's' that problem might have been considered.

[enough]

6. Having lived through TMI downwind, I was especially interested in these two paragraphs:

snip>

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.

In Chernobyl, a peculiar design feature that the general public had never heard of--a positive reactivity void coefficient--caused first one explosion and then, very likely, a second. Such explosions supposedly couldn't happen in nuclear reactors, but it turned out they could in some types. Water flashing to steam had caused reactivity to escalate (the positive feedback loop from water voiding), prompting more water to flash to steam, leading to more overpower, etc. In addition, overpressure from the boiling waters in the cooling pipes lifted the top of the poorly designed reactor vessel, rupturing all pipes and control-rod systems, putting the reactor completely out of control. It was, as major reports done by various national and international authorities would later put it, a "worse than worst-case accident."

snip>