Entries in engineering (2)

Wednesday
Aug312011

FLY THE PLANE

I know it’s been a while since I’ve posted here, and I still don’t have a full post together.  But I would like to write briefly about a book I read recently, Atul Gawande’s The Checklist Manifesto.

In the book, Gawande advocates for the use of checklists as a means of improving outcomes in medicine.  He bases his analysis on three key cases:  The use of coordination checklists to ensure essential communication between the parts of a construction team, the use of “read-do” and “do-confirm” checklists (routine and contingency) in the airline industry (with a particular look at the case of US Airways Flight 1549, the recent “Miracle on the Hudson”), and the design and testing of the World Health Organization’s Safe Surgery Checklist.

The book is a great example of popular nonfiction:  The information is interesting, the narrative is compelling, and the argument is sound.  The tradeoffs involved in the WHO’s design process were also interesting to me as an engineer.  A checklist (in this use) isn’t an algorithm for amateurs, but a tool to help someone who already has a great deal of expertise.  The key is to identify the tasks where a reminder is of greatest benefit; maximize the product of the likelihood that a checklist item will avoid a task being missed by the magnitude of the consequences if it is overlooked.  Extremely high-level goals often end up omitted, since they won’t be forgotten in any case.  On the other hand, sometimes important things are easy to forget in crisis situations; the subject line of this post comes from a checklist for restarting a dead jet engine (the result, one hopes, of some embarassing simulator incidents).  When the tasks themselves are unknown, the key is identifying which communication tasks have the highest probability of identifying serious potential problems before they actually occur, so the risk can be mitagated.

If you’re intersted in medicine or engineering or like reading nonfiction in general, read it.

 

Monday
Mar142011

An Earthquake Energy Crisis

On Friday, Japan experienced the worst earthquake in its recorded history (in world history, the fifth largest since 1900).

One thing getting a lot of attention is the situation at Japan’s nuclear reactors.  11 plants were shut down in the aftermath of the quake.  However, generators one and three Fukushima I have encountering coolant problems post-shutdown, and hydrogen explosions (from vented coolant) have blown off the roofs of the generator buildings (note: not the reactor containment vessels).   There are also worries of a meltdown at Fukushima I-2 and reported problems with several generators Fukushima II.)

Fortunately, those were not problems with the shutdown procedure itself, all the reactors were brought sub-critical.  However, even with no fusion ongoing, the decay of existent radioactive isotopes releases enough heat to require a functioning coolant system for several days to prevent the fuel rods from melting.  (Which would be a disaster: Newer Boiling Water Reactors (BWRs) have tertiary containment designed to contain a full meltdown (a “core catcher”), Fukushima I predates that design.)  Unfortunately, venting of coolant steam during emergency cooling can result in the release of some radioisotopes: Some Cesium and Iodine (byproducts from the fuel rods if primary containment (cover on the fuel rods) is breached, Nitrogen-16 (from the oxygen in the water), Tritium (Hydrogen-3; from the decay of Boron-11 or Boron-12, from the boric acid used to suppress the fission reaction), and Carbon-14).

While some prognosticators are predicting none of the 11 reactors will come back online ever (which would mean really interesting things for Japan’s long-term energy situation), I’d bet that all but Fukushima I (and maybe II) will be up again after inspections and repairs.  But that’s “relatively quickly” in nuclear reactor terms, so that still means that 20% of Japan’s current generating capacity is offline for months at least.

Further reading:  Here’s a lengthy description of the sort of safety devices / procedures implemented at a BWR like the ones at Fukushima I.  And here’s a more detailed analysis of the situation at Fukushima I specifically (I can’t verify the author’s identity or expertise, but the article makes some interesting (and specific) predictions; his assumptions about the worst-case scenario are too optimistic, though the post has now been moved to here and edited for correctness).

ETA: I may yet be forced to eat my words.  Units 2 and 4 at Fukushima I have evidently also had explosions, and those have suffered actual breaches to the containment.  Unit 4 wasn’t running before the earthquake, but it’s still filled with spent fuel.  And unit 2 is probably in the middle of a partial meltdown with a ruptured containment vessel.

(Update again: Word now is that the inner reactor vessel is ruptured, not the outer containment.  The design goes something like this:  Fuel rod, casing, reactor vessel (the inner part of the “double boiler”), containment (the outer part of the “double boiler” and the last layer designed to hold in the core), building (not really designed to keep anything in, mostly there to keep the weather out).  The fuel rods and casings are almost certainly damaged in reactors 1-3, the reactor vessel is damaged in 2, and the building is damaged in 1 and 3.)

The disaster is currently rated at INES Level 4 (“accident with local consequences”). Three Mile Island was 5, Chernobyl was 7. Earlier today, Intrade gave 50%, 38%, and 13% odds that it will be raised to 5, 6, and 7, respectively, before the end of March.  Now those odds are at 95%, 46%, and 20%.