Fukushima worries

7:30 last night ran a story on the possible next big problem at Fukushima:  one of the  fuel rod cooling pools appears to have been damaged, and if another large earthquake causes it to lose its water (sitting as it is high in a building), the exposed fuel rods would heat which may lead to a fire which may spread radioactive material far and wide.   The claim is that there is enough radioactivity there to cause the evacuation of Tokyo, if the wind was blowing the wrong way.

I haven't heard of the men making this claim, but they didn't exactly sound like Helen Caldicott types.  (Although there are her type around, including the Japanese Ambassador who featured on the story last night, even though his apparent over-the-top sounding claim that it has the potential to “destroy the world, the environment, and our civilization" didn't get a mention.)

Of course, one can go to some pro nuclear industry sites to read people who dismiss the danger.  This guy, for example, says (to paraphrase) "nah, Tepco says the pool is safe, and why wouldn't we trust them?  And besides which, the exposed fuel rods wouldn't cause a fire anyway."  Yet further down in comments someone says:

The risk of zircaloy fire in exposed fuel has been well documented for decades. Suggesting that it can't happen or that it's even unlikely is way out of bounds. This is especially true given your admission that the fuel in the unit 4 pool is relatively fresh. There's more than enough decay heat in the newer assemblies to melt them if they're exposed. Once that fuel goes molten the situation could easily spread to the other spent assemblies and result in a serious fire and release or even an excursion. You can't just wave this off. It's a real possibility if the pool is breached. I agree that it wouldn't be the planet killer that the doomsayers are calling it, but it would still be a level 7 incident in it's own right.

To which the response is:

 I think you've misinterpreted my position, here. I actually do think a failure in the structure of SP4 would be a very bad thing indeed, precisely for the reasons you indicate. I maintain my doubts about the zirc fire contingency, namely because outside of the freshest fuel, none of the fuel in the pool has sufficient heat to get anywhere close to this. Meanwhile, the "freshest" fuel is now a over year old - meaning the source term on the decay heat has decreased substantially. Again, I have provided my data for this, and you are free to check my assumptions.

 Suddenly his confidence about there being no possibility of a dangerous fire seems more equivocal.

 The most amazing thing about the story is this:   how silly is it to put a vital cooling pool 30 m in the air in a building in an earthquake zone?    I know Fukushima is old, and all, but really - what were the engineers who designed this thinking?

And yet when a disaster strikes, it's all "trust us - we're engineers".