Steven Carter wrote:
http://bravenewclimate.com/2011/03/13/fukushima-simple-explanation/best non-biased explanation I've read so far. The focus is this: the tsunami de-actiavted the diesel generators which would've kept the coolant system functioning after power was lost. There's no risk of meltdown--that term is way overused by the media--because the reaction has been stopped. It's venting/controlling/cooling the gases that is the issue. The solution is to configure a way by which on-site diesel generators can be installed so that they can (a) withstand a 9.0 earthquake and (b) be far enough off the ground not to be drowned in the potentially accompanying tsunami.
edit: Of course, as the facts have been hard to determine given the slow information flow from Japan, there's now this:
http://www.dailymail.co.uk/news/article-1367684/Nuclear-plant-chief-weeps-Japanese-finally-admit-radiation-leak-kill-people.htmlTo the engineers: Does the term "meltdown" have proper application when dealing with spent nuclear fuel (as in the reactor #4 scenario), as well as fuel in the reactor core?
The first link is a pretty good article, but based upon the "update" times at the bottom, it is a number of days old. So it doesn't cover much of what is happening now.
To your question about "meltdown", I am not a nuclear engineer, but I play one on this forum.
That article mentions this and it seems to be repeated a lot on TV that the term "meltdown" is not really a well defined term and can mean different things to different people. The bottom line is that if your cooling can't keep up with the amount of heat your product you run the risk of a failure of the cladding on the fuel. When the cladding fails you now are releasing radioactive elements. In the case of the Japanese plant this is happening in in the reactors and in the spent fuel pools. What most people think of as a "meltdown" is when this progresses to the point that fuel elements melt and create a lava like material (corium) that flows and worst case eats (via heat and chemical reaction) through the bottom of the reactor and in absolute worst case down into the ground with the resulting steam explosions and spreading of radioactive material!
With that said, I believe that most (all?) talk you will see about this type of meltdown is via a reactor core that can't be cooled. However the spent fuel area contains fuel that (if I understand this correctly) still radioactively hot (still reacting?) and needs to cool over a long period of time (years) before it can be removed from the pool. The pools contain water to transmit heat away from the fuel and to block radiation. Part of this blocking is to allow for people to work nearby, but also boric acid is disolved into this water to absorb neutrons (which slows reactions). I think you could envision a scenario (might be playing out in Japan right now) in which without the water and associated boric acid you can have spent fuel rods who might have a similar failure mode as described above in the reactor core. That the cladding fails, radioactive material is released and if criticality is achieved the heat could increase to the point that the fuel could then melt creating a meltdown scenario. Clearly the problem here is that there is no containment for the spent fuel pools. I think in the US they try to design fuel rods in such a way that in the case of a total loss of water in the spent fuel pools that they cladding will not fail. Also I think they try to arrange the rods in the pool in such a away that criticality can't be reached, but I have seen one mention somewhere that they will allow for some storage optimization techniques (aka try to pack it in tightly) in ways that increase the risk for criticality.
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Richard Casto
1972 Porsche 914
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http://motorsport.zyyz.comMoney can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.
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