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Surely they must have non-trivial passive safety features at the spent fuel pools, but I'm not impressed yet. It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II
Surely they must have non-trivial passive safety features at the spent fuel pools, but I'm not impressed yet.
I presume that normally the reactor is shut down, cooled down, some time passes until the hotter fission products in the canisters decay, and then they are moved to the storage pools where they remain for a longer time until the remaining fission products are not too hot for handling by humans and then they're moved off-site.
But, throughout, the fuel rods are keept under active cooling, which has failed in this case. So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
Sweden is rather famous for being a country interested in environmental issues. It's rather less famous for being the world's biggest per capita consumer of nuclear power. These two things taken together results in the Swedish nuclear waste program, which has been called "the rolls-royce of nuclear waste programs".
European Tribune - ***How Sweden deals with nuclear waste
The fuel spends 5 years inside the reactor core until it is spent. It is now intensely radioactive and also gives off lots of heat. To make it easier to deal with it, the spent fuel is stored at the nuclear power plant for one year in cooling ponds filled with water. After one year 90 % of the radioactivity has diminished and the fuel is put in special transportation casks, loaded onto m/s Sigyn and shipped to Clab.
Zirconium oxidizes spontaneously. Normally this is good, as the oxide sticks to the zirconium as a tough protecting layer, much as aluminum instantly oxidizes to form the tough layer which is actually what you are looking at when you look at aluminum.
But. At high temperature the oxide of zirconium flakes away and the zirconium keeps burning. Also, the affinity of zirconium for oxygen is so fierce at high temperatures that zirconium will pull the oxygen out of steam (vaporized water) leaving hydrogen which will burn as soon as it meets more oxygen--which is presumably what fueled the several large explosions of reactor buildings.
At the "low" temperatures of normal operation (above the boiling point of water but well below the melting point of zirconium) ziconium is benign and stable, but at the high temperatures of a meltdown it is malign and burns uncontrollably.
Both zirconium and hydrogen release large amounts of heat when they burn. The Fates are kind.
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