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Spent fuel rods immersed in water : what is inflammable?

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II
by eurogreen on Tue Mar 15th, 2011 at 06:36:00 AM EST
[ Parent ]
The water may have partially evaporated and exposed the Zirconium casing?

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
by Migeru (migeru at eurotrib dot com) on Tue Mar 15th, 2011 at 07:27:57 AM EST
[ Parent ]
There, too, the rods were reportedly partially out of water, and after all the hydrogen must have been generated due to overheating. As for what burned, after the explosion, it didn't have to be something inside the cooling pond, just inside the reactor building.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Mar 15th, 2011 at 07:49:26 AM EST
[ Parent ]
Depending on how "spent" the fuel rods are : they surely represent all the potential of a reactor meltdown, without the reactor casing to keep it in?

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

by eurogreen on Tue Mar 15th, 2011 at 07:58:25 AM EST
[ Parent ]
eurogreen:
Surely they must have non-trivial passive safety features at the spent fuel pools, but I'm not impressed yet.
Possibly not.

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

by Migeru (migeru at eurotrib dot com) on Tue Mar 15th, 2011 at 08:26:45 AM EST
[ Parent ]
For a description of a state-of-the-art spent fuel management programme, see Starvid's How Sweden deals with nuclear waste
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".


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
by Migeru (migeru at eurotrib dot com) on Tue Mar 15th, 2011 at 08:35:39 AM EST
[ Parent ]
Well, about the stage relevant here, we don't learn any details from Starvid:

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.


*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Mar 15th, 2011 at 08:39:44 AM EST
[ Parent ]
But that is an important detail: under normal operation, spent fuel is stored at the reactor for a year, presumably because it is too radioactive to handle to take off-site. I believe units 4-6 of DaiIchi were only recently shut down for maintenance and unit 3 had recently had its fuel replaced. So there may be a lot of very active spent fuel on site, in need of constant cooling.

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
by Migeru (migeru at eurotrib dot com) on Tue Mar 15th, 2011 at 08:44:08 AM EST
[ Parent ]
I believe one of the NYT articles wrote that "fortunately" the number of spent fuel in the storage pools was small. Will try to find the quote.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Mar 15th, 2011 at 08:48:27 AM EST
[ Parent ]
I failed to find the source; but downthread, ceebs is quoting another saying that while the spent fuel pool of the No. 5 and 6 reactors is only one third full, that of the No. 4 reactor is 100% full...

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Mar 15th, 2011 at 09:29:21 AM EST
[ Parent ]
It was a a comment on the Reuters site, but with no link to the actual source

Any idiot can face a crisis - it's day to day living that wears you out.
by ceebs (ceebs (at) eurotrib (dot) com) on Tue Mar 15th, 2011 at 09:54:53 AM EST
[ Parent ]
Zirconium is what surrounds the fuel.  It is used because it is strong at operating temperatures (the fuel, though formed into a ceramic, is not strong) and has low neutron absorption and therefore does not effect or interfere with the fission reactions.  The fuel rods are hollow tubes of zirconium alloy with pellets of fuel inside.  

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.

by Gaianne on Thu Mar 17th, 2011 at 02:18:23 AM EST
[ Parent ]
So Zirconium cooled with water is a fantastically stupid choice for spent fuel storage. Definitely not "passively safe storage".

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
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 03:43:52 AM EST
[ Parent ]

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