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Topic: Zirconium, vapour, hydrogen  (Read 4570 times)

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Offline Enthalpy

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Zirconium, vapour, hydrogen
« on: March 17, 2011, 04:14:14 PM »
Hello you all!

You guessed, said zirconium is the cladding of fissile fuel rods... Which produces hydrogen when not cooled properly and getting in contact with vapour.

First, could you confirm that this is a banal metal-water reaction, leading to metal oxide and hydrogen? Following a bizarre article in Wikipedia, many people imagine water being dissociated by moderate heat and staying dissociated until the mixture explodes, which would look like a double miracle to me.

Then, could this reaction be avoided if water were alkaline, for instance through a volatile amine? Or does PH rather play no role more at such temperatures, which I believe to be red hot? Could some other inhibitor be added to water?

Thanks!

Offline DevaDevil

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Re: Zirconium, vapour, hydrogen
« Reply #1 on: March 17, 2011, 04:28:43 PM »
ZrO2 + 4 H+ + 4 e- <--> Zr + 2 H2O, E0 = -1.43 V
2 H+ + 2e- <--> H2, E0 = 0V

So indeed for:

Zr + 2H2O <--> ZrO2 + 2 H2, Ecell0 = 1.43 V


Unfortunately for alkaline watery solution:
ZrO(OH)2 + H2O + 4e- <--> Zr + 4 OH-, E0 = -2.32 V


so this would not work.

Offline Enthalpy

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Re: Zirconium, vapour, hydrogen
« Reply #2 on: March 21, 2011, 09:02:22 PM »
Thank you!

Offline Enthalpy

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Re: Zirconium, vapour, hydrogen
« Reply #3 on: March 25, 2011, 04:11:28 PM »
Zirconium resists well corrosion by water thanks to its good oxide layer. But what if hot sea water is used? Most metals protected by the oxide (aluminium...) corrode even in cold sea water, because chlorine degrades the oxide layer. At Fukushima, sea water is even hot.

Worse, at least one zirconium chloride dissolves in water evolving hydrogen, which I understand as a catalytic action of salt for the ordinary metal-water reaction, right?

Could this explain the formation of hydrogen, in competition with the reaction of hot zirconium with vapour?

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