According to Asahi Shinbun (in Japanese; 1:25AM JST 5/10/2011), TEPCO has started to mix "hydrazine" (N2H4) with the water that is being poured into the Spent Fuel Pools in Reactors 3 and 4 at Fukushima I Nuke Plant.
Hydrazine, I just learned, is:
... a colourless flammable liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia. However, hydrazine has physical properties that are closer to those of water.
Hydrazine is highly toxic and dangerously unstable, and is usually handled while in solution for safety reasons.
Hydrazine is used within both nuclear and conventional electrical power plant steam cycles to control concentrations of dissolved oxygen in an effort to reduce corrosion.
Corrosion? What is TEPCO afraid of that may corrode in the Spent Fuel Pools? The pools themselves? Racks? Fuel rod assembly? And why would they corrode?
(Where is Murphy?)
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5 comments:
Hydrazine is used in power plants to prevent corrosion during _normal operation_.
When high temperature (300C or more) hot water/steam is lead in piping even very small amount of dissolved oxygene results in corrosion on the internal walls of piping. This may cause leaks after period of operation (years). Hydrazine chemically bounds to dissolved oxygene and this way prevents corrosion.
I don't know why Tepco adds hydrazine to SFP but I don't think that the purpose is corrosion prevention.
Other facts about hydrazine (poisonois, carcinogene etc) are true.
My understanding is that salt water – the seawater used to cool the reactors during the disaster – is very corrosive to the extremely high-spec engineering of such plants.
Using seawater not only renders the reactors unviable, it also has the potential to weaken their structures significantly through corrosion.
For example, if there's another earthquake + tsunami event in the next few years, that is, before long-term decontamination and burial of the site have taken place, the reactors may lose even more integrity than they have already lost to date.
I suppose "Could the cooling system lose integrity totally because of corrosion?" is a question that has been asked, hence the use of hydrazine.
Let's hope it works.
Using oxygen scavengers to treat circulating hot water heating systems or boiler 'make up' water is routine because, as you note, oxygen rich water will attack iron and steel components. In this case I suspect it is the racks that hold the spent fuel rods.
Since TEPCO's normal cooling system for these spent fuel pools is broken they lose a large amount of water daily to evaporation. They have to 'make up' this loss with fresh water being sprayed in from above so that water is very oxygen rich and must be treated.
You ask "Where is Murphy?"
He is everywhere all the time, hence those awful fuel pool clips in your other post...
There is something elephantine missing in the public picture of the Fukushima disaster; something just not being admitted to. What is it? Who is involved? How can we find out?
Hydrazine strikes me as a drastic step for improving conductivity, as corrosion will have long since set in, starting with the tsunami - is there any parallel here with the insane use of Corexit in the Gulf of Mexico oil disaster?
joeb
Robbie001 sez:
I think the hydrazine is being used as a reducing agent to lower the free oxygen ratio below the level needed for a hydrogen explosion. Hydrazine generally produces nitrogen gas and H2O as a by product of reduction.
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