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?)