Thermodynamic evaluation on effect of sea water to degraded nuclear fuel in severe accident of LWR

In the Fukushima-Daiichi nuclear power plant accident, a large amount of sea water was introduced into reactor pressure vessels. Not only sodium chloride but also several minor elements contained in sea water, such as K, Ca, Mg, and S, possibly reacted with degraded fuel debris or molten corium. Considering possible chemical reactions, various concerns, such as volatilization of fission products, characterization of fuel debris, and formation of corrosive gases are pointed out. Thermodynamic evaluation can give useful information on the general tendency of these sea-water effects. The volatility of Cs, Sr, and Te is potentially increased owing to the change in stable chemical species. Corrosive gases, such as HCl and H₂S, are possibly generated from sea water heated at high temperatures. These phenomena are predicted to be varied by changing the oxygen potential. (author)