2017 Volume 66 Issue 2 Pages 62-70
Concentration of SO42－ and HCO3－ which affect to corrosion for carbon steels were estimated by analysis using pH, Cl－ concentration and electrical conductivity κ, in the spent fuel pools （SFP） of Fukushima Daiichi Nuclear Power Station （1F） in which sea water and/or fresh water were injected. Electrical conductivity κ in the SFP of 1F Unit 1 in which fresh water was injected, were presumed accurately by analysis using observed Cl－ concentration, concentration of SO42－ and HCO3－ which were estimated. The pH measurements exceeded the estimate in 1F Units 2 and 3 where sea water was injected. Each of dissolution reaction of iron, dissociation of H4N2, and the production of ammonia by the decomposition of H4N2 has been evaluated as not the cause of the high pH by itself. It was estimated that the calcium ions from the concrete debris had been continuously supplied to water in SFP of the unit 3 during purification treatment period. It was evaluated that self-passivation conditions of carbon steel were achieved in the water chemistry after the purification process completed for the Fukushima Daiichi Nuclear Power Station of Units 2 to 4. In addition, it was evaluated that self-passivation of carbon steel was achieved in the environment of unit 1.
