Effects of Temperature on the Corrosion Potential of Stainless Steel Under Gamma-Ray Irradiation

The structural materials of the instruments used in Fukushima Daiichi nuclear power station are exposed to the corrosive condition under the gamma-ray irradiation.  In order to determine the effects of the temperature of water under gamma-ray irradiation on the corrosion potential of stainless steel, the measurements of the corrosion potential under gamma-ray irradiation condition was performed.  The dissolved oxygen concentration was aerated condition in each temperature in this study.  And the corrosive condition under the irradiation was evaluated by the water radiolysis calculation and the measurements of the included hydrogen peroxide in the water after the irradiation.  As parameters, the temperature of water and the gamma-ray dose rate were changed.  The major results are listed as follows;

(1)     The corrosion potentials rose about 400 mV by the gamma-ray irradiation in all temperature conditions.

(2)     The potential was low with higher temperature under irradiation with the aerated condition.  It was assumed that the lower dissolved oxygen concentration with higher temperature will cause the dependency of the corrosion potential on the temperature under irradiation.

(3)     The generation of some ppm of hydrogen peroxide was confirmed by the measurements of hydrogen peroxide concentration.  It was indicated that the increase of the corrosion potential by the irradiation was caused by the generation of the high concentration of hydrogen peroxide. 

(4)     It was confirmed that the generation of hydrogen peroxide was lower in higher temperature condition due to the lower dissolved oxygen concentration in high temperature.  It was indicated that lower potential in high temperature water was caused by not only lower dissolved oxygen but also lower generation of hydrogen peroxide.