Corrosion mitigation of structural materials by the photoelectric method in BWR

Hydrogen water chemistry and Noble metal chemical addition were applied to actual BWR plants to protect structural materials from IGSCC (InterGranular Stress Corrosion Cracking) so far. The important parameter of the susceptibility of IGSCC is the corrosion potential of the materials and the recommended value to mitigate IGSCC is reported as -230mV vs. SHE. In this paper, we discussed the other method to lower the corrosion potential below -230mV vs. SHE. Some n-type semiconductors are excited by photons irradiation and generate photoelectric current. The stainless steel coated with the semiconductor, therefore, has some possibility of shifting the corrosion potential in the negative direction under the photons irradiation. From the laboratory measurements under ultraviolet rays irradiation, the corrosion potential of stainless steel coated with TiO2 shifted in the negative direction by a few hundred mV. Evaluation of photon flux produced by Cherenkov radiation in the BWR are also carried out and the corrosion potentials of the stainless steel coated with TiO2 are estimated. (author)