Corrosion of stainless steel in spent Cs adsorption tank containing salt

Kato, Chiaki   ; Sato, Tomonori  ; Yamagishi, Isao ; Arisaka, Makoto ; Terada, Atsuhiko  

Electrochemical test of stainless steel (SUS316L) in zeolite containing artificial seawater under gamma-ray irradiation as a basic study on the local corrosion generation conditions of the used adsorption tower used for contaminated water treatment at the Fukushima Daiichi Nuclear Power Plant Accident. In addition, a drying test using the second Cs adsorption tower (SARRY) mock-up was conducted to report the change of Cl concentration in the tower and to investigate the possibility of local corrosion in the used Cs adsorption tower. The steady natural immersion potential of stainless steel became noble by gamma irradiation, and the potential increased as the absorbed dose rate increased. On the other hand, in the zeolite coexisting system, the potential increase under gamma irradiation was suppressed. The mechanism of increasing the potential of stainless steel under gamma irradiation is that HO generated by radiation activates the cathode reaction of stainless steel and that the potential of zeolite decreases to suppress the formation of HO. Also, from the dry test of the mock-up specimen, as the temperature of the zeolite layer rises, the residual water is sucked up by the dry zeolite layer, so that the salt content of the residual water is precipitated in the heat generating part and the evaporated water condenses on the inner surface of the container. It was confirmed that the residual water Cl concentration decreased due to the heat generation in the adsorption tower, which was confirmed by the mock-up test specimen. It was expected as a mitigation measure.