ステンレス鋼製再処理用機器へのカソード防食の適用性に関する研究

Abstract

An application of a cathodic protection method with an impressed current system to control the corrosion of austenitic stainless steel in a boiling nitric acid solution was studied to improve corrosion resistance and to extend the operation life of components in a fuel reprocessing plant. Plate-type specimens made of ultralow carbon type 304 stainless steel (SUS304ULC) were immersed in 3 mol·dm−3 boiling nitric acid solutions including 10 and 1.7 g·dm−3 vanadium ions. Electrochemical potentiostatic tests and cathodic protection tests were performed using electrochemical test cells. The selected protective potential was below the transition potential between the passive and trans-passive states based on anodic polarization measurement. Corrosion rates in the solution with and without the protection were measured by potentiostatic tests. Additionally, the outer surface of the tube-type specimen of SUS304ULC was studied under the same condition. From the obtained results, corrosion rates of plate-type specimens with cathodic protection were observed to decrease by 1/40 and 1/10 those of the specimens without cathodic protection in the solutions including 10 and 1.7 g·dm−3 vanadium ions, respectively. In the case of tube-type specimens, outer surface thickness loss was decreased from 24 to 3 μm by the protection, and platinum was chosen as the anode because it showed no corrosion loss like gold and no cracking like zirconium. Authors concluded that the cathodic protection method can be expected as one of the methods of maintaining components in a fuel reprocessing plant.