In spent nuclear fuel reprocessing, metal ions from dissolved fuel in nitric acid solutions act as oxidants, leading to intergranular corrosion of stainless-steel components. For the long-term use and the safe and stable operation of reprocessing equipment, it is essential to assess the corrosion state of these materials and accurately evaluate their lifespan. Advanced methods for calculating corrosion are therefore indispensable. However, due to the high radiation levels after reprocessing, direct observation of corrosion is challenging. Thus, the process requires a highly accurate method for predicting corrosion volume that accounts for the complexity of the reprocessing environment.
 In this study, experiments were conducted to simulate corrosion on the inner surface of a high-radioactive liquid waste concentrator, identified as the most susceptible to severe corrosion. The effects of operating conditions, such as oxidant concentration and boiling, on stainless steel corrosion were electrochemically investigated. A corrosion evaluation method that reflects actual operating conditions was also developed. As shown in Fig. 1ab, we replicated the corrosion state of the concentrator's inner surface. We propose that monitoring the following factors during the concentration process is essential, as they increase the corrosion reaction rate: rising nitric acid concentration in the solution, depressurized boiling, and the concentration of metal ions such as ruthenium, vanadium, and cerium.

Part of this work was performed under the contract research by Secretariat of Nuclear Regulation Authority, Japan