혁신형 소형모듈원자로 무붕산 냉각수 환경에서 pH 조절제가 Alloy 690의 일반 부식거동에 미치는 영향 = Influence of pH agents on General Corrosion Behavior of Alloy 690 in Boron-Free Coolant Conditions of Innovative Small Modular Reactor

다국어 초록 (Multilingual Abstract)

The use of boric acid presents several limitations, such as the inability to control reactivity in real time, the induction of axial power offset, and the generation of liquid radioactive waste. To overcome these issues, an Innovative Small Modular Reactor (i-SMR) adopts boron-free water chemistry, enhancing system safety and reducing radioactive waste production. The absence of boron in the coolant chemistry also enables the consideration of alternative pH control agents instead of lithium hydroxide (LiOH). Among potential alternatives, potassium hydroxide (KOH) has been suggested as a promising candidate based on previous studies and thus it is essential to evaluate the corrosion behavior of Ni-based alloys in KOH environments. The immersion tests were performed to evaluate the corrosion behavior of Alloy 690 under water chemistry conditions of i-SMR. In both LiOH- and KOH- containing solutions, the formed oxide films showed polyhedral or rounded morphologies, showing no significant differences. From weight change measurements, the corrosion rate of Alloy 690 in LiOH-containing solutions was approximately 27% higher than that in KOH-containing solutions. Electrochemical corrosion tests conducted at ambient temperature and pressure produced results consistent with those of the immersion tests; LiOH-containing solutions showed higher corrosion current density and KOH-containing solutions a more stable film. Analyses of the solution properties were performed to identify the dominant factor governing the corrosion behavior in each solution. These results indicate that hydration-induced effects more strongly promote corrosion in LiOH-containing solutions, whereas the higher electrical conductivity of KOH-containing solutions is theoretically expected to enhance corrosion. Therefore, hydration-induced effects are identified as the dominant factor governing corrosion behavior under the conditions examined in this study.