Corrosion sensitivity of 304 stainless steel to KOH vs. LiOH in nuclear pressurized water reactor water chemistry

Lithium hydroxide (LiOH) is currently used to control the pH of reactor coolant in pressurized water reactors (PWRs), helping to mitigate corrosion caused by boric acid added for reactivity control. However, the cost and demand for isotopically enriched Li-7 have risen significantly since 2015. Potassium hydroxide (KOH) is a promising alternative, being cost-effective and having a proven track record in VVER (Vodo-Vodyanoi Energetichesky Reaktor, Russian, for Water-Cooled Water-Moderated Reactor) reactors for over 40 years. This study investigates the corrosion behavior of 304 stainless steel in PWR-simulated environments with LiOH and KOH additions, under both normal operating and crevice water chemistry conditions. The cross-sectional oxide characterization was performed using transmission electron microscopy, diffraction analysis, secondary ion mass spectrometry, atom probe tomography, and electrochemical impedance spectroscopy. These advanced characterization techniques complement the more classical weight measurements. The sensitivity and corrosion behavior of 304 SS in chemistries with KOH vs. LiOH additions in PWRs are discussed. Comparative analysis reveals that, without the addition of external stress and irradiation, KOH does not degrade corrosion performance relative to LiOH at normal concentrations and may in fact improve resistance under crevice-like conditions, supporting its viability as a substitute in modern PWR coolant systems.