The effect of pH agents on corrosion and low cycle fatigue behaviors of 316L stainless steel in boron-free small modular reactor environments

Recently, boron-free primary coolant environments have been incorporated into several small modular reactor (SMR) designs, replacing the typical pressurized water reactor (PWR) chemistry based on LiOH and boric acid. In these boron-free SMRs, KOH and NH₃ are considered as alternative pH control agents to replace LiOH. Nonetheless, austenitic stainless steels continue to be widely used as structural materials, as in PWRs, and thus, the assessment of corrosion-related damage in alternative pH agent environments is necessary. This study investigates the corrosion and low-cycle fatigue (LCF) behaviors of 316 L SS in boron-free SMR environments with KOH and NH₃. Results indicate that the corrosion and LCF behaviors of 316 L SS in these alternative pH agents are comparable to those in the PWR environment. The corrosion and crack tip oxide layer thickness vary between the two test environments, though the behavior of constituent elements remained similar. A comparison of microstructural and mechanical properties among the two tested environments, with the LiOH environment from the literature, is further discussed.