Corrosion Behavior of SS316H in Non-isothermal Fluoride Fuel Salt

Abstract

This study investigates the impact of thermally driven mass transfer on the corrosion behavior of SS316H in molten NaF-BeF₂-UF₄-ZrF₄ salt using a static, non-isothermal system. A vertical temperature gradient from 717 °C (bottom) to 634 °C (top) was established over 6.5 inches without a forced salt circulation. SS316H samples were placed at heights of 0, 3, and 6.5 inches and exposed for 5, 10, and 15 days. Despite the absence of forced convection, significant mass transfer effects were observed. The hottest sample exhibited the greatest chromium depletion, while cooler regions showed less. Metallic deposition occurred on colder samples and in the surrounding salt, indicating directional transport driven by the thermal gradient. These results demonstrate that thermal gradients alone can induce notable corrosion-related mass transfer, challenging the conventional reliance on thermal convection loops. This highlights the need to consider temperature-driven mass transport in evaluating materials for molten salt reactor environments.