Formation of UO2 on stainless steel 316 corroded in NaCl-KCl-UClx (x = 3,4) salts: Effect of crucible material

Stainless steel 316 was corroded in high temperature NaCl-KCl-UCl x (x = 3,4) salts to investigate the effect of uranium-containing salts. The NaCl-KCl-UCl x salts were prepared through the electrochemical oxidation of uranium rods. The ratio of UCl 3 and UCl 4 in the UCl x salts was determined by X-ray absorption near-edge structure (XANES) analysis. The presence of UCl 4 was further confirmed by the accelerated corrosion behaviors depending on the UCl x concentration. After exposing stainless steel 316 to NaCl-KCl-UCl x salts at 750 °C for 100 h using alumina , boron nitride , and glassy carbon crucibles, UO 2 was formed on the surface in various forms, such as layers and/or particles. Additional corrosion experiments with NaCl-KCl-UCl x -BaO salts were conducted to investigate the UO 2 formation mechanisms. Results indicate that UO 2 formation occurs via two pathways: reactions between salts and stainless steel 316 or deposition of UO 2 formed in the salts. Regardless of how it forms, it is evident that UCl 3 and UCl 4 can produce UO 2 through reactions with oxygen-related compounds (oxides, O 2- , O 2 ). The formation of UO 2 can mitigate chromium depletion, but the precipitation of UO 2 may lead to additional challenges. This study suggests the importance of both crucible selections for U-containing molten salt corrosion experiments and the consideration of UO 2 formation in molten salt reactor environments.