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Corrosion of 316 SS in direct contact with Zircaloy-4 in repository relevant conditions.

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Title: Corrosion of 316 SS in direct contact with Zircaloy-4 in repository relevant conditions.
Authors: Nguyen, Steven1 (AUTHOR), Weber, Juliane1,2 (AUTHOR) weberj@ornl.gov, Zhang, Maximilian1 (AUTHOR), Caporuscio, Florie3 (AUTHOR), Migdissov, Artaches3 (AUTHOR), Rock, Marlena3 (AUTHOR), Finkeldei, Sarah1 (AUTHOR) sfinkeld@uci.edu
Source: Journal of Nuclear Materials. May2026, Vol. 627, pN.PAG-N.PAG. 1p.
Subjects: Stainless steel, Nuclear fuel claddings, Radioactive waste canisters, Corrosion & anti-corrosives, Electrolytic corrosion, Chromite, Phase equilibrium, Groundwater
Abstract: • Hydrothermal corrosion experiments using synthetic Mont Terri groundwater show increase in pH and lowering of redox potential as corrosion proceeds. • Consistency between experimental Mont Terri groundwater experiments and thermodynamic modeling suggest that corrosion of iron in 316 SS will control pH and redox potential of groundwater in case of waste canister failure. • Zircaloy-4 contact enhances the corrosion of 316 SS due to Chromite formed exclusively at interface between 316 SS and Zircaloy-4 at 250 °C. The effects of interfacial contact between 316 stainless steel (316 SS) waste canister and spent fuel cladding material (Zircaloy-4) in case of water intrusion into a deep geological repository are investigated. Hydrothermal corrosion experiments of 316 SS and Zircaloy-4 in direct contact were performed at elevated temperatures in MilliQ water and simulated Mont Terri groundwater. Hematite, magnetite, chromite, and baddeleyite form as secondary phases. pH of the Mont Terri solution increases with corrosion duration and magnetite forms preferentially instead of hematite. Thermodynamic modeling shows that iron oxidation in 316 SS controls the pH and redox potential of the aqueous environment and is in good agreement with experimental Mont Terri results, showing that experimental Mont Terri results trend to equilibrium. All oxides except hematite are predicted to exist at thermodynamic equilibrium based on calculations, implying that experimentally formed hematite will be reduced or transformed to magnetite at equilibrium. The thermodynamically predicted chromite was observed to form only at the interface where 316 SS was in contact with Zircaloy-4 at 250 °C, showing that contact with Zircaloy-4 seems to accelerate the 316 SS corrosion to thermodynamic equilibrium. In conclusion, Mont Terri groundwater readily trends towards thermodynamic equilibrium, leading to a pH and redox buffered system that is dominated by iron in solution coming from the accelerated corrosion of 316 SS caused by Zircaloy-4 contact. [Display omitted] [ABSTRACT FROM AUTHOR]
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Abstract:• Hydrothermal corrosion experiments using synthetic Mont Terri groundwater show increase in pH and lowering of redox potential as corrosion proceeds. • Consistency between experimental Mont Terri groundwater experiments and thermodynamic modeling suggest that corrosion of iron in 316 SS will control pH and redox potential of groundwater in case of waste canister failure. • Zircaloy-4 contact enhances the corrosion of 316 SS due to Chromite formed exclusively at interface between 316 SS and Zircaloy-4 at 250 °C. The effects of interfacial contact between 316 stainless steel (316 SS) waste canister and spent fuel cladding material (Zircaloy-4) in case of water intrusion into a deep geological repository are investigated. Hydrothermal corrosion experiments of 316 SS and Zircaloy-4 in direct contact were performed at elevated temperatures in MilliQ water and simulated Mont Terri groundwater. Hematite, magnetite, chromite, and baddeleyite form as secondary phases. pH of the Mont Terri solution increases with corrosion duration and magnetite forms preferentially instead of hematite. Thermodynamic modeling shows that iron oxidation in 316 SS controls the pH and redox potential of the aqueous environment and is in good agreement with experimental Mont Terri results, showing that experimental Mont Terri results trend to equilibrium. All oxides except hematite are predicted to exist at thermodynamic equilibrium based on calculations, implying that experimentally formed hematite will be reduced or transformed to magnetite at equilibrium. The thermodynamically predicted chromite was observed to form only at the interface where 316 SS was in contact with Zircaloy-4 at 250 °C, showing that contact with Zircaloy-4 seems to accelerate the 316 SS corrosion to thermodynamic equilibrium. In conclusion, Mont Terri groundwater readily trends towards thermodynamic equilibrium, leading to a pH and redox buffered system that is dominated by iron in solution coming from the accelerated corrosion of 316 SS caused by Zircaloy-4 contact. [Display omitted] [ABSTRACT FROM AUTHOR]
ISSN:00223115
DOI:10.1016/j.jnucmat.2026.156516