Hydrogen Effects on Air Oxidation of Zirlo Alloy (NUREG/CR-6851, ANL-04/14)

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Publication Information

Manuscript Completed: August 2004
Date Published:
October 2004

Prepared by:
K. Natesan, W.K. Soppet
Argonne National Laboratory
9700 South Cass Avenue
Argonne, Illinois 60439

S. Basu, NRC Project Manager

Prepared for:
Division of Systems Analysis and Regulatory Effectiveness
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6512

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An experimental program was conducted to generate data on the air oxidation kinetics of unirradiated Zirlo cladding with preoxidation and prehydriding to simulate inventory of spent fuel discharge after a medium or high level of fuel burnup. The oxide layer on the cladding was formed by a preoxidation step in a steam environment for 140 h at 550°C, which resulted in an oxide thickness in the range of 25–30 µm. Prehydriding treatment was done by charging hydrogen to cladding and the process was tailored to produce hydrogen concentration in the range of 100–1000 wppm, typical of medium to high burnup cladding. The prehydrided and prehydrided/steam-preoxidized specimens were subsequently oxidized in air at temperatures in the range of 300–600°C. The maximum air oxidation times ranged between 300 h at 600°C and ≈1000 h at 300°C. Weight-change and oxide-thickness were measured on the specimens exposed at various times to establish the kinetics of the scaling process as a function of temperature. Extensive metallography and hardness measurements were performed on the tested specimens to examine the oxide scale development and hydrogen ingress into the material. Weight-change and oxide-thickness data, generated in the present program, were used to develop correlations to depict the air oxidation behavior of prehydrided alloys with and without steam preoxidation. A comparison of the oxidation data on Zirlo with and without prehydriding (performed in gas phase hydrogen and/or in steam) indicated that hydrogen concentration in the range of 100–1000 wppm had minimal effect on the Zirlo oxidation rate in air at temperatures in the range of 300–600°C.

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