STP681: Chemical Interaction Between Uranium Oxide and Zircaloy-4 in the Temperature Range Between 900 and 1500°C

    Hofmann, P
    Senior scientists and metallurgists, Institut für Material- and Festkorperforschung, Projekt Nukleare Sicherheit, Kernforschungszentrum Karlsruhe, Karlsruhe,

    Politis, C
    Senior scientists and metallurgists, Institut für Material- and Festkorperforschung, Projekt Nukleare Sicherheit, Kernforschungszentrum Karlsruhe, Karlsruhe,

    Pages: 24    Published: Jan 1979


    Abstract

    Chemical interactions between the UO2 fuel and the Zircaloy-4 cladding material under power cooling mismatch (PCM) conditions are described. The out-of-pile uranium oxide (U02)/Zircaloy-4 reaction experiments were performed with short Zircaloy-4 tubular specimens filled with U02 pellets at temperatures between 900 and 1500°C under variable U02/Zircaloy-4 contact pressures and under inert gas conditions. The annealing periods varied between 3 and 60 min.

    Due to the thermodynamic instability between U02 and Zircaloy, U02 is partially reduced by Zircaloy at the high temperatures investigated. The extent of the UO2/Zircaloy reaction as well as the composition of phases depends decisively on whether a good solid contact between U02 and Zircaloy has been established. If a solid contact exists, a (U-Zr)-alloy rich in uranium and an oxygen stabilized α-Zr(O) phase are formed.

    The degree of chemical interaction between U02 and Zircaloy is determined by oxygen diffusion in the Zircaloy and the α-Zr(O)-phase formed. The UO2-Zircaloy reactions obey a parabolic rate law whose temperature dependence is given in the corresponding Arrhenius plot. The formation of oxygen-stabilized °-Zr(O) implies heavy embrittlement of the Zircaloy cladding above 1200°C. Thin oxide layers on the cladding tube inner surface prevent UO2/Zircaloy reactions from taking place below 1100°C. Simulated fission products (cesium, iodine, tellurium) in UO2 exert practically no influence on the extent of the reaction.

    A comparison of the out-of-pile test results with those of in-pile experiments exhibits a very good agreement with respect to the phases formed.

    Keywords:

    zirconium, zirconium alloys, power cooling mismatch condition, uranium oxide, fission products, chemical interactions, oxygen diffusion, Arrhenius plot


    Paper ID: STP36700S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP36700S


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