STP1023: Enhanced Low-Temperature Oxidation of Zirconium Alloys Under Irradiation

    Cox, B
    Program consultant and metallurgical engineer, Chalk River Nuclear Laboratories, Chalk River, Ontario

    professor of nuclear engineering, University of Toronto, Toronto, Ontario

    Fidleris, V
    Program consultant and metallurgical engineer, Chalk River Nuclear Laboratories, Chalk River, Ontario

    Pages: 21    Published: Jan 1989


    Abstract

    The linear growth of relatively thick (>300 nm) interference-colored oxide films on zirconium alloy specimens exposed in the Advanced Test Reactor (ATR) coolant at ⩽55°C was unexpected. Initial ideas were that this was a photoconduction effect. Experiments to study photoconduction in thin anodic zirconium oxide (ZrO2) films in the laboratory were initiated to provide background data. It was found that, in the laboratory, provided a high electric field was maintained across the oxide during ultraviolet (UV) irradiation, enhanced growth of oxide occurred in the irradiated area. Similarly enhanced growth could be obtained on thin thermally formed oxide films that were immersed in an electrolyte with a high electric field superimposed. This enhanced growth was found to be caused by the development of porosity in the barrier oxide layer by an enhanced local dissolution and reprecipitation process during UV irradiation. Similar porosity was observed in the oxide films on the ATR specimens. Since it is not thought that a high electric field could have been present in this instance, localized dissolution of fast-neutron primary recoil tracks may be the operative mechanism. In all instances, the specimens attempt to maintain the normal barrier-layer oxide thickness, which causes the additional oxide growth. Similar mechanisms may have operated during the formation of thick loosely adherent, porous oxides in homogeneous reactor solutions under irradiation, and may be the cause of enhanced oxidation of zirconium alloys in high-temperature water-cooled reactors in some water chemistries.

    Keywords:

    zirconium alloys, oxidation, irradiation effects


    Paper ID: STP18869S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP18869S


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