STP824: Characterization of ZrO2 Films Formed In-Reactor and Ex-Reactor to Study the Factors Contributing to the In-Reactor Waterside Corrosion of Zircaloy

    Stehle, H
    Division general manager, Fuel Element Laboratories, and senior consultant, Kraftwerk Union Aktiengesellschaft, Erlangen,

    Garzarolli, F
    Division general manager, Fuel Element Laboratories, and senior consultant, Kraftwerk Union Aktiengesellschaft, Erlangen,

    Garde, AM
    Principal development engineer and supervisor, Core Materials Development, Combustion Engineering, Inc., Windsor, Conn.

    Smerd, PG
    Principal development engineer and supervisor, Core Materials Development, Combustion Engineering, Inc., Windsor, Conn.

    Pages: 22    Published: Jan 1984


    Abstract

    An examination has been conducted of irradiated oxides which were formed during the waterside corrosion of Zircaloy-clad fuel rods operating in several pressurized-water reactors (PWR's), in order to understand the corrosion behavior. The structural integrity of the oxide layer was found to be excellent. The thermal conductivity remained high for oxides up to 70 μm thick.

    Scanning electron microscope (SEM) examinations revealed that the bulk of the oxide had a spherical, granular microstructure providing for interconnected porosity, mainly at the triple points. With the exception of the steam autoclaved specimens, a thin inner layer was detected close to the metal substrate; this inner layer had a microstructure which was difficult to resolve with the SEM. The in-reactor corrosion enhancement was greater for oxides which had a more pronounced granular appearance at the metal-oxide interface.

    Post-irradiation corrosion testing in autoclaves indicated a pronounced memory effect only for those specimens which previously had a high in-reactor enhancement.

    The analyses of potential impurities in the oxide gave no indication of a significant enrichment of any chemical species from the primary coolant water.

    The modest in-reactor corrosion enhancement observed in the PWR environment may be partly due to irradiation accelerated recrystallization of the oxide, especially at the inner layer, and partly due to changes in the corrosive medium present in the porous outer section of the oxide.

    Keywords:

    zirconium alloys, pressurized water reactors, waterside corrosion, microstructure of oxide layer, thermal conductivity of oxide layers, memory effect, impurities


    Paper ID: STP34487S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP34487S


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