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    STP1543

    Understanding the Drivers of In-Reactor Growth of β-Quenched Zircaloy-2 BWR Channels

    Published: 2014


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    Abstract

    The performance of boiling water reactor (BWR) fuel channels of standard and β-quenched Zircaloy-2 has been evaluated, aiming to determine the impact of β-quenching on in-reactor growth of channels. An extensive database of BWR fuel channel growth and bow from different reactors has been collected. Channel bow, driven by differential growth between opposite channel sides, is a key parameter for the safe performance of the fuel. Hot cell examinations have been performed on channels with burn-up between 45 and 60 MWd/kgU. Oxide thickness and hydrogen content measurements at different sides and elevations have been conducted, as well as metallography and high resolution transmission electron microscopy (TEM) work, including measurement of dislocation density and characterization of size, crystal structure and chemistry of second phase particles (SPPs). From the results of multiple inspection campaigns and hot cell examinations, the effects of texture and hydrogen uptake on in-reactor growth of channels are differentiated. The β-quenching heat treatment of Zircaloy-2 sheets is effective in considerably weakening the texture of the material, which in turn reduces bulk irradiation growth caused by anisotropic deformation of grains. The growth of β-quenched Zircaloy-2 channels has been found to be driven mainly by volume change caused by hydrogen uptake, which is essentially independent of texture, with a known relationship between hydrogen uptake and growth. Hydrogen uptake, and thereby in-reactor channel growth, accelerates in β-quenched material at certain fluence levels, and is linked to evolution of SPPs during irradiation. Zircaloy-2 is known to exhibit dissolution and amorphization of Fe–Cr rich particles, coupled with slower dissolution of Fe–Ni particles. In this study, the dissolution of SPPs of β-quenched Zircaloy-2 has been found to be faster relative to non-β-quenched material, which is associated to the hydrogen uptake late in life that drives the growth of channels with very weak texture.

    Keywords:

    beta-quenching, irradiation growth, hydrogen pickup


    Author Information:

    Romero, Javier
    Westinghouse Electric Company, Hopkins, SC29061

    Dahlbäck, Mats
    Westinghouse Electric Sweden AB, Västerås, SE

    Hallstadius, Lars
    Westinghouse Electric Sweden AB, Västerås, SE

    Ivermark, Maria
    Westinghouse Electric Sweden AB, Västerås, SE

    Ledergerber, Guido
    Kernkraftwerk Leibstadt AG,


    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP154320130020