STP1529: In Situ Scanning Electron Microscope Observation and Finite Element Method Analysis of Delayed Hydride Cracking Propagation in Zircaloy-2 Fuel Cladding Tubes

    Kubo, Toshio
    Nippon Nuclear Fuel Development Co., Ltd., Oarai-machi, Ibaraki

    Muta, Hiroaki
    Osaka Univ., Suita, Osaka

    Yamanaka, Shinsuke
    Osaka Univ., Suita, Osaka

    Uno, Masayoshi
    Fukui Univ., Fukui-shi, Fukui

    Ogata, Keizo
    Japan Nuclear Energy Safety Organization, Minato-ku, Tokyo

    Pages: 33    Published: Apr 2012


    Abstract

    The objective of the present research is to build a modeling method for delayed hydride cracking (DHC) of zirconium alloys. DHC tests were carried out on Zircaloy-2 cladding tubes in the chamber of a scanning electron microscope to directly observe the crack propagation and measure the crack velocity in the radial direction. These in situ observations showed that a sharply tipped crack propagated at a relatively high rate, while the velocity decreased when the crack tip was blunted, supporting the occur-rence of intermittent crack propagation that could be expected from the DHC mechanism. V-KI curves or diagrams of crack velocity, V, versus stress intensity factor at a crack tip, KI, were obtained as a function of 0.2 % offset yield stress, hydride orientation, and pre-crack depth. The steady state crack velocity and the threshold stress intensity factor for the onset of the crack propagation tended to increase or decrease, respectively, with an increase in the 0.2 % offset yield stress. Analyses of stress distribution and hydrogen diffusion around a crack tip were made using a finite element computer code. The analyses showed that a strong hydrostatic pressure field was generated concentrically around the crack tip and hydrogen diffused towards the crack tip according to the hydrostatic pressure gradient. The crack velocity was estimated from the calculated hydrogen flux rate assuming the critical hydrogen quantity for the crack propagation. There was good agreement between the experiments and the calculations regarding the crack velocity and its dependency on KI. Calculations showed that the increase in the 0.2 % offset yield stress would accelerate the crack propagation by increasing the hydro-static pressure at the crack tip.

    Keywords:

    BWR, fuel cladding tube, Zircaloy-2, PCI, delayed hydride cracking, hydrogen diffusion, hydride, in situ observation, FEM analyses


    Paper ID: STP152920120018

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP152920120018


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