STP918

    Cracking at Nozzle Corners in the Nuclear Pressure Vessel Industry

    Published: Jan 1986


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    Abstract

    Cracks in nozzle corners at the pressure boundary of nuclear reactors have been frequently observed in service. These cracks tend to form with radial orientations with respect to the nozzle central axis and are believed to be initiated by thermal shock. However, their growth is believed to be primarily due to a steady plus a fluctuating internal pressure. Due to the impracticality of fracture testing of full-scale models, the Oak Ridge National Laboratory instituted the use of an intermediate test vessel (ITV) for use in fracture testing which had the same wall thickness and nozzle size as the prototype but significantly reduced overall length and diameter. In order to determine whether or not these ITVs could provide realistic data for full-scale reactor vessels, laboratory models of full-scale boiling water reactors and ITVs were constructed and tested. After briefly reviewing the laboratory testing and correlating results with service experience, results obtained will be used to draw some general conclusions regarding the stable growth of nonplanar cracks with curved crack fronts which are the most common precursors to fracture of pressure vessel components near junctures. Use of linear elastic fracture mechanics is made in determining stress-intensity distributions along the crack fronts.

    Keywords:

    stress intensity factors, nuclear pressure vessels, nozzle corner cracks, intermediate test vessels, boiling water reactors, photoelasticity


    Author Information:

    Smith, CW
    Alumni professor, Virginia Polytechnic Institute and State University, Blacksburg, VA


    Paper ID: STP19325S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP19325S


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