The Feasibility of Using a Risk-informed Approach for Calculating Reactor Pressure Vessel Heatup and Cooldown Operating Curves

    Volume 4, Issue 9 (October 2007)

    ISSN: 1546-962X

    CODEN: JAIOAD

    Published Online: 20 September 2007

    Page Count: 11


    Gamble, Ron
    Sartrex Corporation Rockville, Maryland

    Server, William
    ATI Consulting, Pinehurst, North Carolina

    Carter, Robert
    Electric Power Research Institute, Charlotte, North Carolina

    (Received 27 June 2006; accepted 26 August 2007)

    Abstract

    The current procedures for calculating pressure-temperature (P/T) limits for normal reactor startup and shutdown are defined by deterministic fracture mechanics methodology in the ASME Code, Appendix G (in both Section XI and Section III). The recent pressurized thermal shock (PTS) re-evaluation effort used a very thorough probabilistic fracture mechanics (PFM) evaluation to develop a technical basis to increase the PTS screening criteria. The feasibility of applying this same PFM methodology to evaluate normal startup and shutdown operation for both pressurized water reactor (PWR) and boiling water reactor (BWR) pressure vessels is described in this paper. The approach taken in this study was to define a new risk-informed margin term to be applied to the stress intensity factor for membrane tension (KIm) in Appendix G. The margin on KIm was determined by finding the value that results in a vessel failure frequency equal to 106 failures/reactor-year when the reactor operates up to the pressure-temperature limits calculated using the risk-informed margin. This simple approach was selected because it results in a minimum change to the current ASME Code procedure, is easy to apply when revising plant operating P/T limits, and allows for an increase in the allowable P/T limits by as much as would be provided by any alternate procedure. The results from this initial study indicate the margin on KIm in Appendix G can be reduced from 2 to 1.5 for PWR vessels for shutdown and potentially reduced from 2 to as low as 1 for startup. The results indicate the margin on KIm in Appendix G can be reduced from 2 to approximately 1 for BWR vessels for shutdown and potentially startup. Additional analyses for PWR and BWR vessels will be needed to develop a comprehensive risk-informed basis for any revisions to the ASME Code, Appendix G.


    Paper ID: JAI100717

    DOI: 10.1520/JAI100717

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    Title The Feasibility of Using a Risk-informed Approach for Calculating Reactor Pressure Vessel Heatup and Cooldown Operating Curves
    Symposium 23rd Symposium on Effects of Radiation on Materials, 2006-06-15
    Committee E10