Technical Basis For Revised P-T Limit Curve Methodology

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ABSTRACT The heatup and cooldown processes for an operating nuclear plant are controlled by pressure-temperature (P-T) limit curves, which are developed based on fracture mechanics analysis. These limits are developed according to Appendix G of the ASME Boiler and Pressure Vessel Code, Section Xl, and incorporate a number of safety margins. A key safety margin is the lower bound fracture toughness curve, or K IA (equivalent to K IR ). Based on the work described in this technical basis paper, Section XI recently approved Code Case N-640 permitting the use of the lower bound static fracture toughness curve, K IC , for calculating operating P-T limit curves. The same change appears in Appendix G of Section XI in the 1999 Addenda. There are two lower bound fracture toughness curves available in Section Xl: K IA , which is a lower bound on all static, dynamic and arrest fracture toughness, and K IC , which is a lower bound on static fracture toughness only. Code Case N-640 changes the fracture toug...

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    ABSTRACT: The question, where can the generation of new material property data reduce overly conservative design in reactor systems, presently exists in the nuclear industry. The question is answered by identifying where conservatism exists relative to determining material property variations. Several areas are reviewed to identify conservatism and the sensitivity of structural integrity evaluation results to the property variations. The areas reviewed were fluence dependence of the transition temperature, fracture toughness, the drop in upper shelf toughness, the arrest toughness, the material thermal properties, and the fatigue crack growth rate.
    Journal of Testing and Evaluation 01/1978; 6(5). DOI:10.1520/JTE10566J · 0.38 Impact Factor


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