Example Calculations Illustrating Methods for Analyzing Ductile Flaw Stability in Nuclear Pressure Vessels

摘要

The report contains example calculations of ductile flaw instability stresses for hypothetical flaws in nuclear pressure vessels. For comparison, three different methods of estimating upper shelf toughness as a function of Charpy impact energy were used, namely: a power law R-curve correlation, the Rolfe-Novak correlation and the Paris J sub 50 correlation. All three methods were used in LEFM calculations including a plastic zone size correction, and gave similar results, with the Paris J sub 50 method being the most conservative at low Charpy upper shelf energy levels. Safety factors based on the tearing modulus ratio Tsub mat/T sup appl can exceed those based on load by considerable amounts and use of them at this time is not recommended. The use of resistance curve data obtained from actual vessel material test specimens is recommended over the use of correlations. Furthermore, evaluation of a recently proposed modified crack extension adjustment procedure for R-curve data, which is not overconservative, is recommended.