Probabilistic fracture mechanics application of dynamic crack arrest by static analogy

This paper reports that the CE/EPRI Crack Arrest Algorithm is designed to predict the arrest behavior of rapidly extending cracks in reactor vessel steels. It is based on a series of tests performed by Combustion Engineering, Inc., where the dynamic behavior of flaws was investigated as these flaws extended into regions of tougher material. These tests demonstrated that the instantaneous stress intensity at the crack tip controlled arrest behavior. This stress intensity depends on the dynamic response of the vessel to the crack extension, and is significantly smaller than the stress intensity calculated for a static flaw of the same size. Thus arrest is much more likely than is predicted by conventional static methods. The new algorithm was incorporated into a computer program designed to perform probabilistic fracture mechanics analysis of PWR reactor vessels. The probabilistic analysis was used to compare the static and CE/EPRI (Static Analogy) crack arrest method for a wide range of transient events. The results show that where tougher material conditions (warmer metal) exist deeper in the wall, the Static Analogy method shows failure probabilities considerably lower than calculated using the static arrest models