A Probabilistic Approach to Update The Lower Bound Fracture Toughness Using Surveillance Pressure Tube Data

Abstract

The fitness for service assessment of pressure tubes requires demonstrating that there is sufficient margin against the rupture of the pressure tube. The CSA-Standard N285.8 specifies a lower bound fracture toughness (Kc,) for zirconium alloy that would provide adequate protection against fracture. A probabilistic approach to establish the lower bound of Kc is desirable, since it can account for variability associated with Kc a population of pressure tubes. The paper presents a probabilistic interpretation of lower bound Kc, which encompasses both aleatory and epistemic uncertainties. The paper proposes a new method to update the lower bound Kc, as new data become available from the testing of surveillance pressure tubes removed from any reactor. The main advantage of the proposed approach is that it provides a practical, risk-informed basis for fracture toughness assessment of the pressure tube.