Sensitivity analysis of input parameters for pressure tube integrity evaluation

Pressure tubes in CANDU reactor are the most important components that contain fuel. The operating experiences show leaks and burst in pressure tubes over the past two decades. The integrity of pressure tubes is, therefore, key concern in CANDU reactor. Once a CANDU reactor put into operation, their integrity could be checked by in-service-inspection. However, comparing to the total number of pressure tubes in a CANDU reactor, only a small number of pressure tubes are selected for inspection, since there is no weld. The inspection scope and results have been treated so far using a deterministic approach. Taking into account the difficulty in inspection sampling and in extrapolating the results to the entire core, a probabilistic approach is necessary. In this study, probabilistic integrity assessments are carried out considering key factors, such as initial hydrogen concentration, defect shape, delayed hydride cracking (DHC) velocity and fracture toughness. The leak and failure probabilities are calculated as a function of time by applying Monte Carlo simulation.