Probabilistic mechanical assessment of ABWR feedwater piping to identify fractures using plant-specific parameters

Abstract

This paper firstly proposes a statistical framework for evaluating the structural integrity of the feedwater piping of an advanced boiling water reactor with ASME III Class I piping design specification, in order to confirm its operational reliability. The process initially involves a design stress reanalysis based on the pressure piping design requirements of Article NB-3600 for ASME III Class I components to determine the sustained and vibratory stresses at node points. Plant-specific parameters of the piping system, such as pipe geometries, static and dynamic (seismic and hydrodynamic) loads, and design transients, were taken from the original design report. Moreover, the accepted results of detailed forces and moments that were obtained from the design stress reanalysis were the input data for a probabilistic fracture mechanics analysis that considered the effects of design stress, crack distribution and inspections on pipe failures. Leak probabilities at individual piping weld joints due to the growth of pre-existing and initiated cracks by the typical aging degradation mechanisms of fatigue and stress corrosion cracking were predicted as a function of time. A numerical investigation proved that the results of two-step analyses agree quantitatively to a certain extent. Based on the assessment, the failure risk of piping system is clarified and can be regarded as the basis of relevant safety regulations and subsequent maintenance activities during the operation of a nuclear power plant.