Piping reliability analysis of AHWR down-comer piping using PFM

Abstract

Probabilistic Fracture Mechanics (PFM) is widely used for the reliability assessment of Nuclear Power Plant (NPP) piping. In PFM, the methods of fracture mechanics and structural reliability theory are combined for assessing the reliability of components, which contain cracks. In this work, reliability assessment of Advanced Heavy Water Reactor (AHWR) down-comer piping is done using PFM. AHWR down-comer piping is made up of SS304LN material. Monte Carlo technique with spherical subset simulation is used for reliability estimation. Crack initiation in pipes because of Inter-Granular Stress Corrosion Cracking (IGSCC) is modelled. These crack growth during the lifetime of the plant due to the fatigue loading and IGSCC is also modelled. The limit state considered is through wall crack (leak) and rupture (break) of the piping. Uncertainty in material sensitization, crack growth rate, length of crack, is considered in this analysis. Computer code is developed which uses Spherical stratification technique for the reliability estimation. Leak probability at the end of life of reactor (after 100 years) is estimated as 2.25×10−6 and break probability is estimated as 1.58×10−9.