Progress and case study on probabilistic assessment of reactor pressure vessels under pressurized thermal shock

Abstract

A certain type of transients may cause the pressurized thermal shock (PTS) in the reactor pressure vessels (RPV) in pressurized water reactors (PWR) and may result in problem of structural integrity of RPV with flaws. The structural integrity assessment methods for RPV under PTS conditions are reviewed. The research progress and situation about these methods, especially probabilistic assessment, are introduced. Probabilistic assessment which uses the probabilistic fracture mechanics (PFM) analysis approach is reviewed, including uncertainty analysis (probability of detection, flaw characterization models, fracture property data, et al.), numerical calculating method on the failure probability, et al. Main PFM computational computer codes for PTS are evaluated. A PFM program is developed to calculate the failure probability. Two typical PTS transients for RPV and their structural integrities are analyzed. The results show that the failure probability for the RPV under these PTS transients is lower than the required value of nuclear safety for the design life of 60 years. Combined with Chinese nuclear power development, a few pieces of advices are proposed for probabilistic assessment of RPV structural integrity under PTS transients.