This study investigates the prestressed concrete containment vessel (PCCV) of the Qinshan Phase II nuclear power plant, focusing on the nonlinear thermo-mechanical coupling behavior and probabilistic safety evaluation of its load capacity under accident pressure conditions. An energy-based elastoplastic damage constitutive model for concrete at elevated temperatures was employed to develop a refined finite element model of the PCCV, comprehensively considering the effects of temperature gradients, material degradation, and thermo-mechanical coupling. Numerical simulation reveals the whole process of mechanical behaviour of the containment from elastic response, damage evolution to final failure. The results show that the stress concentration around the equipment opening was caused by the geometric discontinuity, which became the weak link of the structure and the first area of damage. To further quantify the influence of the variability in concrete strength, a stochastic damage response analysis was conducted based on the probability density evolution theory (PDET). The probabilistic evolution of damage and displacement responses at key locations was obtained, and the time-dependent reliability of the structure under different damage thresholds was evaluated. The results indicate that the randomness of concrete material strength significantly affects the damage propagation path and failure mode of the containment structure. The proposed analysis framework provides a theoretical and numerical foundation for risk assessment and reliability-based design of nuclear containment structures under accident conditions.
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