INTEGRATING PHYSICAL DEGRADATION MODELING WITHIN THE SEISMIC FRAGILITY ANALYSIS OF NUCLEAR POWER PLANT EQUIPMENT

摘要

In reality, the equipment properties are affected by physical degradation due to equipment usage, so that the actual seismic resistance (capacity) weakens with time. In this study, a physical modeling approach describing the equipment degradation progression with the equipment aging is integrated in a framework of time-dependent estimation of equipment fragility in the Seismic Probabilistic Safety Analysis (SPSA) of Nuclear Power Plants (NPPs), based on the conventional log-normal fragility model. Monte Carlo (MC) simulation is used to propagate the uncertainties affecting both the physical degradation process and the seismic fragility parameters. A piping system of a secondary cooling circuit of an experimental accelerator-driven system is taken as case study, wherein, a flow of an organic diathermic oil results in a gradual creep deformation process of the piping system.