Implementing SPRA probabilistic fragility analysis of four typical nuclear structures

In this paper the procedures used and the results obtained in the Seismic Probabilistic Risk Assessment (SPRA) fragility analysis are presented for four typical structures that include three year enclosures and buildings, and a turbine building complex of a pressurized water reactor (PWR) nuclear power plant (NPP) located East of the Rocky Mountains. The major procedures include structural modeling, structural dynamic analysis, failure mode and strength capacity evaluation, determination of randomness and uncertainty parameters of variables involved, and the SPRA fragility and the medium High Confidence Low Probability of Failure (HCLPF50) calculation in terms of the peak ground acceleration (PGA). The three-dimensional (3-D) structural models developed have different features from each other including a fixed-base stick model of a reinforced concrete structure physically separated from a housed tank, a stick model of a reinforced concrete structure including the effects of the housed tank response and structure-foundation interaction (SFI), a fixed-base full size steel frame structure, and a stick model with a combination of reinforced concrete and steel frame members and including the SFI effects. The 3-D response spectrum dynamic analyses were performed directly on these structure models using the site specific free field 50th percentile Uniform Hazard Spectrum shape (UHS) based on a 10,000 year return period earthquake factored to a Review Level Earthquake (RLA) Zero Period Ground Acceleration (ZPGA) of 0.4 g. Different failure modes were evaluated using the associated failure criteria for the structure models. Some insights are expected from the typical application of the SPRA probabilistic fragility analysis of nuclear structures