Risk-Consistent Vertical Ground Motion Spectra for Seismic Probabilistic Risk Assessment

September 13, 2019
Publication: 25th Conference on Structural Mechanics in Reactor Technology

Seismic Probabilistic Risk Assessment (SPRA) of nuclear power plants (NPPs) is typically performed using three major analysis components: probabilistic seismic hazard, seismic fragility, and plant response analyses. The seismic hazard output is used to construct a Reference Earthquake (RE) ground motion spectrum for seismic response analysis in the horizontal and vertical directions. The seismic response analysis develops the probability distributions of the RE seismic demands on the plant structures, systems, and components (SSCs). The seismic fragility analysis combines the RE demands with the probability distributions of the individual SSC seismic capacities to develop conditional probabilities of failure given the ground motion level. The plant response analysis combines the seismic fragilities of the SSCs into a single plant-level fragility. The seismic hazard curve is convolved with the plant-level fragility to quantify seismic risk, e.g., for core damage or large early release. The seismic hazard curve for a single “reference” ground motion parameter is typically used in the quantification. The reference ground motion parameter is often the horizontal peak ground acceleration (PGA) or sometimes the horizontal spectral acceleration (Sa) at a natural frequency that dominates the seismic responses of the SSCs that drive the risk. The outcome of the convolution integral is insensitive to the selection of this parameter if the slopes of the hazard curves for the range of applicable parameters are equal at return periods adjacent to the RE ground motion level. The seismic responses of the risk-dominant SSCs are typically considered to increase linearly with the reference ground motion parameter magnitude in the vicinity of the RE.

Markets: Nuclear