Fragility analysis and probabilistic performance evaluation of nuclear containment structure subjected to internal pressure

Abstract

Based on the detailed three-dimensional finite element model of the nuclear containment structure, this study presents fragility analysis and probabilistic performance evaluation of the nuclear containment structure subjected to internal pressure. To realize automatic running of nonlinear finite element analysis of the nuclear containment structure, Python and Matlab scripts are developed. Confidence intervals of fragility parameters are estimated by the statistical inference method and bootstrap method. An analytical method for constructing the confidence interval of the fragility curve is proposed in this study, and confidence interval of the fragility curve predicted by the proposed method is compared with the bootstrap method. Moreover, statistics of the cumulative failure probability of the nuclear containment structure are estimated by bootstrap method and the proposed Taylor series expansion method . Finally, probabilistic safety margins of the nuclear containment structure are evaluated by the median value method and confidence interval method. Results indicate that statistical uncertainty has almost no effect on the mean value of the fragility parameters. However, statistical uncertainty has some effects on the variability of the fragility parameterβS. In general, the influence of statistical uncertainty on fragility parameterβSis greater than that of fragility parameterPm. Confidence intervals of Pm estimated by the statistical inference method and bootstrap method are almost the same, and statistical inference method overestimates the confidence interval of fragility parameterβS. The proposed method for constructing confidence interval provides almost the same prediction of the confidence interval of the fragility curve as the bootstrap method. In general, statistics of the cumulative failure probability of the nuclear containment structure calculated by the bootstrap method and the proposed Taylor series expansion method are almost the same. The difference between the safety margin calculated by the median value method and the safety margin with 95% confidence level calculated by confidence interval method is negligible.