The wall-thinning is one of the most important age-related degradation phenomena in nuclear piping, because several accidents of wall-thinned pipe failures have occurred. Furthermore, in recent years, several plants in Japan have experienced severe earthquakes. Therefore, failure probability analysis and fragility evaluation of piping systems, taking both wall-thinning and seismic response stresses into consideration, have become increasingly important in seismic probabilistic risk assessment.

In Japan Atomic Energy Agency, in order to evaluate the failure probability of aged pipes with wall-thinning, a probabilistic analysis code PASCAL-EC (Probabilistic Analysis of Structural Components in Aging LWR – considering Erosion Corrosion) has been developed. In this study, to evaluate the seismic fragility of a wall-thinned pipe, a model of seismic response stress considering the wall-thinning effect, a failure evaluation method for wall-thinned pipes, and functions related to uncertainties treatment have been introduced to PASCAL-EC. In this paper, the improved PASCAL-EC is outlined and preliminary results of the seismic fragility evaluation performed using this code are provided.

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