Probabilistic Safety Assessment of the Off-Site Power System of the Kori Nuclear Power Plant Against Typhoon-Induced High Winds Considering Korean Transmission Tower Fragility

As climate change increases typhoon intensity and frequency, typhoon-induced high winds increasingly threaten nuclear power plant (NPP) safety by disrupting off-site power systems. Previous probabilistic safety assessments (PSAs) evaluated this risk using transmission tower fragility models derived from high-wind fragility equations developed for NPP structures, systems, and components. However, these models do not adequately reflect the structural characteristics of Korean transmission towers. In this study, a PSA of the off-site power system at the Kori NPP site under typhoon-induced high winds was performed using a universal voltage-class-based fragility model developed for Korean transmission towers. To isolate the effect of the fragility model on risk estimates, the typhoon hazard, network, and damage correlation conditions were set identically to those adopted in previous research. The Korean universal fragility model produced a higher median wind speed but a lower high-confidence-of-low-probability-of-failure capacity, resulting in an increase in the estimated annual risk. Because the lower HCLPF extends the probability of damage to lower wind speeds, which occur more frequently, the annual risk increases despite the greater median capacity. The risk-contribution analysis showed that the overall risk was governed by the overlap between the 0–50% range of the fragility curve and the hazard below its 100-year return period, rather than by the median failure wind speed. The analysis further demonstrated that the choice of logarithmic standard deviation shifts the governing wind-speed range. Therefore, realistic assessments require fragility models developed specifically for Korean transmission towers. These findings provide a quantitative basis for estimating the frequency of loss of off-site power events at NPPs, thereby contributing to resilient and sustainable infrastructure management.