Gungyu Kim

1. The power system constitutes a fundamental component of modern infrastructure (Liu et al., 2025). Disruptions within power networks extend beyond temporary interruptions in electricity supply an...

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.

The reliability of the off‐site power system (OPS) during earthquakes is critical for the safety and recovery of nuclear power plants (NPPs). However, conventional seismic probabilistic safety assessments (SPSAs) have only considered the OPS in a limited way, leaving its impact inadequately evaluated. This study presents a system‐level safety assessment of the OPS at the Kori NPP. The results were integrated into the loss of essential power (LEP) event within the plant’s SPSA to analyze associated changes in risk. Sensitivity analysis identified key components that significantly influence network reliability, and path‐level evaluation highlighted vulnerable components and path characteristics. The results demonstrate that incorporating the OPS into LEP event assessment enables a more accurate evaluation of seismic risk. These findings provide quantitative evidence that can guide maintenance prioritization, assess the cost‐effectiveness of new substations and transmission paths, and inform seismic risk management strategies for the OPS.

Earthquakes affect not only nuclear power plants (NPPs) but also the surrounding infrastructure and essential response agencies. According to the emergency‐response procedures stipulated by the Nuclear Safety and Security Commission, organizations such as fire departments, police stations, local governments, and Korea Hydro and Nuclear Power (KHNP) support personnel are required to implement resident protection measures and facilitate nuclear‐accident recovery. This study derived quantitative indicators of earthquake‐induced damage conditions in the vicinity of NPPs. Focusing on the Hanul NPP site, scenarios were applied assuming safe shutdown earthquake levels of 0.2 g and 0.3 g, as well as the maximum possible earthquake magnitude in the Korean Peninsula (Mw 7.0). Using domestic attenuation relationships and building fragility curves based on spectral acceleration, the probabilities of building‐level damage and time‐dependent human casualties were estimated. The analysis indicated that as earthquake magnitude increases, damage to major public facilities—such as local government offices, fire stations, health centers, and hospitals—increases rapidly, reaching levels close to Extensive–Complete under the Mw 7.0 scenario. Widespread damage is also expected in KHNP residential complexes that accommodate nuclear plant personnel. Time‐of‐day analysis confirmed that residential facilities experience concentrated casualties at night (22:00–06:00), whereas office facilities show casualty concentration during daytime working hours. Building‐level assessments were performed to reflect Korea’s seismic characteristics and building fragility. Time‐dependent casualties and peak casualty occurrence periods were identified, and the vulnerability of support facilities directly involved in nuclear‐accident response was quantified. These results provide quantitative evidence to inform accident‐management and emergency‐response planning, serving as baseline data for enhancing the safety of communities surrounding NPPs.