Following the Fukushima accident and subsequent EU Stress Test, the Swiss regulatory authority ENSI mandated all Swiss nuclear power plants, including the Nuclear Power Plant Leibstadt (KKL), to conduct comprehensive hazard assessments for extreme meteorological events with return periods 1,000 year and 10,000 years. These analyses are subject to regular updates and must utilize state-of-the-art scientific methods.
In response, KKL recently updated the hazard analysis by applying advanced methods and a fully automated workflow to assess meteorological hazards such as extreme air and river temperatures, wind gusts, rain- and snowfall, and snow load.
Considering regulatory requirements, these hazards were evaluated using extreme value statistics. KKL applied the block maxima method due to its simplicity and easier automation compared to peaks-over-threshold, enabling reliable extrapolation to rare events given sufficient high-quality data.
To ensure robust regional representation, weather data from multiple stations, including other Swiss NPP sites, were systematically selected and evaluated. Custom scripts automated the entire process, from data preparation to hazard curve visualization, supporting users through model checks and addressing numerical challenges not adequately solved by standard tools. Seasonal variations were modelled using truncated Fourier series, and parameter estimation relied on Maximum Likelihood, with model validation achieved via likelihood ratio tests and simulated series comparisons. Confidence intervals for hazard curves were derived by parametric bootstrapping.
Climate change impacts were integrated into the assessment by including a linear trend in the model and by interpolating a pessimistic climate scenario (RCP8.5). Conservative projections were ensured by applying the more adverse of the two trend estimates.
The derived return level estimates provide a sound, transparent basis for deterministic and probabilistic safety analyses at KKL, fully aligned with the latest regulatory requirements.
Beyond hazard analysis, KKL’s climate resilience strategy comprises continuous plant improvements and adaptation measures. Over the past decade, the plant has systematically implemented technical upgrades, including aerodynamic modifications to the cooling tower, main condenser renewal, replacement of critical chillers, and stepwise digitalization and qualification of safety I instrumentation and control systems.
Operational experience has shown that, since the main condenser renewal in 2021, no power reductions due to high temperatures have been necessary. The plant maintains stable and redundant cooling by taking advantage of regulated Rhine water levels and robust groundwater cooling systems, while site elevation ensures a dry site concept.
Online weather information, enhanced monitoring, adaptive operational procedures, and specific countermeasures for all identified extreme weather scenarios further strengthen the plant resilience.
Operational experience has shown minimal impact of climate change on KKL systems to date, with no recorded weather-induced SCRAMs or I&C failures. Ongoing monitoring and renewal projects position KKL to sustain a high level of resilience and safe operation in the face of evolving climate challenges, aligned with the most recent regulatory requirements.
The resilience strategy at KKL encompasses also regular reassessment of hazards and vulnerabilities, seasonal readiness measures, staff training, preventive maintenance, and routine emergency preparedness drills. Real-time situational awareness, ongoing learning, and effective communication and risk management processes support long-term safe operation and regulatory compliance. This systematic and proactive approach is further enhanced by active participation and collaboration in national and international expert networks, research projects, and working groups. Engagement in these activities ensures access to the latest developments and best practices, while also contributing valuable operational experience—thus further strengthening climate resilience and preparedness for both current and future climate challenges.