A European multi-hazard assessment for Nuclear Power Plants with applications to other infrastructure types with operational time windows

Within the course of the EU project NARSIS (New Approach to Reactor Safety ImprovementS), sites of decommissioned nuclear power plants (NPPs) were investigated for external hazards using a multi-hazard approach.

The starting point was a review of existing multi-hazard frameworks, as well as their application to real world locations. From this knowledge, after significant screening, external hazards were analysed at different site locations in Europe using stochastic event sets for earthquake, flood, lightning, tornadoes, tsunami, hail and other perils in order to identify key scenarios along the hazard curves. These were built from existing national and supranational stochastic event sets.

The joint probability at each site of certain threshold events occurring was calculated, and relevant risk scenarios were chosen based on these hazard thresholds. Most importantly, the concept of joint operational time windows was investigated. Because the overall hazard for events is generally low, the chance of two low probability events is often screened out. However, during the damage and recovery window of these events (the operational time), the joint probabilities are much higher, thus affecting the infrastructure. Including the cascading effects, aftershocks, secondary effects and associated event sequences, provides a new insight into the probabilities of multi-hazard events and the implications for multi-risk.

Historical events from the loss database CATDAT and other records are chosen where joint operational time windows have occurred to show empirical examples of joint occurrences and cascades in the past for European and international examples.

Joint probabilities for significant events at decommissioned NPPs are presented within the NARSIS project and the application to multi-risk within Probabilistic Safety Assessments (PSA), however it is the application to other industrial types and infrastructure which shows the need for integration of multi-hazard (coinciding or cascading) events into operational management plans as well as important thought processes for building standards and use.