Main lessons learned from the Clearinghouse topical operational experience report (TOER) on external hazards and their possible use for the design of new reactors

The European Network on Operating Experience Feedback (OEF) for Nuclear Power Plants, or 'European Clearinghouse' (CH), was established by European nuclear safety regulators to promote the regional sharing of operating experience, the dissemination of lessons learned from nuclear power plants operation, and the understanding of the role of OEF systems in the safe and reliable operation of NPPs. In the frame of the CH, a consortium constituted of GRS, IRSN and SÚRO performed an in-depth analysis of events related to external hazards that occurred or were reported during the period between 2017 and 2020 for external flooding events, and the period between 2010 and 2020 for the other external hazards events. Those events were selected either from the IRS database or from the national databases VERA, SAPIDE and DBEvents respectively; they were divided in nine groups: - Group 1: extreme weather conditions; - Group 2: external flooding; - Group 3: earthquakes; - Group 4: external fires; - Group 5: lightning strikes; - Group 6: fouling events with fouling of water intake entrance and biofouling caused by external environment; - Group 7: chemical events comprising corrosion caused by external environment and chemical fouling caused by external environment; - Group 8: man-induced events with effects of nearby industries (river/sea traffic hazards, air traffic hazards, road traffic hazards, fire and explosion as well as working in NPP vicinity); - Group 9: other, including solar magnetic disturbances. Indicative statistical analyses were performed with respect to the number of events of each group, the relative distribution by mode of event detection, the relative distribution of the safety relevance, and the relative distribution of the systems affected. However, the most important part of the indepth analysis was the derivation of high-level lessons learned, which were derived from the most important events in the respective groups. To support or justify those high-level lessons learned, the relevant events were described in detail to illustrate the recommended actions including their purposes. In addition, the actual (observed) consequences motivating the recommended action were provided based on event specific causes or lessons learned. For each event group, the related recommendations have been assigned to 4 groups: (1) prediction and monitoring; (2) design and equipment related features; (3) procedures and training; and (4) review and management. The paper aims at summarizing the main lessons learned from the Clearinghouse TOER on external hazards, with examples of lessons learned/recommendations that can be used for the design of new reactors. (author)