The ETH Zurich curated nuclear events database: Layout, event classification, and analysis of contributing factors

•Largest open database of 1250 nuclear events focused on worldwide safety significance.•Convenient user-friendly custom-made user interface.•Analysis of severity, origin, operating mode, failure chains, contributors, and others.•Pre-eminence of design related failures in safety systems unreliability.•Pronounced impact of human and organizational factors in the occurrence of events. We present an open database of nuclear events focused on worldwide safety significance with potentials for precursors. Explaining our events collection method and classification approach, each of the 1250 events in the database has been subjugated to coherent breakdown of features such as significance, origin, operating conditions, failure chains, contributing factors, severity of failures, and others. The events have been analyzed by experts and researchers in nuclear technology and safety, and are accessible using a custom-made user interface, making the database the largest open, comprehensive, curated, and user-friendly database in the world. We find that the majority of events (52%) have originated outside the nuclear island compared to within (48%). The most commonly affected components are related to the emergency power and emergency core cooling systems (ECCS). Design residuals are the major contributor to systems’ unreliability, with an occurrence frequency of more than 20%. Finally, the importance of vigilance by the plant staff and regulators is highlighted, as the contribution of human/organizational factors is found to be similar to that of technical factors.