The European Network on Operating Experience Feedback (OEF) for Nuclear Power Plants has been established to enhance nuclear safety through dissemination of lessons learned from Nuclear Power Plant (NPP) events, and to provide help in Operational Experience Feedback (OEF) process primarily to nuclear safety Regulatory Authorities and to their Technical Support Organizations within the EU. One of the main Clearinghouse deliverables is Topical Study and so far, there are twenty studies already published. The most recent one is Topical study on NPP Design Deficiency. Topical study on NPP Design Deficiency has been conducted to review the worldwide OE from events where design deficiencies are addressed. The sources of analysed events are the IAEA International Reporting System (IRS), the US NRC Licensee Event Reports (LER), the French Institut de Radioprotection et de Surete Nucleaire (IRSN), and the German Gesellschaft fur Anlagen und Reaktorsicherheit mbH (GRS) Operational Experience (OE) databases. The main objective of this study was to extract the generic and case-specific lessons from the events contained in the databases, and to provide recommendations to the members of the European Clearinghouse. More specifically, study was aimed to reveal latent weaknesses of nuclear power plants created in the design phases i.e. before start of NPP operation. Thousands of the event reports have been screened and 774 were selected for further study. For the purpose of the study all applicable events were categorised, in the first place, to provide events phenomenology type's distribution. The objective was to group the events around a common topic which presents a general issue. All selected event reports were classified into families according to different criteria. Finally, the six Common Major Issues have been defined to properly summarise most of the concerns related to design. Accordingly, the 29 recommendations are grouped under six topics: Unanalysed condition, Robustness of design, Ageing, Internal and External Hazard, and Quality of Documentation. Additional finding in this study came from the evaluation of the detection mode, i.e. how design deficiencies have been detected by licensees. It has been identified that, for IRS database, the design issues have been most often revealed by an event with actual consequences, rather than, as it would be desirable, by engineering reviews, inspections or surveillance activities. The number of detection by actual consequences is increasing over time. Therefore, design reviews and other methods to detect design deficiencies need to be more encouraged. Licensees have been probably already informed about all important events described in this study through different OE communication channels and implemented appropriate actions to prevent reoccurrence on their site. Therefore, recommendations from described reports should be used to check if applicable ones have been adequately implemented in affected NPPs, or if further assessment should be performed, to prioritize necessary changes. However, it is also important to note that design process management flaws are evident in all events on which main recommendations are based. Therefore, a successful management should establish high level of safety and strong culture of safety. To establish effective safety strategy necessary for preventing accidents and mitigating the consequences, management should integrate good design and engineering features by providing adequate safety margins, diversity and redundancy.
