and illustrate some vulnerabilities of the plant electrical system to over voltage transients. It identified electrical equipment involved, failure modes, contributing factors, actual and potential consequences, and corrective actions. Initiating factors and associated root causes were also analysed. The analysis of International Operation Experience Feedback revealed number of events that involved disturbances in the plant electrical systems, and which may have features in common with the Forsmark-1 event. It underlines the importance of sharing lessons learned from design modifications made at another unit of similar design that if known, it could have identified susceptibility of emergency diesel generators to common mode failure before the event occurred. This paper also summarizes international projects that were initiated by Forsmark event, as well as important lessons that still can be learned from Forsmark event. This paper presents actions taken at nuclear power plants and regulatory authorities in different countries to prevent similar event to occur. K e y w o r d s: Forsmark event, nuclear power plant, disturbances in the plant electrical systems
This paper presents main results of a comprehensive study performed by the European Clearinghouse on Operating Experience Feedback of NPP with the support of IRSN (Institut de S?reté Nucléaire et de Radioprotection) and GRS (Gesellschaft für Anlagen und Reaktorsi-cherheit mbH). Physical ageing mechanisms of structure, systems and components that eventually lead to ageing related systems and components failures at nuclear power plants were the main focus of this study. The analysis of ageing related events involved operating experience reported by NPP operators in France, Germany, USA and to the IAEA/NEA International Reporting system, on operating experience for the past 20 years (i.e. 1990-2009). A list of ageing related events was populated. Each ageing related event contained in the list was analyzed and results of analysis were summarized for each commodity group for which the ageing degradation appeared to be a dominant contributor or direct cause. The most common degradation mechanisms/ageing effects for each specific component/commodity group, their risk significance and consequences to the plant performance are described. This paper provides insights into ageing related operating experience as well as recommendations to deal with the physical ageing of nuclear power plant SSC important to safety.
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