[en] The contribution includes the official statistics on the accident following the earthquake and tsunami on March 11, 2011 on the Japanese island Honshu and the nuclear power plant Fukushima Daiichi. The plant was automatically shutdown as consequence of the earthquake. New calculations allow the reconstruction of the accident progress and the meltdown. Estimations of the released radioactivity, esp. the radionuclides I-131 and Cs-137 into the atmosphere and the ocean are summarized. The construction of water cleaning facilities for the contaminated waste water in the leaking tanks, water-tight barriers and the planning for the enclosure for the destroyed reactor buildings are described.

[en] As a result of the 13th amendment to the Atomic Energy Act (August 2011), 8 nuclear power plants have been permanently switched off. Since these nuclear power plants were not prepared for shutdown, applications for a permit to decommission the facilities at that time were not yet placed or prepared. Until the granting of the decommissioning permit, the following were found to be these installations with still valid operating licence, but without authorization for power operation, in an operating phase that also simplifies the "post-operational phase"- or "permanent non-power operation". In the first few years, for many of these facilities there was no sufficient number of transport and storage containers for spent fueld elements available at the site, so that this operating condition lasted a very long time. The long period between the completion of the operation and the granting of the decommissioning permit has not been considered in detail. For this period, therefore, there were no specific regulations. The safety and system availability for (longer-term) post-operation under consideration of the current requirements given by the German rules and regulations are sufficiently guaranteed. Likewise, the evaluation of the available operating experience of German nuclear power plants does not identify new findings with respect to the noted item list or the existing standards. Based on the evaluation according the state of the art in science and technology and the analyses carried out the available operating experience (reportable events and forwarding messages) German nuclear power plants, in the view of GRS, no new measures have to be taken. Based on the results of the evaluation of the operating experience, the following measures were taken probabilistic investigations. For the PWR and BWR plant under consideration the expected value for the fuel rod damage frequency was in the same order of magnitude as in the investigations on non-commercial operation. Also from the determined frequency of fuel rod damage there are no indications deficiencies. The safety systems available in post-operation and their redundancies appear as follows sufficient and adequate. In the installations under consideration, fires and earthquakes can cause the largest releases of activity from sources other than the nuclear fuel. However, the potential radiation exposure due to these events are, it is significantly lower than the exposure due to design basis accidents.

[en] The safety of nuclear installations is based on staggered safety levels. These safety levels comprise technical measures as well as organisational and administrative measures. For technical measures detailed regulations exist which command requirements like necessary redundancy levels, diversity and inservice inspections. The assessment of these various measures is performed in deterministic and probabilistic analyses. Compared to the technical measures there is no comparable systematic description of the measures foreseen by human actions. The safety significance of a specific human action within the staggered safety concept can be assessed only in detailed and time consuming analyses. There has been no fast and simple method to cover technical, organisational, and administrative measures in one assessment. Therefore, GRS has developed such a method on behalf of the German Ministry for Environment, Nature Conservation and Reactor Safety (BMU). This presentation is based on the findings of this research project 1. The method was developed and tested in co-operation with two German NPP. The method is therefore applicable for German NPP or NPP with similar design in power operation modes. There may be limits in the application for, shut-down states of operation and for NPP of different design. Main basis of the method developed are the International Nuclear Event Scale (INES) and probabilistic approaches. The INES has four categories in the aspect 'defense- in-depth', taking into account the level 0. The experience shows that these four categories are sufficient to communicate the safety significance of an event to the public. INES has the goal to assess quickly the safety significance of an event in nuclear installations. But, the human factors area is not covered in detail. In the method developed the human factor aspects are considered taking into account PSA approaches. The barriers based on administrative and organisational measures are assessed due to their effectiveness which is estimated on data used in PSA. During the development of the method it was taken care the method was compatible to the INES aspect 'defence-in-depth'. This should avoid difficulties for the acceptance of the method, because INES is well established. It was shown that the classification of the safety significance into 4 classes was sufficient for practice use. The method developed by GRS is intended to: - assess the potential significance of a postulated human error (proactive analyses), - assess the actual safety significance of a specific human action within an event (reactive analysis), - assess the actions taken after events to prevent recurrence

[en] The preliminary report on the accident progress in the nuclear power plants as a consequence of the earth quake on 11th March 2011 describes the chronologic sequence of the accident in the different units of the power plant. The measures for mitigation of the accident impact at the site of Fukushima Daiichi and Fukushima Daini included the efforts to reach and maintain stable plant conditions. The issue radiological situation includes an estimation of the air-borne radionuclide release, the contamination of the environment and the sea water, measures for protection of the public. The lessons learned following the NISA and IAEA fact finding missions and the open questions are summarized.

[en] The new IAEA Safety Fundamentals states regarding the operating experience feedback: The feedback of operating experience from facilities and activities - and, where relevant, from elsewhere - is a key means of enhancing safety. Processes must be put in place for the feedback and analysis of operating experience, including initiating events, accident precursors, near misses, accidents and unauthorized acts, so that lessons may be learned, shared and acted upon. This presentation deals with the proposal of the ETSON (European TSO Network) to optimize the European operating experiences feedback (OEF). It is generally recognized that the efficiency of nuclear safety supervision by public authorities is based on two key requirements: - the existence of a competent authority at national level, benefiting from an appropriate legislative and regulatory basis, from adequate (quantitatively and qualitatively) human resources, particularly for inspection purposes, - the availability of resources devoted to highly specialised independent technical expertise, in order to provide competent authorities with pertinent technical opinions on: -- the safety files provided by operators, for the purpose of licensing corresponding activities, -- the exploitation for regulatory purposes of the operating experience feed back from licensed nuclear installations. There are two worldwide systems intended to learn lessons from experience: the WANO (World Association of Nuclear Operators) system established by the licensees with access restricted to operating organizations and the IRS system jointly operated by IAEA and OECD/NEA accessible to regulators and to some other users nominated by the regulators in their countries. The IRS itself is dedicated to the analysis of safety significant operating events. NEA/CNRA runs a permanent working group on operating experience (WGOE). WGOE provides among other things also generic reports on safety concerns related to operating experiences and organizes workshops and conferences on specific OEF topics. IAEA organises, besides the yearly meeting of the IRS coordinators, consultancies and technical committees on the subject. (orig.)

[en] 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)

[en] The operational experience (OE) feedback provides improvements in all industrial activities. Identification of the most important and valuable groups of events within accumulated experience is important in order to focus on a detailed investigation of events. The paper describes the new ranking method and compares it with three others. Methods have been described and applied to OE events utilised by nuclear power plants in France and Germany for twenty years. The results show that different ranking methods only roughly agree on which of the event groups are the most important ones. In the new ranking method the analytical hierarchy process is applied in order to assure consistent and comprehensive weighting determination for ranking indexes. The proposed method allows a transparent and flexible event groups ranking and identification of the most important OE for further more detailed investigation in order to complete the feedback. (orig.)

[en] This paper presents a study performed by the European Clearinghouse of the Joint Research Centre on Operational Experience for nuclear power plants in cooperation with IRSN and GRS covering events reported by nuclear power plants in relation to external hazards. It summarizes the review of 235 event reports from 3 different databases. The events were grouped in 9 categories according to the nature of the external hazard involved, and the specific lessons learned and recommendations that can be derived from each of these categories are presented. Additional 'cross-cutting' recommendations covering several or all the external hazards considered are also discussed. These recommendations can be useful in preventing this type of events from happening again or in limiting their consequences. The study was launched in 2010 and therefore it does not cover the Fukushima event. This paper presents the main findings and recommendations raised by this study. (orig.)

[en] Highlights: • Analysis of operating experience for the past twenty years. • Identifying events that involved failures of EDGs or its supporting systems in NPPs. • Compiling categorized lessons learned based on specific EDG-related failures. • Designating generic recommendations intended to tackle the identified EDG failures. - Abstract: This study focuses on specific operating experience related to emergency diesel generators (EDG) at nuclear power plants. The study aims at analysing operating experience for the past twenty years and identifying events that involved failures of EDG or its supporting systems. The selected operating experience was analysed in order to identify type of failures, attributes that contributed to the failure, failure modes, discuss risk relevance, summarize important lessons learned and provide recommendations. For the purpose of this study EDG failure is defined as EDG fail to function on demand (i.e. fail to start, fail to run) or during testing, or an unavailability of an EDG, except of unavailability due to regular maintenance. The Gesellschaft für Anlagen und Reaktorsicherheit mbH (GRS) and Institut de Radioprotection et de Sûreté Nucléaire (IRSN) databases were screened to select all the events between 1990 and 2010 related to this topic. Besides IRSN and GRS operating experience, the operating experience contained in the IAEA/NEA International Reporting System for Operating Experience as well as the U.S. Licensee Event Reports were also analysed. The selected events were analysed in depth. Causes, root causes, contributing factors, consequences and lessons learned were determined. The events were classified into categories in order to establish main conclusions on the topic. A trend analysis was performed wherever possible, by assigning the reported events into different categories regarding chronology of occurrence, failure types, components involved, failure mode, failure causes, failure detection, etc. Subsequently, generic recommendations related with the analysed EDG failures were compiled. The focus of this paper is on the lessons learned from the analysed operating experience as well as on designating generic recommendations for the specific EDG-related issues encountered rather than presenting selected statistical results.

[en] Highlights: • Analysis of operating experience related to emergency diesel generators events at NPPs. • Four abundant operating experience databases screened. • Delineating important insights and conclusions based on the operating experience. - Abstract: This paper is aimed at studying the operating experience related to emergency diesel generators (EDGs) events at nuclear power plants collected from the past 20 years. Events related to EDGs failures and/or unavailability as well as all the supporting equipment are in the focus of the analysis. The selected operating experience was analyzed in detail in order to identify the type of failures, attributes that contributed to the failure, failure modes potential or real, discuss risk relevance, summarize important lessons learned, and provide recommendations. The study in this particular paper is tightly related to the performing of statistical analysis of the operating experience. For the purpose of this study EDG failure is defined as EDG failure to function on demand (i.e. fail to start, fail to run) or during testing, or an unavailability of an EDG, except of unavailability due to regular maintenance. The Gesellschaft für Anlagen und Reaktorsicherheit mbH (GRS) and Institut de Radioprotection et de Sûreté Nucléaire (IRSN) databases as well as the operating experience contained in the IAEA/NEA International Reporting System for Operating Experience and the U.S. Licensee Event Reports were screened. The screening methodology applied for each of the four different databases is presented. Further on, analysis aimed at delineating the causes, root causes, contributing factors and consequences are performed. A statistical analysis was performed related to the chronology of events, types of failures, the operational circumstances of detection of the failure and the affected components/subsystems. The conclusions and results of the statistical analysis are discussed. The main findings concerning the testing, maintenance, safety consequences, determining eventual chronological trend, detection of failures are summarized