Summary Report of Events related to Design Deficiency

This summary report presents the results of a comprehensive study described in the topical study ‘Events related to design deficiency’. The study has been conducted to review the recent worldwide operating experience and to draw from it the lessons learned and recommendations to improve the safety performance of nuclear power plants (NPPs). The work covers all kinds of commercial power reactors currently or recently in operation and all off-power modes of operation. The sources of operating experience for the study are the international reporting system for operating experience (IRS) database, the licensee event reports (LERs) of the United States Nuclear Regulatory Commission (US NRC), the French operational experience database Sapide and the German operational experience database VERA. Thousands of event reports were screened to select those more relevant for the objectives of the study. This resulted in a list of 774 event reports. After different approaches applied in examining pre-defined categories and families of events, it was concluded that six common major issues could be defined to present the areas of concern in the best way. Accordingly, the 29 recommendations from this study are distributed under these topics: unanalysed conditions, instrumentation and control, robustness of design, ageing, internal and external hazards, and quality of documentation. These recommendations are expected to help the licensees and the regulatory authorities to recognise latent weaknesses dating from the design phases of the NPPs, before the start of NPP operation, and perform adequate measures to prevent the occurrence of events similar to those described in this report. The report can also be used as a good reference for new NPP construction projects.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

Continued safe operation of nuclear power generation plants during the Covid-19 pandemic

An important goal of any pandemic response strategy is to assure the continued reliability of the electricity grid. Electricity production and delivery, two of the most important elements of economic and social infrastructure, must remain reliable during a pandemic because many parts of the infrastructure (e.g. food supply, water, transportation, public health) cannot function without a stable, reliable supply of electricity. More than 100 nuclear power reactor units are currently in operation in the EU and their continued operation during a pandemic is essential to maintain grid stability and ensure the needed power supplies in combination with the other sources of power generation. This report provides an overview of the findings of an investigation into the pandemic preparedness and response actions of nuclear power plant operating organisations in EU and some third countries operating nuclear power reactors. The investigation has been performed by means of media monitoring and information gathering during approximately three weeks, from 16 March – 3 April 2020.JRC.G.10-Knowledge for Nuclear Security and Safet

Review of current Severe Accident Management (SAM) approaches for Nuclear Power Plants in Europe

The Fukushima accidents highlighted that both the in-depth understanding of such sequences and the development or improvement of adequate Severe Accident Management (SAM) measures are essential in order to further increase the safety of the nuclear power plants operated in Europe. To support this effort, the CESAM (Code for European Severe Accident Management) R&D project, coordinated by GRS, started in April 2013 for 4 years in the 7th EC Framework Programme of research and development of the European Commission. It gathers 18 partners from 12 countries: IRSN, AREVA NP SAS and EDF (France), GRS, KIT, USTUTT and RUB (Germany), CIEMAT (Spain), ENEA (Italy), VUJE and IVS (Slovakia), LEI (Lithuania), NUBIKI (Hungary), INRNE (Bulgaria), JSI (Slovenia), VTT (Finland), PSI (Switzerland), BARC (India) plus the European Commission Joint Research Center (JRC). The CESAM project focuses on the improvement of the ASTEC (Accident Source Term Evaluation Code) computer code. ASTEC,, jointly developed by IRSN and GRS, is considered as the European reference code since it capitalizes knowledge from the European R&D on the domain. The project aims at its enhancement and extension for use in severe accident management (SAM) analysis of the nuclear power plants (NPP) of Generation II-III presently under operation or foreseen in near future in Europe, spent fuel pools included. In the frame of the CESAM project one of the tasks consisted in the preparation of a report providing an overview of the Severe Accident Management (SAM) approaches in European Nuclear Power Plants to serve as a basis for further ASTEC improvements. This report draws on the experience in several countries from introducing SAMGs and on substantial information that has become available within the EU “stress test”. To disseminate this information to a broader audience, the initial CESAM report has been revised to include only public available information. This work has been done with the agreement and in collaboration with all the CESAM project partners. The result of this work is presented here.JRC.F.5-Nuclear Reactor Safety Assessmen

Enhancing Safety: the Challenge of Foresight - ESReDA Project Group Foresight in Safety

This Deliverable is the result of a joint effort by experts, working in the fields of risks management, accident analysis, learning from experience and safety management. They come from 10 countries mainly from Europe and also from USA and Australia. Their expertise covers several industrial sectors. They attempted to provide useful information, both from a theoretical and a practical point of views, about "Foresight in Safety". Safety is still an ongoing issue for which a number of subjects remain under debate (e.g. is goal of safety to ensure that 'as few things as possible go wrong' or to ensure that ‘as many things as possible go right’?). Anyway, we can assume that safety is to act in a way for both the process continues to be run right and that errors and failures to not lead to a major accident. Even if "foresight in safety" is the implicit underlying goal of every practitioner in safety, the outlines of its domain remain blurred and the relevant topics associated with it have never been clearly defined. A humble ambition of this Deliverable is to display some aspects of "foresight in safety" according to the current state of practices and scientific knowledge.JRC.G.10-Knowledge for Nuclear Security and Safet

Topical study on NPP Design Deficiency

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 Sûreté Nucléaire (IRSN), and the German Gesellschaft für 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.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

Sharing Lessons Learned Between Industries in EU

Recent events in nuclear industry remind us on importance of continuous sharing of the knowledge and experience gained through evaluations of incidents and accidents. We frequently use experience from our daily life activities to improve our performance and avoid some mistakes or unwanted events. In the similar way we can use other industries experience. These experiences can be applied to improve nuclear safety. For example, Safety Culture, which has a great influence on the level of nuclear power plants safety, is similarly presented in other industries. Mechanisms which led to accidents from weak safety culture in one branch of other industry could be comparable to those in nuclear industry. Some other industries have many more cumulative years of experience than nuclear industry. Aviation and Oil industries are typical representatives. Part of their experience can be used in nuclear industry too. Number of reports from nuclear power plants showed us that not only specific equipment related causes lay behind accidents; there are also other causes and contributors which are more common for all industries. Hence lessons learned in other industry should be assessed and used in nuclear industry too. In the European Union, a regional initiative has been set up in 2008 in support of EU Member State nuclear safety authorities, but also EU technical support organizations, international organizations and the broader nuclear community, to enhance nuclear safety through improvement of the use of lessons learned from operational experience of nuclear power plants (NPPs). The initiative, called “the EU Clearinghouse on Operational Experience Feedback for NPP”, is organized as a network operated by a centralized office located at the Joint Research Centre of the European Commission. The reduction of occurrence and significance of events in NPPs and their safe operation is its ultimate goal. Among others EU Clearinghouse provides services such as technical and scientific work to disseminate the lessons learned from past operating experience as well as background research in OEF for its members and also publishes information on recent operational experiences. In European Union there are several organisations and institutions which are involved in incidents and accidents evaluation as well as in dissemination of lessons from events. The EU Clearinghouse is evaluating how other hazardous industries are organized to capture experience related to events and to disseminate the lessons learned. It is also trying to identify and establish contacts with repositories of operating experience from other comparable industries, so the best practice and lessons learned could be applied in nuclear industry.JRC.F.5-Nuclear Reactor Safety Assessmen

Sharing Lessons Learned Between Industries in EU

Recent events in nuclear industry remind us on importance of continuous sharing of the knowledge and experience gained through evaluations of incidents and accidents. We frequently use experience from our daily life activities to improve our performance and avoid some mistakes or unwanted events. In the similar way we can use other industries experience. These experiences can be applied to improve nuclear safety. For example, Safety Culture, which has a great influence on the level of nuclear power plants safety, is similarly presented in other industries. Mechanisms which led to accidents from weak safety culture in one branch of other industry could be comparable to those in nuclear industry. Some other industries have many more cumulative years of experience than nuclear industry. Aviation and Oil industries are typical representatives. Part of their experience can be used in nuclear industry too. Number of reports from nuclear power plants showed us that not only specific equipment related causes lay behind accidents; there are also other causes and contributors which are more common for all industries. Hence lessons learned in other industry should be assessed and used in nuclear industry too. In the European Union, a regional initiative has been set up in 2008 in support of EU Member State nuclear safety authorities, but also EU technical support organizations, international organizations and the broader nuclear community, to enhance nuclear safety through improvement of the use of lessons learned from operational experience of nuclear power plants (NPPs). The initiative, called “the EU Clearinghouse on Operational Experience Feedback for NPP”, is organized as a network operated by a centralized office located at the Joint Research Centre of the European Commission. The reduction of occurrence and significance of events in NPPs and their safe operation is its ultimate goal. Among others EU Clearinghouse provides services such as technical and scientific work to disseminate the lessons learned from past operating experience as well as background research in OEF for its members and also publishes information on recent operational experiences. In European Union there are several organisations and institutions which are involved in incidents and accidents evaluation as well as in dissemination of lessons from events. The EU Clearinghouse is evaluating how other hazardous industries are organized to capture experience related to events and to disseminate the lessons learned. It is also trying to identify and establish contacts with repositories of operating experience from other comparable industries, so the best practice and lessons learned could be applied in nuclear industry.JRC.F.5-Nuclear Reactor Safety Assessmen

Overview of recent activities on Safety Culture and Human and Organisational Factors carried out at the Joint Research Centre of the European Commission

The Institute for Energy and Transport (IET) of the Joint Research Centre (JRC) of the European Commission (EC) is since more than ten years active in the field of Safety Culture (SC) and Human and Organisational Factors (HOF). Several activities related to SC and HOF have been and are carried out in the frame of the EU Nuclear Safety Clearinghouse for Operating Experience Feedback (Clearinghouse). The Clearinghouse was established in 2008 to enhance nuclear safety through the lessons learned from 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. Additionally to these activities, during the Fukushima accident, Clearinghouse has been regularly providing reports on the status and progress of the accident to the EU Regulatory Authorities. Moreover, experts, selected from the JRC staffing, were directly engaged in the EU-wide risk and safety assessments of nuclear power plants known as "the Stress Tests". After Chernobyl accident many projects were funded by the European Union to increase the Safety of the Ukrainian and Russian Nuclear Power Plants through the TACIS programme. Currently there are several ongoing project directed to enhance the cultural, procedural and technical capability and effectiveness in operating Ukrainian NPPs. Two of them are directly aiming at improving SC and HOF: 1) "Improvement of Safety Culture Management at NNEGC Energoatom and its NPPs" and 2) "The Enhancement of Nuclear Safety by extending the understanding the influence of human factors". These projects are managed by the EC Directorate-General for International Cooperation and Development (DG DEVCO), with the technical and scientific support of the Joint Research Centre. Due to the similarity with the safety approaches in other major hazard industries, Clearinghouse is involved in different activities where the other industries have developed their own Operational Experience Feedback programs. Their repositories of experience, mainly in the form of reports, are a very valuable source for numerous studies ranging from the ones aiming to extract the best Lessons Learned from individual events to the more comprehensive ones where common areas for improvement are identified on the basis of the assessment of similar events in specific industry branches. In addition, studies where different industries provide inputs from their databases are performed too. The JRC also contributed to one of the latest concluded international projects carried out by the European Safety, Reliability and Data Association (ESReDA) Project Group for Dynamic Learning from Accident Investigation (PG DLAI). The main objectives of the project were to work out recommendations on how to capture, document, disseminate and implement insights, recommendations and experiences obtained from the investigations of high-risk events. Finally it is worth to mention some other JRC projects focused on nuclear safety: Nuclear Reactor Accident Analysis and Modelling (NURAM); Knowledge Management, Training and Education in Reactor design and Operation (CAPTURE); and Support to DG ENER Nuclear Reactor Safety Policy and International Standards (NUSP). Through all of these projects Safety Culture specific characteristics and attributes are always highlighted to remind all stakeholders of its importance for the safe operation of NPPs.JRC.G.10-Knowledge for Nuclear Security and Safet

Human Based Roots of Failures in Nuclear Events Investigations

Objective: Improvement of quality of the event investigations in the nuclear industry through analysis of the existing practices, identifying and removing the existing Human and Organizational Factors (HOF) and management related barriers. Background: Accidents are still recurring despite the plenty of efforts to prevent them because human and organizational factors' issues are typically not well addressed. Methods: Survey based study of human and organizational factors limiting the effectiveness currently existing event investigation practices typical for nuclear industry of 12 European countries. Results: System of operational experience feedback from information based on event investigation results is not enough effective to prevent and even to decrease frequency of recurring events. The latent root causes of failures found through investigation are related to weaknesses in safety culture of personnel and managers. These weaknesses include focus on costs or schedule, political manipulation, arrogance, ignorance, entitlement and/or autocracy. The potential improvements could be targeted to increasing competencies and capabilities of event investigation teams, elaboration of comprehensive software, increasing level of independency of investigation, ensuring of positive approach, adequate support and impartiality of management. Conclusion: Effectiveness of event investigation and operational experience feedback process is not perfect mainly due to existing methodological, HOF-related and/or knowledge management related constraints. Upgrades in safety culture of organization’s personnel and its senior management especially seem to be an effective way to improvement. Application: Results of this study could be applicable in nuclear power plants as well as in other high-risk industries.JRC.F.5-Nuclear Reactor Safety Assessmen

Simulation of steam generator plugging tubes in a PWR to analyze the operating impact

A number of Nuclear Power Plants (NPPs) with Pressurized Water Reactors (PWR) in the world have replaced their steam generators (SG) due to degradation of the SG tubes caused by different problems. Several methods were attempted to correct the defects of the tubes, but eventually the only permanent solution was to plug them. The consequences of plugging the tubes are the decrease of heat transfer surface, the reduction of the flow area and subsequent reduction of the primary system mass flow and for a fraction of plugged tubes higher than a given value, the reduction of reactor output and economic losses. The objective of this paper is to analyse whether steam generator tube plugging has an impact in the effectiveness of accident management actions. An analysis with Relap5 Mod 3.3 patch03 for the Spanish reactor Ascó-2, a 3-loop 2940.6 MWth Westinghouse PWR, in which plugging of steam generator tubes are simulated, is presented in order to find the limit for the adequate operation of the plant. Several steady state calculations were performed with different fractions of plugged SG tubes, by modelling the reduction of the primary to secondary heat transfer surface and the reduction of the primary coolant mass flow area in the tubes as well. The results of the analysis yield that plugging 12% of the SG tubes is around the limit for optimal reactor operation. To complete the study two events, in which the steam generators are used to cooldown the plant, were simulated to find out if the plugging of SGs tubes could influence the efficiency of the operator actions described in the Emergency Operating Procedures (EOPs) to handle this kind of events. The selected events have been the rupture of one tube of a SG (SGTR) and a small break LOCA (SBLOCA). Two transient cases with no plugging at all (0%) and 12% SG tube plugging were performed. The actions of the corresponding EOPs for SG tube rupture and SBLOCA were coded in the input deck. The results show no significant impact on operator actions.JRC.F.5-Nuclear Reactor Safety Assessmen