Analysis of Events Related to Flooding at NPPs

This summary report presents the selected results of a statistical and engineering analysis of flooding and flooding protection related events registered in the following four databases: IRSN (Institut de Radioprotection et de Sûreté Nucléaire), GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH), U.S. NRC (Nuclear Regulatory Commission) Licensee Event Reports (LERs), and the IAEA/NEA International Reporting System (IRS) during the last 20 years. In total 263 events reports are analysed including potential flooding. The events were analysed and classified into thirteen categories. The frequencies of all categories and families were presented for each database separately and for all events combined. This allowed comparison of events characteristics among all databases and cumulative results. A trend analysis was also performed. Finally, selected events were used to derive findings (lessons learned). No trend was identified over the whole analysed period. However, it is noticeable that the number of events is decreasing for all databases in recent couple years. Most of the events occurred during power operation, for all except for the one database. In the majority of events a real flood occurred, except for one database where potential flood events are dominant. Valves and passive components are the dominant direct causes in all databases, while seals and drainage are also important for the two databases. Training, qualification and procedures, with design configuration and analysis, are the most important root causes and causal factors for all databases, while maintenance activity and the equipment performance are also important for one database. Systems most often affected by flood are (reactor) auxiliary systems for all databases and additionally the waste management systems for one database. The majority of events do not have safety relevance except for one database, where low safety relevant events are dominant. The main purpose of corrective actions is: prevention, early identification and reduction of flood; fulfilment of the probable maximum flood requirements; reducing flood risk from non-safety systems and improving maintenance, review and inspection. Flooding and flooding protection related selected events were analysed in detail and the main conclusions are presented as list of more than 90 specific and 16 generic lessons learned. Findings are grouped related to the systems that has main role during the flooding event (i.e., non-safety systems interaction, buildings infrastructure and major cooling systems) and related to the type of activities that are (root) cause for the flooding event (i.e., maintenance, inspection, operating experience, analysis and configuration management). Generic findings are also addressing lessons learned related to mitigation, communication, modifications, requirements and configuration management. The findings from this summary report could be used as recommendations and are expected to help the licensees and regulatory authorities to prevent flooding events from occurring, to protect safety systems from flood and to improve flooding protection and mitigation.JRC.G.10-Knowledge for Nuclear Security and Safet

Development of the Statistical Tool for Operating Events Database Analysis Operating Events Ranking Tool OPERATE

This report contains a specification and implementation description for the statistical tool (desktop software program) which will allow detailed reporting and flexible ranking of operational events. The program is named Operational Events Ranking Tool (OPERATE). The initiating idea was that detail statistical reporting with a robust and consistent way of selecting most important events for more detailed investigation is very important. This provides better insight and saves the need for complete detail investigation which is neither feasible nor useful. It allows also to identify events trends and patterns across large databases. The foundation for the statistical reporting and ranking is defined by the events parameters which are the base for reporting, grouping and ranking. This requires that each event should have characterisation which allows use of selected parameters for grouping and ranking. The set of parameters could be in general user-defined, but for initial OPERATE implementation a fixed set of parameters is defined based on the WANO operating experience programme and the IRS coding schemes. Five parameters are used for events grouping: Activity, Direct cause, Systems, Components, and Root cause & Causal factor. Seven parameters are used for ranking: Frequency, Trend, Extension, Multiple, Safety, Category and Consequences. Some other parameters are used for statistics reports and future criteria (e.g. Vendor, Reactor type, Time of event, Status and Group of staff). An important part of the implemented method is the way how ranking indexes are calculated. This is done in a consistent way based on previous experience and new research. OPERATE allows for each ranking index to be valued on the basis of relative importance determined by the experts' judgement evaluated with analytical hierarchy process (AHP). In this way weighting is easily determined and the importance of different parameters could be consistent. The tool is capable of analysing ranking for all groupings based on the expert and AHP determined relative importance. In order to investigate the ranking confidence (uncertainty and sensitivity), the tool can analyse ranking for user-selected variations of parameters importance (e.g. ±30% weighting for all ranking indexes etc.). This is useful to determine the sensitivity of the results, which could expose the criticality of certain ranking parameters and respected weights. In addition to ranking results OPERATE is able to produce nineteen different reports about events (e.g. frequencies for all parameters values on yearly and average base, etc.) which could help further focus on experts investigation. In parallel to the program development five years of US NRC LERs events (2007-2011) has been characterised in order to demonstrate and verify the tool. These results are presented in the report. OPERATE is a very flexible tool with potential for further use and development.JRC.F.5-Nuclear Reactor Safety Assessmen

Feasibility Study for Applicability of Ageing PSA Model Results in Risk-informed Decision Process

The aim of this case study was to demonstrate the benefits of using ageing probabilistic safety analysis (PSA) results in risk-informed decision process. First stage of the activities was aimed on the development of dataset which reflects age-dependent reliability behaviour for selected components using plant-specific, VVER specific and generic data. The second part describes the integration process of time-dependent reliability dataset in PSA model, quantification and comparison between aging (APSA) and base case PSA decision making results. Practical insights and conclusions are also presented. The report was prepared by the Nuclear & Radiation Safety Center (NRSC), Yerevan, Armenia, in cooperation with the Institute for Energy and Transport, EC Joint Research Centre, Petten, Netherlands, in the framework of the EC JRC Ageing PSA Network Task 8 activities.JRC.F.5-Nuclear Reactor Safety Assessmen

Enhancing Safety: the Challenge of Foresight

We live in a world where advancement in technology coupled with human’s creative and innovative mind has led to the design of safer and better performing infrastructures (nuclear power plants, chemical process plants, high speed trains, spaceplanes, etc.), which are necessary for modern society. However, due to the interconnected socio-economic and technological landscape that is rapidly evolving, safety continues to have many new challenges (known unknowns, unknown unknowns) that add onto changed variants of the old challenges (e.g. modified knowns). Additionally, governance and legislation can be slow to catch up with this dynamic pace of change. At times, overregulation can occur, resulting in a significant resource investment towards compliance for existing infrastructure operators or for aspiring start-ups that would like to enter the market, but end up struggling or even abandoning the sector. Inspired by this background, the European Safety and Reliability Data Association’s Foresight in Safety Project Group prepared the 53rd ESReDA seminar with a purpose to launch an open dialogue with stakeholders in the safety arena. Thus, by providing an open forum where experiences in foresight in safety approaches from different sectors could be shared, cross-fertilisation of ideas, such as how foresight could be mainstreamed into safety practice in a more consistent manner, could be discussed. The project group will build on this rich compendium of experiences in its future endeavours.JRC.E.7-Knowledge for Security and Migratio

Horizon Scanning for Nuclear Safety, Security & Safeguards Yearly Report - 2019

Horizon Scanning (HS) is a systematic outlook to detect early signs of potentially important developments. JRC.I.2 unit has created and, with the help of partner JRC Knowledge Management Units, has tested a methodology for a horizon scanning process at JRC level. Benefiting from this support and following this methodology, JRC.G.10 unit has collected throughout the year 2019 a number of ideas related to nuclear technology, later on filtered and clustered in the so called 'sense-making workshops'. This report presents the outcome of this exercise.JRC.G.10-Knowledge for Nuclear Security and Safet

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

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

European Atlas of Natural Radiation

Natural ionizing radiation is considered as the largest contributor to the collective effective dose received by the world population. The human population is continuously exposed to ionizing radiation from several natural sources that can be classified into two broad categories: high-energy cosmic rays incident on the Earth’s atmosphere and releasing secondary radiation (cosmic contribution); and radioactive nuclides generated during the formation of the Earth and still present in the Earth’s crust (terrestrial contribution). Terrestrial radioactivity is mostly produced by the uranium and thorium radioactive families together with potassium. In most circumstances, radon, a noble gas produced in the radioactive decay of uranium, is the most important contributor to the total dose. This Atlas aims to present the current state of knowledge of natural radioactivity, by giving general background information, and describing its various sources. This reference material is complemented by a collection of maps of Europe displaying the levels of natural radioactivity caused by different sources. It is a compilation of contributions and reviews received from more than 80 experts in their field: they come from universities, research centres, national and European authorities and international organizations. This Atlas provides reference material and makes harmonized datasets available to the scientific community and national competent authorities. In parallel, this Atlas may serve as a tool for the public to: • familiarize itself with natural radioactivity; • be informed about the levels of natural radioactivity caused by different sources; • have a more balanced view of the annual dose received by the world population, to which natural radioactivity is the largest contributor; • and make direct comparisons between doses from natural sources of ionizing radiation and those from man-made (artificial) ones, hence to better understand the latter.JRC.G.10-Knowledge for Nuclear Security and Safet

Operational Events Groups Ranking Sensitivity Analysis

Collecting and assessment of operational experience has numerous attractions and benefits in all major industrial activities. Understanding of the most important difficulties with limited access to the industry wide operational experience and its proper application are still subject of ongoing research. One special problem is to identify the most important groups of events from the collected experience because it is not feasible to in-vestigate in sufficient details all of them. This paper is analyzing how events groups' prioritization is sensitive to the selected ranking method and to the events grouping. The base for the analysis was set of twenty years of experience from nuclear power plants in two countries. The method difference is mainly related to the type of ranking indexes used (regarding equations and logic) and weighting factors applied (i.e., is importance of ranking indexes equal or not). The finding is that sensitivity is large because different ranking approaches and groupings produce important changes in rankings. The fact is that different ranking approaches have fairly good agreement related to the top listed groups of events. However, the precise events groups order differs significantly between methods and different groupings. Further assessment of ranking methods seems im-portant in order to make better judgment about most preferred ranking method and groupings. This is important in order to increase credibility of ranking results and relax ranking process.JRC.F.5-Nuclear Reactor Safety Assessmen

Uncertainty Analysis of Method-based Operating Event Groups Ranking

Safe operation and industrial improvements are coming from the technology development and operational experience (OE) feedback. A long life span for many industrial facilities makes OE very important. Proper assessment and understanding of OE remains a challenge because of organization system relations complexity and because of an amount of OE events acquired. One way to improve OE events understanding is to focus their investigation and analyze in details the most important. The OE ranking method is developed to select the most important events based on the basic event parameters and the analytical hierarchy process applied at the level of event groups. This paper investigates further how uncertainty in the model is affecting ranking results. An analysis was performed on the set of two databases from the 20 years of nuclear power plants in France and Germany. From all uncertainties the presented analysis selected ranking indexes as the most relevant for consideration. Here the presented analysis of uncertainty clearly shows that considering uncertainty is important for all results, especially for event groups ranked closely and next to the most important one. Together with the previously performed sensitivity analysis uncertainty assessment provides additional insights and a better judgment of the event groups importance in further detail investigation.JRC.F.5-Nuclear Reactor Safety Assessmen