PSAM 16 - Session T13 Overview

PSAM 16 Conference Session T13 Overview

Session Chair: Dave Grabaskas (dgrabaskas@anl.gov)

Paper 1 FL328

Lead Author: Florian Berchtold Co-author(s): Gerhard Mayer mayer.gerhard@grs.de Marina Röwekamp marina.roewekamp@grs.de

Presenter of this paper: Marina Roewekamp (marina.roewekamp@grs.de)

Consideration of Long-Lasting External Flooding Within PSA – Modelling Supplementary Emergency Measures
A methodological approach has been developed to adequately consider supplementary emergency measures in long-lasting hazard events within Level 1 probabilistic safety analysis (PSA). Those measures are established in the short-term using the available time during long-lasing events and have not been planned in advance. The methodology has been applied to a riverine flooding event of a reference nuclear power plant (NPP) site. In this context, two assumptions have been made: the site will not be accessible by road or rail, and there will be a consequential complete loss of offsite power. Consequently, the operation of the emergency diesel generators over a period exceeding seven days at maximum and a permanent exchange of the shift personnel are needed. Two supplementary emergency measures ensuring the supply of the plant with fuel and shift personnel have been analysed in detail. The supply is ensured via a ferry service using amphibious vehicles or with helicopter transport. These measures were implemented and quantified in an existing Level 1 PSA model of the reference NPP, taking into account the event-specific boundary conditions. The quantification revealed that ensuring the shift exchange provides a significantly higher contribution to the success of the mitigation measures than ensuring the fuel supply. This paper presents the results of the methodological enhancements and extensions as well as its application to an exemplary German NPP site.

Consideration of Long-Lasting External Flooding Within PSA – Modelling Supplementary Emergency Measures

A methodological approach has been developed to adequately consider supplementary emergency measures in long-lasting hazard events within Level 1 probabilistic safety analysis (PSA). Those measures are established in the short-term using the available time during long-lasing events and have not been planned in advance. The methodology has been applied to a riverine flooding event of a reference nuclear power plant (NPP) site. In this context, two assumptions have been made: the site will not be accessible by road or rail, and there will be a consequential complete loss of offsite power. Consequently, the operation of the emergency diesel generators over a period exceeding seven days at maximum and a permanent exchange of the shift personnel are needed. Two supplementary emergency measures ensuring the supply of the plant with fuel and shift personnel have been analysed in detail. The supply is ensured via a ferry service using amphibious vehicles or with helicopter transport. These measures were implemented and quantified in an existing Level 1 PSA model of the reference NPP, taking into account the event-specific boundary conditions. The quantification revealed that ensuring the shift exchange provides a significantly higher contribution to the success of the mitigation measures than ensuring the fuel supply. This paper presents the results of the methodological enhancements and extensions as well as its application to an exemplary German NPP site.

Paper FL328 | Download the paper file. | Download the presentation pdf file.

A PSAM Profile is not yet available for this author.
Presenter Name: Marina Roewekamp (marina.roewekamp@grs.de)

Bio: - Diploma in Physics PhD (Dr. rer. nat. In Physical Chemistry / Materials Science) from University of Bonn - Senior Chief Expert for Hazards and PSA at GRS – the Federal German Nuclear Technical Safety Organization – for > 33 years - PSA work: mainly performing and/or reviewing Level 1 PSA, particularly for Internal and External Hazards (incl. hazard combinations) - Member of the German PSA Expert Panel for > 15 years - Former Chair and actual Vice Chair of OECD/NEA/CSNI Working Group on Risk Assessment (WGRISK) - Chair of OECD/NEA CSNI Expert Group on Fire Risk (EGFR) and of Management Board of OECD/NEA FIRE (Fire Events Records Exchange) Project - Consultant and/or reviewer for various IAEA Guides (SSG-64, SSG-67, SSG-68, DS523 (revision of SSG-3 on Level 1 PSA), DS528 (revision of SSG-4 on Level 2 PSA), TECDOCS on MUPSA, Advanced PSA Methods, Safety Assessment of Nuclear Installations Against Combinations of External Hazards, etc. - IAPSAM Board of Directors member since

Country: Germany
Company: Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH
Job Title: Chief Senior Expert

Paper 2 JS148

Lead Author: Joy Shen Co-author(s): Michelle T Bensi: mbensi@umd.edu Mohammad Modarres: modarres@umd.edu

External Flood Fragility Development and Integrating Novel Tools to the XFPRA framework
This presentation explores the development of external flood fragility functions for nuclear power plants. It also explores the stochastic conversion of external flood height to an internal flood height using novel probabilistic risk assessment (PRA) tools such as Bayesian networks augmented with Monte Carlo simulations. PRAs in the nuclear industry are traditionally performed with event tree and fault tree analyses (ETA/FTA). The challenges to these tools include the binary state assumptions (failed or un-failed), the limitations in modeling dependencies, and the static treatment of time. These challenges are particularly relevant and limiting when modeling external flood risks. For example, components may partially fail, requiring a multi-state failure model. Furthermore, correlations between components may exist due to location, manufacturing, and maintenance. In addition, the effects of a flood event are spatially and temporally dynamic. These challenges prompt an investigation to integrate other tools in the traditional ETA/FTA framework. This presentation describes the initial research activities to explore the development of flooding fragility models and stochastically linking external flooding to internal component fragility, using Bayesian networks augmented with Monte Carlo simulations, addressing the previously mentioned challenges. Future work will include integrating these tools into the ETA/FTA framework and its application to a comprehensive flooding scenario.

External Flood Fragility Development and Integrating Novel Tools to the XFPRA framework

This presentation explores the development of external flood fragility functions for nuclear power plants. It also explores the stochastic conversion of external flood height to an internal flood height using novel probabilistic risk assessment (PRA) tools such as Bayesian networks augmented with Monte Carlo simulations. PRAs in the nuclear industry are traditionally performed with event tree and fault tree analyses (ETA/FTA). The challenges to these tools include the binary state assumptions (failed or un-failed), the limitations in modeling dependencies, and the static treatment of time. These challenges are particularly relevant and limiting when modeling external flood risks. For example, components may partially fail, requiring a multi-state failure model. Furthermore, correlations between components may exist due to location, manufacturing, and maintenance. In addition, the effects of a flood event are spatially and temporally dynamic. These challenges prompt an investigation to integrate other tools in the traditional ETA/FTA framework. This presentation describes the initial research activities to explore the development of flooding fragility models and stochastically linking external flooding to internal component fragility, using Bayesian networks augmented with Monte Carlo simulations, addressing the previously mentioned challenges. Future work will include integrating these tools into the ETA/FTA framework and its application to a comprehensive flooding scenario.

Paper JS148 | | Download the presentation PowerPoint file.

Name: Joy Shen (jshen132@umd.edu)

Bio:

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Paper 3 MB157

Lead Author: Michelle Bensi Co-author(s): • Somayeh Mohammadi (somayeh@terpmail.umd.edu) • Tao Liu (liut8@vcu.edu) • Camille Levine (clevine1@umd.edu) • Ahmad Al-Douri (clevine1@umd.edu) • Ray Schneider(schneire@westinghouse.com) • Zeyun Wu (zwu@vcu.edu) • Katrina Groth (kgroth@umd.edu) • Zhegang Ma (zhegang.ma@inl.gov)

Uncertainty in External Hazard Probabilistic Risk Assessment (PRA): A Structured Taxonomy
Probabilistic risk assessment (PRA) systematically assesses the risks posed to or by a complex system such as a nuclear power plant. Such systems are often comprised of physical structures, mechanical components, and humans that interact with or control the system or respond to system upsets. This complex interdependence leads to many sources of uncertainty that must be characterized in the PRA. This problem is exacerbated when exploring the impacts of external hazards (e.g., earthquakes, floods, and fires) on complex systems due to the additional need to understand and characterize the hazard and its impacts. This study defines a framework for identifying and categorizing the common sources of uncertainty encountered in performing external hazard PRAs for nuclear power plants. The framework may be more generally applicable to the assessment of a wide range of facilities involving potentially high consequence external hazard events. Commentary on drivers of uncertainty in external hazard PRA (XHPRA) (particularly within the context of external flooding hazards) and current gaps/challenges are also provided.

Uncertainty in External Hazard Probabilistic Risk Assessment (PRA): A Structured Taxonomy

Probabilistic risk assessment (PRA) systematically assesses the risks posed to or by a complex system such as a nuclear power plant. Such systems are often comprised of physical structures, mechanical components, and humans that interact with or control the system or respond to system upsets. This complex interdependence leads to many sources of uncertainty that must be characterized in the PRA. This problem is exacerbated when exploring the impacts of external hazards (e.g., earthquakes, floods, and fires) on complex systems due to the additional need to understand and characterize the hazard and its impacts. This study defines a framework for identifying and categorizing the common sources of uncertainty encountered in performing external hazard PRAs for nuclear power plants. The framework may be more generally applicable to the assessment of a wide range of facilities involving potentially high consequence external hazard events. Commentary on drivers of uncertainty in external hazard PRA (XHPRA) (particularly within the context of external flooding hazards) and current gaps/challenges are also provided.

Paper MB157 | Download the paper file. | Download the presentation PowerPoint file.

Name: Michelle Bensi (mbensi@umd.edu)

Bio: Michelle (Shelby) Bensi, Ph.D. is an assistant professor in the Department of Civil and Environmental Engineering at the University of Maryland (UMD). Dr. Bensi’s research centers on the application of probabilistic risk assessment concepts and tools as well as statistical/machine learning techniques to problems involving engineered systems exposed to natural hazards. Dr. Bensi focuses primarily on topics related to the probabilistic assessment of natural hazards (e.g., seismic, coastal, inland flooding, precipitation), risk-informed applications, and disaster resilience. Prior to joining the UMD faculty, Dr. Bensi served as an engineer at the United States Nuclear Regulatory Commission where she was heavily involved in the agency's response to the Fukushima Dai-ichi reactor accidents. Dr. Bensi serves as a member of the American Nuclear Society and American Society of Mechanical Engineers (ANS/ASME) Joint Committee on Nuclear Risk Management (JCNRM).

Country: USA
Company: University of Maryland
Job Title: Assistant Professor

Paper 4 SI142

Lead Author: Tamas Siklossy Co-author(s): Attila Bareith bareith@nubiki.hu Barnabas Toth tothb@nubiki.hu Bence Burjan burjan@nubiki.hu

Assessing the Impact of Combined External Events on the Safety of NPP Paks
Originally, mostly single external hazards were considered in the definition of the design basis of the Paks NPP in Hungary. Accordingly, the analysis and evaluation of plant resistance against design basis loads as well as the probabilistic safety assessment (PSA) of the plant have been limited to these single external hazards. However, some specific requirements of the Hungarian Nuclear Safety Codes as well as international recommendations and lessons learned from the Fukushima Dai-ichi NPP accident pointed out the need for systematically assessing the combinations of external hazards for the Paks NPP so that their impact on plant safety can be determined, understood and evaluated. The assessment has lately been completed by following the commonly exercised steps in this domain: hazard selection and screening, probabilistic hazard assessment, evaluation of plant protection, plant response and fragility analysis, development of event sequence models for hazard initiated plant transients, and risk quantification and evaluation of results. The analysis proved to be a significant challenge due to scarcity of data, lack of knowledge as well as limitations of existing PSA methodologies. Detailed assessment was performed for the following combinations of external hazards: handling of dangerous substances under severe meteorological conditions; multiple accidents in nearby industrial facilities due to a common initiator of natural origin; earthquake occurring during extremes of ambient temperature; storm; extreme wind and snow; extreme low or extreme high ambient temperature. Risk induced by the combinations of extreme wind and snow as well as earthquake during extreme warm weather was quantified using either a detailed PSA model or a bounding assessment, as shown appropriate. This paper presents an overview of systematically considering combinations of external events in the design basis and in the probabilistic safety assessment of NPP Paks. Important methodological aspects as well as key analysis results and findings are summarized.

Assessing the Impact of Combined External Events on the Safety of NPP Paks

Originally, mostly single external hazards were considered in the definition of the design basis of the Paks NPP in Hungary. Accordingly, the analysis and evaluation of plant resistance against design basis loads as well as the probabilistic safety assessment (PSA) of the plant have been limited to these single external hazards. However, some specific requirements of the Hungarian Nuclear Safety Codes as well as international recommendations and lessons learned from the Fukushima Dai-ichi NPP accident pointed out the need for systematically assessing the combinations of external hazards for the Paks NPP so that their impact on plant safety can be determined, understood and evaluated. The assessment has lately been completed by following the commonly exercised steps in this domain: hazard selection and screening, probabilistic hazard assessment, evaluation of plant protection, plant response and fragility analysis, development of event sequence models for hazard initiated plant transients, and risk quantification and evaluation of results. The analysis proved to be a significant challenge due to scarcity of data, lack of knowledge as well as limitations of existing PSA methodologies. Detailed assessment was performed for the following combinations of external hazards: handling of dangerous substances under severe meteorological conditions; multiple accidents in nearby industrial facilities due to a common initiator of natural origin; earthquake occurring during extremes of ambient temperature; storm; extreme wind and snow; extreme low or extreme high ambient temperature. Risk induced by the combinations of extreme wind and snow as well as earthquake during extreme warm weather was quantified using either a detailed PSA model or a bounding assessment, as shown appropriate. This paper presents an overview of systematically considering combinations of external events in the design basis and in the probabilistic safety assessment of NPP Paks. Important methodological aspects as well as key analysis results and findings are summarized.

Paper SI142 | Download the paper file. | Download the presentation PowerPoint file.

Name: Tamas Siklossy (siklossyt@nubiki.hu)

Bio: After seven years of being a research fellow, Mr. Siklossy has in 2017 been nominated as the head of the Risk Assessment Division of NUBIKI Nuclear Safety Research Institute, a TSO in Hungary. As his primary research topic, he has been working in the field of level 1 PSA of natural external events, especially on meteorological events and river contamination. Moreover, he has also been involved in many different areas of PSA development as well as review.

Country: HUN
Company: NUBIKI Kft.
Job Title: Head of Risk Assessment Division