PSAM 16 - Session T23 Overview

PSAM 16 Conference Session T23 Overview

Session Chair: Yasser HAMDI (yasser.hamdi@ymail.com)

Paper 1 MB158

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

Identifying and Prioritizing Sources of Uncertainty in External Hazard Probabilistic Risk Assessment: Project Activities and Progress
There are inherently significant sources of uncertainty in external hazard probabilistic risk assessment (XHPRA) for nuclear power facilities. The state of knowledge and practice associated with these uncertainties varies across hazard groups (e.g., earthquakes, wind, and flooding). There is currently a research need to build upon the existing state of knowledge to develop a technically sound, risk-informed strategy for identifying and characterizing drivers of hazard uncertainty in XHPRA for multiple classes of hazards. This paper summarizes the ongoing progress of a multi-year research project that seeks to: (1) develop a structured process for identifying, evaluating, categorizing, and communicating the impact of uncertainties on XHPRAs, (2) investigate the spectrum of uncertainties associated with realistically parsing hazard information into the XHPRA, (3) understand how uncertainties in the physical hazard characteristics/timing interfaces with plant response strategies (e.g., plant physics and human reliability), and (4) assess the combined impact of these uncertainties (and uncertainty reduction efforts) on the development of the XHPRA. This research will ultimately help to facilitate the prioritization of uncertainty reduction activities based on their risk significance, risk reduction benefit, and value.

Identifying and Prioritizing Sources of Uncertainty in External Hazard Probabilistic Risk Assessment: Project Activities and Progress

There are inherently significant sources of uncertainty in external hazard probabilistic risk assessment (XHPRA) for nuclear power facilities. The state of knowledge and practice associated with these uncertainties varies across hazard groups (e.g., earthquakes, wind, and flooding). There is currently a research need to build upon the existing state of knowledge to develop a technically sound, risk-informed strategy for identifying and characterizing drivers of hazard uncertainty in XHPRA for multiple classes of hazards. This paper summarizes the ongoing progress of a multi-year research project that seeks to: (1) develop a structured process for identifying, evaluating, categorizing, and communicating the impact of uncertainties on XHPRAs, (2) investigate the spectrum of uncertainties associated with realistically parsing hazard information into the XHPRA, (3) understand how uncertainties in the physical hazard characteristics/timing interfaces with plant response strategies (e.g., plant physics and human reliability), and (4) assess the combined impact of these uncertainties (and uncertainty reduction efforts) on the development of the XHPRA. This research will ultimately help to facilitate the prioritization of uncertainty reduction activities based on their risk significance, risk reduction benefit, and value.

Paper MB158 | 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 2 AL239

Lead Author: Albena Stoyanova Co-author(s): Olivier Nusbaumer (olivier.nusbaumer@kkl.ch) Pavol Zvoncek (pavol.zvoncek@kkl.ch) Devi Kompella (devi.kompella@relsafe.co.in) Karthik Ravichandran (karthik.ravichandran@relsafe.co.in) Rahul Agarwal (rahul.agarwal@relsafe.co.in)

Seismically-induced Internal Fire and Flood (SIFF) Assessment at Leibstadt NPP, Switzerland
Seismically induced secondary hazards such as seismically-induced fire and flood (SIFF) events have gained greater attention following major earthquakes like the Tōhoku and Virginia Earthquakes in 2011 and Kashiwazaki-Kariwa earthquake in 2007. Secondary hazards/effects proved to be of higher likelihood than originally assumed in the plant design basis. Different organizations like USNRC, EPRI, ASME, IAEA and WENRA worked to strengthen the requirements and methods for evaluating the protection against such hazards. The Swiss regulatory authority (ENSI) has also issued heightened requirements for seismic verification of existing Nuclear Power Plants (NPPs), mandating deterministic and probabilistic SIFF assessments. To fulfil ENSI requirements and to stay up-to-date with international developments, KKL performed a systematic and comprehensive assessment of SIFF events based on the state-of-the-art EPRI methodology (EPRI-3002012980), covering both deterministic and probabilistic aspects in an integrated manner. The main objectives of the project were to: (i) apply a robust, stage-wise, top-down screening process using qualitative and quantitative criteria (e.g. walkdown observations, seismic fragility estimates, risk measures); (ii) demonstrate the plant safe shutdown capability for unscreened SIFF events, if any; (iii) evaluate quantitatively the additional risk impact due to SIFF using PSA; and (iv) analyze the risk associated with explosive materials, seismic interactions and radiological aspects. The data and analysis from the latest fire and flood deterministic and probabilistic studies at KKL were used as a starting point in the project, including about 3800 potential fire ignition sources and 9100 flood sources. External experts were engaged for independent peer reviews, one of whom was a principal contributor to EPRI SIFF guidance (EPRI-3002012980). This paper describes the methods used and the insights gained from the SIFF study at KKL and depicts how a systematic top-down screening approach has proved to be effective and practical. It also discusses some relevant observations and recommendations for future similar industrial projects.

Seismically-induced Internal Fire and Flood (SIFF) Assessment at Leibstadt NPP, Switzerland

Seismically induced secondary hazards such as seismically-induced fire and flood (SIFF) events have gained greater attention following major earthquakes like the Tōhoku and Virginia Earthquakes in 2011 and Kashiwazaki-Kariwa earthquake in 2007. Secondary hazards/effects proved to be of higher likelihood than originally assumed in the plant design basis. Different organizations like USNRC, EPRI, ASME, IAEA and WENRA worked to strengthen the requirements and methods for evaluating the protection against such hazards. The Swiss regulatory authority (ENSI) has also issued heightened requirements for seismic verification of existing Nuclear Power Plants (NPPs), mandating deterministic and probabilistic SIFF assessments. To fulfil ENSI requirements and to stay up-to-date with international developments, KKL performed a systematic and comprehensive assessment of SIFF events based on the state-of-the-art EPRI methodology (EPRI-3002012980), covering both deterministic and probabilistic aspects in an integrated manner. The main objectives of the project were to: (i) apply a robust, stage-wise, top-down screening process using qualitative and quantitative criteria (e.g. walkdown observations, seismic fragility estimates, risk measures); (ii) demonstrate the plant safe shutdown capability for unscreened SIFF events, if any; (iii) evaluate quantitatively the additional risk impact due to SIFF using PSA; and (iv) analyze the risk associated with explosive materials, seismic interactions and radiological aspects. The data and analysis from the latest fire and flood deterministic and probabilistic studies at KKL were used as a starting point in the project, including about 3800 potential fire ignition sources and 9100 flood sources. External experts were engaged for independent peer reviews, one of whom was a principal contributor to EPRI SIFF guidance (EPRI-3002012980). This paper describes the methods used and the insights gained from the SIFF study at KKL and depicts how a systematic top-down screening approach has proved to be effective and practical. It also discusses some relevant observations and recommendations for future similar industrial projects.

Paper AL239 | Download the paper file. | Download the presentation PowerPoint file.

Name: Albena Stoyanova (Albena.Stoyanova@kkl.ch)

Bio: Nuclear Engineer with 27 years wide range experience in International projects in different NPP and Waste management facilities (ref. Empressarios Agrupagos-Spain, Framatome-France, Atomenergoexport and Atomenergoproejekt-Russia, ONET Technologies-France, Parsons-Bulgaria, ANDRAD-Rumania etc). Born and educated in Bulgaria. Worked in Research&Design Institute "Energoproejekt" Bulgaria, Kozloduy NPP Bulgaria, ONET Technologies Bulgaria, Olkiluoto Unit 3 NPP Finland, Oskarshamn Unit 2 Sweden. Since 2019 in Leibstadt NPP Switzerland as PSA Specialist. Knowleadge and experience fields: – WWER / BWR / EPR technology; – Licensing of new NPPs (WWER in Bulgaria and EPR in Finland); – Deterministic and Probabilistic Safety Assessment of modernized and new NPP; – Design, Safety Assessment and Licensing of Waste Management Facilities; – Konfiguration and Project Management; – Environment Impact Analysis.

Country: CHE
Company: Leibstadt Nuclear Power Plant
Job Title: Specialist Probailistic Safety Assessment

Paper 3 NA252

Lead Author: Daichi Nagai Co-author(s): Koji Shirai, shirai@criepi.denken.or.jp / Koji Tasaka, kotasaka@criepi.denken.or.jp

Internal Flooding Fragility Experiments using Full-scale Fire Doors to Evaluate Door Failure Water Height and Leakage Flow Rate under Hydrostatic Pressure Loads
The Central Research Institute of Electric Power Industry (CRIEPI) is developing an internal flooding PRA (IF-PRA) guide for nuclear power plants in Japan. One of the questions of interest in the internal-flooding scenario modeling is that of how susceptible to failure structures and components are to the water ingress or spray. In IF-PRA, as doors can be flooding propagation paths, flooding could propagate to adjacent areas through gaps between doors and frames as well as doors opened by static head due to flooding depths. Therefore, it is very important to clarify the characteristics of flooding propagation modeling through doors. CRIEPI has performed hydrostatic pressure tests using one-hour rating fireproof door which is often used in nuclear power plants. In this study, the door which size is about 1.0 m width and 2.1 m height attached to 7.5 m3 rectangular water tank. By filling the tank with water until door swing to open due to the door latch failure, water height and leakage flow rate were measured. According to the test results, we found that the door failure could be occurred when the static head reached around 1.3 m for forward direction while no failure were occurred for opposite direction. Moreover, the leakage flow rate through the gaps of the door perimeter could be also affected by the direction in which the static head loaded on the door.

Internal Flooding Fragility Experiments using Full-scale Fire Doors to Evaluate Door Failure Water Height and Leakage Flow Rate under Hydrostatic Pressure Loads

The Central Research Institute of Electric Power Industry (CRIEPI) is developing an internal flooding PRA (IF-PRA) guide for nuclear power plants in Japan. One of the questions of interest in the internal-flooding scenario modeling is that of how susceptible to failure structures and components are to the water ingress or spray. In IF-PRA, as doors can be flooding propagation paths, flooding could propagate to adjacent areas through gaps between doors and frames as well as doors opened by static head due to flooding depths. Therefore, it is very important to clarify the characteristics of flooding propagation modeling through doors. CRIEPI has performed hydrostatic pressure tests using one-hour rating fireproof door which is often used in nuclear power plants. In this study, the door which size is about 1.0 m width and 2.1 m height attached to 7.5 m3 rectangular water tank. By filling the tank with water until door swing to open due to the door latch failure, water height and leakage flow rate were measured. According to the test results, we found that the door failure could be occurred when the static head reached around 1.3 m for forward direction while no failure were occurred for opposite direction. Moreover, the leakage flow rate through the gaps of the door perimeter could be also affected by the direction in which the static head loaded on the door.

Paper NA252 | Download the paper file. |

Name: Daichi Nagai (nagai3915@criepi.denken.or.jp)

Bio: Daichi Nagai is a research scientist at Central Research Institute of Electric Power Industry (CRIEPI). His work focuses specifically on internal flooding PRA and fire protection engineering. Research interest: Probabilistic risk assessment, multi-hazard PRA .

Country: JPN
Company: Central Research Institute of Electric Power Industry (CRIEPI)
Job Title: Research Scientist

Paper 4 MA222

Lead Author: Marina Roewekamp Co-author(s): John A. Nakoski, John.Nakoski@nrc.gov Attila Bareith, bareith@nubiki.hu Dana Havlín Nováková, dana.havlinnovakova@sujb.cz

Consideration of Combined Hazards Within PSA - A WGEV and WGRISK Perspective
After the Fukushima reactor accidents, combinations of hazards have gained more and more attention. As a result, the importance of adequate consideration of hazard combinations, particularly involving external hazards, in all types of safety assessments of nuclear installations has been recognized by the experts involved. Several national as well as international activities are ongoing with respect to combinations of hazards, including the extension of IAEA Safety Guides to better cover combined hazards, and one of the currently ongoing activities conducted jointly by the OECD Nuclear Energy Agency (NEA) Working Groups on Risk Assessment (WGRISK) and on External Events (WGEV) entitled “Combinations of External Hazards – Hazard and Impact Assessment and Probabilistic Safety Analysis (PSA) for Nuclear Installations”. This activity was initiated in 2020 addressing the state-of-the-art practices used in considering combinations of external hazards in the design and safety assessment of nuclear installations. The first phase of the activity covered a survey of members of both Working Groups in order to develop an informed understanding of the regulatory requirements and the technical approaches in WGEV and WGRISK member countries with regard to the treatment of combined external hazards and integrated hazard impacts. The survey included questions on regulatory requirements for hazard combinations analysis and their consideration in safety analyses, the use of a specific terminology and the frequencies for reviews and updates of the assessment. The survey questions also covered the specific approach for hazard combinations in the frame of siting and licensing for new nuclear power plants (NPPs) and possible differences compared to operating ones, the use of specific PSA guidance for hazard combinations and its application to support risk-informed decision-making (RIDM), and the review of protective measures against hazard combinations by the regulators. Individual member states provided examples of experiences with respect to hazard combinations. PSA needs were also considered in the survey including the underlying methodologies for identifying, interpreting, and screening combined external hazards as well as performing probabilistic hazard assessment suitable for use in PSA. Methodologies for plant response and fragility analysis, development of event sequence models including the role of plant personnel, and risk quantification along with the treatment of uncertainties were in the scope of the survey. PSA modelling of internal events and hazards consequential to external hazards or combinations of external hazards was also addressed in the survey. In the second phase of the activity, a joint workshop of WGEV and WGRISK will take place to involve a broader range of engineers, scientists, risk analysts and other experts in this field to address key issues and identify technology gaps. Insights from the survey on which hazards realistically should be combined will be discussed, with a specific focus on risk assessment for accidents induced by combinations of hazards at full power as well as in low power and shutdown states. The discussions are expected to help better identify and characterize important hazard combinations and understand the state-of-the-art in assessing the integrated impact of combined hazards and in developing PSA for combined external hazards. This paper presents the status of this international activity and some intermediate results with respect to PSA for combined external hazards.

Consideration of Combined Hazards Within PSA - A WGEV and WGRISK Perspective

After the Fukushima reactor accidents, combinations of hazards have gained more and more attention. As a result, the importance of adequate consideration of hazard combinations, particularly involving external hazards, in all types of safety assessments of nuclear installations has been recognized by the experts involved. Several national as well as international activities are ongoing with respect to combinations of hazards, including the extension of IAEA Safety Guides to better cover combined hazards, and one of the currently ongoing activities conducted jointly by the OECD Nuclear Energy Agency (NEA) Working Groups on Risk Assessment (WGRISK) and on External Events (WGEV) entitled “Combinations of External Hazards – Hazard and Impact Assessment and Probabilistic Safety Analysis (PSA) for Nuclear Installations”. This activity was initiated in 2020 addressing the state-of-the-art practices used in considering combinations of external hazards in the design and safety assessment of nuclear installations. The first phase of the activity covered a survey of members of both Working Groups in order to develop an informed understanding of the regulatory requirements and the technical approaches in WGEV and WGRISK member countries with regard to the treatment of combined external hazards and integrated hazard impacts. The survey included questions on regulatory requirements for hazard combinations analysis and their consideration in safety analyses, the use of a specific terminology and the frequencies for reviews and updates of the assessment. The survey questions also covered the specific approach for hazard combinations in the frame of siting and licensing for new nuclear power plants (NPPs) and possible differences compared to operating ones, the use of specific PSA guidance for hazard combinations and its application to support risk-informed decision-making (RIDM), and the review of protective measures against hazard combinations by the regulators. Individual member states provided examples of experiences with respect to hazard combinations. PSA needs were also considered in the survey including the underlying methodologies for identifying, interpreting, and screening combined external hazards as well as performing probabilistic hazard assessment suitable for use in PSA. Methodologies for plant response and fragility analysis, development of event sequence models including the role of plant personnel, and risk quantification along with the treatment of uncertainties were in the scope of the survey. PSA modelling of internal events and hazards consequential to external hazards or combinations of external hazards was also addressed in the survey. In the second phase of the activity, a joint workshop of WGEV and WGRISK will take place to involve a broader range of engineers, scientists, risk analysts and other experts in this field to address key issues and identify technology gaps. Insights from the survey on which hazards realistically should be combined will be discussed, with a specific focus on risk assessment for accidents induced by combinations of hazards at full power as well as in low power and shutdown states. The discussions are expected to help better identify and characterize important hazard combinations and understand the state-of-the-art in assessing the integrated impact of combined hazards and in developing PSA for combined external hazards. This paper presents the status of this international activity and some intermediate results with respect to PSA for combined external hazards.

Paper MA222 | Download the paper file. | Download the presentation pdf file.

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