PSAM 16 - Session M25 Overview

PSAM 16 Conference Session M25 Overview

Session Chair: Marina Roewekamp (marina.roewekamp@grs.de)

Paper 1 DB190

Lead Author: David Blanchard

Use of a Risk-Informed Performance-Based Advanced Reactor Design Standard to Categorize and Classify Components for a Current Generation Nuclear Power Plant
A number of standards and guidelines have been developed for use in the US for the purpose of risk informing the design of advanced reactors. Some of these documents are directed at specific reactor types, others are technology neutral. The objectives of each of these standards and guidelines are directed at appropriately combining deterministic, probabilistic, and performance-based design methods during development of the plant design. This paper describes the application of one of these risk-informed performance-based (RIPB) design standards to the categorization and classification of components for a current generation light water reactor. While the selected standard was developed for use in the design of an advanced reactor, the purpose of this exercise was to identify what components would have been classified as safety related, non-safety related (with special treatment requirements) and non-safety related (no special treatment requirements) had insights from the plant specific PRA been available at the time the plant was licensed. The plant is a PWR that began operation in the early 1970s. The RIPB design standard that was selected was ANS/ANSI 30.3, ‘Light-Water Reactor Risk-Informed Performance-Based Design-202x’ which recently concluded final balloting. ANS/ANSI 30.3 permits the selection of licensing basis events using any of a spectrum of approaches from traditional deterministic methods supplemented by PRA to starting with risk significant accident sequences of the PRA and adjusting them deterministically. For the purpose of this exercise, the licensing basis for the PWR under examination was set aside and the accident sequences of the at power Level 1 internal events PRA considered as candidates for licensing basis events. A blend of deterministic and probabilistic methods were used in performing the categorization and classification of plant components. ANS/ANSI 30.3 endorses the deterministic criterion of ANS/ANSI 58.14 for initial classification of SSCs. For the subject PWR, the ANS/ANSI 58.14 criterion was applied to the cut sets from the accident sequences of the PRA. This provided a measure of plant capability defense-in-depth in selecting components that are candidates for being relied upon in managing safety. ANS/ANSI 30.3 provides flexibility in the determination of risk significance of components in that it does not endorse specific measures of importance or thresholds. In this exercise, categorization of components was performed simply by requantifying the accident sequences of the PRA to demonstrate the collective effectiveness of the ANS/ANSI 58.14 selected components in managing risk. Risk importance measures were used, but only to identify candidates for addition to or deletion from the list of selected components. In accordance with ANS/ANSI 30.3 requirements, engineering rationale based on plant design features and operating characteristics were developed when changes were made to the initial ANS/ANSI 58.14 defense-in-depth based selection of components. The paper provides definitions for ‘plant capability defense-in-depth’ and ‘risk significance’ that were used in the evaluation. Also described are the methods used to apply the ANS/ANSI 58.14 deterministic criterion using the logic models of the PRA. The final list of components classified as safety related and non-safety related with special treatment were found to be necessary and sufficient only for a subset of the accident sequences of the Level 1 internal events PRA. The paper discusses methods for pruning the PRA accident sequences to identify those that might be candidates for design basis and licensing basis events. While the plant under investigation is not likely to change its current licensing basis, the methods used in performing this categorization and classification can be beneficial in other applications of the PRA (e.g., implementation of 10CFR50.69, risk-informed cyber security, etc.).

Use of a Risk-Informed Performance-Based Advanced Reactor Design Standard to Categorize and Classify Components for a Current Generation Nuclear Power Plant

A number of standards and guidelines have been developed for use in the US for the purpose of risk informing the design of advanced reactors. Some of these documents are directed at specific reactor types, others are technology neutral. The objectives of each of these standards and guidelines are directed at appropriately combining deterministic, probabilistic, and performance-based design methods during development of the plant design. This paper describes the application of one of these risk-informed performance-based (RIPB) design standards to the categorization and classification of components for a current generation light water reactor. While the selected standard was developed for use in the design of an advanced reactor, the purpose of this exercise was to identify what components would have been classified as safety related, non-safety related (with special treatment requirements) and non-safety related (no special treatment requirements) had insights from the plant specific PRA been available at the time the plant was licensed. The plant is a PWR that began operation in the early 1970s. The RIPB design standard that was selected was ANS/ANSI 30.3, ‘Light-Water Reactor Risk-Informed Performance-Based Design-202x’ which recently concluded final balloting. ANS/ANSI 30.3 permits the selection of licensing basis events using any of a spectrum of approaches from traditional deterministic methods supplemented by PRA to starting with risk significant accident sequences of the PRA and adjusting them deterministically. For the purpose of this exercise, the licensing basis for the PWR under examination was set aside and the accident sequences of the at power Level 1 internal events PRA considered as candidates for licensing basis events. A blend of deterministic and probabilistic methods were used in performing the categorization and classification of plant components. ANS/ANSI 30.3 endorses the deterministic criterion of ANS/ANSI 58.14 for initial classification of SSCs. For the subject PWR, the ANS/ANSI 58.14 criterion was applied to the cut sets from the accident sequences of the PRA. This provided a measure of plant capability defense-in-depth in selecting components that are candidates for being relied upon in managing safety. ANS/ANSI 30.3 provides flexibility in the determination of risk significance of components in that it does not endorse specific measures of importance or thresholds. In this exercise, categorization of components was performed simply by requantifying the accident sequences of the PRA to demonstrate the collective effectiveness of the ANS/ANSI 58.14 selected components in managing risk. Risk importance measures were used, but only to identify candidates for addition to or deletion from the list of selected components. In accordance with ANS/ANSI 30.3 requirements, engineering rationale based on plant design features and operating characteristics were developed when changes were made to the initial ANS/ANSI 58.14 defense-in-depth based selection of components. The paper provides definitions for ‘plant capability defense-in-depth’ and ‘risk significance’ that were used in the evaluation. Also described are the methods used to apply the ANS/ANSI 58.14 deterministic criterion using the logic models of the PRA. The final list of components classified as safety related and non-safety related with special treatment were found to be necessary and sufficient only for a subset of the accident sequences of the Level 1 internal events PRA. The paper discusses methods for pruning the PRA accident sequences to identify those that might be candidates for design basis and licensing basis events. While the plant under investigation is not likely to change its current licensing basis, the methods used in performing this categorization and classification can be beneficial in other applications of the PRA (e.g., implementation of 10CFR50.69, risk-informed cyber security, etc.).

Paper DB190 | | Download the presentation PowerPoint file.

A PSAM Profile is not yet available for this author.

Paper 2 AN186

Lead Author: Antonios Zoulis

Expansion and Use of Risk-Informed Process for Evaluations
The Risk-Informed Process of Evaluations (RIPE) can be used to defer or eliminate compliance issues with a minimal safety impact using existing regulations. The Nuclear Regulatory Commission (NRC) approved this initiative that utilizes licensee’s previously approved risk-informed initiatives to inform licensing actions in January 2021. The initiative leverages current regulations and uses risk information to identify low safety significant issues that US licensees can use to submit plant-specific regulatory actions for issues that would support a streamlined review by the NRC using existing programs and processes that are consistent with Regulatory Guide 1.174, “An Approach for Using Probabilistic Risk Assessment In Risk-Informed Decisions On Plant-specific Changes to the Licensing Basis” (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100910006). The NRC expanded the use of RIPE to include other risk-informed initiatives and to allow for Technical Specification changes. In addition, the first application using the RIPE process was submitted involving the diverse feedwater actuation requirement in the 10 Code of Federal Regulations 50.62 “Requirements for reduction of risk from anticipated transients without scram (ATWS) events for light-water-cooled nuclear power plants.” This paper will discuss the expansion of RIPE and the first use of the initiative and lessons-learned from that submittal.

Expansion and Use of Risk-Informed Process for Evaluations

The Risk-Informed Process of Evaluations (RIPE) can be used to defer or eliminate compliance issues with a minimal safety impact using existing regulations. The Nuclear Regulatory Commission (NRC) approved this initiative that utilizes licensee’s previously approved risk-informed initiatives to inform licensing actions in January 2021. The initiative leverages current regulations and uses risk information to identify low safety significant issues that US licensees can use to submit plant-specific regulatory actions for issues that would support a streamlined review by the NRC using existing programs and processes that are consistent with Regulatory Guide 1.174, “An Approach for Using Probabilistic Risk Assessment In Risk-Informed Decisions On Plant-specific Changes to the Licensing Basis” (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100910006). The NRC expanded the use of RIPE to include other risk-informed initiatives and to allow for Technical Specification changes. In addition, the first application using the RIPE process was submitted involving the diverse feedwater actuation requirement in the 10 Code of Federal Regulations 50.62 “Requirements for reduction of risk from anticipated transients without scram (ATWS) events for light-water-cooled nuclear power plants.” This paper will discuss the expansion of RIPE and the first use of the initiative and lessons-learned from that submittal.

Paper AN186 | Download the paper file. | Download the presentation PowerPoint file.

Name: Antonios Zoulis (antonios.zoulis@nrc.gov)

Bio: Mr. Zoulis joined the NRC in 2006 as Reliability and Risk Engineer in the Office of Nuclear Reactor Regulation. Since joining the NRC, Mr. Zoulis has served in positions of increasing responsibility in NRR, NSIR and the Regions. He supported the NRC response to the Fukushima Daiichi accident in Headquarters and the Japan Site Team in the US Embassy in Tokyo. Antonios also completed a two-year detail to DHS Countering WMD Office working on material and radiological security issues with the interagency. Currently, he is the Branch Chief for the Probabilistic Risk Assessment Oversight Branch in the Office of NRR’s Division of Risk Assessment. Prior to the NRC, Antonios spent 11 years at Entergy Nuclear Northeast, as a senior PRA engineer and as the Equipment Reliability lead for the Entergy Fleet. Antonios holds a Bachelor and Master of Science degrees in Mechanical Engineering and a Master of Business Administration. He is a licensed Professional Engineer in the state of Maryland.

Country: USA
Company: Nuclear Regulatory Commission
Job Title: Branch Chief

Paper 3 DG72

Lead Author: David Grabaskas

Risk Management and Risk Aversion, from Benefit to Impediment
Risk management is a critical tool for improving the probability of project success by identifying, assessing, prioritizing, and attempting to control threats to project realization. For industries that require high operational reliability due to the potential consequences of system failure, such as the nuclear, aerospace, and chemical sectors, a major focus of risk management is the preservation of process safety. Due to the nature of the processes or systems under consideration, the associated process safety analyses (such as risk and safety assessments) and safety features can require significant resources. These costs are typically tolerated either due to the need to satisfy regulatory requirements or based on the assumption that they generally decrease the occurrence of unwanted events and therefore improve the probability of project success. However, as the level of acceptable or tolerable risk from unwanted events decreases, the required resources necessary for ensuring and demonstrating satisfaction of these criteria can grow and in turn can become one of the dominant impediments to project success. This paper outlines a high-level theoretical framework for the consideration of dominant project risks, which includes potential project failure from both system unreliability and the inability to achieve project completion due to the resource needs and innovation losses associated with extreme risk aversion. Utilizing such an integrated approach permits an attempt to optimize the probability of successful project realization while also providing valuable insight into the proper level of acceptable risk.

Risk Management and Risk Aversion, from Benefit to Impediment

Risk management is a critical tool for improving the probability of project success by identifying, assessing, prioritizing, and attempting to control threats to project realization. For industries that require high operational reliability due to the potential consequences of system failure, such as the nuclear, aerospace, and chemical sectors, a major focus of risk management is the preservation of process safety. Due to the nature of the processes or systems under consideration, the associated process safety analyses (such as risk and safety assessments) and safety features can require significant resources. These costs are typically tolerated either due to the need to satisfy regulatory requirements or based on the assumption that they generally decrease the occurrence of unwanted events and therefore improve the probability of project success. However, as the level of acceptable or tolerable risk from unwanted events decreases, the required resources necessary for ensuring and demonstrating satisfaction of these criteria can grow and in turn can become one of the dominant impediments to project success. This paper outlines a high-level theoretical framework for the consideration of dominant project risks, which includes potential project failure from both system unreliability and the inability to achieve project completion due to the resource needs and innovation losses associated with extreme risk aversion. Utilizing such an integrated approach permits an attempt to optimize the probability of successful project realization while also providing valuable insight into the proper level of acceptable risk.

Paper DG72 | Download the paper file. |

Name: David Grabaskas (dgrabaskas@anl.gov)

Bio:

Country: USA
Company: Argonne National Laboratory
Job Title: Manager, Safety and Risk Assessments Group

Paper 4 FF205

Lead Author: Fernando Ferrante Co-author(s): Karl Fleming, karlfleming@comcast.net Ed Parsley, eparsley@jensenhughes.com Charlie Young, cyoung@jensenhughes.com Leo Shanley, lshanley@jensenhughes.com

Enhancement of the Use of Defense-in-Depth and Safety Margin for Decision-Making Purposes
Both Defense-In-Depth (DID) and Safety Margin (SM) have been longstanding key concepts in nuclear applications, well before Probabilistic Risk Assessment (PRA) became a staple of risk applications in this field. A detailed review of key references on the subject of DID/SM in RIDM indicates that these topics are overdue for a more efficient, integrated approach, as RIDM applications continue to gain acceptance and implementation experience worldwide. As the use of PRA and RIDM continues to expand, different perspectives on DID/SM can challenge the incorporation of additional risk modeling and wider, more comprehensive application of PRA in nuclear power plants (NPPs). In particular, challenges from a deterministic-oriented perspective against more risk-informed applications, as well as their expansion in areas where PRA is not used as heavily, can lead to misperceptions that DID/SM principles are not aligned with respect to risk insights obtained via risk assessment inputs. A careful investigation and discussion of DID/SM as overarching principles of nuclear safety was performed to highlight that they are not intended to be substituted by PRA methods, tools, and results. Rather, the approach is to derive key elements of DID (i.e., design, programmatic, and scenario-based) that also accounted for SM inputs in a more logical, structured manner. A number of key conclusions were derived from this investigation, including the need for an enhanced, more efficient approach. Using key characteristics on how to treat DID/SM in RIDM, a recommended framework for an improvement implementation of DID/SM in RIDM is proposed, recognizing that DID/SM aspects are essential nuclear safety principles. As a different perspective than typically applied in current RIDM guidance, SM is identified as a fundamental input into the DID principle that can be better contextualized in RIDM as a supporting element (rather than a distinct and completely separate element). A significant discussion of how design, programmatic, and scenario-based DID aspects can be used in areas where PRA insights are already heavily used as well as in other areas not traditionally reliant on such inputs is discussed (including qualitative as well as quantitative risk inputs). A modern PRA model from an existing NPP site is used to showcase how risk insights on the achievement and preservation of DID/SM apply in the context of RIDM. The overall approach was based on leveraging existing guidance worldwide, considering approaches that appropriately bring the information together in a practical manner, as well as an investigation with actual implementable examples.

Enhancement of the Use of Defense-in-Depth and Safety Margin for Decision-Making Purposes

Both Defense-In-Depth (DID) and Safety Margin (SM) have been longstanding key concepts in nuclear applications, well before Probabilistic Risk Assessment (PRA) became a staple of risk applications in this field. A detailed review of key references on the subject of DID/SM in RIDM indicates that these topics are overdue for a more efficient, integrated approach, as RIDM applications continue to gain acceptance and implementation experience worldwide. As the use of PRA and RIDM continues to expand, different perspectives on DID/SM can challenge the incorporation of additional risk modeling and wider, more comprehensive application of PRA in nuclear power plants (NPPs). In particular, challenges from a deterministic-oriented perspective against more risk-informed applications, as well as their expansion in areas where PRA is not used as heavily, can lead to misperceptions that DID/SM principles are not aligned with respect to risk insights obtained via risk assessment inputs. A careful investigation and discussion of DID/SM as overarching principles of nuclear safety was performed to highlight that they are not intended to be substituted by PRA methods, tools, and results. Rather, the approach is to derive key elements of DID (i.e., design, programmatic, and scenario-based) that also accounted for SM inputs in a more logical, structured manner. A number of key conclusions were derived from this investigation, including the need for an enhanced, more efficient approach. Using key characteristics on how to treat DID/SM in RIDM, a recommended framework for an improvement implementation of DID/SM in RIDM is proposed, recognizing that DID/SM aspects are essential nuclear safety principles. As a different perspective than typically applied in current RIDM guidance, SM is identified as a fundamental input into the DID principle that can be better contextualized in RIDM as a supporting element (rather than a distinct and completely separate element). A significant discussion of how design, programmatic, and scenario-based DID aspects can be used in areas where PRA insights are already heavily used as well as in other areas not traditionally reliant on such inputs is discussed (including qualitative as well as quantitative risk inputs). A modern PRA model from an existing NPP site is used to showcase how risk insights on the achievement and preservation of DID/SM apply in the context of RIDM. The overall approach was based on leveraging existing guidance worldwide, considering approaches that appropriately bring the information together in a practical manner, as well as an investigation with actual implementable examples.

Paper FF205 | Download the paper file. | Download the presentation pdf file.

Name: Fernando Ferrante (fferrante@epri.com)

Bio: Fernando Ferrante is a Principal Project Manager at the Electric Power Research Institute (EPRI) in the Risk and Safety Management group (RSM). Ferrante joined EPRI in 2017 as a Principal Technical Leader in RSM. He was promoted to Principal Project Manager within RSM in March 2021, gaining responsibility for direct oversight of RSM staff involved in human reliability, fire risk assessment, external flooding PRA, along with RIDM framework activities. Dr. Ferrante held positions as a risk analyst at the U.S. Nuclear Regulatory Commission and senior engineer at the Defense Nuclear Facilities Safety Board. Dr. Ferrante holds a Bachelor of Science degree in Mechanical Engineering from University College London, in the United Kingdom, and a Doctor of Philosophy degree in Civil Engineering from Johns Hopkins University.

Country: ---
Company: Electric Power Research Institute
Job Title: Program Manager