ML24271A013

PSAM17 NRC Research Activities Presentation

ML24271A013
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Issue date:	09/27/2024
From:	Coyne K NRC/RES/DRA
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An Overview of Current Risk-Informed Decision-Making Research Activities at the US Nuclear Regulatory Commission Kevin Coyne US Nuclear Regulatory Commission Kevin.Coyne@nrc.gov

Outline

• NRCs Risk Informed Decision Making Objectives

• Key Research Activities

• Reactor Oversight - SPAR Models and the SAPHIRE code, Precursor Program

• Operating Experience Data

• PSA Standards Activities

• Fire Research

• Advanced Reactors

• Forward Looking Activities

• Conclusions and Questions

PSA Research Objectives

• Support the reactor oversight and operating experience programs;

• Remove obstacles to the implementation of risk-informed regulation (e.g., licensing activities);

• Expand the use of PSA and risk evaluation to encompass advanced reactor designs; and

• Support continuous advancement in the PSA state-of-the-art and state-of-practice

Standardized Plant Analysis Risk (SPAR)

Models

• SPAR models are plant-specific, NRC-developed, probabilistic risk assessment models that use standardized modeling conventions and industry averaged data

• Standardization increases efficiency of

- data updates,

- generating risk insight reports, and

- analysis of conditions across multiple plant models

• Currently maintain 67 SPAR models, representing all currently operating U.S. nuclear plants.

- All include Level 1 PRA modeling (core damage frequency) for internal hazards, high winds, and seismic hazards.

- Twenty-three models include fire PRA modelling

- Six models for new reactors designs (e.g., ABWR, US EPR, APWR).

SAPHIRE Computer Code

• Systems Analysis Programs for Hands-on Integrated Reliability Evaluations (SAPHIRE) computer code is used to develop and run the SPAR models

• Developed by Idaho National Laboratory, under sponsorship of the NRC, and maintained under a quality assurance program

• Includes modern fault tree/event tree capabilities as well as additional features that support NRC event and condition assessment (ECA) activities:

- Efficiently calculated changes in core damage frequency

- Enhanced common cause failure modelling

• SAPHIRE recent activities have focused on:

- improve computational speed,

- enhancement of large early release calculational capabilities,

- success path quantification for high failure probabilities, and

- development of a cloud-based SAPHIRE code

• More information available here: https://www.nrc.gov/about-nrc/regulatory/research/obtainingcodes.html#6

Accident Sequence Precursor (ASP) Program

• Determines risk significance of two broad categories of reactor operational events:

- Degraded plant conditions characterized by the unavailability or degradation of equipment in the absence of a specific initiating event, or

- The occurrence of an initiating event (e.g., a reactor trip) with or without any other degraded plant conditions

• Program initiated in 1979 following issuance of WASH-1400

- As noted in NUREG/CR-0400, it is important that potentially significant sequences and precursors be subjected to the kind of analysis contained in WASH-1400

• Provides an input for NRC performance metrics

Accident Sequence Precursor (ASP) Program

• Risk metric of interest is either the change core damage probability (CDP) (for degraded plant conditions) or the conditional core damage probability (CCDP) (for an initiating event)

• A precursor is defined as a CDP greater than or equal to 10-6 or an initiating event with a CCDP greater than 10-6 or the CCDP of a non-recoverable loss of feedwater or condenser heat sink (whichever is larger)

• Several categories of precursors are trended, including: losses of offsite power, initiating events, degraded conditions, and BWR/PWR trends

• More information available here: https://www.nrc.gov/about-nrc/regulatory/research/asp.html

Accident Sequence Precursor (ASP) Program

Operating Experience Data

• In collaboration with Idaho National Laboratory, the NRC collects, analyzes, and publishes operating experience (OpE) data consistent with our PRA Policy Statement

• A key input for OpE data is provided by the Institute for Nuclear Power Operation (INPO) under their Industry Reporting and Information System (IRIS)

• Plant identifiers are removed and industry average data is published on a public website (https://nrcoe.inl.gov/ )

• The industry averaged data is analyzed periodically to develop:

- updated reliability parameter estimates for use in SPAR models

- initiating events trends and insights;

- component and system studies;

- and common cause failure insights.

Operating Experience Data Loss of Offsite Power Initiating Event Frequency and Recovery Time Trend

PSA Standards Activities

• U.S. law requires that federal agencies emphasize where possible the use of standards developed by private, consensus organizations.

• To meet this requirement, the NRC leverages PSA consensus standards developed by ASME and ANS under the Joint Committee on Nuclear Risk Management (JCNRM)

• Regulatory Guide (RG) 1.200 uses a combination of NRC staff positions, the use of national consensus standards, and peer reviews form the basis of establishing PRA acceptability.

• This approach helps to obviate the need for an in-depth review of the base PSA by the NRC staff when reviewing licensing actions

PSA Standards - Current Status

• Anticipate inclusion in the next revision of RG 1.200:

- ASME/ANS RA-S-1.1-2024 - Level 1/Large Early Release Frequency (LERF)

- ASME/ANS RA-S-1.2-2024 - Level 2 PRA

- ASME/ANS RA-S-1.5 - Level 1/Level 2 PRA standard for advanced LWRs during preconstruction and preoperational stages

- ASME/ANS RA-S-1.6 - The Level 1/LERF PRA standard addresses low-power and shutdown

• Endorsed for trial use in RG 1.247 - ASME/ANS RA-S-1.4-2021:

Non-LWR PRA

• Lower priority:

- ASME/ANS RA-S-1.3: Level 3 PRA standard

- ASME/ANS RA-S-1.7: Level 1/Level 2/Level 3 PRA standard for multi-unit PRA models

Fire Research Activities

• Recent focus on developing enhanced methods to address high energy arcing faults (in cooperation with EPRI, NIST, SNL, and OECD)

• NUREG-2262/EPRI 3002025942 improves realism in several areas:

- electrical fault clearing times

- improved technical basis for zones of influence,

- improved estimates for cable fragility, and

- mitigation credit for electrical raceway fire barrier systems.

New LWR and Non-LWR Advanced Reactor Research In support of new approaches to advanced reactor licensing (e.g., use of the Licensing Modernization Project approach described in NEI 18-04), several activities are ongoing or planned:

• Risk metrics for advanced non-LWR reactors

• Identification of data sources for non-LWR reactor designs

• Development of guidance for addressing uncertainties, and

• Building knowledge and experience with PRA modelling challenges unique to new and advanced reactors (e.g., passive systems)

Continuous Advancement -

Level 3 PRA Project

• Project is for a multi-unit site and covers all modes of operation and all hazards. Includes spent fuel and dry cask storage.

• Objectives include: (1) reflect technical advancements since the completion NUREG-1150, (2) extract new risk insights to enhance decision-making, (3) enhance the staffs PRA capabilities, and (4) obtain insights into the costs of developing Level 3 PRA models.

• Accomplishments include:

• Piloting Level 2 and Level 3 PRA Standards and Peer Reviews

• Piloting streamlined expert elicitation guidance (ISLOCA)

• Significant knowledge management enhancement for agency staff

• The staff anticipates issuing the remaining project reports for public comment in 2024 and 2025.

Continuous Advancement -

Forward Looking Activities The NRC maintains an active Future Focused Research Program -

several projects are associated with PSA areas of interest:

• Dynamic PRA (DPRA) Study (complete) - Literature surveys, workshops, and an application of a DPRA tool to a reactor application.

• Apply the Licensing Modernization Project Methodology on an Operating Reactor (complete) - This project applied results from the ongoing Level 3 PRA project to gain experience with the overall LMP methodology and to identify key risk-insights on operating LWR reactor technology.

• A Performance Monitoring Strategy to Enhance Consistency in Risk-Informed Decision-Making (ongoing) -focused on identifying sources of variability in reactor oversight decision making.

• Preparing Risk Assessment for Hydrogen Production and Use (ongoing) -update and improve the realism of PRA methodology to better assesses risks associated with hydrogen at applications at nuclear power plants.

Questions?