“Regulatory Risk-Informed Activities and Supporting PRA Technical Acceptability”

1. “Regulatory Risk-Informed Activities and Supporting PRA Technical Acceptability” Presented toNuclear Energy Standards Coordination Collaborative (NESCC) November 2014, Washington DC Presented by Mary Drouin US Nuclear Regulatory Commission

2. Commission PRA Policy Statement -- 1995 (1 of 2) • The use of PRA technology should be increased in all regulatory mattersto the extent supported by the state-of-the-art in PRA methods and data and in a manner that complements the NRC’s deterministic approach and supports the NRC’s traditional defense-in-depth philosophy • PRA and associated analysis (e.g., sensitivity studies, uncertainty analyses, and importance measure) should be used in regulatory matters, where practical within the bounds of the state-of-the-art, to reduce unnecessary conservatism . . . . Where appropriate, PRA should be used to support the proposal for additional regulatory requirements in accordance with 10 CFR 50.109 (Backfit Rule). Appropriate procedures for including PRA in the process for changing regulatory requirements should be developed and followed . . . .

3. Commission PRA Policy Statement – 1995 (2 of 2) • PRA evaluations in support of regulatory decisions should be as realistic as practicable and appropriate supporting data should be publicly available for review • The Commission’s safety goals for nuclear power plants and subsidiary numerical objectives are to be used with appropriate consideration of uncertainties in making regulatory judgments on the need for proposing and backfitting new generic requirements and nuclear power plant licenses.

4. Risk-Informed Initiatives • Staff became more aggressive in implementing risk-informed initiatives • Reactor examples: • Risk informed pressurized thermal shock • Risk informed categorization of structures, systems and components for special treatment • Reactor oversight process • Risk-informed technical specifications • Risk-informed changes to licensing basis • All activities depend on a technically acceptable PRA

5. Challenges in Using Results/Insights from PRAs • Results from different PRAs vary over and above that caused by design and operational differences, as a result of differing assumptions, level of detail, and approximations • Uncertainty analyses are needed to assess the robustness of the PRA model • Uncertainties associated with • Parameter values (initiating event frequencies, failure rates, human error probabilities) • Choice of models or modeling assumptions (e.g., seal LOCA model, success criteria) • Incompleteness in coverage of contributors to risk • E.g., low power and shutdown modes, external hazards • Sabotage, errors of commission, aging effects • No standard or guidance to address many of these issues

6. Commission Direction Setting Initiative 13 -- 1997 • Staff “should increase its focus and emphasis on interacting with both industry groups and professional societies and technical institutes to develop new codes, standards, and guides . . . . would then be endorsed by the NRC. Further, the NRC’s initial activities should focus on standards development in probabilistic risk assessment.” • Staff met with ASME in summer of 1997 to propose development of a PRA standard

7. A Full Scope Site PRA • January 1998, ASME initiated effort in development of PRA standards • Level 1 (including large early release) for reactor at-power considering internal events and internal flood Risk Sources Reactor Core Spent Fuel Pool Dry Cask Storage Reactor “Type” Operating LWRs New Advanced LWRs Non-LWRs Site Operating StatesDesign/COL At-power Low-power/shutdown Refueling Storage Risk CharacterizationLevel 1 Level 2 Level 3 (Fuel damage frequency) Release Frequency Consequences Hazard SourcesInternalExternal • Internal Events • Natural phenomena (e.g., earthquakes, volcanoes) • Internal Floods • Weather related (e.g., hurricanes, high winds) • Internal Fires • Man made phenomena (e.g., industrial accident, aircraft crash) • Extra-terrestial (e.g., solar flare, meteor)

8. Regulatory Guide (RG) 1.200: “An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities” • Provides “one acceptable approach for determining whether the technical adequacy of the PRA….is sufficient to provide confidence in the results, such that the PRA can be used in regulatory decisionmaking for light-water reactors” • As such, RG 1.200 was structured, by design: • To focus on the technical acceptability of the base PRA • To address technical adequacy of the PRA results used for an application • So that when used in support of an application…will obviate the need for an in-depth review of the base PRA by the staff • To focus staff review on key assumptions and areas identified by peer reviewers as being of concern

9. Licensing Risk-Informed Licensing Changes 50.69 Risk-Informed Categorization and Treatment of SSCs 50.48(c) Fire Protection, National Fire Protection Association Standard NFPA 805 10 CFR part 52 Licenses, Certifications, And Approvals For Nuclear Power Plants RG 1.200 Supports Risk-Informed Activities in Defining PRA Technical Adequacy ... APPLICATION APPLICATION SPECIFIC REGULATORYGUIDE ... Regulatory Guide 1.206 Regulatory Guide 1.174 Regulatory Guide 1.201 Regulatory Guide 1.205 Regulatory Guide 1.200 GENERIC SUPPORTING GUIDANCE National PRA Consensus Standards and Industry Related Guidance  RG 1.200 is invoked by other regulatory guides

10. RG 1.200: Staff Regulatory Position • Provides staff position on • What constitutes a technically acceptable PRA and peer review • How to use a national consensus standard and industry peer review in demonstrating compliance with staff position • Provides staff endorsement of published PRA standards and associated peer review guidance • Demonstrating that the PRA used in regulatory applications is of sufficient technical adequacy • Documentation to support a regulatory application • Does not provide a staff position on other risk analysis approaches

11. RG 1.200: Scope Risk Sources Reactor Core Spent Fuel Pool Dry Cask Storage Reactor “Type” Operating LWRs New Advanced LWRs Non-LWRs Site Operating StatesDesign/COL At-power Low-power/shutdown Refueling Storage Risk CharacterizationLevel 1 Level 2 Level 3 (Fuel damage frequency) Release Frequency Consequences Hazard SourcesInternalExternal • Internal Events • Natural phenomena (e.g., earthquakes, volcanoes) • Internal Floods • Weather related (e.g., hurricanes, high winds) • Internal Fires • Man made phenomena (e.g., industrial accident, aircraft crash) • Extra-terrestial (e.g., solar flare, meteor)

12. Standard Scope (At present) Risk Sources Reactor Core Spent Fuel Pool Dry Cask Storage Reactor “Type” Operating LWRs New Advanced LWRs Non-LWRs Site Operating StatesDesign/COL At-power Low-power/shutdown Refueling Storage Risk CharacterizationLevel 1 Level 2 Level 3 (Fuel damage frequency) Release Frequency Consequences Hazard SourcesInternalExternal* • Internal Events • Natural phenomena (e.g., earthquakes, volcanoes) • Internal Floods • Weather related (e.g., hurricanes, high winds) • Internal Fires • Man made phenomena (e.g., industrial accident, aircraft crash) • Extra-terrestial (e.g., solar flare, meteor) *Standard may not cover all specific events

13. Implementation Challenges(1 of 4) • The goal is to make good safety decisions. Therefore, the technical acceptability required of a PRA for a specific application is a function of the role the results play in that decision. • Some applications depend on results from a limited number of PRA elements (e.g., single Allowed Outage Time extension), others (e.g., categorization of Structures, Systems and Components into risk significant groups) require a broader scope. • The decisionmaking process involves determining what PRA results are required to generate the required risk insights, and whether the PRA contains the appropriate elements to model the impact of the change.

14. Implementation Challenges(2 of 4) • Because of this flexibility, some level of review will always be required for applications to licensing issues. A well conducted peer review of the PRA, however, can help to focus regulatory review by identifying key assumptions and approximations and assessing their potential impact on the PRA results and insights. • Not meeting the Standard in all aspects does not preclude using the PRA for a specific decision if those elements that do not meet the Standard have no impact on the application. • The degree of confidence in the results can vary even if the Standards are met, because of differences in assumptions and approximations.

15. Implementation Challenges(3 of 4) • Standard and RG 1.200 focus is on “what constitutes a technically acceptable PRA?” • It does not provide guidance on how to develop a technically acceptable PRA • It does not address how to implement acceptable methods, tools and data • Supporting guidance is needed to address risk significant “issues”

16. Implementation Challenges(4 of 4) • Examples of a few supporting guidance documents: • NUREG-1855, “Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decisionmaking” • NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Final Report, (NUREG/CR-6850, EPRI 1011989) • NUREG-1792, “Good Practices for Implementing Human Reliability Analysis (HRA)” • NUREG-1842, “Evaluation of Human Reliability Analysis Methods Against Good Practices” • NUREG/CR-6823 "Handbook of Parameter Estimation for Probabilistic Risk Assessment"

17. Path Forward • Continue to support ASME and ANS in • Developing remaining standards • Maintaining and updating existing standards to address new methods, information, etc. • Work with stakeholders to address and resolve technical issues • Develop supporting guidance to reduce uncertainties and help make implementation effective, efficient and consistent