ML24309A079

November 2024 PRA Counterparts Meeting Presentation on Significance Determination Process Overview and Guidance Updates

ML24309A079
Person / Time
Issue date:	11/30/2024
From:	Alex Garmoe NRC/NRR/DRO/IRAB
To:
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Download: ML24309A079 (27)

Text

SDP Overview Alex Garmoe Senior Reactor Analyst PRA Counterparts Meeting November 2024

SDP and NRC Regulatory Framework

• NRC roles include rulemaking, licensing, oversight, and more

• SDP supports the oversight roles outlined in red (inspection, performance assessment, enforcement)

• Operating reactor performance assessed via Performance Indicators and Inspection results (Findings)

• Enforcement

- Focused on non-compliance with requirements (License, CFR, etc.)

- Cited (response required) or Non-Cited (credit CAP) violations

- Severity Level, perhaps a civil penalty

• SECY-98-144 (approved by Commission SRM) discussed moving toward risk-informed, performance-based regulation

- Long-time view that safety is assured through compliance, though we now understand there are nuances to that thinking

- ROP brought in more risk-informed approaches reflecting that its not as simple as compliance = safety

• Findings

- Focused on non-adherence to self-imposed standards

- Significance (color), additional inspection SDP and NRC Regulatory Framework

• Start with a question or issue of concern

- Could ultimately be nothing, could be somethingdont know at this point

• Multiple risk-informed screenings applied

- Very Low Safety Significance Issue Resolution process

- Was failure to meet a requirement or standard within the licensees ability to foresee and correct - is it a Performance Deficiency?

- Minor vs more-than-Minor questions and examples

• If you get here, SDP begins Initial Issue Screening

• Qualitative Safety Goals were included in the Commissions 1986 Safety Goal Policy Statement

1. Individuals bear no significant additional risk to life and health

2. Societal risks to life and health should be comparable to or less than the risk of generating electricity from viable competing technologies and should not be a significant addition to other societal risks Qualitative Safety Goals

• Quantitative Health Objectives established as a measure to determine that the Qualitative Safety Goals are met

1. Risk of prompt fatalities from reactor accidents should not exceed 0.1% of the sum of prompt fatality risk from other accidents to which members of the public are generally exposed

2. Risk of cancer fatalities from reactor operation should not exceed 0.1% of the sum of cancer fatality risks from all other causes Quantitative Health Objectives

• Prompt fatality QHO

- Risk of prompt fatality to general population of all other accidents to which they are generally exposed was 5E-4 per year

- Applying 0.1% safety goal criteria to the total accident risk 5E-7 per year

- Considering early risk to individuals (IER) within one mile of the plant, QHO is generally met if LERF < 1E-5 per year (math in NUREG 1860 Appendix D)

• LERF goal of 1E-5 per year will generally ensure the prompt fatality QHO is met From QHOs to SDP Thresholds

• Cancer fatality QHO

- Cancer fatality rate to the general population from all other causes was 2E-3 per year

- Applying 0.1% safety goal criteria to the total cancer risk 2E-6 per year

- Considering latent risk to individuals (ILR) within 10 miles of the plant, QHO is generally met if CDF < 1E-4 per year (math in NUREG 1860 Appendix D)

• CDF goal of 1E-4 per year will generally ensure the latent cancer QHO is met From QHOs to SDP Thresholds

• Determine whether Finding is Green, White, Yellow, or Red

• Informed by calculated CDF and LERF when quantitative assessment is possible

• Actual initiating events assessed using CCDP and CLERP instead

- The incremental CCDP is equal to the deltaCDF if the averaging is done for a period of one year

• Deterministic SDPs when quantitative calculations not possible Significance Determination Process Color CDF LERF Green

<1E-6

<1E-7 White 1E-6 to 1E-5 1E-7 to 1E-6 Yellow 1E-5 to 1E-4 1E-6 to 1E-5 Red

>1E-4

>1E-5 QHO surrogates

• SDP risk analyses differ from other NRC risk processes

- SDP is evaluating the increase in risk due to a performance deficiency

- Nominal test and maintenance is typically used for SSCs not directly affected by the PD

• MD 8.3 evaluates what actually happened, regardless of PD

- A PD has very likely not yet been identified

- Limited information to support a risk analysis

- Actual equipment unavailability is included

• ASP also evaluates what actually happened, regardless of PD

- May differ from MD 8.3 evaluation since much more information is available

- May differ from SDP since ASP does not limit analysis to impact of PD

- Actual equipment unavailability is included Significance Determination Process

Significance Determination Process 255-day timeline 120 days to exit 45 days to issue IR 90 days to finalize

Significance Determination Process Information exchange with inspectors Information exchange with SRAs Interaction with SES Sponsor Letter/Reg Conf and follow-up

Significance Determination Process Inspector/Branch level involvement Region-wide involvement Agency-wide involvement

• NRC uses SPAR models developed by Idaho National Labs

- INL provided with licensee risk model information

• Models use generic data supplemented by plant-specific data

• Event trees and fault trees model Initiating Event propagation and failure modes of components and include human error, dependencies, and common cause failures

• Significant uncertainties (aleatory and epistemic)

• SPAR/Saphire have good tools for assessing uncertainty

• Over-conservatisms, non-conservatisms, and inaccuracies in SPAR models are addressed during SDPs

- No need to spend effort on endless refinement once were confident that the quantitative color is unlikely to change Detailed Risk Evaluations

Decisions Along The Way

• IFRB

- Regional-level meeting to approve the performance deficiency, plan for significance evaluation, resources needed, and key messages for licensee

- Establish single management point of contact for communications

• SERP

- Agency-level meeting to approve the preliminary significance evaluation and enforcement

- Decision-makers from region, HQ technical division, program division, Office of Enforcement

• Post Conference Review (Final SERP)

- A second SERP to approve the final significance evaluation after consideration of additional information provided by the licensee

• Confidence in the color matters more than absolute precision

- Significant uncertainties and modeling limitations

• SDP uses the concept of best available information

• Recognition and consideration of uncertainties and sensitivities

- Exposure time, recoverability

• Risk-informed consideration of qualitative factors at the SERP

• Operating reactor assessment process relies upon timely SDP completion

• Level of effort can be beyond that commensurate with the safety significance of issues Important Concepts

SDP and Efficiency

• ROP and SDP help focus resources and effort on issues of potentially greater significance

• IMC 0612 and SDP promote efficiency by offering continuous exit path to VLSSIR, minor, or Green

• IFRB ensures early alignment on issue to be assessed and how

• Enhanced Best Available Information guidance being issued soon is intended to focus information exchange on the most applicable and influential items

• Extensive opportunity for information exchange and dialogue throughout the process - early and often

• All stakeholders, internal and external, in the process have a role in efficient implementation

• Issue Screening Guidance: IMC 0612

• SDP Guidance: IMC 0609

• RASP Handbook for detailed risk evaluations

• Internal team (GREATR) reviews and revises guidance : Initial Characterization of Findings App A: At-power SDP App B: Emergency Preparedness App H: Containment Integrity App C: Occupational Radiation Safety App I: Licensed Operator Requal App D: Public Radiation Safety App J: SG Tube Integrity App E: Security App K: Maintenance Risk/Risk Mgmt App F: Fire Protection App L: B.5.b App G: Shutdown Operations App M: Qualitative SDP Guidance Documents

Guidance Updates

• IMCs and IPs are periodically reviewed for updating as a standard practice

• RASP Handbook revisions ongoing - led by GREATR

- Volume 1 revision expected in 2025

• Re-organizing of IMC 0609 Attachment 1 to improve usability

- Not a lot of changes other than re-organizing

- Eliminating planning SERP for initiating event evaluations

- SERP form edits based on experience and feedback

Guidance Updates

• IMC 0609 Attachment 4 and Appendix K updates to route PRA configuration control issues recently issued

• IMC 0609 Appendix F comprehensive updates issued this year

• Security and EP SDPs in various stages of being evaluated for updates, potentially sizeable changes

• IMC 0308 Attachment 3 (SDP Basis) updated to incorporate new Best Available Information guidance

- Discussed at July bi-monthly public meeting with ROP Taskforce

- Not a change to process or practice but enhancing existing limited guidance

• Numerous other fairly routine document updates in progress

Why Develop a BAI Decision Guide?

• Effectiveness review of SDP timeliness in 2022 timeframe

- Purpose to identify any potential enhancements to the SDP that could help improve the timeliness of findings

- Timeliness matters due to regulatory uncertainty, inspection of corrective actions, maintain currently reflective assessment program, efficient use of resources

- Report: ML22335A003

- Recommendation 5: Reinforce existing program guidance on the use of best available information at each process stage in the SDP

• Current guidance in IMC 0609 is limited and limiting

Development of Guide

• Goal to improve quality of information exchange

• Not intended to change our process or restrict the flow of information

• Informed by experiences with considering information submitted during SDPs

• Keep guidance high-level and flexible to accommodate all situations and defer to case-specific judgment

• Considerations, not requirements, not all-encompassing

• Intended to frame the mindset around what makes information better or more applicable than the current state of knowledge

• Exhibit to IMC 0308, Attachment 3 (SDP Basis)

• Maintain existing overall process

• Considerations, not requirements, and not all-encompassing

• Flexible to accommodate different situations

• Improve quality of information exchange

Questions