ML22286A229

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October 13, 2022 PRA Counterparts Meeting Presentation on Significance Determination Process Overview
ML22286A229
Person / Time
Issue date: 10/13/2022
From: Alex Garmoe
NRC/NRR/DRO/IRAB
To:
Alex Garmoe, NRR/DRO/IRAB, 415-3814
References
Download: ML22286A229 (15)
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SDP Overview Alex Garmoe Senior Reactor Analyst Division of Reactor Oversight Office of Nuclear Reactor Regulation

SDP and NRC Regulatory Framework

  • NRC roles include rulemaking, licensing, oversight, and much more
  • SDP supports the roles outlined in red (inspection, performance assessment, enforcement)
  • Operating reactor performance assessed via Performance Indicators and Inspection results (Findings)
  • Enforcement

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

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

- Severity Level

  • Finding

- Focused on safety significance of non-adherence to self-imposed standards

- Significance (color)

  • Long-time view that safety is assured through compliance
  • ROP brought in more risk-informed approaches that have revealed that its not as simple as compliance = safety 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
  • Individuals bear no significant additional risk to life and health
  • 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
  • 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
  • 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

- 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 (NUREG 1860 Appendix D)

- IER calculated as approx. 3E-7 per reactor year when considering worst case internal initiator

- 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 (NUREG 1860 Appendix D)

- ILR calculated as approximately 4E-7 per reactor year when considering worst case accident sequence

  • 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 conditions assessed using CCDP and CLERP instead

<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

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

  • 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)
  • Over-conservatisms and inaccuracies removed from SPAR 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

- 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

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

- Decision-makers from region, HQ technical division, NRR/DRO, OE

  • Post Conference Review

- 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

Questions

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