ML17174B290

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2017 NEI Risk-Informed Regulation and Fire Protection Fire Forum Slides
ML17174B290
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Issue date: 06/26/2017
From: Michael Cheok, Mary Drouin, Jonathan Evans, Anders Gilbertson, Matthew Humberstone, Markhenry Salley, Brett Titus, Jennifer Whitman
NRC/NRR/DRA, NRC/RES/DRA
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Nuclear Energy Institute
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Download: ML17174B290 (146)
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NRC Support of Risk-Informed Regulation NEI Risk Informed Regulation Forum June 26, 2017 Mike Cheok Director Division of Risk Analysis Office of Nuclear Regulatory Research

Background

Commission Policy statement on use of PRA Approach for using PRAs in plant specific changes (RG 1.174 and application specific RGs)

Approach for determining technical adequacy of PRAs (RG 1.200, NUREG-1855) 2

We are Now More Advanced Analytical improvements support more advanced risk-informed initiatives Risk insights have enhanced reactor safety and improved decision-making Investments in infrastructure, capacity, and methods are underway to address technical and cultural challenges 3

PRA Models Have Improved Industry models have improved in scope, technical adequacy, and level of detail NRC SPAR models have also improved in these areas.

4

Risk Insights have Improved Safety SBO risk reduced Maintenance Rule, NFPA 805, the ROP and risk informed ISI, etc. have also improved safety Insights from Fire PRAs are driving safety improvements Mitigation of beyond design basis equipment, also known as FLEX equipment are now in use 5

The NRC is Reviewing Several Major Risk-Informed Initiatives Tornado Missile Risk Evaluator PRA Method Vetting Panel Technical Specifications Task Force (TSTF) 505:

risk-informed completion times (4b)

TSTF-425: risk-informed surveillance frequencies (5b) 50.69: risk-informed structure, system, or component (SSC) categorization 6

PRA Must Be Suitable for the Application 4b, Risk-Informed Completion Times NFPA-805, Risk-Informed Required Fire Protection

  • Greater reliance scope, level of on PRA detail,
  • More flexibility technical 50.69 SSC Categorization for licensee robustness,
  • More complex and plant staff review representation 5b, Risk-Informed Surveillance Frequencies Risk-Informed Inservice Inspection 7

NRC is Upgrading the Infrastructure Needed to Support RIDM Facts and Observations (F&O) independent assessment process Improved guidance (e.g., Regulatory Guide 1.174 update)

Interactions with industry to improve LAR consistency and quality 8

We are Collaborating to Improve PRA Realism Improving fire PRA methods Seeking stakeholder input on human error probability estimates and common-cause failure modeling Potential methods for modeling credit of FLEX equipment and RCP seals Enhancing probabilistic flooding hazard analyses 9

We are Improving PRA Capacity in the NRC The NRC Grow Your Own program Support from other NRC Offices and from contractors Risk-Informed Thinking workshops 10

Process Updates to Support a Risk-Informed Culture Enhanced review guidance and office procedures place greater emphasis on using risk insights Greater collaboration between PRA specialists and traditional reviewers 11

Key Documents in Support of Risk-Informed Decisionmaking NEI Risk Informed Regulation Forum June 26, 2017 Mary Drouin, Anders Gilbertson Division of Risk Analysis Office of Nuclear Regulatory Research

OUTLINE Status and Plans for:

RG 1.174, REV. 3

  • Draft published as Draft Guide (DG) - 1285

- Originally published for comment in 2012

  • NRC resumed development of DG in March 2016
  • Revised DG-1285 was published* in April 2017, for a 45-day public review and comment period that concluded on May 22
  • NRC has received and is in the process of resolving public comments

RG 1.174, REV. 3

  • Major changes include:

- Enhanced guidance on defense-in-depth (DID)

- Language on large early release frequency for new reactors

- Language on containment performance expectations for new reactors

- A stronger tie to guidance on uncertainty in NUREG-1855

- Language on combining risk results (i.e., risk aggregation)

- Emphasis on acceptance guideline boundaries as gradual transitions

- Language on DID from relevant guidance documents 4

RG 1.174, REV. 3 - NEXT STEPS

  • Aug/Sept 2017: ACRS Subcommittee and Full Committee reviews/meetings
  • February 2018: RG finalized for publication
  • March 2018: Anticipated final issuance of RG 1.174, Revision 3 5

RG 1.200 Provides NRC regulatory position on:

  • Consensus PRA standards and industry PRA programs
  • Demonstrating acceptable PRA used to support a regulatory application
  • Documentation to support a regulatory submittal 6

RG 1.200, REV 2 RG currently endorses:

  • NEI 05-04 (Process for Performing Follow-on PRA Peer Reviews Using the ASME PRA Standard, Rev 2)

NEW AND REVISED STANDARDS AND GUIDANCE

  • Level 2 PRA standard - out for trial use
  • Low Power and Shutdown standard - out for trial use
  • Non-LWR PRA standard - out for trial use
  • Seismic PRA - in ballot process, to be issued as a Code Case
  • Level 3 PRA - in ballot process, to be issued for trial use
  • Advanced LWR PRA standard - expected issuance for trial use in 2017
  • New edition to Level 1/LERF PRA standard - expected in 2018 8

NEW AND REVISED STANDARDS AND GUIDANCE (Continued)

  • NEI Peer Review Guidance 12-13 on external hazards PRA
  • Appendices to NEI Peer Review Guidance addressing resolution of Facts and Observations (F&Os) - issued Feb 2016
  • NEI guidance 16-04 on new methods - draft issued Feb 2016 (update to be issued in mid-to-late summer 2017) 9

RG 1.200, REV 3 - PATH FORWARD

  • Issue a series of Draft Guides (DG)

- As standards are issued, DG will be issued providing a draft staff position

  • Public review and comment period would be open over the entire time
  • Allows for trial use of standards to be piloted before finalizing RG
  • Incorporate lessons learned from past decade
  • Rev 3 tentative schedule

- Draft Guide: 2018

- Final RG: 2019 10

Best Practices and Common Pitfalls Division of Risk Assessment Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission

Best Practices

  • Looking at previous submittals (e.g.

coordinating committees)

  • On-going communication with NRC staff
  • Audits/Observations 2

Best Practices

- Familiarizes staff with licensees strategy and goals for LAR

- Allows for clarifications to reduce acceptance review pitfalls

  • Looking at previous submittals (e.g.

coordinating committees)

- Helps licensee anticipate and address common RAIs

- Minimizes deviations from acceptable approaches/templates 3

Best Practices

  • On-going communication with NRC staff

- Having PRA personnel engage NRC staff

- Raises chances of efficient resolution to RAIs (i.e. reduces need for multiple RAIs)

  • Audits/Observations

- Assist with NRC review on complex or pilot reviews 4

Common Pitfalls with PRA reviews

  • Peer-reviewed PRA
  • F&Os
  • Applicability of External Hazards
  • Scope of review 5

Common Pitfalls with PRA reviews

  • Outdated Peer-reviewed PRA

- Peer-Reviewed internal events needed to support all applications

  • Complex sequence of gap assessment(s) and focused scope peer review(s) undesirable

- Peer-Reviewed Fire PRA should be used when one exists

- All hazards require technically adequate disposition consistent with application 6

Common Pitfalls with PRA reviews (contd)

  • F&Os

- Resolution of all F&Os should summarize technical issue

- Fixing documentation should summarize method that was documented

- Licensee summarization of F&O sometimes too short and hard to interpret

- Reported resolution should refer to application specific needs, if inapplicable need explanation about why inapplicable.

7

Common Pitfalls with PRA reviews (contd)

  • F&Os (contd)

- F&Os can only be closed out (and excluded from NRC LAR submittal) by:

  • A peer-review
  • F&O closure review per the acceptable process

- F&Os resolved with an upgrade still need a peer review

- Potentially obviates the need for a more in-depth review 8

Common Pitfalls with PRA reviews (contd)

  • Applicability of External Hazards

- Discussing IPEEE without addressing new hazard information since completing IPEEE

- Addressing impact on baseline risk without addressing impact on application specific change-in-risk 9

Common Pitfalls with PRA reviews (contd)

  • Scope of review

- Providing inapplicable or unclear risk results (e.g. providing delta risk using average maintenance instead of incremental risk for one-time TS changes)

- Providing multiple sensitivity study results without an comprehensive final result

- Deviating from acceptable approaches without fully describing new approach 10

Looking towards Future

  • Applications with greater reliance on PRA (NFPA-805, TSTF-505) warrant step improvement in PRA, PRA review, and documentation of PRA review.
  • Post approval PRA maintenance for living programs

- Methods new to licensee/plant need peer-review

- Methods new to industry need NRC acceptance 11

Review Process for Risk-Informed TSTF Reviews Jennifer Whitman, Acting Chief Technical Specifications Branch Office of Nuclear Reactor Regulation 2017 NEI Risk-Informed Regulation and Fire Protection Forum

There have been 8 risk-informed technical specification initiatives.

1 End States 5 Surveillance requirements 2 Missed 6 Entry into 3.0.3 Surveillances 3.0.3 3 Flexibility in Mode 7 Non-TS Operability Restraints Requirements 4 Completion Times 8 Criterion 4 of 50.36 See SECY 15-0135, Item 5, ML15243A474 2

Initiative 4b, will be used for the context of this discussion.

1 End States 5 Surveillance requirements 2 Missed 6 Entry into 3.0.3 Surveillances 3.0.3 3 Flexibility in Mode 7 Non-TS Operability Restraints Requirements 4 Completion Times 8 Criterion 4 of 50.36 3

The more complex travelers have included industry report to support them. Example 4b 4

Following approval of the report, a traveler is submitted with a model LAR.

5

The NRC will develop a SE for the traveler and a model SE for plant LARs.

6

Finally, the NRC will develop a plant specific SE for each LAR.

7

Both the traveler review and LAR review process address risk-informed submittals.

Traveler Review LIC-600 Under review LAR Review LIC-101 Recently Updated ML16061A451 8

LIC-600 treats risk-information similar to other review areas.

TBD 9

LIC-600 will be issued to include insights related to unsuspending a traveler.

LIC-600 TSTF-505 TSTF-505 TSTF-505 revision issued suspended revised issued 10

Risk related review, per LIC-101, depends on the use of risk information in LAR.

Uses risk-informed guidance, Risk-informed 1.174, 1.177, RG 1.200, 1.201 or review 1.205 Sufficient deterministic information, Limited risk but supplemental risk information is review provided Completely consistent with No risk review deterministic requirements See page 34 of 59 of Appendix B of LIC-101, Revision 11 5

If there is risk information there will be a risk review even for CLIIPs.

Uses risk-informed guidance, Risk-informed 1.174, 1.177, RG 1.200, 1.201 or review 1.205 Sufficient deterministic information, Limited risk but supplemental risk information is review provided Risk review even for consolidated line item improvement program (CLIIPed) changes. 12

Risk-informed technical specification changes remains a priority for the NRC staff.

13

NRC Staff Expectations on PRA Technical Adequacy Documentation in Support of Risk-Informed Applications Division of Risk Assessment Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission

PRA Must Be Suitable for the Application 4b, Risk-Informed Completion Times NFPA-805, Risk-Informed Required scope, level of Fire Protection

  • Greater reliance on detail, PRA technical 50.69 SSC Categorization
  • More flexibility for robustness, licensee and plant
  • More complex staff representation 5b, Risk-Informed review Surveillance Frequencies Risk-Informed Inservice Inspection 2

PRA Technical Adequacy Overview

  • Staff review of

- F&Os

- Application specific key assumptions

- Applications specific (change-in-risk) methods

  • Application Specific guidance documents sometimes provide additional guidance (RG 1.201, NEI 04-10 Revision 1, etc.)
  • Guidance aims to assure the quality and uniformity of staff reviews 3

Internal Events PRA

  • Submit PRA quality information based on RG 1.200, Revision 2

- Peer- Reviewed against 2009 ASME/ANS PRA Standard with RG 1.200 clarifications

  • Submit all peer review F&Os applicable to the parts of the PRA required for the application

- address the impact of those F&Os on the application 4

External Hazards

  • Use of an External Event or Fire PRA

- Licensee should identify hazard contribution to the application

- Use RG 1.200 to support the technical adequacy of the methods

- Submit all F&Os 5

External Hazards (other than fire)

  • Use of non-PRA method for external events

- Submittals would not use RG 1.200 to support the technical adequacy of the methods

- Explanation of contribution of risk of excluded external hazards (both to total and to application change in risk)

  • Demonstration of insignificant contribution or
  • Estimate of bounding contribution

- Individual Plant Examination of External Events generally acceptable to support screening after update to current plant conditions and hazards 6

F&O Closure

  • Original option to conduct a focused or full scope peer review
  • New F&O closure process provides one acceptable option to close F&Os (ML17079A427)

- Plans to incorporate it into the next revision to RG .1200

- NRC is planning to conduct periodic sample audits on licensee

- F&O resolutions containing PRA upgrades cannot be closed by this process

  • Closure process potentially obviates the need for a more in-depth review 7

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Improving Fire PRA Realism with Quality Research Mark Henry Salley P.E.

Chief, Fire and External Hazards Analysis Branch U.S. Nuclear Regulatory Commission June 26 28, LeMeridien Charlotte, NC markhenry.salley@nrc.gov 301.415.2474

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Purpose of Presentation

  • Provide High Level Overview of Current NRC Office of Nuclear Regulatory Research (RES)

Major Projects and their Part in Improving Fire PRA Realism

  • High Energy Arc Fault (HEAF) Generic Issue will be discussed in a separate presentation

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Fire Research Plan

  • The Office of Nuclear Regulatory Research (RES) is currently developing a 5year Fire Research Plan
  • The plan describes a set of projects that focus on fire safety research to ensure realism in regulatory guidance and methods
  • The projects main focus areas are:

- fire and electrical circuit analysis, fire hazard analysis, high energy arc faults (HEAFs), fire probabilistic risk assessment (PRA) & human reliability analysis (HRA), training and FAQ support

  • NRC is collaborating with EPRI under a MOU on a number of projects
  • Aim to maximize stakeholder input on projects through public meetings and comments For additional information contact:

Tammie Rivera, tammie.rivera@nrc.gov U.S. NRC, Office of Nuclear Regulatory Research

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Circuit Analysis JACQUEFIRE III

- Harmonization of recommendations from Volume 1 & 2

- Recommendations on treatment of

  • Clarification of terminology and figures
  • Justification for classification changes
  • Shorting switch
  • Spurious Operation Duration
  • Current Transformers

- Currently with NRC publications

- Presentation with NEI at 2017 RIC

  • Information forms much of the Technical Basis for NEI 0001 Rev.4

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Current Transformer Testing

  • Issue

- Fireinduced open circuit causes a secondary fire in a separate location

[NEI 0001, Rev. 2, Section 3.5.2.1]

  • Resolution

- Based on available literature, engineering principles, and expert judgement, NUREG/CR7150 Vol. 1 recommended not considering failure mode for CTs with turns ratio 1200:5 or less

- NRC sponsored testing to understand if larger CT ratios were concern.

[EPRI participation and observation]

- NEI recommended discontinuing testing [Item 27, ML15279A048]

  • Results

- NUREG/CR7228, Published May 2017

- No secondary fire or potential for secondary fires observed

- JACQUEFIRE used results to support recommendation

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Instrumentation Circuit Testing

  • Issue

- Limited understanding of fireinduced failure modes for instrumentation circuits [see NUREG/CR6776]

- PIRT ranked as top research priority and recommended additional testing

  • Resolution

- Limited scope radiant testing at SNL to advance state of knowledge [81 FR 80688]

  • Results

- Signal decay ranged from 0 to more than 21 minutes

  • Questions the assumptions used for Instrument Circuits Fire Damage

- Draft report under review

  • How do these results impact MCR Fire Human Reliability Analysis ?

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Electrical Cable Fire Retardant Coatings

  • Issue

- Unclear guidance on delay added by coating for ignition and functionality (i.e., damage) [NUREG/CR6850 / EPRI 1011989]

  • Resolution

- 1) Literature survey, 2) scoping tests, 3) fullscale testing

  • Results

- Information to support Cable Tray Ignition FAQ

- Analysis of data underway

- Report estimated late 2017

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Contact Information Gabriel Taylor, PE Felix Gonzalez, PE T : 301.415.0781 T: 301.415.2413 E : gabriel.taylor@nrc.gov E: felix.gonzalez@nrc.gov

  • JACQUEFIRE
  • Cable Coating
  • Current Transformer
  • Instrumentation

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC RES Technical Support to NRR

  • Issue

- Industry submits Frequently Asked Questions (FAQs) and other fire analysis methods to NRR for review

  • Resolution

- Ongoing FAQ Reviews

  • 1) Cable Tray Fires, 2) VEWFDS, 3) Transient Weighting Factors,
4) HEAF Non Suppression, 5) Maintaining Frequency Bins Apportioning

- Vetting Panel Support

  • 1) Fire Location Factor, 2) Transients Fires, 3) Liquid Spill HRR
  • Results

- Support development of FAQ closure guidance

- Support review and assessment of industry reports submitted to vetting panel

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Improved Heat Release Rate (HRR)

Guidance

  • Issue

- NUREG/CR6850 (EPRI 1011989) HRR guidance, developed from limited experimental data, can lead to some overly conservative fire PRA results

  • Resolution

- Joint work with EPRI

  • Electrical Enclosure HRR,
  • Obstructed Plume Methodology,
  • Pumps and Motors HRR,
  • Cabinet to Cabinet Propagation,
  • Results

- RACHELLEFire II Report estimated late 2017

- Transients HRR Report estimated mid 2018

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC FIRE PRA Realism

  • Issue

- Fire PRAs can be made more realistic

  • Resolution

- Identify contributors to potential overconservatism

- Explore new/improved methods for coupling fire frequencies, HRR distributions, fire growth profiles, and fire detection and suppression effectiveness

- Develop/Improve the associated tools, methods, and data

  • Result

- Update to EPRI 1011989,NUREG/CR6850

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Update to NUREG/CR6850

  • Multiple sources need to be consolidation in order to update the guidance document to reflect the most recent methods, tools, and data

- Supplement 1 to NUREG/CR6850 (17 FAQs published in 2010)

- Multiple Recent Frequently Asked Questions (FAQs)

  • FAQ 130005 Cable Fires Special Cases: SelfIgnited and Caused by Welding and Cutting
  • FAQ 130004 Clarifications on Treatment of Sensitive Electronics
  • FAQ 130006 Modeling Junction Box Scenarios in a Fire PRA
  • FAQ 140009 Treatment of Well Sealed MCC Electrical Panels Greater than 440V
  • Etc...

- Multiple New NUREGs

  • NUREG2178 Refining And Characterizing Heat Release Rates From Electrical Enclosures During Fire
  • NUREG/CR7150 Joint Assessment of Cable Damage and Quantification of Effects from Fire
  • Etc...

- This would be a Major Step on Improving Fire PRA Realism

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Contact Information David W. Stroup, PE Nicholas Melly T : 301.415.1649 T: 301.415.2392 E : david.stroup@nrc.gov E: nicholas.melly@nrc.gov

  • Technical Support to NRR Fire PRA Realism

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Realism in Fire HRA

- NUREG1921, EPRI/NRCRES Fire HRA Guidelines filled this gap

  • Guidance addresses firespecific impacts on operators (i.e., more representative & realistic for fire events)
  • NUREG1921 did not provide guidance for performing detailed HRA for main control room abandonment (MCRA) scenarios

- Fire PRAs results could be conservative without a justifiable way to credit operator actions in MCRA scenarios, especially loss of control (LOC) scenarios

- Fire HRA could be inconsistent with asoperated plant if influencing factors on operator reliability in MCRA scenarios are not appropriately understood

- Effective fixes on how to better support operators responding to MCRA scenarios cannot be developed without a qualitative HRA that addresses the real impacts of the remote shutdown design, MCRA procedures, communication strategies, etc.

  • NUREG1921, as stateoftheart in HRA & with development of guidance for operator actions outside the MCR, also has been used as the basis for other advances in HRA, such as:

- EPRIs Approach to HRA for External Events With a Focus on Seismic, (EPRI 3002008093, 2016)

- NRC/RESs Level 2 HRA approach for L3PRA project

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Current Fire HRA Research: MCRA

  • NRC/RES is working collaboratively with EPRI under MOU to address fire HRA for MCRA scenarios
  • This work is being developed

- using the combination of NRCs & industrys experience in HRA & fire HRA/PRA

- with an understanding of latest available psychological research & literature

- With input from peer reviews, NRR, NRCs Advisory Committee on Reactor Safeguards (ACRS) PRA Subcommittee

- Testing at NPP sites is being planned (which is important for realism!)

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Fire HRA Research for MCRA Scenarios Results

  • Two products are planned:

- Supplement 1 to NUREG1921: Qualitative HRA Guidance for MCRA Scenarios

- Supplement 2 to NUREG1921: HRA Quantification Guidance for MCRA Scenarios

  • In addition, updated guidance to NUREG/CR6850 on modeling MCRA scenarios is provided in Supplement 1
  • For additional information, please contact:

- Dr. Susan E. Cooper, Sr. Reliability & Risk Engineer, NRC/RES/DRA/HFRB, Susan.Cooper@nrc.gov,

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Fire PRA Training

  • NRC RES and EPRI continue to provide specialized training since 2005
  • Five Modules: IFire PRA II Electrical Analysis III Fire Analysis IV Fire HRA V Advanced Fire Modeling

- Modules offered to allow participants to take 4 modules per year

  • NRC Host at White Flint Headquarters

- Electrical Analysis, Fire Analysis, & Advanced Fire Modeling

- Fire PRA & Fire HRA

  • Approximately 65 participants registered for 2017
  • Future considerations:

- Annually publish a NUREG/CP with updated training materials so individuals who took the training in previous years will have access to the latest information

- Offer webinars for modules

- For additional information contact:

Tammie Rivera, tammie.rivera@nrc.gov U.S. NRC, Office of Nuclear Regulatory Research

Seismic PRAs -

10CFR50.54(f) Responses Brett Titus Nuclear Regulatory Commission June 28, 2017 Pre-decisional Information - for internal use only

Objectives

  • Provide a brief history of NTTF Recommendation 2.1: Seismic and the 50.54(f) request for information
  • Describe the purpose and scope of the project
  • Explain the process and level of effort associated with the task 2

Background

  • March 11, 2011 - Earthquake and subsequent tsunami impact Fukushima Daiichi nuclear power plant
  • July 12, 2011 - Near Term Task Force report recommendations (ML111861807)
  • March 12, 2012 - NRC issues 50.54(f) letter requesting licensees to reevaluate seismic hazards using latest methods and guidance (ML12053A340) 3

Rec 2.1- Background NTTF 2.1 - Hazard Reevaluations Licensees reevaluate hazard based on present day guidance/methods used to define the design PHASE 1: Information Gathering basis for new reactors.

NTTF 2.1 - Interim Actions/Expedited Approach If the design basis does not bound reevaluated hazard: Licensees evaluate the need for interim actions while the longer-term integrated assessment is performed.

NTTF 2.1 - Focused Eval or Integrated Assessment/Seismic PRA If the design basis does not bound reevaluated hazard: Licensees determine the effectiveness of the existing DB and any other planned or installed features for protection and mitigation against the reevaluated hazard.

Regulatory Actions PHASE 2:

NRC staff determines whether additional regulatory actions are necessary to provide additional Regulatory protection against the updated hazards Decision Making 4

Screening, Prioritization and Implementation Guidance (SPID)

Endorsed February 2013

  • Guidance for licensees to address the 50.54(f) letter in a uniform, technically sound, optimized way
  • Provides guidance on hazard evaluation, screening, and elements of seismic PRA 5

Contents of SPID

1. Purpose and Approach
2. Seismic Hazard Development
3. GMRS Comparisons and Screening of Plants
4. Seismic Hazard and Screening Report
5. Prioritization (Schedule)
6. Seismic Risk Evaluation
7. Spent Fuel Pool Evaluation Four appendices to SPID with detailed guidance on special topics 6

Seismic - High Exceedance 7

Seismic Evaluations

  • GMRS SSE for frequencies 1-10 Hz and > 10 Hz &

GMRS > SSE by 2x or more = Seismic PRA needed for 18* plants

  • Seismic PRA final determinations and schedule

- Letter dated Oct. 27, 2015 (ML15194A015)

- Elements: reevaluated hazard, fragility, plant response

- Review: Verify completeness and suitability; assess SCDF/SLERF and importance measures; and, if necessary, screen potential safety improvements 8

Seismic PRA Dates Sept 2017 Mar 2018 Mar 2019 Mar 2017 Sep 2018 Sep 2019 Beaver Valley Peach Bottom Columbia Vogtle VC Summer Palisades Diablo Canyon North Anna Robinson January 2017 Jan 2018 Jan 2019 January 2020 Jun 2017 Dec 2017 Jun 2018 Dec 2018 Jun 2019 Watts Bar Dec 2019 Callaway

  • DC Cook Oconee Dresden Browns Ferry Indian Point 2 Pilgrim* Indian Point 3 Sequoyah 9

Seismic PRA Submittals

  • Licensees prepare their Seismic PRA

- Seismic Hazard

- Seismic Fragility

- Systems/Accident Sequences

- Risk Quantification

  • Seismic PRA is Peer Reviewed using ASME/ANS PRA Standard (RA-Sa-2009)
  • Deltas between the SPID approach and the ASME/ANS Standard (SPID Section 6.6.2)
  • Peer Review assesses the adequacy of methodologies and their implementation (SPID Section 6.7 )

10

Seismic PRA Reviewer Checklist

  • Provides specific staff guidance on 16 topics

- SPID contains specific guidance which is either prescriptive or different than the Standard

  • Staff guidance for each Seismic PRA Supporting Requirement

- Clarifies governing requirement when there are differences between the Standard and the SPID

- Relies on peer review findings (internal events and seismic) to balance the need for a detailed review of the Seismic PRA model by the staff

  • NEI Comments received and dispositioned (ML17041A329) 11

SPRA Reviewer Checklist

  • Intended to ensure appropriate scope, consistency, and focus during NRCs Seismic PRA quality review
  • Maintains fidelity of review with endorsed SPID guidance
  • Aids in documenting the staffs review findings, including any deviations, deficiencies, and resolutions
  • Does not represent additional guidance or interpretation for the licensee 12

Rec 2.1- Background NTTF 2.1 - Hazard Reevaluations Licensees reevaluate hazard based on present day guidance/methods used to define the design PHASE 1: Information Gathering basis for new reactors.

NTTF 2.1 - Interim Actions/Expedited Approach If the design basis does not bound reevaluated hazard: Licensees evaluate the need for interim actions while the longer-term integrated assessment is performed.

NTTF 2.1 - Focused Eval or Integrated Assessment/Seismic PRA If the design basis does not bound reevaluated hazard: Licensees determine the effectiveness of the existing DB and any other planned or installed features for protection and mitigation against the reevaluated hazard.

Regulatory Actions PHASE 2:

NRC staff determines whether additional regulatory actions are necessary to provide additional Regulatory protection against the updated hazards Decision Making 13

Depth of Review

  • Review depth is commensurate with safety implications of a beyond design basis event and associated risk
  • Review time dependent on:

- Quality of submittal

- Number and significance of peer review findings

- Uniqueness/departure from guidance and accepted methods

- Plant-specific relationship to actionable threshold 14

Phase 2 Decision-making SPRA Review Flowchart Senior Backfit consideration Management No further is warranted Review regulatory actions Panel Group 1: Regulatory action not warranted Group 2: Regulatory action should be considered under backfit Recommend Plant provisions as Group 1, 2, or 3 Group 3: Regulatory action may be needed, but more thorough consideration is needed first SPRA Tech Review Board Additional Information Needed from Staff or Licensee Draft Recommendation for TRB Consideration Provide Status Updates: Prior to Issuing RAIs, Completion of Review Stage 2, and Completion of Review Stage 3 SPRA Tech Review Team (typ) 15

Senior Management Review Panel

  • Phase 2 Decision-making Guidance Memorandum (ML16237A103)
  • NRR Division Directors

- Division of Japan Lessons-Learned (JLD or responsible division)

- Division of Risk Assessment (DRA)

- Division of Operating Reactor Licensing (DORL) 16

SPRA Technical Review Board

  • Three management/senior-level staff experts with diverse backgrounds and specialties
  • Provide consistency across the review teams

- Questions/RAIs

- Application of guidance and thresholds

- Responsible for recommendation to Senior Management Review Panel (SMRP) 17

Seismic PRA Technical Review Team

  • Diverse team with specialized skillsets and areas of responsibility

- Technical Team Lead (Project Manager)

- Seismic Hazard Reviewer (Hazard)

- Civil/Structural/Mechanical Reviewer (Fragility)

- Plant Response Reviewer (Risk) 18

Planned Flow of Review

  • Stage 1 (approx. 1 month)

- Submittal is received and distributed to team

- Team kickoff meeting

- Read through submittal and evaluate completeness

- Provide feedback to Tech Team Lead 19

Planned Flow of Review

  • Stage 2 (approx. 5 months)

- Work to complete SPRA Checklist

- Team discussion including potential questions

- Meet with Seismic PRA TRB (if questions are needed)

- Review responses to questions (as necessary)

- Provide completed Seismic PRA Checklist (and other input as necessary) to Tech Team Lead

- Meet with Seismic PRA TRB 20

Planned Flow of Review

  • Stage 3 (as directed by Seismic PRA TRB)

- More detailed investigation

- More dialogue (questions/answers) with licensee

- Provide additional input to Tech Team Lead

- Meet with Seismic PRA TRB 21

Planned Flow of Review

  • NRC will prepare a response letter to licensee informing them of the SMRPs decision and next steps, if any 22

Ongoing Review Effort

  • Peer Review Observations
  • Vogtle Electric Generating Plant Submittal (ML17088A130)

- Low SCDF/SLERF

- 128 Pages

- 10 Not Met or CC-I Supporting Requirements

  • April submittal - roughly halfway through review
  • Very useful Checklist Crosswalk summary (Best Practice) 23

Questions?

Brett Titus Sr. Project Manager NRC/NRR/JLD Brett.Titus@nrc.gov 301-415-3075 24

Acronym List PRAs - Probabilistic Risk Assessments CFR - Code of Federal Regulations NTTF - Near Term Task Force EPRI - Electric Power Research Institute GMRS - Ground Motion Response Spectrum SSE - Safe Shutdown Earthquake SCDF - Seismic Core Damage Frequency SLERF - Seismic Early Release Frequency NEI - Nuclear Energy Institute ASME - American Society of Mechanical Engineers ANS - American Nuclear Society RAI - Request for Additional Information 25

Crediting Mitigating Strategies in Risk-Informed Decision Making Matt Humberstone Ph.D.

Reliability and Risk Analyst PRA Operations and Human Factors Branch Division of Risk Assessment Office of Nuclear Reactor Regulation June 28, 2017 1

OBJECTIVE

  • Project History

- Interactions

  • Areas of Credit

- Recent Activities

- Agency Interactions (Regions, RES, NRR)

  • Communications
  • Path Forward 2

Project History

  • Fukushima orders required strategies to maintain/restore core cooling, containment, and spent fuel pool cooling
  • Licensees installed equipment can be utilized for multitude of uses beyond the orders (outages, defense-in-depth)
  • Mitigating Strategies (MS) could provide added safety enhancements
  • The NRC wants to encourage safety enhancements
  • Need to provide proper regulatory footprint

Overall Approach

  • Industry

- Developed tiered approach to crediting portable equipment

- Guidance in NEI 16-06

- NRC has engaged

  • NRC

- Identified areas of application

- Following submittals

- Engage with Industry 4

Interactions with NEI

  • NEI 16-06, Crediting Mitigating Strategies in Risk-Informed Decision Making (ML16286A297) (August, 2016)

- Tier 1: Qualitative assessment

- Tier 2: Semi-quantitative streamlined assessment

- Tier 3: Full PRA (RG 1.200 compliant) (new section when submitted)

- Tier 1 and Tier 2

- Listed areas of additional staff focus

- Developed a publicly available internal memo (ML17031A269)

- Highlighted some possible concerns 5

Areas of Potential Credit

  • Accident Sequence Precursor (ASP) Program
  • License Amendment Requests
  • Qualitative/Quantitative Credit
  • Security
  • Target Sets / Force on Force / EALs
  • Regulatory Analysis - Rulemaking
  • Issue Resolution
  • Generic Issue Resolution 6

Recent Communications

  • SRA Counterpart meeting - October 2016 and May 2017
  • Inspector Newsletter article - October2016 and April 2017
  • Deputy EDO and RA briefing - April 2017
  • NRC Reporter article - April 2017
  • RIC Session -March 2016 and March 2017
  • Internal RISC update - February 2017
  • Public RISC - February 2017
  • Division Director counterpart meeting - November 2016
  • JNRA Bilateral meeting - November 2016
  • ET Significant Topic briefing - November 2016
  • IAEA Technical meeting - November 2016
  • ACRS- Reliability and PRA Subcommittee - September 2016 7

Path Forward

  • Communication plan

- Communications with JLD

- SharePoint site

- Risk analyst / SRA engagement

  • Monitor RIDM program areas for additional application specific guidance changes
  • Continue work on draft guidance documents

- RASP Handbook update

- NOED technical guideline/SRA Engagement

  • Engage stakeholders

- Memo on NRRs review of NEI 16-06

- Guidance Updates 8

Questions?

9

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC High Energy Arc Fault (HEAF)

Generic Issue Mark Henry Salley P.E.

Chief, Fire and External Hazards Analysis Branch U.S. Nuclear Regulatory Commission June 2628, Le Meridien Charlotte, NC markhenry.salley@nrc.gov 301.415.2474

NEI RiskInformed September Regulation 21-24, 2014, and Fire Milwaukee, WI Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC 2 Electrical Enclosures Failure Modes 3

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC What is a HEAF?

  • High Energy Arc Faults (HEAFs) are energetic or explosive electrical equipment faults characterized by rapid release of energy in the form of heat, light, vaporized metal and pressure increases due to high current arcs between energized electrical conductors or between energized electrical components and neutral or ground.

- First phase: short, rapid release of electrical energy which may result in projectiles (from damaged electrical components or housing) and/or fire(s) involving the electrical device itself, as well as any external exposed combustibles, such as overhead exposed cable trays or nearby panels, that may be ignited during the energetic phase

  • Arc Temperatures in the range of 35,000 F (19,426 C)

- Second phase, i.e., the ensuing fire(s): is treated similar to other postulated fires within the zone of influence

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Safety Significance

  • GDC 3 Structures, systems, and components important to safety shall be designed and located to minimize, consistent with other safety requirements, the probability and effect of fires and explosions.
  • GDC 17 The onsite electric power supplies, including the batteries, and the onsite electric distribution system, shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure.

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Background of the HEAF Program

  • OECD Fire Incident Records Exchange Project (FIRE)

- Analysis of High Energy Arcing Fault (HEAF) Fire Events, NEA/CSNI/R(2013)6

- 48 of 415 fire events collected represent HEAFinduced fire events (over 10%)

https://www.oecd nea.org/nsd/docs/2013/csnir2013 6.pdf

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Background of the HEAF Program CSNI WGIAGE Task on High Energy Arcing Faults (2009 - 2013)

  • Task Report A Review of Current Calculation Methods Used to Predict Damage from High Energy Arcing Fault (HEAF) Events, NEA/CSNI/R(2015)10

- Insights from operating experience with partly significant HEAF events http://www.oecd nea.org/nsd/docs/2013/csni

- Literature study on methods for r201510.pdf predicting HEAF consequences

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Realistic Quantification of Hazard

  • NRC testing has been, and will continue to be, informed by Operating Experience and NPP configurations:

- LERs describe numerous threephase arc faults with failure of an upstream breaker

- Real plant equipment used in testing

- Voltage, current, arc duration within the bounds observed in LERs

- Damage observed comports with LERs

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Example of Recent US Electrical Enclosure HEAF Experience SONGS, 2001 Robinson, 2010 Brunswick, Feb 2016

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Example of Recent US Bus Duct HEAF Experience Diablo Canyon Bus Duct (OpE) Zion Bus Duct (testing) Columbia Bus Duct (OpE) 2000 February 9th 2016 2009

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC U.S. Operating Event History (OpE) Duration

  • Operating Event history shows that breakers do not always work as expected (design vs. real world)
  • HEAF events typically persist for timeframes much longer than design fault clearance times through the mechanism of breaker failures or other complicating factors Event Hold Time Cause Waterford; 06/10/1995 Unknown Breaker Failure; restricted movement of the trip latch roller bearing Prairie Island; 08/03/2001 Unknown >2 seconds Breaker Failure; Ionizing gas from the breaker was the initiator Songs; 02/03 2001 Unknown; >2 Seconds Breaker Failure; Ionizing gas from the breaker was the initiator Robinson; 03/27/2010 812 seconds Breaker Failure; Loss of DC Control Power Diablo Canyon 05/15/2000 11 seconds Location; Voltage Decay Columbia 10/20/2009 Unknown Aging 10

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC U.S. OpE- Three Phase Faults

  • Most HEAF event that we are aware of quickly progress to three phase faults. This is evident from a number of LERs:

- The Kewaunee HEAF event (LER 8700900) involved a phaseto ground fault, which progressed to a phasetophase fault which accounted for the extensive bus damage.

- The Prairie Island HEAF event (LER 010500) involved a C phase ground arcing event, which quickly involved all phases.

- The Zion HEAF event (LER 9400501) states that the failure started as a single phase to ground fault which rapidly evolved into a three phase to ground fault.

11

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC U.S. Operating Event History (OpE) - Overpressurization

  • HEAF events can lead to overpressurization of compartments and challenge fire rated barriers even when breaker protection works as expected

- Turkey Point HEAF EventMarch 18, 2017

  • Fault Cleared in 35.8 cycles (or ~0.6 seconds)
  • The protective relays operated as expected
  • Fire Door D0703, located 4.4m (14.5 ft.) away from the origin of the fault was damaged and the latch mechanism was deformed
  • Damage was caused by the overpressurization of the room corresponding to the increase in pressure at the onset of the arc event
  • The damaged door defeated the 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> rated barrier between the 3A and 3B 4kV switchgear rooms

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing

  • 26 fullscale experiments carried out at KEMA high energy test facility between 20142016.

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Test #3: 480 V, 35 kA, 8 seconds Copper Bus Bars

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Test #15: 10 kV, 15 kA, 3 seconds Oilfilled breaker (oil removed), copper bus bars

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Test #23: 480 V, 40 kA, 7 seconds Aluminum bus bars

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Test #26: 4.16 kV, 26 kA, 3.5 seconds Bus Duct, copper bus bars, aluminum housing

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Results

- Potentially much larger ZOI

- Potentially greater likelihood of maintaining an arc at low voltages

- Higher risk of fire propagation

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Results

  • New Failure Mode: Test 23 Test 26 Conductive Products of Combustion

- Conductive AL byproducts coated facility

- Shorted out equipment and damaged electrical circuits

  • Fort Calhoun HEAF event June 7, 2011

- Adjacent cabinets affected by conductive smoke and soot

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Phase I Testing Report

  • Report on the Testing Phase (20142016) of the High Energy Arcing Fault Events (HEAF) Project:

Experimental Results from the International Energy Arcing Fault Research Program, NEA/CSNI/R(2017)7 https://www.oecd nea.org/nsd/docs/2017/csni r20177.pdf

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Postulated HEAF Mitigation HEAF Shields

  • Proposed lightweight shielding to limit the extent of damage from a HEAF events

- objective is to minimize damage to risksignificant targets beyond the faulted switchgear and to prevent damage and ignition overhead cable trays:

- In order for HEAF Shields to be Successful:

  • What is the Design Basis?
  • What is the Acceptance/Rating/Qualification Test Method?
  • How does the Installed HEAF Shield match what was Tested?

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Postulated HEAF Mitigation Louvers / Solid Tops Misconceptions:

  • The force of the HEAF energy will be directed by vent louver

- Energy will only travel in direction of the vents and will prevent significant energy/mechanical damage targets located above or away from the vent path

  • Solid tops on switchgears always contain the HEAF and prevent damage to targets above

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Aluminum HEAF Generic Issue

- The NRC has performed a screening review as part of the GI process related to HEAF events involving aluminum components

- The generic issue review panel (GIRP) determined that the seven screening criteria were met in accordance with management directive 6.4 (ML14245A048) and is in the process of finalization and release of the screening phase document

- The staff has recommended a two phase approach to address the generic issue and identified both short term and long term actions

- GIRP memo currently in concurrence

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Information Notice (IN) 2017XX

  • High Energy Arc Faults in Electrical Equipment Containing Aluminum Components

- OECD/NEA international test program insights

- 6 U.S. operating experience events involving aluminum components Plant Date Fort Calhoun June 7, 2011 Columbia August 5, 2009 Diablo Canyon May 15, 2000 Zion April 3, 1994 Shearon Harris October 9, 1989 Kewaunee July 10, 1987

- Expect to be Issued Summer 2017

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC NRC Regulatory Actions

  • Short Term Actions
  • Long Term Actions

- Industry survey on - Perform additional extent of Aluminum focused HEAF testing

- Estimate the risk from designed to quantify potential ZOI the ZOI with Aluminum increases identified - Update and revise by testing and OpE current HEAF guidance

- Determine if in NUREG/CR6850 additional actions are Appendix M and necessary FAQ 070035

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC PIRT & Phase II Testing

  • Phase II testing to be conducted as an NEA/OECD International Project with more focused objectives
  • International Phenomena Identification and Ranking Table (PIRT) exercise held in February 2017
  • Early Insights:

- Aluminum oxidation and byproducts

- Pressure effects

- Target characterization and sensitivity

- Mitigating factors (HEAF shields)

  • OECD/NEA Phase II Testing currently under development

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Develop Long Term DefenseinDepth Solution Safe Shutdown Protect & Preserve Safe Shutdown Rapid Detection & Mitigation Fuse/Breaker/Relay Protection HEAF Shields, Prevention Safe Work Practices, Maintenance, ArcProof Cabinets

NEI RiskInformed Regulation and Fire Protection Forum June 26-28, 2017, Le Meridien Charlotte, NC Contact Information Nicholas Melly Kenneth Hamburger T : 301.415.2392 T: 301.415.2022 E : Nicholas.melly@nrc.gov E: Kenneth.hamburger@nrc.gov Gabriel Taylor, PE David W. Stroup, PE T : 301.415.0781 T : 301.415.1649 E : gabriel.taylor@nrc.gov E : david.stroup@nrc.gov

Guidance on Treatment of Uncertainty in Risk-Informed Decisionmaking (NUREG-1855)

NEI Risk Informed Regulation Forum June 28, 2017 Mary Drouin Senior Program Manager Division of Risk Analysis Office of Nuclear Regulatory Research

Background

Originally published in March 2009 Developed in collaboration with EPRI EPRI 1016737, Treatment of Parameter and Model Uncertainty for PRAs EPRI 1026511, Practical Guidance on the Use of PRA in Risk-Informed Applications with a Focus on the treatment of Uncertainty Revision 1 better structures the guidance to licensees and further clarifies the NRC staff decisionmaking process in addressing uncertainties Web-Based course developed and is available on our public website https://www.nrc.gov/reading-rm/training/nureg-1855/

2

Why is the Guidance Needed?

In dealing with uncertainties associated with PRAs, the decision maker needs to:

Understand to what extent the results are impacted by the uncertainties Understand whether there are uncertainties that are impacting the results that may challenge the acceptance guidelines Determine if the driver for the large uncertainties can be identified and remediated 3

There are Three Different Types of Uncertainties Associated with PRAs Completeness uncertainties Are risk-significant events included?

Parameter Uncertainties What is the confidence in our ability to predict PRA parameters?

Model Uncertainties What is the confidence in the models for the specific accident scenarios?

4

Overall Process Part 1 - Guidance to Licensees and the NRC Staff Stage A - Determine the approach for the treatment of uncertainties Part 2 - Guidance to Licensees Stage B -- Assess if the PRA has the needed scope and level of detail to support the risk-informed decision Stage C -- Assess completeness uncertainties Stage D -- Assess the parameter uncertainties Stage E -- Assess model uncertainties Stage F -- Develop the strategies to address key uncertainties in the application 5

Overall Process (contd)

Part 3 - NRC Process Stage G -- NRCs risk-informed review process The guidance in Stages A through G are based on the NRC risk-informed decisionmaking process, and the treatment of uncertainties is consistent with the ASME/ANS PRA standard 6

Overall Process (contd) 7

How is Aggregation Treated?

Contributions from applicable hazards and plant operational states are combined to generate the risk results The level of detail - the uncertainties and the degree of conservatisms in the various hazards -

may differ The various levels of detail may bias the overall risk results The contributors to the risk need to be understood and their bases should be taken into account in the decisionmaking process 8

NRC Review Process NRC staff seeks to answer Is the scope and level of detail of the PRA appropriate for the application?

Is the PRA model acceptable?

What is the proximity of the risk metric results to the acceptance guidelines?

How do parameter and model uncertainties each affect the risk metric results?

Is the acceptability of the application adequately justified?

9

Treatment of PRA Uncertainties in Risk-Informed Decisionmaking The staff review begins with determining the proximity of the application risk metric results to the acceptance guidelines and the licensees justification 10

Regime 1 - Risk Results Well Below the Acceptance Guidelines The staff would Look for an assessment which shows that parameter uncertainties do not affect the risk results Determine whether the key assumptions made in the PRA will be appropriately monitored Determine whether degraded performance can be detected in a timely fashion Likely place less importance on the use of compensatory measures, depending on the justification that is provided Examine the peer review findings to identify any of particular relevance to the application Generally not perform an audit on the application 11

Regime 2 - Risk Results do not Challenge the Acceptance Guidlines The staff would Look for an assessment which shows that parameter uncertainties do not affect the risk results Examine the application to determine that the proposed performance monitoring is appropriate and adequate Determine whether degraded performance can be detected in a timely fashion Consider if greater depth of review of the uncertainty aspects of the application should be performed Examine the peer review findings with a higher degree of scrutiny than for applications that fall into Regime 1 Likely perform an audit on the application PRA 12

Regime 3 - Risk Results Challenge the Acceptance Guidelines The staff would Expect that parameter uncertainties do not affect the risk results Expect that the proposed performance monitoring is adequate Expect that degraded performance can be detected in a timely fashion Expect that compensatory measures be in place Examine the peer review findings with an even higher degree of scrutiny Consider if greater depth of review of the uncertainty aspects of the application should be performed Likely perform an audit of the application PRA to determine the cause of the change in risk 13

Regime 4 - Risk Results Significantly Exceed the Acceptance Guidelines The staff would Typically not accept such applications unless they represent an overall reduction in risk Expect the licensee to identify areas of the PRA that are conservative and then perform a more realistic assessment to support the application Expect that parameter uncertainties do not affect the risk results Examine the application to ensure that the proposed performance monitoring is adequate Expect that degraded performance can be detected in a timely fashion Thoroughly review the peer review findings Determine the appropriateness of compensatory measures Review in greater detail the uncertainty aspects of the application Perform a more in-depth audit of the application PRA to determine the cause of the change in risk 14

Risk-Informed Application When aggregating the results from different hazards, the staff evaluates whether the licensee demonstrates understanding of The individual risk contributions and the uncertainty associated with each hazard AND The sources and effects of conservatisms and model uncertainties that significantly impact the results For staff acceptance Licensee has demonstrated an acceptable treatment of uncertainties AND Demonstrated an acceptable risk effect to the plant 15

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