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01_03 Task 2 Comp Select
	ML19162A418
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Issue date:	06/13/2019
From:	Nick Melly; NRC/RES/DRA
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	T. Rivera
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NUREG/CR-6850 FIRE PRA METHODOLOGY Module 1 Internal Event, At-Power Probabilistic Risk Assessment Model for SNPP Task 2: Fire PRA Component Selection Nicholas Melly - Nuclear Regulatory Commission Fire PRA Workshop June 24, 2019 - June 28, 2019 Rockville, MD U.S. NRC HQ

Component Selection Purpose (per 6850/1011989)

Purpose:

Describe the procedure for selecting plant components to be modeled in a Fire PRA Fire PRA Component List

- Key source of information for developing Fire PRA Model (Task 5)

Used to identify cables that must be located (Task 3)

Process is iterative to ensure appropriate agreement among fire PRA Component List, Fire PRA Model, and cable identification Fire PRA Workshop 2019, Rockville, MD Slide 2 Module 1: Internal Event, At-Power PRA Model for SNPP

Corresponding PRA Standard Element Primary match is to element ES - Equipment Selection

- ES Objective (as stated in the PRA standard):

Select plant equipment that will be included/credited in the fire PRA plant response model.

Fire PRA Workshop 2019, Rockville, MD Slide 3 Module 1: Internal Event, At-Power PRA Model for SNPP

HLRs (per the PRA Standard)

HLR-ES-A: The Fire PRA shall identify equipment whose failure caused by an initiating fire, including spurious operation, will contribute to or otherwise cause an initiating event (6 SRs)

HLR-ES-B: The Fire PRA shall identify equipment whose failure, including spurious operation, would adversely affect the operability/functionality of that portion of the plant design to be credited in the Fire PRA (5 SRs)

HLR-ES-C: The Fire PRA shall identify instrumentation whose failure, including spurious operation, would impact the reliability of operator actions associated with that portion of the plant design to be credited in the Fire PRA (2 SRs)

HLR-ES-D: The Fire PRA shall document the fire PRA equipment selection, including that information about the equipment necessary to support the other fire PRA tasks (e.g., equipment identification, equipment type, normal, desired, failed states of equipment), in a manner that facilitates fire PRA applications, upgrades, and peer review (1 SR)

Fire PRA Workshop 2019, Rockville, MD Slide 4 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Scope (per 6850/1011989)

Fire PRA Component List should include the following major categories of equipment:

Equipment whose fire-induced failure (including spurious actuation) causes an initiating event Equipment needed to perform mitigating safety functions and to support operator actions Equipment whose fire-induced failure or spurious actuation may adversely impact credited mitigating safety functions Equipment whose fire-induced failure or spurious actuation may cause inappropriate or unsafe operator actions Fire PRA Workshop 2019, Rockville, MD Slide 5 Module 1: Internal Event, At-Power PRA Model for SNPP

Component Selection Approach (per 6850/1011989)

Step 1: Identify Internal Events PRA sequences to include in fire PRA Model (necessary for identifying important equipment)

Step 2: Review Internal Events PRA model against the Fire Safe Shutdown (SSD) Analysis and reconcile differences in the two analyses (including circuit analysis approaches)

Step 3: Identify fire-induced initiating events based on equipment affected Step 4: Identify equipment subject to fire-induced spurious operation that may challenge the safe shutdown capability Step 5: Identify additional mitigating, instrumentation, and diagnostic equipment important to human response Step 6: Include potentially high consequence related equipment Step 7: Assemble the Fire PRA Component List Fire PRA Workshop 2019, Rockville, MD Slide 6 Module 1: Internal Event, At-Power PRA Model for SNPP

Component Selection General Observations Two major sources of existing information are used to generate the Fire PRA Component List:

Internal Events PRA model Fire Safe Shutdown Analysis (Appendix R assessment)

Just tweaking your Internal Events PRA is probably NOT sufficient - Requires additional effort

- Consideration of fire-induced spurious operation of equipment

- Potential for undesirable operator actions due to spurious alarms/indications

- Additional operator actions for responding to fire (e.g., opening breakers to prevent spurious operation)

Just crediting Appendix R components may NOT be conservative

- True that all other components in Internal Events PRA will be assumed to fail, but:

May be missing components with adverse risk implications (e.g., event initiators or complicated SSD response)

May miss effects of non-modeled components on credited (modeled) systems/components and on operator performance Still need to consider non-credited components as sources of fires Fire PRA Workshop 2019, Rockville, MD Slide 7 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Overview of Scope In Appendix R In Internal Events PRA CDF/LERF vs.

New* analysis resources tradeoff

- multiple spurious

- new sequences In Fire PRA perhaps not all of Appendix R New*

not all internal event sequences Fire PRA Workshop 2019, Rockville, MD Slide 8 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Assumptions The following assumptions underlie this procedure:

A good quality Internal Events PRA and Appendix R Safe Shutdown (SSD) analysis are available Analysts have considerable collective knowledge and understanding of plant systems, operator performance, the Internal Events PRA, and Appendix R SSD analysis Steps 4 thru 6 are applied to determine an appropriate number of spurious actuations to consider Configurations, timing, length of sustained spurious actuation, cable material, etc., among reasons to limit what will be modeled Note that HS duration is a current FAQ topic Fire PRA Workshop 2019, Rockville, MD Slide 9 Module 1: Internal Event, At-Power PRA Model for SNPP

From: Lessons Learned and Insights In-process FAQs FAQ 08-0051 Issue:

The guidance does not provide a method for estimating the duration of a hot short once formed This could be a significant factor for certain types of plant equipment that will return to a fail safe position if the hot short is removed or if MSO concurrence could trigger adverse impacts

- General approach to resolution:

Analyze the cable fire test data to determine if an adequate basis exists to establish hot short duration distributions

- Status:

Approved, but limited to AC hot shorts only Will be revisited with lessons learned from DESIREE-FIRE test results for DC hot shorts (NUREG/CR-7100)

Fire PRA Workshop 2019, Rockville, MD Slide 10 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Inputs/Outputs Task inputs and outputs:

Inputs from other tasks: Equipment considerations for operator actions from Task 12 (Post-Fire HRA)

Inputs from the MSO Expert Panel Reviews Could use inputs from other tasks to show equipment does not have to be modeled (e.g., Task 9 - Detailed Circuit Analysis or Task 11 -

Fire Modeling to show an equipment item cannot spuriously fail or be affected by possible fires)

Outputs to Task 3 (Cable Selection) and Task 5 (Risk Model)

Choices made in this task set the overall analysis scope Fire PRA Workshop 2019, Rockville, MD Slide 11 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details Step 1: Identify sequences to include and exclude from Fire PRA Some sequences can generally be excluded Sequences requiring passive/mechanical failures that can not be initiated by fires (e.g., pipe-break LOCAs, SGTR, vessel rupture)

Sequences that can be caused by a fire but are low frequency (e.g., ATWS in a PWR)

It may be decided to not model certain systems (i.e., assume failed for Fire PRA) thereby excluding some sequences (e.g., main feedwater as a mitigating system not important)

Possible additional sequences (recommend use of expert panel to address plant specific considerations)

Sequences associated with spurious operation (e.g., vessel/SG overfills, PORV opening, letdown or other pressure/level control anomalies)

MCR abandonment scenarios and other sequences arising from Fire Emergency Procedures (FEPs) and/or use of local manual actions Corresponding PRA Standard SRs: PRM-B5,B6 Fire PRA Workshop 2019, Rockville, MD Slide 12 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Step 2: Review the internal events PRA model against the fire safe shutdown analysis Identify and reconcile:

Differences in functions, success criteria, and sequences (e.g.,

Appendix R - no feed/bleed; PRA - feed/bleed)

Front-line and support system differences (e.g., Appendix R -

Need HVAC; PRA - Do not need HVAC)

System and equipment differences due to end-state and mission considerations (e.g., Appendix R - cold shutdown; PRA - hot shutdown)

Other miscellaneous equipment differences Include review of manual actions (e.g., actions needed for safe shutdown) in conjunction with Task 12 (HRA)

Corresponding PRA Standard SRs: ES-A3(a), ES-B1,B3 Fire PRA Workshop 2019, Rockville, MD Slide 13 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Step 3: Identify fire-induced initiating events based on equipment affected Consider equipment whose failure (including spurious actuation) will cause automatic plant trip Consider equipment whose failure (including spurious actuation) will likely result in manual plant trip, per procedures Consider equipment whose failure (including spurious actuation) will invoke Technical Specification Limiting Condition of Operation (LCO) necessitating a forced shutdown while fire may still be present (prior EPRI guidance recommended consideration of <8 hr LCO)

Compartments with none of the above need not have initiator though can conservatively assume simple plant trip Corresponding PRA Standard SRs: ES-A1,A3 & PRM-B3,B4,B5,B6 Fire PRA Workshop 2019, Rockville, MD Slide 14 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Since not all equipment/cable locations in the plant (e.g., all Balance of Plant systems) may be identified, judgment involved in identifying likely cable paths

- Need a basis for any case where routing is not verified

- Routing by exclusion (e.g., from a fire area, compartment, raceway) is a common and acceptable approach Should consider spurious event(s) contributing to initiators Related PRA standard SR: CS-A11 Fire PRA Workshop 2019, Rockville, MD Slide 15 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Instrument Air Compartment Compartment Compartment Compressor XX YY ZZ Cables judged Compartment Compartment to be here AA BB Compartment Compartment MCCs CC DD Fires cause loss of instrument air Fires assumed to cause loss of Fires assumed to cause loss instrument air of MCC(s) & subsequent effects (including loss of instrument air)

Fire PRA Workshop 2019, Rockville, MD Slide 16 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Step 4: Identify equipment whose spurious actuation may challenge the safe shutdown capability Examine multiple spurious events within each system considering success criteria PRA standard has specific requirements for multiple spurious events Review system P&IDs, electrical single lines, and other drawings Focus on equipment or failure modes not already on the component list (e.g., flow diversion paths)

Review/Incorporate PRA related scenarios identified by the MSO Expert Panel to identify new components/failure modes Review Internal Events System Notebooks to identify components/failure modes screened based on low probability combinations Fire PRA Workshop 2019, Rockville, MD Slide 17 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Steps In Procedure/Details (Cont.)

Step 4: Identify equipment whose spurious actuation may challenge the safe shutdown capability (cont.)

Be aware of any failure combinations that could cause or contribute to an initiating event Any new failure combinations that could cause or contribute to an initiating event should be addressed in Step 3 Any new equipment/failure modes should be added to component list for subsequent cable-tracing and circuit analysis Corresponding PRA Standard SRs: ES-B2,B3 Fire PRA Workshop 2019, Rockville, MD Slide 18 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Flow Diversion Path Examples from main to diversion takes 2 spurious flowpath path hot shorts to open diversion Div A MOV Div B MOV path Included in model takes 1 spurious to diversion hot short &

from main path flowpath failure of check Div A MOV valve to open CheckValve diversion path Screened from model if not potential high consequence event Fire PRA Workshop 2019, Rockville, MD Slide 19 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection Example of a New Failure Mode of a Component App. R ensures MSIVs will close / remain closed Containment so as to isolate vessel1 Main Steam Line Reactor Vessel Inboard MSIV Outboard MSIV Fire PRA concerned with MSIVs closing / remaining closed AND will not spuriously close when want valves to remain open so as to use condenser as heat sink1 1

different cables and corresponding circuits and analyses may need to be accounted for Fire PRA Workshop 2019, Rockville, MD Slide 20 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 2: Fire PRA Component Selection MSO Expert Panel This approach complements but is not part of the published consensus methodology (6850/1011989)

Reference Documents NEI 00-01, Revision 2, Guidance for Post-Fire Safe Shutdown Circuit Analysis, May 2009 Focused on use of the generic list of MSOs provided in Appendix G, and the guidance provided in Section 4.4, Expert Panel Review of MSOs NEI 04-02 Frequently Asked Question (FAQ) 07-0038, Lessons Learned on Multiple Spurious Operations WCAP-16933-NP, Revision 0, PWR Generic List of Fire-Induced Multiple Spurious Operation Scenarios, April 2009 NRC Regulatory Guide 1.205, Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants, Revision 1, December 2009 Fire PRA Workshop 2019, Rockville, MD Slide 21 Module 1: Internal Event, At-Power PRA Model for SNPP