ML19162A421

01_06 Task 14 Risk Quant

ML19162A421
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Issue date:	06/13/2019
From:	Nick Melly NRC/RES/DRA
To:
T. Rivera
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ML19162A411	List: ML19162A412 ML19162A413 ML19162A414 ML19162A415 ML19162A416 ML19162A417 ML19162A418 ML19162A419 ML19162A420 ML19162A421
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NUREG/CR-6850 FIRE PRA METHODOLOGY Module 1 Internal Event, At-Power Probabilistic Risk Assessment Model for SNPP Task 14: Fire Risk Quantification Nicholas Melly - Nuclear Regulatory Commission Fire PRA Workshop June 24, 2019 - June 28, 2019 Rockville, MD U.S. NRC HQ

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 2 Fire Risk Quantification Purpose (per 6850/1011989)

Purpose:

Describe the procedure for performing fire risk quantification Provides a general method for quantifying the final Fire PRA Model to generate the final fire risk results

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 3 Fire Risk Quantification Corresponding PRA Standard Element Primary match is to element FQ - Fire Risk Quantification FQ Objectives (as stated in the PRA standard):

(a) quantify the fire-induced CDF and LERF contributions to plant risk (b) understand what are the significant contributors to the fire-induced CDF and LERF

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 4 Fire Risk Quantification HLRs (per the PRA Standard)

HLR-FQ-A: Quantification of the Fire PRA shall quantify the fire-induced CDF HLR-FQ-B: The fire-induced CDF quantification shall use appropriate models and codes, and shall account for method-specific limitations and features HLR-FQ-C: Model quantification shall determine that all identified dependencies are addressed appropriately HLR-FQ-D: The frequency of different containment failure modes leading to a fire-induced large early release shall be quantified and aggregated, thus determining the fire-induced LERF

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 5 Fire Risk Quantification HLRs (per the PRA Standard)

HLR-FQ-E: The fire-induced CDF and LERF quantification results shall be reviewed and significant contributors to CDF and LERF, such as fires and their corresponding plant initiating events, fire locations, accident sequences, basic events (equipment unavailabilities and human failure events), plant damage states, containment challenges, and failure modes, shall be identified. The results shall be traceable to the inputs and assumptions made in the Fire PRA HLR-FQ-F: The documentation of CDF and LERF analyses shall be consistent with the applicable SRs

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 6 Fire Risk Quantification Scope (per 6850/1011989)

Task 14: Fire Risk Quantification Obtaining best-estimate quantification of fire risk Step 1: Quantify Final Fire CDF Model Step 2: Quantify Final Fire LERF Model Step 3: Conduct Uncertainty Analysis

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 7 Task 14: Fire Risk Quantification General Objectives

Purpose:

perform final (best-estimate) quantification of fire risk Calculate CDF/LERF as the primary risk metrics Include uncertainty analysis / sensitivity results (see Task 15)

Identify significant contributors to fire risk Carry along insights from Task 13 to documentation, but this is not an explicit part of quantifying the Fire PRA model Carry along residual risk from screened compartments and scenarios (Task 7); both (final fire risk and residual risk) are documented in Task 16 to provide total risk perspective

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 8 Task 14: Fire Risk Quantification Inputs/Outputs Task inputs:

Inputs from other tasks:

Task 5 (Fire-Induced Risk Model) as modified / run thru Task 7 (Quantitative Screening),

Task 10 (Circuit Failure Mode Likelihood Analysis),

Task 11 (Detailed Fire Modeling), and

Task 12 (Post-Fire HRA Detailed Analysis)

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 9 Task output:

Output is the quantified fire risk results, including the uncertainty and sensitivity analyses, directed by Task 15 (Uncertainty and Sensitivity Analysis); all of which is documented per Task 16 (Fire PRA Documentation)

Task 14: Fire Risk Quantification Inputs/Outputs (Cont.)

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 10 Task 14: Fire Risk Quantification Steps in Procedure Four major steps in the procedure*:

Step 1: Quantify CDF Step 2: Quantify LERF Step 3: Perform uncertainty analyses, including propagation of uncertainty bounds, as directed under step 4 of Task 15 Step 4: Perform sensitivity analyses as directed under step 4 of Task 15

• In each case, significant contributors are also identified

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 11 Task 14: Fire Risk Quantification Quantification Process Characteristics of the quantification process:

Procedure is general; i.e., not tied to a specific method (event tree with boundary conditions, fault tree linking)

Can calculate CDF/LERF directly by explicitly including fire scenario frequencies or first calculate CCDP/CLERP and then combine with fire scenario frequencies Quantify consistent with relevant ASME-ANS PRA Standard (RA-Sa-2009) supporting requirements

Many cross-references from FQ to internal events section (Part 2) for most aspects of risk quantification

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 12 Task 14: Fire Risk Quantification Steps in Procedure/Details Step 1 (2): Quantify Final Fire CDF/LERF Model Step 1.1 (2.1): Quantify Final Fire CCDP/CLERP Model

Corresponding SRs: FQ-A1, A2, A3, A4, B1, C1, D1, E1

Final HRA probabilities, including dependencies

Final cable failure probabilities

Final cable impacts Step 1.2 (2.2): Quantify Final Fire CDF/LERF Frequencies

Corresponding SRs: FQ-A1-A4, B1, C1, D1, E1

Final compartment frequencies

Final scenario frequencies

Final fire modeling parameters (i.e., severity factors, non-suppression probabilities, etc.)

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 13 Task 14: Fire Risk Quantification Steps in Procedure/Details (Cont.)

Step 1 (2): Quantify Final Fire CDF/LERF Model (cont.)

Step 1.3 (2.3): Identify Main Contributors to Fire CDF/LERF

Corresponding SRs: FQ-A1-A3, E1

Contributions by fire scenarios, compartments where fire ignition occurs, plant damage states, post-fire operator actions, etc.

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 14 Task 14: Fire Risk Quantification Steps in Procedure/Details (Cont.)

Step 3: Propagate Uncertainty Distributions Probability distributions of epistemic uncertainties propagated through the CDF and LERF calculations Monte Carlo or Latin hypercube protocols

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 15 Task 14: Fire Risk Quantification Steps in Procedure/Details (Cont.)

Step 4.1: Identification of Final Set of Sensitivity Analysis Cases Review sensitivity cases identified in Task 15 Finalize sensitivity cases for Step 4.2

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 16 Task 14: Fire Risk Quantification Steps in Procedure/Details (Cont.)

Step 4.2: CDF and/or LERF Computations and Comparison Mean CDF/LERF values computed for each sensitivity analysis case considered in Step 4.1 The results should be compared with the base-case considered in Steps1 and 2

Fire PRA Workshop 2019, Rockville, MD Module 1: Internal Event, At-Power PRA Model for SNPP Slide 17 Mapping HLRs & SRs for the FQ Technical Element to NUREG/CR-6850, EPRI TR 1011989 Technical element HLR SR 6850/1011989 sections that cover SR Comments FQ A

Quantification of the Fire PRA shall quantify the fire-induced CDF.

1 14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2, 14.5.2.3 2

14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2, 14.5.2.3 3

14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2, 14.5.2.3 4

14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2 B

The fire-induced CDF quantification shall use appropriate models and codes and shall account for method-specific limitations and features.

1 14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2 C

Model quantification shall determine that all identified dependencies are addressed appropriately.

1 14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2 D

The frequency of different containment failure modes leading to a fire-induced large early release shall be quantified and aggregated, thus determining the fire-induced LERF 1

14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2 E

The fire-induced CDF and LERF quantification results shall be reviewed, and significant contributors to CDF and LERF, such as fires and their corresponding plant initiating events, fire locations, accident sequences, basic events (equipment unavailabilities and human failure events), plant damage states, containment challenges, and failure modes, shall be identified. The results shall be traceable to the inputs and assumptions made in the Fire PRA 1

14.5.1.1, 14.5.1.2, 14.5.2.1, 14.5.2.2, 14.5.2.3 F

The documentation of CDF and LERF analyses shall be consistent with the applicable SRs.

1 n/a Documentation not covered in 6850/1011989 2

n/a Documentation not covered in 6850/1011989