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01_04 Task 5 Risk Model
	ML19162A419
Person / Time
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 5: Fire-Induced Risk Model Development Nicholas Melly - Nuclear Regulatory Commission Fire PRA Workshop June 24, 2019 - June 28, 2019 Rockville, MD U.S. NRC HQ

Fire PRA Risk Model Purpose (per 6850/1011989)

Purpose:

Describe the procedure for developing the Fire PRA model to calculate CDF, CCDP, LERF, and CLERP for fire ignition events Fire Risk Model Key input for Quantitative Screening (Task 7)

Used to quantify CDF/CCDP and LERF/CLERP Process is iterative to ensure appropriate agreement among fire PRA Component List, Fire PRA Model, cable identification, and quantitative screening Fire PRA Workshop 2019, Rockville, MD Slide 2 Module 1: Internal Event, At-Power PRA Model for SNPP

Fire PRA Risk Model Corresponding PRA Standard Element Primary match is to element PRM - Equipment Selection PRM Objectives (as stated in the PRA standard):

(a) to identify the initiating events that can be caused by a fire event and develop a related accident sequence model. (b) to depict the logical relationships among equipment failures (both random and fire induced) and human failure events (HFEs) for CDF and LERF assessment when combined with the initiating event frequencies Fire PRA Workshop 2019, Rockville, MD Slide 3 Module 1: Internal Event, At-Power PRA Model for SNPP

Fire PRA Risk Model HLRs (per the PRA Standard)

HLR-PRM-A: The Fire PRA shall include the Fire PRA plant response model capable of supporting the HLR requirements of FQ HLR-PRM-B: The Fire PRA plant response model shall include fire-induced initiating events, both fire induced and random failures of equipment, fire-specific as well as non-fire-related human failures associated with safe shutdown, accident progression events (e.g., containment failure modes), and the supporting probability data (including uncertainty) based on the SRs provided under this HLR that parallel, as appropriate, Part 2 of this Standard, for Internal Events PRA HLR-PRM-C: The Fire PRA shall document the Fire PRA plant response model in a manner that facilitates Fire PRA applications, upgrades, and peer review Fire PRA Workshop 2019, Rockville, MD Slide 4 Module 1: Internal Event, At-Power PRA Model for SNPP

Fire PRA Risk Model Scope (per 6850/1011989)

Task 5: Fire-Induced Risk Model Development Constructing the PRA Model Step 1-Develop the Fire PRA CDF/CCDP Model Step 2-Develop the Fire PRA LERF/CLERP Model Fire PRA Workshop 2019, Rockville, MD Slide 5 Module 1: Internal Event, At-Power PRA Model for SNPP

Fire PRA Risk Model General Comment/Observation Task 5 does not represent any changes from past practice, but what is modeled is largely based on Task 2 with HRA input from Task 12 Bottom line - Just tweaking your Internal Events PRA is probably NOT sufficient Fire PRA Workshop 2019, Rockville, MD Slide 6 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 5: Fire Risk Model Development General Objectives

Purpose:

Configure the Internal Events PRA to provide fire risk metrics of interest (primarily CDF and LERF)

Based on standard state-of-the-art PRA practices Intended to be applicable for any PRA methodology or software Allows user to quantify CDF and LERF, or conditional metrics CCDP and CLERP Conceptually, nothing new here - Need to build the PRA model reflecting fire induced initiators, equipment and failure modes, and human actions of interest Fire PRA Workshop 2019, Rockville, MD Slide 7 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 5: Fire Risk Model Development Inputs/Outputs Task inputs and outputs:

Inputs from other tasks: (Note: Inclusion of spatial information requires cable locations from Task 3)

Sequence considerations, initiating event considerations, and components from Task 2 (Fire PRA Component Selection)

Unscreened fire compartments from Task 4 (Qualitative Screening)

HRA events from Task 12 (Post-Fire HRA)

Output to Task 7 (Quantitative Screening) which will further modify the model development Can always iterate back to refine aspects of the model Fire PRA Workshop 2019, Rockville, MD Slide 8 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 5: Fire Risk Model Development Steps in Procedure Two major steps:

Step 1: Develop CDF/CCDP model Step 2: Develop LERF/CLERP model Fire PRA Workshop 2019, Rockville, MD Slide 9 Module 1: Internal Event, At-Power PRA Model for SNPP

Task 5: Fire Risk Model Development Steps in Procedure/Details Step 1 (2): Develop CDF/CCDP (LERF/CLERP) models Step 1.1 (2.1): Select fire-induced initiators and sequences and incorporate into the model Corresponding SRs: PRM-A1, A2, A3, B1-B15 Fire initiators are generally defined in terms of compartment fires or fire scenarios Each fire initiator is mapped to one or more internal event initiators to mimic the fire-induced impact to the plant Initiating events previously screened in the internal events analysis may have to be reconsidered for the Fire PRA Final mapping of fire initiator to internal events initiators is based on cable routing information (Task 3)

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