ML19162A420
| ML19162A420 | |
| Person / Time | |
|---|---|
| Issue date: | 06/13/2019 |
| From: | Nick Melly NRC/RES/DRA |
| To: | |
| T. Rivera | |
| Shared Package | |
| ML19162A411 | List: |
| References | |
| Download: ML19162A420 (25) | |
Text
NUREG/CR-6850 FIRE PRA METHODOLOGY Module 1 Internal Event, At-Power Probabilistic Risk Assessment Model for SNPP Task 4: Qualitative Screening Task 7: Quantitative Screening Nicholas Melly - Nuclear Regulatory Commission Fire PRA Workshop June 24, 2019 - June 28, 2019 Rockville, MD U.S. NRC HQ
Qualitative / Quantitative Screening Scope (per 6850/1011989)
Task 4: Qualitative Screening First chance to identify very low risk compartments Task 7: Quantitative Screening Running the Fire PRA model to iteratively screen / maintain modeled sequences at different levels of detail Fire PRA Workshop 2019, Rockville, MD Slide 2 Module 1: Internal Event, At-Power PRA Model for SNPP
Qualitative Screening Corresponding PRA Standard Element Primary match is to element QLS - Qualitative Screening QLS Objectives (as stated in the PRA standard):
(a) The objective of the qualitative screening (QLS) element is to identify physical analysis units whose potential fire risk contribution can be judged negligible without quantitative analysis (b) In this element, physical analysis units are examined only in the context of their individual contribution to fire risk. The potential risk contribution of all physical analysis units is reexamined in the multicompartment fire scenario analysis regardless of the physical analysis units disposition during qualitative screening Fire PRA Workshop 2019, Rockville, MD Slide 3 Module 1: Internal Event, At-Power PRA Model for SNPP
Qualitative Screening HLRs (per the PRA Standard)
HLR-QLS-A: The Fire PRA shall identify those physical analysis units that screen out as individual risk contributors without quantitative analysis (4 SRs)
HLR-QLS-B: The Fire PRA shall document the results of the qualitative screening analysis in a manner that facilitates Fire PRA applications, upgrades, and peer review (3 SRs)
Fire PRA Workshop 2019, Rockville, MD Slide 4 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 4: Qualitative Screening Objectives and Scope The objective of Task 4 is to identify those fire compartments that can be shown to have a negligible risk contribution without quantitative analysis This is where you exclude the office building inside the protected area Task 4 only considers fire compartments as individual contributors Multi-compartment scenarios are covered in Task 11(b)
Compartments that screen out qualitatively need to be re-considered as potential Exposing Compartments in the multi-compartment analysis (but not as the Exposed Compartment)
Fire PRA Workshop 2019, Rockville, MD Slide 5 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 4: Qualitative Screening Required Input and Task Output To complete Task 4 you need the following input:
List of fire compartments from Task 1 List of Fire PRA equipment from Task 2, including location mapping results List of Fire PRA cables from Task 3, including location mapping results Task Output: A list of fire compartments that will be screened out (no further analysis) based on qualitative criteria Unscreened fire compartments are used in Task 6 and further screened in Task 7 Fire PRA Workshop 2019, Rockville, MD Slide 6 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 4: Qualitative Screening A Note.
Qualitative Screening is OPTIONAL!
You may choose to retain any number of potentially low-risk fire compartments (from one to all) without formally conducting the Qualitative Screening Assessment for the compartment However, to eliminate a compartment, you must exercise the screening process for the compartment Example 1: Many areas will never pass qualitative screening, so simply keep them Example 2: If you are dealing with an application with limited scope (e.g., NFPA 805 Change Evaluation) a formalized Qualitative Screening may be pointless Fire PRA Workshop 2019, Rockville, MD Slide 7 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 4: Qualitative Screening Screening Criteria (per 6850/1011989)
A Fire Compartment may be screened out** if:
No Fire PRA equipment or cables are located in the compartment, and No fire that remains confined to the compartment could lead to:
An automatic plant trip, or A manual trip as specified by plant procedures, or A near-term manual shutdown due to violation of plant Technical Specifications (In the case of tech spec shutdown, consideration of the time window is appropriate)
No firm time window is specified in the procedure - Rule of thumb:
consistent with the time window of the fire itself Analyst must choose and justify the maximum time window considered Corresponding PRA Standard SRs: QLS-A1, A2
(**Note: screened compartments are re-considered as fire source compartments in the multi-compartment analysis - Task 11c)
Fire PRA Workshop 2019, Rockville, MD Slide 8 Module 1: Internal Event, At-Power PRA Model for SNPP
Mapping HLRs & SRs for the QLS Technical Element to NUREG/CR-6850, EPRI TR 1011989 Technical HLR SR 6850/101198 Comments Element 9 section that covers SR QLS A The Fire PRA shall identify those physical analysis units that screen out as individual risk contributors without quantitative analysis 1 4.5 2 4.5 3 4.5 4 n/a Additional screening not covered in 6850/1011989 B The Fire PRA shall document the results of the qualitative screening analysis in a manner that facilitates Fire PRA applications, upgrades, and peer review 1 n/a Documentation is discussed in Section 16.5 of 6850/101198 2 n/a Documentation is discussed in Section 16.5 of 6850/101198 3 n/a Documentation is discussed in Section 16.5 of 6850/101198 Fire PRA Workshop 2019, Rockville, MD Slide 9 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening General Objectives (per 6850/1011989)
Purpose:
Allow (i.e., optional) screening of fire compartments and scenarios based on contribution to fire risk. Screening is primarily compartment-based (Tasks 7A/B). Scenario-based screening (Tasks 7C/D) is a further refinement (optional)
Screening criteria not the same as acceptance criteria for regulatory applications (e.g., R.G. 1.174)
Screening does not mean throw away - Screened compartments/scenarios will be quantified (recognized to be conservative) and carried through to Task 14 as a measure of the residual fire risk Fire PRA Workshop 2019, Rockville, MD Slide 10 Module 1: Internal Event, At-Power PRA Model for SNPP
Quantitative Screening Corresponding PRA Standard Element Primary match is to element QNS - Quantitative Screening QNS Objective (as stated in the PRA standard):
The objective of the quantitative screening (QNS) element is to screen physical analysis units from further (e.g., more detailed quantitative) consideration based on preliminary estimates of fire risk contribution and using established quantitative screening criteria Fire PRA Workshop 2019, Rockville, MD Slide 11 Module 1: Internal Event, At-Power PRA Model for SNPP
Quantitative Screening HLRs (per the PRA Standard)
HLR-QNS-A: If quantitative screening is performed, the Fire PRA shall establish quantitative screening criteria to ensure that the estimated cumulative impact of screened physical analysis units on CDF and LERF is small (1 SR)
HLR-QNS-B: If quantitative screening is performed, the Fire PRA shall identify those physical analysis units that screen out as individual risk contributors (2 SRs)
HLR-QNS-C: VERIFY that the cumulative impact of screened physical analysis units on CDF and LERF is small (1 SR)
HLR-QNS-D: The Fire PRA shall document the results of quantitative screening in a manner that facilitates Fire PRA applications, upgrades, and peer review (2 SRs)
Fire PRA Workshop 2019, Rockville, MD Slide 12 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Inputs/Outputs Inputs from other tasks for compartment-based screening (7A/B):
Fire ignition frequencies from Task 6, Task 5 (Fire-Induced Risk Model),
Task 12 (Post-Fire HRA Screening), and Task 8 (Scoping Fire Modeling) (7B only)
Fire PRA Workshop 2019, Rockville, MD Slide 13 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Inputs/Outputs (Cont.)
Inputs from other tasks for scenario-based screening (7C/D) include inputs listed above plus:
Task 9 (Detailed Circuit Failure Analysis), and/or Task 11 (Detailed Fire Modeling), and/or Task 12 (Detailed Post-Fire HRA), and Task 10 (Circuit Failure Mode Likelihood Analysis) (7D only)
Fire PRA Workshop 2019, Rockville, MD Slide 14 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Inputs/Outputs (Cont.)
Outputs to other tasks:
Unscreened fire compartments from Task 7A go to Task 8 (Scoping Fire Modeling)
Unscreened fire compartments from Task 7B go to Task 9 (Detailed Circuit Failure Analysis) and/or Task 11 (Detailed Fire Modeling) and/or Task 12 (Detailed Post-Fire HRA)
Unscreened fire scenarios from Task 7C/D go to Task 14 (Fire Risk Quantification) for best-estimate risk calculation Fire PRA Workshop 2019, Rockville, MD Slide 15 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Overview of the Process Make more realistic via circuit analysis Perform any one, Unscreened compartment two, or all three Make more realistic via based on where or scenario based on calculated fire modeling you will get more realistic results CDF/CCDP/LERF/CLERP for the least resources Make more realistic via more detailed HRA Screens?
If NO, iterate as necessary Fire PRA Workshop 2019, Rockville, MD Slide 16 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Steps in Procedure Three major steps in the procedure:
Step 1: Quantify CDF/CCDP model Step 2: Quantify LERF/CLERP model Step 3: Quantitative screening Fire PRA Workshop 2019, Rockville, MD Slide 17 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Steps in Procedure/Details Step 1: Quantify CDF/CCDP models Step 1.1: Quantify CCDP model Fire-induced initiators are set to TRUE (1.0) for each fire compartment, CCDP calculated for each compartment This step can be bypassed, if desired, by using fire frequencies in the model directly and calculating CDF Step 1.2: Quantify CDF Compartment fire-induced initiator frequencies combined with compartment CCDPs from Step 1.1 to obtain compartment CDFs Fire PRA Workshop 2019, Rockville, MD Slide 18 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Steps in Procedure/Details (Cont.)
Step 1: Quantify CDF/CCDP models (cont.)
Step 1.3: Quantify ICDP (optional)
ICDP includes unavailability of equipment removed from service routinely Recommend this be done if will use PRA for configuration management Fire PRA Workshop 2019, Rockville, MD Slide 19 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Steps in Procedure/Details (Cont.)
Step 2: Develop LERF/CLERP models Exactly analogous to Step 1 but now for LERF, CLERP Like ICDP, ILERP is optional Fire PRA Workshop 2019, Rockville, MD Slide 20 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Establishing Quantitative Screening Criteria This is an area that has evolved beyond 6850/1011989 6850/1011989 cumulative screening criteria are based in part on screening against a fraction of the internal events risk results Published PRA standard echoes 6850/1011989 (SR QNS-C1)
Regulatory Guide 1.200 took exception to SR QNS-C1 NRC staff position: screening criteria should relate to the total CDF and LERF for the fire risk, not the internal events risk That is, screening should be within the hazard group (e.g., fire)
An update to the PRA standard is pending and will likely revise QNS-C1 to reflect NRC staff position Bottom line: If you plan to use your fire PRA in regulatory applications, pay attention to RG 1.200 and watch for the PRA standard update Fire PRA Workshop 2019, Rockville, MD Slide 21 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Screening Criteria for Single Fire Compartment Step 3: Quantitative screening, Table 7.2 from NUREG/CR-6850 Quantification Type CDF and LERF ICDP and ILERP Compartment Screening Compartment Screening Criteria Criteria (Optional)
Fire Compartment CDF CDF < 1.0E-7/yr Fire Compartment CDF ICDP < 1.0E-7 With Intact Trains/Systems Unavailable Fire Compartment LERF LERF < 1.0E-8/yr Fire Compartment LERF ILERP < 1.0E-8 With Intact Trains/Systems Unavailable Note: The standard and RG 1.200 do not establish screening criteria for individual fire compartments - only cumulative criteria (see next slide)
Fire PRA Workshop 2019, Rockville, MD Slide 22 Module 1: Internal Event, At-Power PRA Model for SNPP
Task 7: Quantitative Screening Screening Criteria For All Screened Compartments Quantification 6850/1011989 NRC Staff Position per RG NRC Staff Position per RG Type Screening Criteria 1.200 for Cat II 1.200 for Cat III Sum of CDF for all < 10% of internal the sum of the CDF the sum of the CDF screened-out fire event average CDF contribution for all screened contribution for all screened compartments fire compartments is <10% of fire compartments is <1% of the estimated total CDF for the estimated total CDF for fire events fire events Sum of LERF for < 10% of internal the sum of the LERF the sum of the LERF all screened-out event average LERF contributions for all screened contributions for all screened fire compartments fire compartments is <10% of fire compartments is <1% of the estimated total LERF for the estimated total LERF for fire events fire events Sum of ICDP for < 1.0E-6 n/a n/a all screened-out fire compartments Sum of ILERP for < 1.0E-7 n/a n/a all screened-out fire compartments Fire PRA Workshop 2019, Rockville, MD Slide 23 Module 1: Internal Event, At-Power PRA Model for SNPP
Sample Problem Demonstration for Task 7 On-line demonstration of Task 7 Question and Answer Session Fire PRA Workshop 2019, Rockville, MD Slide 24 Module 1: Internal Event, At-Power PRA Model for SNPP
Mapping HLRs & SRs for the QNS Technical Element to NUREG/CR-6850, EPRI TR 1011989 Technical HLR SR 6850/101198 Comments Element 9 section that covers SR QNS A If quantitative screening is performed, the Fire PRA shall establish quantitative screening criteria to ensure that the estimated cumulative impact of screened physical analysis units on CDF and LERF is small 1 7.5.3 Specific screening criteria are identified in 6850/1011989 B If quantitative screening is performed, the Fire PRA shall identify those physical analysis units that screen out as individual risk contributors 1 7.5.1, 7.5.2 2 7.5.1, 7.5.2 C Verify that the cumulative impact of screened physical analysis units on CDF and LERF is small 1 7.5.3 Specific screening criteria are identified in 6850/1011989 D The Fire PRA shall document the results of quantitative screening in a manner that facilitates Fire PRA applications, upgrades, and peer review 1 n/a Documentation is discussed in Section 16.5 of 6850/101198 2 n/a Documentation is discussed in Section 16.5 of 6850/101198 Fire PRA Workshop 2019, Rockville, MD Slide 25 Module 1: Internal Event, At-Power PRA Model for SNPP