ML23131A047
| ML23131A047 | |
| Person / Time | |
|---|---|
| Site: | 99902049 |
| Issue date: | 05/17/2023 |
| From: | Holtec, SMR |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML23131A044 | List: |
| References | |
| 160-USNRC-045 | |
| Download: ML23131A047 (1) | |
Text
NRC Meeting:
Probabilistic Safety Analysis Overview May 17th, 2023
Introductions
NRC Staff Holtec Staff holtec.com I smrllc.com I Page 2 HOLTEC I N l [~N A TI ON,\\ L
Meeting Agenda
Introductions
Purpose and Outcome Overview of PSA Quality Control Process Overview of Sample Approaches holtec.com I smrllc.com I Page 3 HOLTEC INT[RN A T I ONAL
Purpose and Outcome
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HOLTEC I NT L KN A TION,\\L PURPOSE: To provide a high-level overview of the SMR-160 PSA modeling approaches and address specific NRC questions related to SMR-160 PSA and design.
OUTCOME: To obtain feedback from the NRC staff on the high-level overview and identify specific topics that the NRC would like to discuss further in future meetings.
holtec.com I smrllc.com I Page 4
Overview of PSA Quality Control Process Overview of PSA Quality Control Process Compliance with RG 1.200 requirements
-,, fjJ?N~l1o~f Compliance with NUREG-0800 requirements and level of detail Following ANS/ASME Standards, including those "in-process" ASME/ANS RA-Sa-2009 (Lvl 1 Standard Endorsed by RG 1.200)
ASME/ANS RA-S-1.1-2022 (Lvl 1 Std Issued May 31, 2022)
ANS/ASME-58.22-2014 (LPSD Pilot Standard)
ASME/ANS-RA-S-1.2-2019 (DRAFT Updated Level 2 Standard)
PSA Groundrules and Assumptions Document (Hl-2210453)
PSA Model Maintenance Procedure (HPP-160-3112)
Gap Assessment(s) holtec.com I smrllc.com I Page 5
Overview of Sample Approaches Initiating Events (Hl-2200399 for Level 1 PSA)
Generic Industry Standards (NUREG/CR-5750)
Other Plant PSAs (IAEA TECHDOC-749/R)
Plant Specific System Level Review Master Logic Diagram holtec.com I smrllc.com I Page 6 HOLTEC I N.I [ RNAT I ON,\\ L
Overview of Sample Approaches Level 1 PSA Accident Sequence Analysis (Hl-2200652}
Four Primary Considerations for Preventing Core Damage Reactivity Control Short Term Decay Heat Removal Inventory Control Long Term Decay Heat Removal Event Tree Development HOLTEC I N T [l<NAT I ONAL Use RELAPS-3D to Evaluate Plant Response to each Level 1 Initiating Event Vary available systems/train to support event tree development Verify Event Tree using specific scenarios for each path holtec.com I smrllc.com I Page 7
Overview of Sample Approaches Accident Sequence Analysis Lev~I 2 PSA Group Level 1 Core Damage Sequences into PDS Bins ATWS or Non-ATWS Scenario Bypass or Non-Bypass Scenario RCS Pressure Availability of Long Term Cooling for Low Pressure Scenarios Availability of eves Injection for loss of DHR Scenarios Develop Containment Event Tree Use MELCOR for Level 2 PDS Accident Progression Evaluate Containment/Containment System Response Determine maximum pressures, temperatures, timing Determine release characteristics holtec.com I smrllc.com I Page 8 HOL TE C I NTfKNAT I ONr\\L
Overview of Sample Approaches Success Criteria HOLTEC I NTLKNATIONAL Develop Systems/Trains Required for Each Event Tree Node Develop System Models based on Success Criteria Determinations holtec.com I smrllc.com I Page 9
Overview of Sample Approaches Systems Analysis Review of System Design Documents Discussions with Designers Identify Data Needs - coordinate with Data analyst System Level Models Developed and Quantified ("'20 Systems)
HOLTEC I NT[liN A TION,\\L Insights and Design Change Recommendations Provided to Designers Integrated System Models Developed and Quantified Included Support Systems Insights and Design Change Recommendations Provided to Designers holtec.com I smrllc.com I Page 10
Overview of Sample Approaches Data Generic H O LTEC I NT[l<NATIONAL Initiating Events (NUREG/CR-6928, NUREG-1829, NUREG/CR-5750)
Component Types and Failure Modes Common Cause Failures Test & Maintenance Design Specific MELCO Dl&C Data holtec.com I smrllc.com I Page 11
Overview of Sample Approaches Human Reliability Analysis Pre-Initiators ASEP Screening Methodology (NUREG/CR-4772)
Post-Initiators SPAR-H Methodology (NIREG/CR-6883)
HOLTEC I Nl ll<NATIONt\\L Plan is to Update to THERP Methodology (NUREG/CR-1278) when procedures are available holtec.com I smrllc.com I Page 12
Overview of Sample Approaches "11K4 *****
HO L TEC I N l [ l< NA l I ON,\\ L Integration and Quantification (Hl-2210104)
Event trees converted to equivalent fault trees to create one-top model Top Logic integrated with system level logic based on required success criteria Quantification (several rounds) performed with cut set reviews at each CDF/LRF level Sequence level Initiating Event level Risk Significant SSCs Identified - Basis Discussed in Separate Meeting SSC Parameter Criteria for Risk Significance Determination Component level basic event Conditional CDF ~ 3 x 1 o-6/yr System level basic event Conditional CDF ~ 1 x 1 o-5/yr Component level basic event Conditional LRF ~ 3 x 10-7/yr System level basic event Conditional LRF ~ 1 x 1 o-6/yr Basic event/contributor Total FV > 0.20 holtec.com I smrllc.com I Page 13
Overview of Sample Approaches Uncertainty and Sensitivity (Hl-2210105)
Epistemic Uncertainty (EPRI 1016737)
Aleatory Uncertainty UNCERT 10,000 Samples Monte Carlo Sampling Method Sensitivity Analysis Performed
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"111a HOLTEC I N l [ ~ N A T I O N,\\ L Recommendations for Design Improvement provided to designers holtec.com I smrllc.com I Page 14
PSA Identified Design Change Suggestions PSA Identified Design Changes
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holtec.com I smrllc.com I Page 15
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PSA Identified Design Change Suggestions
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PSA Identified Design Change Suggestions PSA Identified Design Changes
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holtec.com I smrllc.com I Page 17
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Risk Importance Measures
-, e tjT RN~ -Jo~ f Fussell-Vesely (FV), commonly known as fraction of total risk FV== P(top)-P(top I A success)
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Risk Achievement Worth (RAW), or risk increase ratio given a SSC fails RAW== P(toplAfailed)
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Conditional CDF (CCDF), or increased CDF when a SSC fails CCDF== CDF
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Industry Guidance RG 1.200, RG 1.201 risk-significance criteria FV > 0.005 RAW > 2 for a component RAW> 20 for common-cause failures (or system-level events)
RG 1.174 risk-acceptance guidelines HOLTEC I N.I [ KNA rl ONA L r
Permanent changes to a plant's licensing basis are considered if calculated 8CDF is in the range of 10-6/yr to 10-5/yr and total CDF < 10-4/yr The ACRS noted that an inappropriately large number of SSCs may be identified as risk-significant using the RG 1.200 criteria for plants with very low estimated CDFs Undue burden on both the licensee and regulatory staff holtec.com I smrllc.com I Page 20
Need for SMR-160 Thresholds Current fleet has a baseline CDF of rv 1 x 10-5/yr HOLTEC I NT[l<NATIONAL RAW of 2 implies a LlCDF of 1 x 10-5/yr and CCDF of 2 x 10-5/yr is risk-significant FV of 0.005 implies a CDF contribution of 5 x 10-8/yr is risk-significant SMR-160 has a baseline CDF of((
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holtec.com I smrllc.com I Page 21
SMR-160 Thresholds and Justification
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Conclusion SMR-160 developed new risk significance criteria HOLTEC I N T[l{N A TION,\\l Consistent with risk significance criteria recently approved by the NRC Preliminary resu lts show ((
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holtec.com I smrllc.com I Page 24
Follow-up on NRC Staff Question:
"Beyond Design Basis" Winds HOLTEC I N T [ l< N A T I ON,\\ L During the 5/3/23 design overview meeting PSA topic, the NRC staff asked how SMR-160 deals with "beyond design basis" winds
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Does this answer the NRC's question regarding "beyond design basis" winds? If not, can the NRC staff provide further clarification to SMR-160 regarding the question and the definition of "beyond design basis" winds?
holtec.com I smrllc.com I Page 25