ML23193B042

Applications of the Extremely Low Probability of Rupture (Xlpr) Code

ML23193B042
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Issue date:	06/11/2023
From:	Nellis C Office of Nuclear Regulatory Research
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Download: ML23193B042 (12)

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A p p l i c a t i o n s o f t h e E x t r e m e l y L o w P r o b a b i l i t y o f R u p t u r e ( x L P R ) C o d e Christopher Nellis Reactor Engineer US Nuclear Regulatory Commission Office of Nuclear Regulatory Research Division of Engineering Reactor Engineering Branch Christopher.Nellis@nrc.gov This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

Approved for public release; distribution is unlimited.

2 O u t l i n e History

> Problem Space

> Development Applications

> Leak-before-break (LBB) Analyses

> LOCA frequency estimation

> Initial forays into AI/ML

3 F r a c t u r e M e c h a n i c s D i f f e r e n t A n a l y s i s A p p r o a c h e s Stress

+

Toughness +

Crack Growth +

Crack Size Life Probabilistic Approach Deterministic Approach Conservatively High Value Conservatively Low Value Conservatively High Value Conservatively High Value Multiple Calculations Aggregated to Give Probability of Failure over Time Single Calculation Plus Margin Gives

Single, Conservative Result

4 H i s t o r y a n d D e v e l o p m e n t o f x L P R NRC and EPRI jointly developed xLPR

> Initial Pilot Study

> xLPR 2.0 released in 2020 Modular Design

> Each module developed by experts

> Allows flexibility of future development Concerns butt-weld degradation in nuclear power plant piping from:

> Fatigue

> Stress-corrosion cracking

> Stress-Corrosion Cracking

> Thermal and Mechanical Fatigue

> Crack Initiation

> Leak Rate Calculations

> Residual Stress Effects

> Water Chemistry

> Ultrasonic Inspections

> Seismic Effects

> Mechanical Mitigation 5

x L P R C o d e C a p a b i l i t i e s a n d L i m i t a t i o n s

> Models Only Certain Failure Modes

> Limited to Butt-Weld Geometry

> Only Performs Component-Level Analyses 5

6 L e a k - B e f o r e - B r e a k A n a l y s e s NRC traditionally used deterministic leak-before-break (LBB) analyses for piping systems

> Assurance a pipe will not suffer rupture event without a detectable leak

> These analyses did not account for PWSCC degradation Regulatory question of whether the PWR piping systems with PWSCC would continue to demonstrate an extremely low probability of rupture consistent with the requirements of GDC 4

> Previous LBB analyses were reevaluated using xLPR

> RVON and RVIN of Westinghouse 2,3, and 4 loop PWR 10 CFR Part 50, Appendix A, General Design Criterion 4 (GDC 4)

> Requires components to accommodate effects of environmental conditions

> Effects from pipe ruptures can be excluded if probability of rupture is extremely low under design basis conditions

7 L B B R e s u l t s Westinghouse four-loop RVON and RVIN DMWs Westinghouse pressurizer surge line nozzle DMWs CE and B&W RCP nozzle DMWs Westinghouse steam generator nozzle DMWs CE hot leg branch line nozzle DMWs CE cold leg branch line nozzle DMWs Westinghouse two-and three-loop RVON and RVIN DMWs Piping Systems Evaluated

8 L B B R e s u l t s Even with PWSCC, all Piping systems continued to meet requirements of GDC 4

> Probability of rupture before leak found extremely unlikely

> When leak rate detection of 1 gpm is considered, no ruptures occur Value of xLPR (and PFM analysis) to make evaluations according to GDC 4 was underlined in this study TLR-RES/DE/REB-2021-09 Probabilistic Leak-Before-Break Evaluation of Westinghouse Four-Loop Pressurized-Water Reactor Primary Coolant Loop Piping using the Extremely Low Probability of Rupture Code TLR-RES/DE/REB-2021-14-R1 Probabilistic Leak-Before-Break Evaluations of Pressurized-Water Reactor Piping Systems using the Extremely Low Probability of Rupture Code 2 TLR Reports Issued

9 L o s s - o f - C o o l a n t A c c i d e n t

( L O C A ) F r e q u e n c y E s t i m a t i o n LOCA frequency estimation supports several aspects of the NRCs regulatory framework

> Initiating event frequencies for Probability Risk Assessments (PRAs)

> Inform maintenance frequencies Explored using xLPRs probability of rupture output as a LOCA frequency

> Do xLPR predictions align with LOCA frequencies estimated in from NUREG-1829 Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process?

Do xLPR results align with all LOCA scenarios

> Small Break LOCA -> 100 gpm

> Medium Break LOCA -> 1,500 gpm

> Large Break LOCA -> 5000 gpm

10 L O C A R e s u l t s With Leak Rate Detection No LOCAs detected with 100,000 realizations With Inservice Inspection Alignment at 25 years but higher at 60 years 1.E-13 1.E-11 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 0

20 40 60 80 Annual frequency of LOCA (yr-1)

Time (yr)

With LRD - No Inspection upper bound LOCAs (LRD)

BG - SBLOCA BG - MBLOCA BG - LBLOCA BL - SBLOCA BL - MBLOCA Bl - LBLOCA With Inspection - No LRD

11 I n i t i a l E x p l o r a t i o n s i n t o A I / M L Regulatory Guide 1.245 requires:

> Estimates of quantities of interest and their uncertainties

> Sensitivity studies

> ML can be leveraged to assist these analyses.

ranked features

H a v e Q u e s t i o n s o r N e e d I n f o r m a t i o n o n x L P R ?

xlpr@nrc.gov xlpr@epri.com 12