ML23193B042
| ML23193B042 | |
| Person / Time | |
|---|---|
| Issue date: | 06/11/2023 |
| From: | Nellis C Office of Nuclear Regulatory Research |
| To: | |
| References | |
| Download: ML23193B042 (12) | |
Text
Applications of the Extremely Low Probability of Rupture (xLPR) Code 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.
Christopher Nellis Reactor Engineer US Nuclear Regulatory Commission Office of Nuclear Regulatory Research Division of Engineering Reactor Engineering Branch Christopher.Nellis@nrc.gov
Outline History
> Problem Space
> Development Applications
> Leak-before-break (LBB) Analyses
> LOCA frequency estimation
> Initial forays into AI/ML 2
Fracture Mechanics Different Analysis Approaches Probabilistic Approach Multiple Calculations Aggregated to Give Probability of Failure over Time Stress + Toughness + Crack Growth + Crack Size Life Single Calculation Conservatively Conservatively Conservatively Conservatively Plus Margin Gives High Value Low Value High Value High Value Single, Conservative Result Deterministic Approach 3
Histor y and Development of xLPR Concerns butt-weld degradation in nuclear power plant piping from:
> Fatigue
> Stress-corrosion cracking 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 4
xLPR Code Capabilities and Limitations
> Stress-Corrosion Cracking
> Thermal and Mechanical Fatigue
> Crack Initiation
> Leak Rate Calculations
> Residual Stress Effects
> Water Chemistry
> Ultrasonic Inspections
> Seismic Effects
> Mechanical Mitigation
> Models Only Certain Failure Modes
> Limited to Butt-Weld Geometry
> Only Performs Component-Level Analyses 5
Leak-Before-Break Analyses 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 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 6
LBB Results Piping Systems Evaluated
- Westinghouse four-loop RVON and RVIN DMWs
- Westinghouse pressurizer surge line nozzle DMWs
- Westinghouse steam generator nozzle DMWs
- Westinghouse two- and three-loop RVON and RVIN DMWs 7
LBB Results 2 TLR Reports Issued Even with PWSCC, all Piping systems continued to meet requirements of GDC 4 TLR-RES/DE/REB-2021-09
> Probability of rupture before leak found Probabilistic Leak-Before-Break Evaluation of Westinghouse Four-extremely unlikely Loop Pressurized-Water Reactor Primary Coolant Loop Piping
> When leak rate detection of 1 gpm is using the Extremely Low Probability of Rupture Code considered, no ruptures occur Value of xLPR (and PFM analysis) to make TLR-RES/DE/REB-2021-14-R1 evaluations according to GDC 4 was Probabilistic Leak-Before-Break Evaluations of Pressurized-Water underlined in this study Reactor Piping Systems using the Extremely Low Probability of Rupture Code 8
Loss-of-Coolant Accident (LOCA) Frequency Estimation 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 9
LOCA Results With Inspection - No LRD With LRD - No Inspection Annual frequency of LOCA 1.E-01 upper bound LOCAs (LRD) 1.E-03 BG - SBLOCA 1.E-05 BG - MBLOCA 1.E-07 BG - LBLOCA 1.E-09 (yr-1)
BL - SBLOCA 1.E-11 BL - MBLOCA 1.E-13 Bl - LBLOCA 0 20 40 60 80 Time (yr)
With Inservice Inspection With Leak Rate Detection Alignment at 25 years but higher at 60 years No LOCAs detected with 100,000 realizations 10
Initial Explorations into AI/ML 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 11
Have Questions or Need Infor mation on xLPR?
xlpr@nrc.gov xlpr@epri.com 12