ML24319A135
| ML24319A135 | |
| Person / Time | |
|---|---|
| Issue date: | 11/21/2024 |
| From: | David Rudland NRC/NRR/DNRL |
| To: | |
| References | |
| Download: ML24319A135 (1) | |
Text
Use of Probabilistic Fracture Mechanics Remarks by David L. Rudland, Ph.D.
Senior Level Advisor for Materials Division of New and Renewed Licenses Office of Nuclear Reactor Regulations Advisory Committee on Reactor Safeguards Meeting of the Subcommittee on Fuels, Materials, & Structures November 21, 2024
Motivation for Probabilistic Analyses
- Early in Life
-Limited data - large uncertainty
-Every discipline gets its own margin
- Loading over-estimated
- Material resistance under-estimated
-Conservatism does not limit operability
- Plants are new
Motivation for Probabilistic Analyses
- Later in Life
-More data & knowledge support improved models - less uncertainty
-Original margin overly burdensome? Do we change the margin with time?
-Issues
- Deterministic margins make all inputs conservative
- Deterministic approaches
-Not well suited to quantifying actual risk
-Solution: Probabilistic analyses -
- Properly account for true uncertainty 11/21/2024 ASME Code Relaxation Effortsl ACRS Sub-Committee Meeting 3
Integrated Decision Making
- Objective is integrated decision making
- Key is risk informed not risk based
- Use of risk insights for passive component integrity 11/21/2024 ASME Code Relaxation Effortsl ACRS Sub-Committee Meeting 4
If CDF is invoked, RG 1.174 submittal may be needed
Probabilistic Fracture Mechanics Probabilistic Fracture Mechanics (PFM) brings together information from the risk-triplet, For example, PFM can be used to estimate the probability of leakage or rupture of a pressure-boundary component The outcome of PFM is inherently a risk-insight U.S. NRC recognizes PFM as a leading technique for managing risk-informed management of long-lived passive components 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 5
What can happen?
How often?
What are the consequences?
PFM is only one Part of Risk-informed Decision Making Update LOCA initiating event frequency Relaxations to design, inspection, maintenance requirements PFM analyses Very small change in failure frequency?
No Yes CDF/LERF Determination CDF/LERF very small Integrated Decision Making Defense in depth Performance Monitoring Increase in risk is small Change meets current regulations Safety Margins 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 6
If CDF is invoked, RG 1.174 submittal may be needed
Piping and Vessel PFM Codes Not exhaustive list Past 1980-2000 Present 2000-2020 Future 2020 - ?
Praise VISA FAVOR VIPER PRO-LOCA WIN-Praise SRRA xLPR V2 FAVPRO xLPR V3+
Prometheus VIPERNOZ Piping Vessel NRC developed Industry developed Joint developed Problem specific Problem specific PROST PRODICAL NURBIT International PASCAL-SP PASCAL PROMISE PIPER-CASS others 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 7
Licensing Reviews and Emergent Issues Risk/PRA Acceptability Risk information submitted outside of the formal risk-informed licensing basis change process Reliance on Licensee Risk Information Qualitative Quantitative Deterministic Reviews Relief Requests Requests with PFM LIC-206, RG 1.245, RIMA Process still being defined Process defined Emergent issues Process defined LIC-504 Risk-Informed Licensing Basis Changes (RD 1.174/RG 1.200 TSTF-505 Risk-informed Completion times NFPA-805 Risk-informed Fire Protection 10CFR 50.69 SSC Categorization 5b Risk-informed Surveillance Frequencies Risk-informed Inservice Inspection Need adequate, consistent information and confidence in results 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 8
Timeline of PFM Applications Not exhaustive list 1990 2000 2010 2020 RPV Weld Inspect Relief RI-ISI 50.61a Transition Break Size PZR Inspect Relief SG Inspect Relief 50.61 50.46 Davis Besse Upper Head RG 1.245 CRDM Thermal Sleeve French SCC Doel/Tihange CMAC Wolf Creek Cracking Future Applications Other Inspection Relief RG1.230 RG1.178 RIMA OE Application Guidance Regulation Peening Upper head inspect Davis Besse Upper Head 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 9
Bases for Past Success
- Computer code bases were technically adequate (V&V)
- RG 1.174 process was followed, or probabilities were very small - performance monitoring was sufficient
- In many cases, deterministic and probabilistic analyses were used
- Sensitivity/uncertainty analyses used to demonstrate impact of important variables 11/21/2024 ASME Code Relaxation Effortsl ACRS Sub-Committee Meeting 10
Past challenges in Piping and Vessels Probabilistic Integrity Analyses
- Incomplete uncertainty characterization
- Code and basis not submitted for review
- Incomplete code technical basis and/or V&V
- Ignored tenants of risk-informed decision making - performance monitoring
- Acceptance criteria
- Guidance being (or has been) developed to address challenges 11/21/2024 ASME Code Relaxation Efforts l ACRS Sub-Committee Meeting 11
Summary
- U.S. NRC recognizes PFM as a leading technique for managing risk-informed management of long-lived passive components
- PFM, used with or without PRA, can be a useful tool in optimizing inspection as long as other risk-informed principles are considered