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xLPR: A Probabilistic Code for Evaluating Piping Integrity
Rob TregoningDave Rudland
Matthew HomiackU.S. NRC
Craig HarringtonEPRI
EPRI Materials Reliability ConferenceChicago, Illinois
August 1-4, 2016
The view expressed herein are those of the authors and do not reflect the views of the U.S. Nuclear Regulatory Commission
2016 EPRI Materials Reliability Conference
• Motivation and Overview of xLPR Development
• Status of Ongoing Activities
• xLPR Application
• Code Maintenance and Development
Outline2
2016 EPRI Materials Reliability Conference
• General Design Criterion (GDC) - 4 of 10 CFR 50 Appendix A allows local dynamic effects of pipe ruptures to be excluded from design basis if pipe ruptures have extremely low probability of occurrence
• Conservative deterministic flaw tolerance analyses were developed and incorporated in NRC’s Standard Review Plan (SRP) 3.6.3 to demonstrate Leak-Before-Break (LBB) and satisfy GDC-4
• SRP 3.6.3 stipulates that no active degradation exist. However, primary water stress corrosion cracking (PWSCC) is active in many LBB approved lines
• No quantitative methodology exists for calculating probability of rupture with active degradation
– Deterministic approaches are ill-suited and have been unsuccessful in demonstrating LBB
– Probabilistic approaches are best suited
3
Motivation for xLPR Development
2016 EPRI Materials Reliability Conference
• Cooperative effort between NRC and EPRI
Organizational Structure4
PEAI
Supporting Organizations
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Crack Mechanism
Loads
Initiation
Crack Coalescence
t=ti
Material Properties
t=t+Dt
yes
Inspection/
Mitigation
Crack Growth
Stability Leakage
Rupture, tf
xLPR Conceptual Flow5
2016 EPRI Materials Reliability Conference
• Rigorous Quality Assurance (QA) program encompasses all aspects of code development and documentation
6
Release
Software Quality Assurance Plan
Program Basis Requirements
Software Project Management Plan
Software ConfigurationManagement PlanWork Plans
DesignRequirements Implementation Test
Quality Assurance Program
- Follows structure and intent of ASME NQA - 1
- Commercial software dedication may be required for use under an Appendix B QA program
2016 EPRI Materials Reliability Conference
• Verification – Establishes correspondence between product and its specifications
– Inputs verified through QA program
– Individual modules and framework verified using test cases
– Test cases demonstrate that logic, equations and variable handing (i.e., input/output) are as intended
• Validation – Establishes whether product is fit for its intended purpose
– Code is being validated using specific historical events
– Sensitivity analysis used to establish the code’s accuracy
7
• Independent Review – Assessing several aspects of code
– Verification
• Independent testing team
– Quality assurance
• External reviews
– Technical adequacy and project management (Continual)
• Project Integration Board
– Technical adequacy (Periodic)
• External Review Board
• Advisory Committee on Reactor Safeguards
Verification, Validation & Review
2016 EPRI Materials Reliability Conference
xLPR V2Framework
report
xLPR V2 Users Manual
xLPR Version 2.0 Technical basis document
NUREG/EPRI Doc
xLPR V2Models/Inputs
Report
xLPR V2Uncertainty
Report
LBB Regulatory Guide
CI TBD
CGR (Coal) TBD
K TBD
WRS TBD
COD TBD
Stability TBD
Leak TBD
ISI TBD
Tiffany TBD
CTM TBD
xLPR V2PIB report
xLPR V2SVVR
LBB Technical Basis Document
Acceptance Group document
ERB reportQA report
• Supports both current and future use of the code
– Technical basis for modules, inputs, and framework
– Code logic and structure
– Quality assurance
– Guidance for users
– External review findings and recommendations
– Regulatory applications
• ~95 formal xLPR documents
– ~80 are QA documents
– ~90 are completed
8
Modular Technical Basis Documents
Documentation
xLPR Documents
2016 EPRI Materials Reliability Conference
• Verification and validation testing– Recently completed actual testing
– Documentation will be completed within the next month
• QA program– Final QA Implementation Review
• V2.0 documentation – Framework subgroup report – September 2016
– Uncertainty report – December 2016
– User’s manual – December 2016
• Final External Review Board meeting and report – to be scheduled
• xLPR V2.0 code release – Fall 2016
– xLPR Roll-out & basic training meeting – Fall 2016
9
Status of Ongoing Activities
2016 EPRI Materials Reliability Conference
Sensitivity &
Methodology
Studies
NRC
EPRI
Real-World
Weld
Studies
NRC
Generalization
Studies
Regulatory
Guide
00~ 9
months24+ months~ 18 months
EPRI
Generalization
Studies?
Conceptual Timeline
PFM Use Regulatory Guidance / SRP
• Creating new memoranda of understanding between NRC and EPRI that will govern future joint research activities
Conceptual Application Plan10
2016 EPRI Materials Reliability Conference
• Focus on application of xLPR to leak-before-break analyses
• Sensitivity studies– Determine drivers to rupture probability and uncertainty in results
– Develop procedures for correctly running the code and interpreting outputs
– Develop procedures for translating outputs to plant failure frequencies
• Real-world weld studies– Model plant-specific welds to address
variety of conditions
– Assess failure probability and effects of mitigation
11
xLPR Application – Joint Research
2016 EPRI Materials Reliability Conference
• Generalization studies– Explore the effects associated with the fleet-wide range of variability in the most significant
LBB-PWSCC parameters
– Determine whether a generic assessment of LBB in lines with PWSCC is achievable
– Identify specific limitations or bounds on generic applicability
• Regulatory guide development– Probabilistic Fracture Mechanics (PFM) tools are increasingly being applied for regulatory
purposes
– PFM is a powerful analytical tool but its use is complex and the results are a complex function of the models, inputs, assumptions and framework
– Regulatory guidance will address
• Use of PFM in LBB applications• Use of PFM in general applications
12
xLPR Application – NRC Research
2016 EPRI Materials Reliability Conference
• Implementation methodologies for NRC regulatory guidance– If NRC is not able to generically address LBB in lines with PWSCC and require no further
action by licensees, additional work will be needed
– Such work could entail only limited analysis of a few plant groups or individual, plant-specific analyses by all licensees
• Identify other xLPR applications– Define a structured screening process to identify legacy analyses with potentially significant
embedded conservatisms that can be quantified using the xLPR Code
– Apply the process to identify high-value examples with significant potential to benefit the fleet if the assumed analytical conservatism can be reduced without adversely impacting safety
– Work with NRC and appropriate industry groups to develop robust technical bases for conservatism reductions where appropriate
13
xLPR Application – EPRI Research
2016 EPRI Materials Reliability Conference
• Once xLPR V2.0 is released, maintenance of the code will be led by a third-party custodian– Code distribution
– Error reporting and bug fixing
– Technical support
– Development and maintenance of pre and post processing tools
• Further code development will be led by users
– EPRI and NRC have no current plans to fund additional development
– EPRI and NRC plan to support the formation of a user’s group
– User group activities will be coordinated by the custodian
– User’s group will determine areas for code development and improvements
14
Code Maintenance and Development
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