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