Initial Development of the Extremely Low Probability of Rupture (xLPR) Version 2.0 Code

2012 ◽  
Author(s):  
D. Rudland ◽  
C. Harrington
Keyword(s):  
Pilot Study ◽  
Piping System ◽  
Primary System ◽  
Development Effort ◽  
Degradation Mechanisms ◽  
Pressurized Water ◽  
Initial Development ◽  
System Pressure ◽  
Version 2.0 ◽  
Low Probability

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. Along with a series of existing qualitative steps to assure safety in LBB-approved lines experiencing PWSCC, NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, is developing a new, modular based, comprehensive piping system assessment methodology to directly assess compliance with the regulations. This project, called eXtremely Low Probability of Rupture (xLPR), will model the effects and uncertainties of relevant active degradation mechanisms and the associated mitigation activities. The resulting analytical tool will be comprehensive with respect to known and significant materials challenges (PWSCC, etc.), vetted with respect to the technical bases of models and inputs, flexible enough to permit analysis of a variety of in-service situations and adaptable such as to accommodate evolving and improving knowledge. A multi-year project has begun that has been focused on the development of a viable method and approach to address the effects of PWSCC as well as define the requirements necessary for such a modular-based assessment tool. As reported in a previous paper, the first version of this code was developed as part of a pilot study, which leveraged existing fracture mechanics based models and software coupled to both a commercial and open source code framework to determine the framework and architecture requirements appropriate for building a modular-based code with this complexity. The pilot study focused on PWSCC in pressurizer surge nozzles, and was meant to demonstrate the feasibility of this code and approach and not to determine the absolute values of the probability of rupture. This paper examines the plans for the xLPR Version 2.0 model which will broaden the scope of xLPR to all LBB-approved primary piping in pressurized water reactors (PWR), using an incremental approach that incorporates the design requirements and lessons learned from previous iterations. After a review of the Version 1.0 final results, this paper will document the plans for Version 2.0 including the revised management structure, the technical scope, and the progress in the code development effort to date.

Extremely Low Probability of Rupture (xLPR) Version 1.0 Code: Pilot Study Problem Results

2011 ◽  
Author(s):  
D. Rudland ◽  
C. Harrington
Keyword(s):  
Pilot Study ◽  
Assessment Tool ◽  
Lessons Learned ◽  
Nuclear Industry ◽  
Piping System ◽  
Primary System ◽  
Degradation Mechanisms ◽  
System Pressure ◽  
Piping Systems ◽  
Low Probability

Nuclear Regulatory Commission (NRC) Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to demonstrate compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. Along with a series of existing qualitative steps to assure safety in LBB-approved lines experiencing PWSCC, NRC staff, working cooperatively with the nuclear industry through a memorandum of understanding with the Electric Power Research Institute, is developing a new, modular based, comprehensive piping system assessment methodology to directly demonstrate compliance with the regulations. This project, called xLPR (eXtremely Low Probability of Rupture), will model the effects and uncertainties of relevant active degradation mechanisms and the associated mitigation activities. The resulting analytical tool will be comprehensive, vetted with respect to the technical bases of models and inputs, flexible enough to permit analysis of a variety of in-service situations and adaptable such as to accommodate evolving and improving knowledge. A multi-year project has begun that will first focus on the development of a viable method and approach to address the effects of PWSCC as well as define the requirements necessary for a modular-based assessment tool. To meet this goal, the first version of this code has been developed as part of a pilot study, which leverages existing fracture mechanics based models and software coupled to both a commercial and an open source code framework to determine the framework and architecture requirements appropriate for building a modular-based code with this complexity. The pilot study focused on PWSCC in pressurizer surge nozzles, and is meant to demonstrate the feasibility of this code and approach and not to determine the absolute values of the probability of rupture. Later development phases will broaden the scope of xLPR to appropriate primary piping systems in pressurized and boiling water reactors (PWR and BWR), using an incremental approach that incorporates the design requirements and lessons learned from previous iterations. This paper specifically examines the xLPR Version 1.0 model, the methods and approach used to couple the deterministic modules within a probabilistic software framework, and the results from the pilot study. A comparison of the results specific to the surge nozzle sample problem is presented. This paper concludes with lessons learned from the pilot study.

scholarly journals Development of Computational Framework and Architecture for Extremely Low Probability of Rupture (XLPR) Code

2010 ◽  
Author(s):  
D. Rudland ◽  
P. Mattie ◽  
R. Kurth ◽  
H. Klasky ◽  
B. Bishop ◽  
...  
Keyword(s):  
Pilot Study ◽  
Nuclear Industry ◽  
Current Status ◽  
Study Phase ◽  
Piping System ◽  
Primary System ◽  
Degradation Mechanisms ◽  
System Pressure ◽  
Piping Systems ◽  
Low Probability

The Nuclear Regulatory Commission (NRC) Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to demonstrate compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB exemptions. Along with the existing qualitative steps to assuring safety in LBB lines with PWSCC, the NRC staff, working cooperatively with the nuclear industry through a memorandum of understanding, is developing a new, modular based, comprehensive piping system assessment methodology to directly demonstrate compliance with the regulations. This tool, called xLPR (eXtremely Low Probability of Rupture), would properly model the effects and uncertainties of both active degradation mechanisms and the associated mitigation activities. The tool will be comprehensive with respect to known challenges, vetted with respect to scientific adequacy of models and inputs, flexible enough to permit analysis of a variety of in-service situations and adaptable such as to accommodate evolving and improving knowledge. A multi-year project has begun that will first focus on the development of a viable method and approach to address the effects of PWSCC as well as define the requirements necessary for a modular-based assessment tool. A prototype xLPR model and pilot study case is first being conducted leveraging existing fracture mechanics models and software coupled to both a commercial and open source code framework to determine the framework and architecture requirements appropriate for building a modular-based code with this complexity. The pilot study phase is focusing on PWSCC in pressurizer surge nozzles. Later development phases will broaden the scope of xLPR to all primary piping systems in pressurized and boiling water reactors (PWR and BWR), using an incremental approach that incorporates the design requirements and lessons learned from previous iterations. This paper specifically examines the prototype xLPR model and includes the methods and approach used to couple existing models and software as modules within a probabilistic software framework. Since the pilot study is currently still ongoing, this paper provides a discussion of the current status and plans to move forward after the pilot study is complete.

Development of the Extremely Low Probability of Rupture (xLPR) Version 2.0 Code

2015 ◽  
Author(s):  
D. Rudland ◽  
C. Harrington ◽  
R. Dingreville
Keyword(s):  
Pilot Study ◽  
Fracture Mechanics ◽  
Lessons Learned ◽  
Primary System ◽  
Cracking Behavior ◽  
Code Structure ◽  
System Pressure ◽  
Piping Systems ◽  
Version 2.0 ◽  
Low Probability

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. US NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, conducted a multi-year project that focused on the development of a viable method and approach to address the effects of PWSCC in primary piping systems approved for LBB. This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations. As reported in previous technical papers, the first version of the xLPR code was developed as part of a pilot study, which leveraged existing fracture mechanics based models and software coupled to both a commercial and open source code framework to determine the framework and architecture requirements appropriate for building a modular-based code with this complexity. Using the lessons learned from the pilot study, the production version of this code, designated as Version 2.0, focuses on those primary piping systems previously approved for LBB. In this version, the appropriate fracture mechanics-based models are employed to model the physical cracking behavior and a variety of computational options are provided to characterize, categorize and propagate problem uncertainties. This paper examines the xLPR Version 2.0 model by presenting a brief overview of the xLPR scope, the code structure, computational framework and fracture mechanics-based models. As a demonstration of the xLPR Version 2.0 capabilities, an example is presented that focuses on PWSCC in large-bore piping systems. This example exercises some functionalities of the xLPR code to demonstrate its application to assess compliance with 10CFR50 Appendix A, GDC-4. This paper concludes with a brief discussion on the path forward and plans for the control and maintenance of the xLPR code.

Uncertainty Sampling of Weld Residual Stress Fields in Probabilistic Analysis: Part II — Examples

2016 ◽  
Author(s):  
Robert E. Kurth ◽  
Cédric J. Sallaberry ◽  
Frederick W. Brust ◽  
Elizabeth A. Kurth ◽  
Michael L. Benson ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Assessment Tool ◽  
Lessons Learned ◽  
Piping System ◽  
Primary System ◽  
Cracking Behavior ◽  
System Pressure ◽  
Piping Systems ◽  
Low Probability

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. US NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, conducted a multi-year project that focused on the development of a viable method and approach to address the effects of PWSCC in primary piping systems approved for LBB. This project, called eXtremely Low Probability of Rupture (xLPR) [1], defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations. Using the lessons learned from the pilot study, the production version of this code, designated as Version 2.0, focused on those primary piping systems previously approved for LBB. In this version the appropriate fracture mechanics-based models are employed to model the physical cracking behavior and a variety of computational options are provided to characterize, categorize and propagate problem uncertainties. One of the most influential uncertainty on risk in the xLPR code is the one associated with weld residual stresses (WRS). WRS plays a key role in both crack initiation and crack growth. PWSCC is mainly driven by tensile stresses, whose major contributors are the tensile weld residual stresses that develop during fabrication of the piping system. Handling the uncertainty involved with WRS within a probabilistic framework is quite challenging. A companion paper presents the selected approach to represent uncertainty within the framework of the xLPR code while respecting a set of requirements in term of smoothness of profile, efficiency of (potential) importance sampling and (for axial WRS) equilibrium. This paper illustrate with examples the implementation of the described methods into xLPR v2.0.

Benchmarking Probabilistic Code for LBB Analysis for Circumferential Cracks

2017 ◽  
Author(s):  
Robert E. Kurth ◽  
Cédric J. Sallaberry ◽  
Bruce A. Young ◽  
Paul Scott ◽  
Frederick W. Brust ◽  
...  
Keyword(s):  
Probability Of Failure ◽  
Primary System ◽  
Degradation Mechanisms ◽  
Detection Systems ◽  
System Pressure ◽  
Piping Systems ◽  
Primary Water ◽  
Low Probability ◽  
Assessment Procedures ◽  
Leak Before Break

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. There are several codes available for addressing the requirements of GDC-4. This paper addresses three of these codes: (1) xLPR 2.0; (2) PROLOCA; and (3) PROMETHEUS. Each of these codes is described and applied to a representative plant where active degradation mechanisms have been found. Conclusions about the design, results, and interpretation of the results is then provided. In all cases the probability of failure of the pipe is found to be extremely low when the crack inspections and leak detection systems are modeled.

Uncertainty Sampling of Weld Residual Stress Fields in Probabilistic Analysis: Part I — Theory

2016 ◽  
Author(s):  
Robert E. Kurth ◽  
Cédric J. Sallaberry ◽  
Frederick W. Brust ◽  
Elizabeth A. Kurth ◽  
Michael L. Benson ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Assessment Tool ◽  
Lessons Learned ◽  
Piping System ◽  
Primary System ◽  
Cracking Behavior ◽  
System Pressure ◽  
Piping Systems ◽  
Low Probability

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. US NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, conducted a multi-year project that focused on the development of a viable method and approach to address the effects of PWSCC in primary piping systems approved for LBB. This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations [1]. Using the lessons learned from the pilot study [2] the production version of this code, designated as Version 2.0, focused on those primary piping systems previously approved for LBB [3]. In this version the appropriate fracture mechanics-based models are employed to model the physical cracking behavior and a variety of computational options are provided to characterize, categorize and propagate problem uncertainties. One of the most influential sources of uncertainty on risk in the xLPR code is the one associated with weld residual stresses (WRS). WRS plays a key role in both crack initiation and crack growth. PWSCC is mainly driven by tensile stresses, whose major contributors are the tensile weld residual stresses that develop during fabrication of the piping system. Handling the uncertainty involved with WRS within a probabilistic framework is quite challenging. This paper presents the selected approach to represent uncertainty within the framework of the xLPR code while respecting a set of requirements in term of smoothness of profile, efficiency of (potential) importance sampling and (for axial WRS) equilibrium. The current WRS sampling scheme employs correlation in order to smooth the shape of the WRS fields through the thickness of a dissimilar metal weld. This method presents an enrichment of the Cholesky decomposition on the correlation matrix, in order to satisfy the other two requirements.

Development of Initial Input Parameters for a Probabilistic Pipe Rupture Assessment Code for Nuclear Reactor Coolant Pressure Boundary Leak-Before-Break Analyses

2010 ◽  
Author(s):  
Eric M. Focht ◽  
Guy DeBoo
Keyword(s):  
Pilot Study ◽  
Nuclear Reactor ◽  
Computer Code ◽  
Nuclear Regulatory Commission ◽  
Primary System ◽  
Reactor Coolant ◽  
System Pressure ◽  
Input Parameters ◽  
Low Probability ◽  
Leak Before Break

The U.S. Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) entered into a cooperative agreement to develop a modular computer code for determining the probability of rupture of reactor coolant pressure boundary piping. The goal of xLPR project (Extremely Low Probability of Rupture), as it is known, is to develop a flexible modular code that satisfies the assessment methodology in the NRC Standard Review Plan (SRP) 3.6.3 leak-before-break analysis. The NRC SRP 3.6.3 provides guidance on satisfying Title 10 of the Code of Federal Regulations Part 50 (10 CFR Part 50) Appendix A, General Design Criteria 4 that requires primary system pressure piping to exhibit an extremely low probability of rupture. The initial phase of the xLPR project is the Pilot Study where the base structure of the code will be developed and tested on a known case. The Pilot Study version of the xLPR code consists of an alpha version where proxy modules and inputs are used and a beta version where the state-of-the art modules and inputs are used. This paper will discuss the input parameters used for the alpha xLPR code.

Predicting Pipe Rupture Frequencies Using xLPR

2020 ◽  
Author(s):  
David L. Rudland
Keyword(s):  
Assessment Tool ◽  
Leak Detection ◽  
Nuclear Regulatory Commission ◽  
Pipe Diameter ◽  
Nozzle Geometry ◽  
Pressurized Water ◽  
Version 2.0 ◽  
Low Probability ◽  
Leak Before Break ◽  
Service Inspection

Abstract Over the last several years, the U.S. Nuclear Regulatory Commission (NRC), in cooperation with the Electric Power Research Institute (EPRI), conducted a multi-year project that focused on the development of a viable method and approach to address the effects of primary water stress corrosion cracking (PWSCC) in primary piping systems approved for leak-before-break (LBB). This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations. Version 2.0 of this code has been completed and is currently awaiting public release. Since the focus of xLPR Version 2.0 is investigating the impacts of active piping degradation on the leak-before-break behavior of reactor coolant piping, questions have been raised to whether xLPR can be used to confirm pipe rupture frequencies developed in other efforts, such as NUREG-1829, “Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process.” This paper discusses an initial study focused on whether xLPR can be used to estimate pipe rupture frequencies. A series of analyses were conducted, based on inputs developed by the xLPR program team, focused on the reactor pressure vessel outlet nozzle geometry of a typical pressurized water reactor. Additional analyses were conducted using the same radius-to-thickness ratio but decreasing the pipe diameter. Due to computer memory restrictions, it was difficult calculating low probability events when considering PWSCC initiation, typical residual stresses, leak detection and in-service inspection. Therefore, to bound the problem, an aggressive weld residual stress was assumed with multiple pre-existing defects. By modifying the size and number of these initial defects, results were generated that indicated the conditional probability of rupture was related to the percentage of the inner circumference cracked and the pipe diameter. Using the PWSCC initiation model from xLPR Version 2, the yearly rupture frequency with leak detection and in-service inspection was calculated. The results indicate that the rupture frequencies in NUREG-1829 appear conservative relative to the results from this study. Due to the limited scope of this study, the assumptions used in these analyses were limited or conservative; therefore, additional analyses are needed for a more robust comparison. However, the results suggest that conducting xLPR analyses with pre-existing defects may be useful in bounding LBB applicability with active degradation.

Preemptive Weld Overlays to Mitigate PWSCC Concerns in PWR Piping System Dissimilar Metal Butt Welds

2005 ◽  
Author(s):  
Peter C. Riccardella ◽  
Marcos L. Herrera ◽  
Arthur F. Deardorff ◽  
Shu S. Tang ◽  
Anthony J. Giannuzzi
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Piping System ◽  
Primary System ◽  
Pressurized Water ◽  
Butt Welds ◽  
Dissimilar Metal ◽  
Structural Reinforcement ◽  
Weld Overlays

Primary water stress corrosion cracking (PWSCC) continues to be a concern in nickel-based alloys (Alloy 600 and the associated weld metals, Alloys 82 and 182) in pressurized water reactors (PWRs). It has caused cracking and leakage in a number of components, including steam generator tubes, vessel head penetrations, and most recently, the dissimilar metal butt welds (DMWs) commonly used to connect vessel nozzles to PWR primary system piping. Weld overlays (WOLs) have been used extensively in the past twenty years to repair nuclear plant piping that has been found to be cracked or leaking due to stress corrosion cracking [1]. This paper summarizes the advantages of and technical justification for applying preemptive weld overlays (PWOLs) before cracking or leakage is observed, to mitigate PWSCC in Alloy 82/182 butt welds. PWOL design is governed by a number of considerations. The PWOL must supply sufficient thickness of resistant material (Alloy 52 weld metal) to provide new structural reinforcement of the original pipe weld sufficient to sustain design basis loads within ASME Code margins. Structural reinforcement calculations are presented demonstrating the achievement of this capability in accordance with ASME Section XI rules for evaluation of flaws in austenitic piping. The PWOL must supply sufficient thickness to effectively reverse the highly tensile residual stresses from the original DMW, including the potential detrimental effects of an in-process repair weld. Residual stress evaluations using elastic-plastic finite element models are presented that demonstrate the achievement of this objective for several typical nozzle geometries. Finally, analyses are presented to demonstrate that a dissimilar metal weld, with PWOL applied, meets the Nuclear Regulatory Commission (NRC) criteria for leak-before-break (LBB).

Models for Use in Probabilistic Pipe Rupture Assessment Code Development

2010 ◽  
Author(s):  
Marjorie A. Erickson ◽  
Mark T. Kirk ◽  
Howard J. Rathbun
Keyword(s):  
Pilot Study ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Leak Rate ◽  
Degradation Mechanisms ◽  
Best Estimate ◽  
Piping Systems ◽  
Crack Stability ◽  
Low Probability

US Nuclear Regulatory Commission (USNRC) Standard Review Plan (SRP) 3.6.3, describes the current methodology for leak-before-break (LBB) piping safety assessment. Specifically, it describes a deterministic assessment procedure that can be used to demonstrate compliance with the 10CFR50 Appendix-A, General Design Criterion 4 (GDC-4) requirement that the primary system pressure piping exhibit an extremely low probability of rupture. However, SRP 3.6.3 does not permit assessment of piping systems with active degradation mechanisms, even though it is known that primary water stress corrosion cracking (PWSCC) has occurred in systems that have been granted LBB exemptions to remove pipe-whip restraints. To address this need, a program is being conducted with the long-term goal of developing a probabilistic assessment tool that can be used to directly demonstrate compliance with 10CFR50 Appendix–A, GDC-4, a tool that would account for the effects of both active degradation mechanisms and the mitigation activities that are being undertaken to address this degradation. This program has been termed “xLPR” as its goal is to demonstrate an eXtremely Low Probability of Rupture in pressure boundary piping systems. This methodology augments current LBB assessment models (leak rate and crack stability models) through the addition of best estimate models describing the initiation and propagation of flaws due to the various degradation mechanisms (fatigue, PWSCC, intergranular stress corrosion cracking (IGSCC), etc.), inspection models, and mechanical and chemical mitigation/remediation models that describe changes in stress state, pipe material and environment caused by mitigation/remediation efforts. Models currently used in LBB assessment will be updated, or replaced, with best estimate, probabilistic models, including those for leak rate and crack stability assessment. All models should account for the full distribution of input variables (where known) in order to account for both epistemic and aleatory uncertainties in as detailed a manner as feasible. This paper summarizes the structure and current activities of the Modeling Task Group within the framework of the overall xLPR Project, and the methodology used to select and develop the models for the xLPR Pilot Study. Preliminary information on the various models chosen for the Pilot Study, and how they are linked within the structure of the overall xLPR probabilistic code, is also provided.

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