Regulatory Experience of Leak-Before-Break (LBB) Technology to the High Energy Piping Systems in Korea

2010 ◽  
Author(s):  
Yeon-Ki Chung ◽  
Jin-Su Kim ◽  
Hae-Dong Chung ◽  
Young-Hwan Choi
Keyword(s):  
Material Properties ◽  
Operating Experience ◽  
Leak Detection ◽  
High Energy ◽  
Leak Rate ◽  
Regulatory Review ◽  
Screening Criteria ◽  
Piping Systems ◽  
Crack Stability ◽  
Leak Before Break

The application of the leak-before-break (LBB) technology to the newly constructed pressurized water reactors (PWRs) has been approved for the several high energy piping systems inside containment in Korea. The main purpose of the LBB application for these systems at the design stage is the removal of the dynamic effects associated with the postulated double-ended guillotine break (DEGB) from design basis loads, as well as to the elimination of the pipe whip restraints and jet impingement barriers so as to increase the access the inspections. LBB technology is based on the low probability of pipe ruptures in the candidate piping systems using fracture mechanics and the insights from the state-of-the-art technology including operating experience. The procedures for LBB application is fundamentally based on the Unite States Nuclear Regulatory Commission (US NRC) requirements as detailed in the standard review plan (SRP) 3.6.3. However, a number of the additional requirements and issues are not specified in the review procedure during regulatory review were imposed and addressed during the review process. The regulatory review is focused on the confirmation on the methods for the elements in the screening criteria and several technical concerns on the determination of material properties, the validation of crack evaluation methods and leak rate estimation in the LBB evaluation considering the adequate margin. Although the application of the LBB has been approved by the safety authority for some high energy systems, the validation of LBB is continuously maintained in consideration of operating experience. In this paper, the regulatory positions for LBB application are described for the areas of screening criteria, leak rate estimation including the capability of leak detection system, material properties, load combination, crack stability methods, and margins in the crack stability evaluations. The issues encountered during the regulatory review such as the dynamic fracture test to consider the dynamic strain aging (DSA) of carbon and low alloy steel, thermal stratification and striping in the pressurizer surge line, water/steam hammer in main steam lines, and estimation of the crack opening area at the pipe-to-nozzle interface considering the asymmetry are also introduced. In addition, several regulatory actions to improve the reliability in the capability of leak detection systems and to clarify the screening criteria such as the corrosion resistance is provided.

Rupture Hardware Minimization in Pressurized Water Reactor Piping

1989 ◽  
Vol 111 (1) ◽  
pp. 64-71 ◽  
Author(s):  
S. K. Mukherjee ◽  
J. J. Szy Slow Ski ◽  
V. Chexal ◽  
D. M. Norris ◽  
N. A. Goldstein ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Ferritic Steel ◽  
High Energy ◽  
Pressurized Water Reactor ◽  
Pipe Failure ◽  
Pressurized Water ◽  
Screening Criteria ◽  
Water Reactor ◽  
Leak Before Break ◽  
Generic Sense

For much of the high-energy piping in light water reactor systems, fracture mechanics calculations can be used to assure pipe failure resistance, thus allowing the elimination of excessive rupture restraint hardware both inside and outside containment. These calculations use the concept of leak-before-break (LBB) and include part-through-wall flaw fatigue crack propagation, through-wall flaw detectable leakage, and through-wall flaw stability analyses. Performing these analyses not only reduces initial construction, future maintenance, and radiation exposure costs, but also improves the overall safety and integrity of the plant since much more is known about the piping and its capabilities than would be the case had the analyses not been performed. This paper presents the LBB methodology applied at Beaver Valley Power Station—Unit 2 (BVPS-2); the application for two specific lines, one inside containment (stainless steel) and the other outside containment (ferritic steel), is shown in a generic sense using a simple parametric matrix. The overall results for BVPS-2 indicate that pipe rupture hardware is not necessary for stainless steel lines inside containment greater than or equal to 6-in. (152-mm) nominal pipe size that have passed a screening criteria designed to eliminate potential problem systems (such as the feedwater system). Similarly, some ferritic steel line as small as 3-in. (76-mm) diameter (outside containment) can qualify for pipe rupture hardware elimination.

Reliability of LBB Evaluation Considering Randomness in Design Parameters

2011 ◽  
Author(s):  
Arindam Chakraborty ◽  
Haiyang Qian ◽  
Angah Miessi
Keyword(s):  
Material Properties ◽  
Factor Of Safety ◽  
Leak Detection ◽  
High Energy ◽  
Design Parameters ◽  
Piping System ◽  
Operating Pressure ◽  
Detection Capability ◽  
Crack Morphology ◽  
Input Parameters

In US, definition of the Leak-Before-Break (LBB) approach and criteria for its use are provided in NUREG-1061. Volume 3 of NUREG-1061 defines LBB as “…the application of fracture mechanics technology to demonstrate that high energy fluid piping is very unlikely to experience double-ended ruptures or their equivalent as longitudinal or diagonal splits.” Current LBB evaluation uses a factor of safety of two (2) on critical flaw size and a factor of safety of ten (10) on detectable leakage to deterministically analyze, that for a given set of input those factors are achieved. Typical input for LBB evaluation consists of pipe geometry, material properties (both elastic and plastic), crack morphology, loads, and operating pressure and temperature. Since LBB has recently been applied for pipes with weld overlays (WOL), thickness, material properties, and crack morphology of WOL also becomes important. However, in real structure all the design parameters (input) for LBB evaluation are inherently random in nature. The current work includes randomness in the critical design input parameters for LBB evaluation. Based on the result of this study reliability (or its compliment, probability of failure) curves are obtained based on the randomness in the critical input parameters. A piping system is considered to fail the LBB evaluation if the actual leakage through the pipe is less than the required leak rate which is calculated as ten times the plant minimum leak detection capability. Separate reliability curves are obtained for various minimum plant leak detection capability piping (e.g.,…, 1, 0.5,…, 0.1 GPMs) and for various piping systems (large diameter pipes such as reactor coolant loop hot leg and cold leg; and small diameter pipes such as pressurizer surge line, etc.). The reliability curves give an insight into the likelihood for a deterministic design input based LBB evaluation to remain valid in view of the in-situ variations.

The Treatment of ISI Uncertainty in Extremely Low Probability of Rupture

2011 ◽  
Author(s):  
Patrick G. Heasler ◽  
Scott E. Sanborn ◽  
Steven R. Doctor ◽  
Michael T. Anderson
Keyword(s):  
Epistemic Uncertainty ◽  
Probability Distributions ◽  
Operating Experience ◽  
Nuclear Regulatory Commission ◽  
Nuclear Industry ◽  
Piping Systems ◽  
Primary Water ◽  
Low Probability ◽  
Regulatory Commission ◽  
Leak Before Break

The U.S. Nuclear Regulatory Commission (NRC) in cooperation with the nuclear industry is constructing an improved probabilistic fracture model for piping systems that in the past have not been susceptible to known degradation processes that could lead to pipe rupture. Recent operating experience with primary water stress corrosion cracking (PWSCC) has challenged this prior position of leak-before-break and which has now become known as “extremely Low Probability of Rupture” (xLPR). This paper focuses on the xLPR model’s treatment of uncertainty for in-service inspection. In the xLPR model, uncertainty is classified as either aleatory or epistemic, and both types of uncertainty are described with probability distributions. Earlier PFM models included aleatory, but ignored epistemic, uncertainty, or attempted to deal with epistemic uncertainty by use of conservative bounds. Thus, inclusion of both types of uncertainty in xLPR should produce more realistic results than the earlier models. This work shows that by including epistemic uncertainty in the xLPR ISI module, there can be a significant effect on rupture probability; however, this depends upon the specific scenarios being studied. Some simple scenarios are presented to illustrate those where there is no effect and those having a significant effect on the probability of rupture.

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.

Comparison of Leak Rates From Alloy 82/182 Butt Weld Cracks for Leak-Before-Break Applications

2006 ◽  
Author(s):  
A. D. Nana ◽  
K. K. Yoon
Keyword(s):  
Fatigue Crack ◽  
Leak Rate ◽  
Alloy 600 ◽  
Base Metals ◽  
Butt Weld ◽  
System Pressure ◽  
Crack Morphology ◽  
Piping Systems ◽  
The Impact ◽  
Leak Before Break

The discovery of leaking cracks in Alloy 82/182 bimetal welds at the V.C. Summer Nuclear Station has lead the industry to reassess the Leak-Before-Break (LBB) analysis of the reactor coolant system pressure boundary piping components involving Alloy 600 base metals and Alloy 82/182 welds. The leaking cracks were attributed to primary-water-stress-corrosion-cracking (PWSCC). To-date, LBB analysis submittals to the NRC have not considered PWSCC cracks in bimetal welds or Alloy 600 base metals and the leak rate calculations have only considered the conventional fatigue crack morphology. There are limited observed in-service leakage cracks of Alloy 82/182 pipe butt welds with plant measured leak rate data. Effects of PWSCC induced crack morphology involving these welds is investigated through various modeling techniques. The differences in leakage prediction when evaluating as a fatigue crack versus assessing as a PWSCC crack is addressed for various PWR LBB piping systems. The impact of this finding to the overall LBB assessment is discussed. Additionally, the LBB results are compared against the results from another paper.

Vertically Integrated Amorphous Silicon Particle Sensors

2004 ◽  
Vol 808 ◽  
Author(s):  
N. Wyrsch ◽  
C. Miazza ◽  
S. Dunand ◽  
A. Shah ◽  
D. Moraes ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Material Properties ◽  
Dark Current ◽  
Silicon Particle ◽  
Particle Beam ◽  
High Energy ◽  
Beta Particle ◽  
Particle Detection ◽  
Glass Substrates ◽  
Hydrogenated Amorphous

ABSTRACTVertically integrated particle sensors have been developed using thin-film on ASIC technology. Hydrogenated amorphous silicon n-i-p diodes have been optimized for particle detection. These devices were first deposited on glass substrates to optimize the material properties and the dark current of very thick diodes (with thickness up to 50 m). Corresponding diodes were later directly deposited on two types of CMOS readout chips. These vertically integrated particle sensors were tested in beta particle beam from 63Ni and 90Sr sources. Detection of single low- and high- energy beta particle was achieved.

Temperature relaxation in strongly-coupled binary ionic mixtures

2021 ◽  
Author(s):  
Robert Sprenkle ◽  
Luciano Silvestri ◽  
M. S. Murillo ◽  
Scott Bergeson
Keyword(s):  
Material Properties ◽  
Inertial Confinement Fusion ◽  
Coulomb Systems ◽  
High Energy ◽  
High Energy Density ◽  
Inertial Confinement ◽  
Relaxation Rates ◽  
Strongly Coupled ◽  
Wide Range ◽  
Temperature Relaxation

Abstract New facilities such as the National Ignition Facility and the Linac Coherent Light Source have pushed the frontiers of high energy-density matter. These facilities offer unprecedented opportunities for exploring extreme states of matter, ranging from cryogenic solid-state systems to hot, dense plasmas, with applications to inertial-confinement fusion and astrophysics. However, significant gaps in our understanding of material properties in these rapidly evolving systems still persist. In particular, non-equilibrium transport properties of strongly-coupled Coulomb systems remain an open question. Here, we study ion-ion temperature relaxation in a binary mixture, exploiting a recently-developed dual-species ultracold neutral plasma. We compare measured relaxation rates with atomistic simulations and a range of popular theories. Our work validates the assumptions and capabilities of the simulations and invalidates theoretical models in this regime. This work illustrates an approach for precision determinations of detailed material properties in Coulomb mixtures across a wide range of conditions.

Simplified LBB Guidance: Stage 1 — Development of a New Software Tool and Initial Scoping Calculations

2018 ◽  
Author(s):  
Peter Gill ◽  
John Sharples ◽  
Chris Aird
Keyword(s):  
Fracture Toughness ◽  
Material Properties ◽  
Software Tool ◽  
Pipe Material ◽  
Loading Conditions ◽  
Design Rules ◽  
Inner Radius ◽  
Inner Diameter ◽  
Stage 1 ◽  
Leak Before Break

This study is focussed on establishing more simplified Leak-before-Break (LbB) guidance for inclusion into Section III.11 of the R6 procedure. The approach adopted has involved the development of a universal software tool for LbB simplified assessments which can be used to perform initial scoping calculations to demonstrate typical LbB cases. It is envisaged that this simplified methodology will enable plant assessment engineers to be more informed on which sites on plant are likely to have LbB successfully applied and to be able to undertake LbB assessments in a more simplistic way than is currently available. Using the developed software tool, a range of LbB calculations for different cracks and loading conditions have been performed to provide guidance on where LbB is more likely to be applied on plant. Loading conditions include primary and secondary stresses, where through-wall changes have been accounted for. The pipe geometries included in this study have been defined by the inner radius and the wall thickness, calculated by minimum pipe thickness required according to meet the design rules of ASME III. The pipe inner radius varies from 40mm to 200mm (80mm to 400mm inner diameter (ID)). All pipe outer diameters are less than 0.5m. All cracks considered in this study are through-wall and circumferential. Pipe material properties are chosen to be broadly representative of an Austenitic Stainless Steel, where the fracture toughness varies from 100 to 180MPa√m and the yield stress is 150MPa.

Ranking of Creep Damage in Main Steam Piping System Girth Welds Considering Multiaxial Stress Ranges

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Marvin J. Cohn ◽  
Fatma G. Faham ◽  
Dipak Patel
Keyword(s):  
Creep Damage ◽  
High Energy ◽  
Sustained Load ◽  
Piping System ◽  
Multiaxial Stress ◽  
Analysis Model ◽  
Principal Stresses ◽  
Piping Systems ◽  
Girth Welds ◽  
Main Steam

A high-energy piping (HEP) asset integrity management program is important for the safety of plant personnel and reliability of the fossil plant generating unit. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The main steam (MS) piping system is one of the most critical HEP systems. Creep damage assessment in MS piping systems should include the evaluation of multiaxial stresses associated with field conditions and significant anomalies, such as malfunctioning supports and significant displacement interferences. This paper presents empirical data illustrating that the most critical girth welds of MS piping systems have creep failures which can be successfully ranked by a multiaxial stress parameter, such as maximum principal stress. Inelastic (redistributed) stresses at the piping outside diameter (OD) surface were evaluated for the base metal of three MS piping systems at the piping analysis model nodes. The range of piping system stresses at the piping nodes for each piping system was determined for the redistributed creep stress condition. The range of piping stresses was subsequently included on a Larson–Miller parameter (LMP) plot for the grade P22 material, revealing the few critical (lead-the-fleet) girth welds selected for nondestructive examination (NDE). In the three MS piping systems, the stress ranges varied from 55% to 80%, with only a few locations at stresses beyond the 65 percentile of the range. By including evaluations of significant field anomalies and the redistributed multiaxial stresses on the outside surface, it was shown that there is a good correlation of the ranked redistributed multiaxial stresses to the observed creep damage. This process also revealed that a large number of MS piping girth welds have insufficient applied stresses to develop substantial creep damage within the expected unit lifetime (assuming no major fabrication defects). This study also provided a comparison of the results of a conventional American Society of Mechanical Engineers (ASME) B31.1 Code as-designed sustained stress analysis versus the redistributed maximum principal stresses in the as-found (current) condition for a complete set of MS piping system nodes. The evaluations of redistributed maximum principal stresses in the as-found condition were useful in selecting high priority ranked girth weldment creep damage locations. The evaluations of B31.1 Code as-designed sustained load stresses were not useful in selecting high priority creep damage locations.

Sign in / Sign up

Export Citation Format

Share Document