bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of NDE Reexamination Locations and Intervals for Grade 91 Piping System Girth Welds
Authors: Cohn Marvin J. , Cronin Michael T. , Faham Fatma G. , Bosko David A. , Liebl Erick 
Published: November 2015

It has become apparent with the development of creep strength enhanced ferritic steels, the mandatory ASME B31.1 Chapter VII and the non-mandatory ASME B31.1 Appendix V guidelines require a more rigorous method to manage the Grade 91 piping integrity at Genesee Unit 3. Given the relatively young age of Genesee Unit 3, three questions have been asked: 1) when do the examinations start, 2) what locations should be examined first, and 3) how often should the same location be reexamined? To ensure that the best value is obtained from the reexamination budget, a five-step process can be effectively used to define and categorize the scope of each set of reexaminations in the girth weld integrity management program. The five processes are performing the following analyses: 1) an evaluation of the historical information, 2) piping system hot and cold walkdowns, 3) as-designed and as-found piping stress analyses, 4) creep life consumption evaluations, including elastic and inelastic axial and radial stress redistributions, and 5) creep crack growth curve analyses. Reexaminations of the few critical lead-the-fleet weldments are performed with lower examination costs and higher confidence.
Evaluations of the Genesee Unit 3 main steam (MS) piping system revealed that the applicable weldment stress is probably the most significant parameter in determining the Grade 91 girth weld critical reexamination locations and intervals. ASME B31.1 piping stress analyses of the MS piping system have sustained load stress variations of more than 100% among the girth welds. The lower bound American Petroleum Institute (API) 579 creep rupture equation for Grade 91 operating at 1,060°F (571°C) indicates that the creep life is a function of stress to the power of 8.9; consequently, a 15% stress increase results in about 2/3 reduction of creep rupture life. Creep crack growth analyses of several of the MS piping system weldments revealed that the creep crack growth time to grow from 1/8 inch to through-wall is a function of stress to the power of 8.8; consequently, a 15% stress increase results in about 2/3 reduction of time for a 1/8-inch crack to grow through-wall.
This evaluation reveals that a few critical lead-the-fleet locations should be reexamined most frequently and justification can be provided for much longer reexamination intervals of the remaining girth welds with much lower applied stresses.
Fabrication, Welding, and Inspection Techniques in Preparation for In-Reactor Testing of Accident Tolerant Fuels
Authors: Barrett Kristine , Teague Michael , Moore Glenn , Woolum Connor , Archibald Kip 
Published: November 2015

After the Fukushima events in 2011, DOE-NE in collaboration with nuclear industry shifted R&D emphasis to accident performance of LWR fuels under extended loss of active cooling and steam exposure. DOE-NE has created a roadmap for the “Development of Light Water Reactor Fuels with Enhanced Accident Tolerance.” The mission of the Accident Tolerant Fuel (ATF) Roadmap is to develop the next generation of LWR fuels with improved performance, reliability, and safety characteristics during normal operations and accident conditions and with reduced waste generation. The ultimate goal of the ATF roadmap is to support the insertion of lead fuel rods (LFRs) or lead fuel assemblies (LFAs) of an Accident Tolerant Fuel into a commercial LWR within 10 years (i.e., by the end of FY-2022). As a step toward this goal, an irradiation test series has been developed to assess the performance of proposed ATF concepts under normal LWR operating conditions. Data generated by this test program will be used to establish the feasibility of certain aspects of proposed ATF concepts, as well as provide information to support screening among concepts; as such, it is an integral part of Phase I: Feasibility Assessment and Down-Selection outlined in the ATF Roadmap. This irradiation test series is planned to be performed as a series of drop-in capsule tests to be irradiated in the Advanced Test Reactor (ATR) operated by the Idaho National Laboratory (INL), and it has been designated as the ATF-1 test series.
Current fission reactors use zirconium-based fuel cladding because of its extremely low macroscopic thermal neutron absorption cross-section, good high temperature strength, and decent corrosion resistance. However, advanced, innovative materials may provide these same benefits while increasing reactor safety margin, core power density, and fuel utilization. These advanced fuel cladding systems will allow revolutionary cladding performance and enhanced fuel mechanical designs, however, challenges exist in design, analysis and fabrication of innovative, never before tested, fuel cladding systems for in-reactor testing. This paper highlights the challenges associated with design, fabrication and welding, and inspection of innovative materials and actions taken to address those challenges in preparation for the Phase I ATR irradiation testing. The lessons learned from Phase I of this experiment can be used to guide researchers for design and analysis of future in-reactor testing of advanced fuel cladding systems.
An Analytical Method for Estimating Welding-Induced Plastic Zone Size for Residual Stress Profile Development
Authors: Pei Xianjun , Song Shaopin , Dong Pingsha 
Published: November 2015

As demonstrated in a recent comprehensive study on construction of full-field residual stress profiles for fitness-for-service assessment of pressure vessel and piping components, a reasonable estimate of welding-induced plastic zone size is necessary for introducing a shell theory based solution form (Song et al, 2015 [1–2]). This paper presents an analytical method for estimating plastic zone size by first solving an equivalent one dimensional heat transfer problem in which weld zone is represented by a line segment with initial temperature at melting. Thermoplasticity conditions are then imposed by assuming elastic perfectly plastic behaviors. Finally, an analytical expression is obtained to relate plastic zone boundary to maximum temperature field distribution experienced by material points within the whole domain over the entire heating and cooling history. The solution can be further expressed by a rather simple form with the identification of a characteristic length parameter that signifies inflection point of temperature distribution. So estimated plastic zone sizes for various welded joint types have been compared with finite element residual stress analysis results in which sequentially coupled welding heat transfer and thermo-mechanical analysis procedures are used. A good agreement has been achieved for all cases analyzed.
Compared with conventional finite element residual stress analysis procedures, this method offers significant simplicity and efficiency, while being reasonably accurate, particularly for applications in residual stress profile estimation and in evaluation of welding induced distortions in complex structures.
Effects of Seat Width on Development of Adhesions in Stainless Steel Trim Spring Operated Pressure Relief Valves
Authors: Bukowski Julia V. , Gross Robert E. , Goble William M. , Harris Stephen P. 
Published: November 2015

Previous research has shown that stainless steel (SS) adhesions form in about half of new SS trim spring operated pressure relief valves (SOPRV). These adhesions require an additional force (beyond the spring force) to be applied by the process fluid to the disc in order for the valve to lift. This additional force may cause the SOPRV to fail its proof test (FPT) or even to fail to open (FTO) in the presence of excess process pressure. This paper expands on the previous findings to show how seat width relates statistically to whether or not these SS adhesions form and, if they do, whether or not they are of sufficient size to cause FPT or FTO.
The findings show it is statistically significant that SOPRV in the study population with seat widths greater than 0.030 inches (in.) formed adhesions more often than SOPRV with seat widths less than or equal to 0.030 in. Furthermore, for this population it is statistically significant that all FPT and FTO occurred on SOPRV with seat widths greater than or equal to 0.030 in. The ramifications of these findings to the safety performance of SS trim SOPRV are discussed.
Comparison of Methods for Evaluation of Crack Growth at Welds in Offshore Risers
Authors: Yin Fengjie , Cerkovnik Mark , Akhtar Wasy , Yang Tracy 
Published: November 2015

In checking the fitness of fatigue critical welded structure, the stress concentration at the weld due to the weld geometry needs to be considered. Where fatigue is assessed using crack growth methodology, two approaches are commonly used. In the offshore industry in regions where BS 7910 [1] is followed, the effect of weld geometry is assessed using the Mk factor approach. The Mk factor directly magnifies the stress intensity. Mk factor solutions are available for T-butt weld joints from the British Standard BS7910.
Alternatively, API579 [2] offers stress intensity solutions that can account for the stress profile through the wall thickness of the pipe. In using this method, the engineer will use an FEA program to find the stress profile for use as an input for the stress intensity factor computation. Since the goal is the assessment of crack growth, the stress profile must represent the cyclic changes in stress. Further, a histogram of such profiles is required.
While the Mk factor approach of BS7910 offers the easier path by supplying factors for pre-solved geometries, the API approach offers an opportunity to refine the solution by conducting relatively simple linear FEA of the un-cracked component. This study compares the two approaches using an example taken from offshore riser fatigue analysis.
Comparison of Different Thermal Aging Models to Assess Fully Aged Toughness in Cast Austenitic Stainless Steels
Authors: Uddin M. F. , Wilkowski G. M. , Kurth R. E. , Brust F. W. , Shim D.-J. , Rudland D. 
Published: November 2015

Thermal embrittlement of cast austenitic stainless steels (CASS) occurs at reactor operating temperatures during the reactor design lifetime of 40 years leading to a reduction in their toughness and an increase in strength. Additionally most US nuclear plants have been given plant life extensions for 60-year operation, and consideration of further extension to 80 years is underway. As the fracture toughness reduces due to thermal embrittlement, some aged CASS materials have the potential to have exceedingly low toughness. CASS can also show high toughness variability due to the variability of its microstructure. Recently an ASME Section XI Code Case N-838 has been proposed to evaluate the flaw tolerance based on probabilistic fracture mechanics (PFM). An assessment of mechanical-property degradation is an input to perform the flaw evaluation procedure in CASS components. There are at least four different models for predicting the change in J-R curves in CASS due to thermal aging. One model is proprietary and the other three are the Argonne/NUREG-CR/4513R1, the French/EDF and a Japanese model.
In this work, two of the thermal aging models were reviewed, reproduced and validated against their example cases for each individual model. Both models were then utilized to assess the fully aged conditions for cases that covers a large spectrum of CASS J R curves with high COV (coefficient of variance). Finally, J-R curves distributions using both Argonne and French models were established by examining the actual chemical compositions of CASS materials found in some US PWR plants. The J-R curves distributions include 21 pipes/fittings in primary pipe loop as well as data from an EPRI report. The calculated toughness variability in a single LBB plant is compared using the Argonne and French models. Additionally the relationship of the “C” and “m” parameters used in the power-law J-R curve equations (J = C×Δam) was explored to determine the proper way to statistically vary the J-R curve in probabilistic analyses.
Fatigue Crack Initiation and Growth Observation for 316 Stainless Steel Subjected to Equi-Biaxial Cyclic Loading
Authors: Iida Satoshi , Abe Shigeki , Nakamura Takao , Kamaya Masayuki 
Published: November 2015

Fatigue accumulation is one of the ageing phenomena considered in the plant design and maintenance. The degree of fatigue damage is evaluated by cumulative usage factor using design fatigue curve, which is determined from results of uniaxial fatigue tests. The stress caused by thermal transients is generally equibiaxial, not uniaxial. Fluid temperature fluctuation due to changes in plant conditions, such as plant start-up and shutdown, is the primary cause of fatigue damage. For accurate fatigue damage evaluation, it is important to be conducted under equi-biaxial condition.
In this study, pressurized disc fatigue test was conducted in order to simulate the cyclic equi-biaxial stress. In order to clarify how the crack initiates and grows under the equi-biaxial stress condition. Cracking behavior was examined by replica observation method. The crack growth rates were identified by the change in the crack length. It was shown that the fatigue crack growth rate under equi-biaxial stress was faster than that under uniaxial stress for the same equivalent stress intensify factor. It was concluded that the reduction in the fatigue life under equi-biaxial stress was brought about by the accelerated crack growth.
European Design Rules for Tubesheets
Authors: Lidonnici Fernando , Site Corrado Delle 
Published: November 2015

Tubesheets are usually designed according to different national or international design codes. The great majority of these standards is based on Gardner’s theory, elaborated more than 60 years ago. On the other hand these pressure components are critical in heat exchanger design, because they are subject to characteristic service damages which require a correct dimensioning and appropriate inspections during service.
This paper is aimed at comparing the different design methods, analyzing the theoretical background behind the rules.
Main focus is made to the alternative design method contained in Annex J of the European Standard EN13445-3.
With reference to the typical configuration of a fixed tubesheet exchanger with flanged connections, the results of the different design approaches are compared in order to find out the optimal configuration.
Benchmark examples are carried out using a commercial computer code with reference to heat exchangers with the tubesheets welded to the shell and bolted to the channel.
The results show the advantage of using Annex J which allows smaller thicknesses of the tubesheet in respect of the conventional approach used by TEMA, ASME Section VIII and EN 13445-3 clause 13.
Predicting the Creep Rupture Behavior of Austenitic Steel Using Finite Element Analysis
Authors: Hamelin Cory J. , Payten Warwick M. 
Published: November 2015

The creep behavior of structural materials is often measured using uniaxial tension creep rupture tests. Unfortunately, the time required for austenitic steel samples to rupture under ideal (i.e. elastic stress) conditions is prohibitive. To accelerate creep rupture in these samples, a tensile stress in excess of the material yield strength is often applied and the post-load deformation is assumed to be largely creep-based. There is currently no method of measuring the creep deformation separately from the yield-induced plastic flow that may occur during such accelerated tests.
Using validated finite element models, the effects of creep and yield-induced plastic strain have been decoupled for a series of accelerated creep tests using 316H austenitic steel. The influence of continued yielding after the initial sample loading was predicted to be significant, which suggests the diffuse necking in the samples due to creep is responsible for stress intensification and further yield through the tests. These results suggest the initial plastic loading in accelerated creep tests may significantly influence the measured creep rupture time in these samples.
Assessment of the Temperature Dependence of Ferritic Steel Fracture Toughness on or Near the Lower Shelf
Authors: Kirk Mark , Erickson Marjorie 
Published: November 2015

Within the American Society of Mechanical Engineers (ASME) the Section XI Working Group on Flaw Evaluation (WGFE) is currently working to develop a revision to Code Case N-830. This revision incorporates a complete and self-consistent suite of models that describe completely the temperature dependence, scatter, and interdependencies between all the fracture metrics (i.e., KJc, KIa, JIc, J0.1, and J-R) from the lower shelf through the upper shelf. A paper presented at the 2014 ASME Pressure Vessel and Piping Conference described most of these models; a companion paper at this conference describes the J-R model. This paper also supports the WGFE effort by performing an assessment of the appropriateness of Wallin’s Master Curve model to represent toughness data on the lower shelf, and by comparing the Master Curve with the current Code KIc curve on the lower shelf.
The work presented in this paper supports the following conclusions:
1. The Master Curve provides a reasonable representation of cleavage fracture toughness (KJc) data at lower shelf temperatures. A statistical evaluation of a large database demonstrates that the Master Curve works well to temperatures approximately 140 °C below To or, equivalently, approximately 160 °C below RTTo.
2. The percentile of cleavage fracture toughness data falling below a KIc curve indexed to RTTo varies considerably with temperature. At lower shelf temperatures as much as half of the data lie below the KIc curve, while at temperatures close to RTTo this percentage falls to approximately ≈ 1.5%. The current guidance of Nonmandatory Appendix A to Section XI to use structural factors of √10 or √2 is one means of addressing this inconsistency.
3. The inconsistent degree to which the KIc curve, with or without structural factors, bounds fracture toughness data cannot be fixed within the current Code framework for two reasons: the KIc curve does not reflect the actual temperature dependence shown by the fracture toughness of ferritic RPV steels, and the ratio of a mean or median toughness curve to a fixed percentile bound is not a constant value. It is for these reasons that in the next revision of Code Case N-830 the ASME WGFE is moving away from use of the KIc curve coupled with structural factors and, instead, is adopting models of fracture toughness that represent both the temperature trends and the scatter in the data with high accuracy.
3D Effects in Fluid Flow During 2D Vibrations: Experimental Analysis of FSI for an Enclosed Hexagonal Assembly
Authors: Sargentini Lucia , Cariteau Benjamin , Magnaud Jean-Paul , Monavon Arnault , Artini Gianluca 
Published: November 2015

The purpose of this study is to improve the knowledge about the core behavior of a sodium fast breeder reactor (Na-FBR) through the fluid-structure interaction analysis during vibrations of short time scale (shutdown of Phénix reactor) as well as long time scale (earthquakes for ASTRID Project).
We designed a test-rig, PISE-1a, composed by one hexagonal assembly enclosed by an hexagonal containment with a narrow gap.
The experimental test-rig PISE-1a is used to determine the dynamic characteristics of the assembly, to calibrate instrumentation and for validating our numerical model.
Free vibration experiments in water allow to assess the added mass and added damping effect on the frequency. The fluid flow is affected by a 3D effect — named down-stroke flow — at the top and the base of the assembly. This effect produces a higher frequency than the 2D theoretical value. Investigation on this phenomena are provided by PIV methodology, which allows to show the displacement of the fluid as predicted by the theoretical analysis.
Fluidelastic Instability in Tube Arrays Subject to Two-Phase Cross Flow: A Porous Medium Approach
Authors: Tixier Eliott , Béguin Cédric , Étienne Stéphane , Pelletier Dominique , Hay Alexander , Ricciardi Guillaume 
Published: November 2015

In nuclear power plants, heat exchangers undergo important flow induced vibrations, fluidelastic instability (FEI) being the most damaging one. Direct numerical simulations of such a phenomenon is currently an impossible task because of the considerable number of tubes and the two-phase nature of the flow.
The novelty of the present approach is to use a porous medium to model the tube bundle and the surrounding flow. The Navier-Stokes equations are averaged on a control volume and the tubes materialized by a porosity field and source terms that model the interactions between the fluid and the solid. New sets of fully coupled equations were developed and solved with a finite element solver using high order time integration schemes. The unsteady porous medium approach already developed for single-phase flow is extended to the Euler-Euler formulation to describe the two-phase mixture. Validation and calibration of the parameters are achieved by comparing the critical flow rate and the forces acting on the tubes with results from direct numerical simulations and experimental data for single-phase flows.
Experimental Testing of Pressure Pulse Propagation in Non-Newtonian Simulants With a Void Fraction of Non-Condensable Gas
Authors: Schmitt Kyle P. , Ligon Thomas C. , Minichiello John C. 
Published: November 2015

This paper describes experimental work performed in support of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) to quantify the propagation and attenuation of pressure pulses as they move through piping systems filled with quiescent non-Newtonian simulants that support a void fraction of non-condensable gas. A subset of experimental results is presented in this paper and is shown to compare favorably to theoretical expectations. In general, the rate of attenuation of the propagating pulse increases with void fraction, pulse peak pressure, and the inverse of pulse duration, all a consequence of rarefaction wave accumulation at the shock front. The data developed from this experimental test program is supporting the development and validation of related analytical and numerical (CFD) models. These models are being developed with the practical objective of determining the length over which a pressure pulse propagating from an ignition event in a gas pocket remains structurally significant to piping at the WTP.
In addition to selected results and key conclusions, specific aspects of test preparation and conduct are discussed in this paper including the generation of pressure pulses with a mechanical impact at the liquid surface; the development of a well-dispersed gas phase (i.e., void fraction) using catalyzed decomposition of hydrogen peroxide in the simulant mixture; the retention of a void fraction by using mixtures with non-Newtonian (i.e., Bingham plastic) properties; and the in situ measurement of void fraction.