bluuebunny/crossref_metadata_2025_split huggingface dataset:
Load Data Evaluation, Stress Analysis and Cycle Counting for the Qualified Thermal Fatigue Assessment of a NPP Component
Authors: Rudolph Jürgen , Maneschy José Eduardo , Cisternas Miguel , Freire José Luiz F. , Costa Felippe M. S. , Silva Bruno , Paiva Vitor E. L. , Suanno Rodolfo 
Published: November 2015

Qualified fatigue assessment based on realistic input data constitutes an essential part of an ageing management strategy for Nuclear Power Plants. In this context and as a continuation of a previous paper PVP2014-28716 the requirements of load data evaluation, stress analysis and cycle counting are detailed based on a real world example from a Brazilian Nuclear Power Plant. One essential prerequisite of any fatigue assessment approach is the availability of realistic load data. In the present analysis, selected operational plant data from the period 2003 to 2012 are used. One further prerequisite is the accurate component stress analysis based on a transient thermal-mechanical Finite Element Analyses.
As an example, a highly loaded nozzle from the Chemical & Volume Control System (CVCS) is chosen to be analyzed. The influences on the fatigue assessment caused by the load-time histories, the stress analysis approaches and the cycle counting method are discussed in detail. The considered operational time period from 2003 to 2012 with respective selected plant data gives a consolidated background. It is one essential aim of the study to show the influence of the load-data input and the (design code conforming) stress analysis method on the resulting calculated cumulative usage factors (CUFs). In the present paper, the stress analysis employs the finite element method. Simplified elastic-plastic (application of ke plasticity factors) procedures are used in order to identify the margins and influences of design and actual loading histories on the resulting CUFs.
The paper concludes with a comprehensive picture including quantification and discussion of the different influencing parameters on the resulting CUFs. This reveals margins in the fatigue design process and solutions of coping with the design code requirements.
Methodological Features of WWER RPV Metal Critical Temperature of Brittleness Prediction on the Base of the Data Scatter and the Chemical Composition
Authors: Orynyak Igor , Zarazovskii Maksym , Radchenko Sergii 
Published: November 2015

For WWER-1000 reactor pressure vessel (RPV) the metal embrittlement monitoring is performed with the usage of the radiation and the temperature surveillance specimens (SS) sets. For the fracture toughness curve indexing the critical temperature of brittleness (CTB) is used, CTB is obtained by the processing of Charpy impact energy data.
Modern codes that regulate WWER RPVs CTB prediction are based on the CTB shift ideology. According to this ideology the CTB is defined as the initial CTB value plus CTB shift due to the radiation, plus CTB shift due to the thermal ageing, plus certain margin. This margin includes the scatter of CTB in the initial state, scatter of CTB shift due to the radiation and scatter of CTB shift due to the thermal ageing.
A tendency of modern WWER RPV integrity assessment codes to provide conservatism with: choosing the CTB in the initial state for the CTB shifts determination; choosing the CTB in the initial state for the CTB determination; taking into account the scatter of CTB in the initial state, scatter of CTB shift due to the radiation and scatter of CTB shift due to the thermal ageing, leads to huge predictive values of CTB and to formal unfulfillment of brittle fracture criterion for RPVs.
This paper demonstrates that the usage of actual CTB data and their scatter (obtained directly from Charpy V-notched impact tests) instead of the shift ideology can be the one of the possible ways of adequate CTB prediction.
The CTB database for welds is created on the base of the results of WWER-1000 RPV surveillance program of all Ukrainian NPPs.
The article presents the results of the thermal aged Charpy V-notched SS tests. The thermal aging has been shown to be practically absent. The CTB thermal shift values, which were obtained in some laboratories, are caused by the CTB scattering in initial and thermal aged states only.
According to the processing results of the irradiated SS tests data, the chromium, manganese and silicon have been found to have the greatest impact on the CTB value.
The CTB dependence on the neutron fluence and chemical composition of WWER-1000 RPV beltline welds has been obtained. A new methodology of CTB curve prediction for WWER-1000 RPV welds is developed. This methodology is expected to be the basis in the modern Ukrainian normative of RPV integrity assessment since it reduces the unreasonably high conservatism inherent to the RPV project, to a more reasonable level.
3-Dimensional Finite Element T-Stress Calculation for Reactor Pressure Vessel Nozzle Blend Radius Semi-Elliptical Surface Cracks
Authors: Qin Minghao , Tang Shu , Ku Francis , Sommerville Daniel V. , Gustin Hal 
Published: November 2015

T-stress is used as an indicator of the condition of crack tip constraint. In current fracture mechanics engineering applications in the U.S. nuclear industry, T-stress generally has been ignored during the calculation of applied stress intensity factors (SIF). Consideration of this crack tip constraint component could affect the evaluation of material fracture behavior, under either plane strain or plane stress or plane strain and plane stress combination. When the T-stress shows that the condition of crack front constraint is not plane strain, incorporation of T-stress may allow reduction of unnecessary conservatisms in such calculations. Under this condition, the allowable stress intensity factor is modified by increasing it above the KIc value, and it potentially increases the predicted allowable flaw sizes.
In this paper, T-stress has been calculated using 3-D finite element analyses (FEA) with a typical semi-elliptical crack in a reactor pressure vessel (RPV) nozzle blend radius. Both thermal and internal pressure load cases are considered.
To verify this finite element analysis approach, this method is applied to comparable literature models. The FEA results are consistent with closed-form solutions for T-stress calculation.
Limit Load Solution and Crack Driving Force Estimation Scheme for Embedded Flaws in Pipeline Girth Welds
Authors: Pépin Aurélien , Tkaczyk Tomasz , O’Dowd Noel , Nikbin Kamran 
Published: November 2015

The acceptability of flaws in a subsea rigid pipeline is usually sanctioned based on the results of an engineering criticality assessment (ECA), carried out considering all loads seen by the pipeline from fabrication to the end of service life. Reel-lay is an efficient installation method, frequently used for installing subsea pipelines. Unlike surface breaking flaws, embedded flaws are not directly assessed in a reeling ECA because the available assessment solutions are too conservative. A work around approach is often used, whereby acceptable surface breaking flaw sizes are deemed acceptable beneath the surface, provided that the embedment depth is equal to or greater than half of the flaw height. However, the results of more recent research work suggest that this approach could be non-conservative in some cases.
In this work, a parametric finite-element (FE) study was carried out to assess the effect of the embedment depth, the crack length and the crack height on the load required to cause collapse of the shorter ligament of an embedded flaw. Subsequently, a closed form limit load solution was developed, and compared against available solutions for pipes subjected to tension. A J-based crack driving force (CDF) estimation scheme was developed for a selected material behaviour. Finally, recommendations were made for the direct reeling ECA of subsea pipelines with embedded flaws.
Determination of Path-Independent J-Integral for Cracks in Residual Stress Fields Using Finite Element Method
Authors: Zhu Xian-Kui 
Published: November 2015

“Hot” residual stresses exist in metal welds due to welding thermal stresses, and “cold” residual stresses occur in mechanical damaged metallic pipes due to large plastic deformation. For a crack in ether a hot or cold residual stress field, residual stresses might have a strong effect on the crack-tip field and the fracture parameter, J-integral. To consider the effect of residual stresses and to ensure the path-independence of J, different correction methods have been developed over the years. Recently, the finite element analysis (FEA) commercial software ABAQUS adopted one of correction methods for determining the residual stress corrected J-integral.
This paper intends to evaluate this new function of ABAQUS and to see if the residual stress corrected J-integral is path-independent. A brief review is first given to the J-integral definition, the conditions of J-integral path-independence or dependence, and the modifications of J-integral to consider the residual stress effect. A modified single edge-notched bend (SENB) specimen is then adopted, and a FEA numerical procedure is developed and used in the numerical tests to evaluate the path-independence of the residual stress corrected J-integral using ABAQUS. Detailed elastic-plastic FEA calculations are carried out for the modified SENB specimen in three-point bending. The residual stress field, crack-tip field, and J-integral with and without consideration of the residual stress effect are determined and discussed.
A New Material Failure Criterion for Numerical Simulation of Burst Pressure of Corrosion Defects in Pipelines
Authors: Zhu Xian-Kui 
Published: November 2015

Accurate burst pressure prediction of corroded pipelines is critical to safety design, integrity assessment and operation management. This paper evaluates five corrosion assessment methods: three flow stress-based ASME B31G, Modified B31G, and RSTRENG, and two ultimate tensile stress (UTS)-based LPC and PCORRC. The UTS-based methods were developed using the elastic-plastic finite element analyses (FEA) and an assumed material failure criterion, i.e., the Mises equivalent stress equals to the true UTS of the material. However, recent numerical investigations showed that the assumed Mises stress-based failure criterion is not valid generally, and may depend on the material hardening response. Thus the UTS-based methods may be inaccurate.
In order to improve the UTS-based corrosion assessment methods, this paper investigates a general stress-based material failure criterion, and proposes a new Mises stress-based criterion that depends on the material strain hardening exponent. This new criterion is then applied to determine burst pressures of corrosion defects in the FEA simulations. With the FEA predicted burst pressures, an improved burst pressure prediction model is developed. It is shown that the proposed material failure criterion can determine more accurate burst pressures, and the improved corrosion model predicts burst pressures agreeing well with experimental data.
Streamwise Dynamics of a Tube Array Subjected to Two-Phase Cross-Flows
Authors: Olala Stephen , Mureithi Njuki W. 
Published: November 2015

Nuclear steam generator tubes in two-phase cross-flow may vibrate due to excitations that emanate from various sources. Of these excitation mechanisms, fluidelastic instability is the most dominant cause of tube failures in the short-term. These failures, other than leading to unscheduled plant shutdowns, may result in leakage of radioactive materials that may ultimately cause accidents and economic loss.
Very limited work has been dedicated to investigating purely streamwise fluidelastic instability in tube arrays. However, recent observations of tube failure caused by streamwise or in-plane instability confirm the importance of streamwise fluidelastic instability analysis.
In the present study, we present detailed dynamic cross-coupling force and phase measurement results for a central cluster of tubes in a rotated triangular tube array of Pitch-to-Diameter ratio (P/D)=1.5 subjected to air-water two-phase cross-flow, for homogeneous void fractions of 0% and 60%. The measured dynamic forces together with previously measured quasi-steady forces are necessary to estimate the time delay which is an important input for the quasi-steady fluidelastic instability model.
Alternative Characterization Rules for Quasi-Laminar Flaws Based on 3D X-FEM Calculations
Authors: Lacroix Valéry , Dulieu Pierre , Bogaert Anne-Sophie 
Published: November 2015

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected, mainly in the lower and upper core shells of the RPVs.
In the frame of the Structural Integrity demonstration of these RPVs according to ASME XI principles, ASME XI IWB-3300 article requires combining closely spaced flaws in order to account for their mechanical interactions. However, it appeared early that the characterization rules were adapted neither to quasi-laminar flaws nor to such densities of flaws.
Therefore, an alternative methodology to derive characterization rules for quasi-laminar flaws has been developed, implemented and validated.
This work, based on 2D eXtended Finite Element Method (X-FEM) calculations and presented during ASME PVP 2014, has led to the proposed ASME Code Case N-848 “Alternative characterization rules for quasi-laminar flaws – Section XI, Division I”.
This 2D approach, even though better suited to quasi-laminar flaws, results however in very conservative proximity rules.
Therefore, it appeared that more realistic — although still conservative — proximity rules based on 3D X-FEM calculations could be developed.
Negative Load Ratio Fatigue Crack Growth Rate Testing on Austenitic Stainless Steel in a Simulated Primary Water Environment
Authors: Platts Norman , Tice David R. , Zhang Wenzhong 
Published: November 2015

Light water reactor coolant environments are known to significantly enhance the fatigue crack growth rate of austenitic stainless steels. However, most available data in these high temperature pressurized water environments have been derived using specimens tested at positive load ratios, whilst many plant transients involve significant compressive as well as tensile stresses. The extent to which the compressive loading impacts on the environmental enhancement of fatigue crack growth and more importantly on the processes leading to retardation of those enhanced rates is therefore unclear, potentially leading to excessive conservatism in current assessment methodologies.
A test methodology using corner cracked tensile specimens has been developed which provides significant advantages over more conventional specimen geometries in terms of autoclave testing at negative load ratios. Finite element analysis of the specimen geometry has been performed to generate effective stress intensity factors, Keff, for specimens loaded in fully reverse loading. Test data generated in both air and water are compared to conventional compact tension specimen data to validate the test methodology.
Study of Fatigue Initiation of Austenitic Stainless Steel in a High Temperature Water Environment and in Air Using Blunt Notch Compact Tension Specimens
Authors: Platts Norman , Tice David R. , Nicholls Jennifer 
Published: November 2015

Fatigue life assessment procedures for components exposed to high temperature pressurised water environments are typically based on NUREG/CR-6909 or broadly similar codes (e.g. proposed ASME code case N-792). The effects of a high temperature water environment on the fatigue life are accounted for by simply adjusting the fatigue life in ambient temperature air by an environmental factor (FEN). This adjustment assumes that the environment affects both initiation (nucleation) and propagation equally, which is potentially over-conservative. Blunt notch compact tension (CT) specimens (along with direct current potential drop (DCPD) crack detection) have been proposed as a means of determining the “true” fatigue initiation life, enabling the relative impact of the environment on initiation and growth to be characterised and the level of conservatism in the FEN approach assessed.
The current work uses a combination of finite element analysis and fatigue testing in both air and water to assess the feasibility of blunt notch CT testing to detect initiation and to quantify the environmental impact. This work indicates significant difficulties with the blunt notch CT test methodology both in terms of quantifying the applicable strain and in terms of detection of the very early stages of initiation which preclude the quantitative application of the technique to study true initiation. Qualitatively, the results suggest that there is still a significant impact of the high temperature water environment on the earliest detectable stages of crack growth in austenitic stainless steels; however the earliest defects detectible by DCPD techniques still involve a significant contribution from short crack growth. Nevertheless, the technique provides a valuable insight into initiation and residual life of components subjected to through wall strain gradients.
Fatigue Crack Growth Calculations for Vessels Considering Subsurface to Surface Flaw Proximity Rules
Authors: Lacroix Valéry , Hasegawa Kunio , Li Yinsheng 
Published: November 2015

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the specific criteria of the re-characterizations are different among the FFS codes. Recently, the authors have proposed a new subsurface-to-surface flaw proximity rule based on the experiments data and the interaction of stress intensity factors. In this study, extended Finite Element fatigue crack growth calculations were carried out for thick wall component like vessels with subsurface flaws, using the proposed subsurface-to-surface flaw proximity rule and the proximity rule provided in the current ASME Code Section XI.
Different, flaw aspect ratios and ligament distances from subsurface flaws to inner surface of vessel were taken into account. As the results, the current proximity rule and proposed one provide relatively similar fatigue lives, whatever the aspect ratios of the initial subsurface flaws. However, when the thickness of the component decreases this similarity between both proximity rules appears not to be valid anymore.
A Bayesian Statistics Based Design Curve Construction Method for Test Data With Extremely Small Sample Sizes
Authors: Wei Zhigang , Luo Limin , Yang Fulun , Rebandt Robert 
Published: November 2015

Fatigue design curve construction is commonly used for durability and reliability assessment of engineering components subjected to cyclic loading. A wide variety of design curve construction methods have been developed over the last decades. Some of the methods have been adopted by engineering codes and widely used in industry. However, the traditional design curve construction methods usually require significant amounts of test data in order for the constructed design curves to be consistently and reliably used in product design and validation. In order to reduce the test sample size and associated testing time and cost, several Bayesian statistics based design curve construction methods have been recently successfully developed by several research groups. Among all of these methods, an efficient Monte Carlo simulation based resampling method developed by the authors of this paper is of particular importance. The method is based on a large amount of reliable historical fatigue test data, the associated probabilistic distributions of the mean and standard deviation of the failure cycles, and an advanced acceptance-rejection resampling algorithm. However, finite element analysis (FEA) methods and a special stress recovery technique are required to process the test data, which is usually a time-consuming process. A more straightforward approach that does not require these intermediate processes is strongly preferred.
This study presents such an approach, in which the only historical information needed is the distribution of the standard deviation of the cycles to failure. The distribution of the mean is directly calculated from the current tested data and the Central Limit Theorem. Neither FEA nor stress recovery technique is required for this approach, and the effort put into design curve construction can be significantly reduced. This method can be used to complement the previously developed Bayesian methods.
Laying the Groundwork for a Large-Scale Spent Nuclear Fuel Transportation System
Authors: Feldman Matthew , Connolly Kevin 
Published: November 2015

The US Department of Energy Office of Nuclear Energy established the Nuclear Fuels Storage and Transportation Planning Project (NFST) to lay the groundwork for implementing interim storage of commercial spent nuclear fuel (SNF), including associated transportation activities. Progress is being made on long lead time, destination-independent aspects of the SNF transportation system in three areas:
• Institutional: stakeholder interactions needed for system success, including development of a transportation plan, policy development to implement Nuclear Waste Policy Act Section 180(c), and identification of a preliminary suite of national transportation routes based on regulatory requirements and coordination with stakeholders with diverse interests.
• Operational: activities required to run a large-scale transportation system; focus is on development of a new routing analysis tool, study of infrastructure near storage sites that may be de-inventoried first, and development of tools for modeling transportation activities.
• Hardware: casks, railcars, and other items necessary to operate the system. Activities are primarily focused on development of railcars compliant with Association of American Railroads Standard S-2043 and studies on the use of rail casks and their ancillary equipment.
NFST is making significant progress in all of these areas for a future transportation system to transport SNF from commercial reactors.
Block Monitoring Method of SG Tube Support Plate With Intelligent ECT for Maintenance Work
Authors: Noda Masaki , Kobayashi Yuki 
Published: November 2015

Intelligent ECT (Eddy Current Testing) probe (I-Probe) has a capability to inspect tubes more productively and more accurately than conventional probes for Steam Generators (SG) as shown in Fig. 1. And I-Probe provides effective “One-Pass” solution by combination with MHI (Mitsubishi Heavy Industries, Ltd.) Intelligent Data Analysis System (MIDAS) [1]. It has been applied to full length tube inspection in Japan since 2003 and there is much field experience to date.
On the other hand, a phenomenon in SG secondary side is known that scale deposits clog holes of quatrefoil type tube support plate (TSP). Water level oscillation of secondary side caused by excessive blockage of scale deposits may decrease operation efficiency and it can be a cause of unintended troubles. Therefore, periodical monitoring of blockage condition and applying countermeasures like secondary side cleaning are very important. A new method has been developed to evaluate blockage condition of every TSP around all tubes automatically using I-Probe data. Also, a new software has been developed to visualize the evaluation results as color maps.
This new method may contribute to increase the reliability of SG maintenance like cleaning, because the new method makes it possible to monitor a whole SG condition more precisely.