bluuebunny/crossref_metadata_2025 huggingface dataset:
Racial disparity in all‐cause mortality among hepatitis C virus‐infected individuals in a general US population, NHANES III
Authors: Emmanuel B. , Shardell M. D. , Tracy L. , Kottilil S. , El‐Kamary S. S.
Published: December 2016

There are few long‐term nationally representative studies of all‐cause mortality among those infected with hepatitis C virus (HCV). When an additional 5 years of data were made publicly available in 2015, the Third National Health and Nutrition Examination Survey Linked Mortality File became the longest nationally representative study in the United States. Our objective was to update the estimated HCV‐associated all‐cause mortality in the general US population and determine any differences by sex, age and race/ethnicity. HCV status was assessed in 9117 nationally representative adults aged 18‐59 years from 1988 to 1994, and mortality follow‐up of the same individuals was completed through 2011 and made publicly available in 2015. There were 930 deaths over a median follow‐up of 19.8 years. After adjusting for all covariate risk factors, chronic HCV had 2.63 times (95% CI: 1.59‐4.37; P=.0002) higher all‐cause mortality rate ratio (MRR) compared with being HCV negative. All‐cause MRR was stratified by sex, age and race/ethnicity. Only race/ethnicity was a significant effect modifier of MRR (P<.0001) as the highest MRR of chronic HCV compared to HCV negative was 7.48 (95% CI: 2.15‐26.10, P=.001) among Mexican Americans, 2.67 (95% CI: 2.67‐5.56, P=.009) among non‐Hispanic Whites and 2.02 (95% CI: 1.20‐3.40, P=.007) among non‐Hispanic Blacks. Racial disparity was seen in the all‐cause mortality as Mexican Americans with chronic HCV had approximately seven times higher mortality rate than HCV‐negative individuals. This suggests that these at‐risk individuals should be targeted for HCV screening and treatment, given the availability of new highly effective HCV therapies.
Reduced nondominant lumbar multifidi cross‐sectional area is a precursor of low back injury in cricket fast bowlers
Authors: Olivier B. , Gillion N. , Stewart A. V. , McKinon W.
Published: December 2016

Asymmetry in the lumbar multifidi muscle (LM) cross‐sectional area (CSA) is associated with low back injury. The aim of this prospective cohort study was to investigate the symmetry of the CSA of LM at L3, L4, and L5, in the context of simultaneous injury monitoring. Injury free, male, right‐handed cricket fast bowlers playing at a nonprofessional level participated in this study. LM CSA at L3, L4, and L5 vertebral levels was measured through the use of ultrasound imaging in prone. The primary outcome measure of the study was the incidence of an injury during a cricket season of eight‐month duration. Twenty‐six fast bowlers (aged 21.8 ± 1.8 years) participated. No difference was found between the nondominant and the dominant LM CSA among injury free bowlers (P>.05). However, in bowlers who sustained a lower back injury during the cricket season, the nondominant CSA at L3 (nondominant median 5.80 cm2, range 3.69 cm2; dominant median 7.38 cm2, range 2.61 cm2; P=.04) and L5 (nondominant median 6.94 cm2, range 2.10 cm2; dominant median 7.38 cm2, range 3.54 cm2; P=.04) is smaller compared to the dominant side. These findings may indicate that a side‐to‐side difference in LM CSA may be a precursor of injury.
A comparison of methods for estimating the incidence of human immunodeficiency virus infection in repeat blood donors
Authors: Brambilla Donald J. , Busch Michael P. , Dodd Roger Y. , Glynn Simone A. , Kleinman Steven H. ,   for the National Heart, Lung, and Blood InstituteRecipient Epidemiology and Donor Evaluation Study‐III (REDS‐III)
Published: December 2016

BACKGROUND

The incidence of human immunodeficiency virus (HIV) in repeat blood donors has been estimated using seven methods. Although incidence is always calculated as cases per person‐time, approaches to selecting cases and calculating person‐time vary. Incidence estimates have not been compared among methods.

STUDY DESIGN AND METHODS

The seven methods were compared in a simulation study. Because three methods used information from donations made before an estimation interval, 8 years of donation and infection history were simulated, and Years 7 and 8 were treated as the estimation interval for all methods. An exponential random variate was assigned to each donor to simulate the time to infection. Infection risk was constant over 8 years in one scenario but increased at various rates in seven other scenarios. The infection risk scenarios were combined with four mixes of donation frequency to generate 32 test conditions.

RESULTS

Three methods produced biased estimates under all conditions. Three other methods were biased under most conditions. Bias from most methods increased as donation frequency declined. The single method that consistently produced unbiased estimates was the only method that involved the standard epidemiological approach of tabulating all interdonation intervals (IDIs) within the estimation interval. Bias was eliminated from one of the consistently biased methods by a simple modification that involved the average IDI in a sample of donors.

CONCLUSION

The standard epidemiological approach is recommended if required data are available. Otherwise, the modified method involving the estimated average IDI should be considered. Investigators should use caution when comparing incidence estimates among studies that use different estimation methods or donation frequencies.
Tensile Comparison of Polydioxanone, Polyglyconate, and Barbed Glycolide‐Trimethylene Carbonate Suture in Canine Cadaveric Tensor Fascia Lata
Authors: Shimizu Naomi , Tarlton John , Friend Ed , Doran Ivan , Parsons Kevin
Published: December 2016

Objective

To compare the mode of failure, load at yield, ultimate load to failure and stiffness of non‐barbed polydioxanone, non‐barbed polyglyconate and barbed glycolide‐trimethylene carbonate (GTC) suture in canine cadaveric fascia.

Study Design

Ex vivo biomechanical study.

Sample Population

18 fascia lata specimens from 9 canine cadavers.

Methods

6 fascia lata specimens were sutured with polydioxanone, 6 with polyglyconate, and 6 with barbed GTC suture. Load at yield, stiffness, ultimate load to failure were measured using tensile strength testing. Statistical analysis was used to compare outcomes between suture materials. The mode of failure was recorded and described.

Results

The load at yield and ultimate load to failure were significantly greater for polydioxanone than barbed GTC (P=.045 and P=.016, respectively). The load at yield and ultimate load to failure was not significantly different between polydioxanone and polyglyconate (P=.687 and P=.586, respectively). The load at yield and the ultimate load to failure was not significantly different between polyglyconate and barbed GTC (P=.194 and P=.109, respectively). Stiffness was not different between constructs (P=.103). Polydioxanone and polyglyconate failed by suture breakage and suture pullout. Barbed GTC failed by suture slippage and suture breakage.

Conclusion

Our results showed that under the conditions of this study, 4‐0 monofilament polydioxanone had a greater load at yield and load to failure than similarly sized, barbed copolymer suture in the fascia lata. This finding may help direct suture choice for fascial closure.
Increasing Efficiency in the Extraction of Solar Heat Stored Underground With Perturb-and-Observe Control
Authors: de Nardin Carlos R. , Fernandes Felipe T. , Longo Adriano J. , Lima Luciano P. , Farret Felix A. , Cruz Dário R.
Published: December 2016

This paper describes a perturb-and-observe (P&O) control aiming to increase the heat exchange between solar heat stored underground and the ambient of a single conditioned room without any heat pump. This P&O control increases or decreases the water flow rate through an underground hosepipe heat exchanger. With this purpose, two power converters were used to activate, respectively, a low power water pump and a fan coil so as to keep the room within the limits of a reference temperature range (between 18 °C and 24 °C). Outside these limits, the P&O control searches for the best heat exchange between the ambient room and the underground soil and, when inside these limits, the water pump and fan coil are turned off. Two identical experimental rooms, referred in this study as “reference” and “test” rooms, had their temperatures measured every 1-min during winter and summer. For comparison purposes, the reference room was left at its natural conditions without any air conditioning. The experimental results show a remarkable improvement in the heat exchange and a considerable reduction in power demand when using the P&O control. As a result, it was obtained an energy saving of approximately 45% in one summer day and 22% in one winter day. It is important to point out that this paper refers, strictly, to the description of a P&O control for heat exchange systems involving solar heat stored underground in a single room.
Effect of Bifilm Oxides on the Dry Sliding Wear Behavior of Fe-Rich Al–Si Alloys
Authors: Akaberi N. , Taghiabadi R. , Razaghian A.
Published: December 2016

The effect of bifilm oxides on the dry sliding wear behavior of Fe-rich (1.5 wt.%) F332 Al–Si alloy under as-cast and T6 heat-treated conditions was investigated. Toward this end, the surface oxides were intentionally incorporated into the molten alloy by surface agitation. The results showed that, after sliding under the applied load of 75 N, due to the presence of bifilms, the wear rate of base (0.2 wt.% Fe) and 1.5 wt.% Fe-containing alloys increased by almost 22% and 14%, respectively. The results also indicated that, despite the positive effect on the hardness, T6 heat treatment adversely affected the wear resistance of alloys made under surface turbulence condition. This negative effect can be attributed to the expansion of bifilms which, during heat treatment, are converted to the potential sites for initiation and propagation of subsurface microcracks. However, the strengthening effect exerted by the thermally modified β-Al5FeSi platelets showed that it can compensate the negative effects of bifilm oxides because it improves the wear rate of 1.5 wt.% Fe-containing F332-T6 alloy by about 5% under the applied load of 75 N.
Effect of Load and Temperature on the Tribological Characteristics of a Steel Pin on Polyoxymethylene Disk Interface
Authors: Larson Matthew G. , Timpe Shannon J.
Published: December 2016

The static and dynamic friction properties of a steel pin on polyoxymethelyne homopolymer disk were studied at temperatures ranging from 22 to 160 °C. Samples were tested at externally applied normal loads ranging from 20 to 80 N. Under this range of temperatures, the friction coefficients displayed a linearly increasing dependence on the load. The load dependence is attributed to an enhanced contribution of the plowing friction mechanism at higher loads. As load increases, the pin asperities penetrate into the hard, injection mold-induced skin layer, causing an increase in the frictional plowing. The coefficient of friction was observed to decrease from 0.08 at 22 °C to 0.05 at 50 °C, and subsequently rise to 0.07 at 160 °C. The initial drop was caused by a decrease in the modulus of elasticity attributed to the rise in molecular mobility with increased available thermal energy. As the temperature increased to 160 °C, however, the further decrease in modulus allowed the penetration of the pin asperities to increase significantly, requiring increased material displacement to initiate frictional motion.
Effects of Opening and Closing Fuel-Injector Valve on Air/Fuel Mixture
Authors: Ishii Eiji , Yoshimura Kazuki , Yasukawa Yoshihito , Ehara Hideharu
Published: December 2016

Lower engine emissions and improved fuel efficiency have recently become more necessary in automobile engines. Fuel injectors need to be designed to decrease late fuel during valve closing and to deal with multiple injections. Fuel-spray behaviors are controlled by the valve-lifts of fuel injectors; therefore, air/fuel mixture simulations that integrate with inner flow simulations in fuel injectors during the opening and closing of valves are essential for studying the effects of valve motions on air/fuel mixtures. We previously developed a late-fuel simulation near the nozzle outlets of a fuel injector during valve closing; fuel flows within the flow paths of the fuel injector were simulated by a front capturing method, and fuel breakups near the nozzle outlets were mainly simulated by a particle method. The inlet boundary of the fuel injector was controlled in order to affect the valve motions on the late-fuel behavior. In this study, we improved the late-fuel simulation by adding a valve opening function. The motion of droplets within the air/fuel mixture region was calculated by using a discrete droplet model (DDM). The injection conditions for the DDM were defined with the results of the improved late-fuel simulation; positions and velocities of droplets at the injection point were defined by using the results of the late-fuel simulation. The simulation results were validated by comparing the simulated fuel breakup near the nozzle outlets and the air/fuel mixtures in the air region with the measured ones, revealing good agreement between them. The effects of opening and closing the valve on the air/fuel mixtures were also studied; the opening and closing of the valve affected the front and rear behaviors of the air/fuel mixture and also affected spray penetrations. The developed simulation was found to be an effective tool for studying the effects of valve motions on the air/fuel mixtures.
Modeling Turbulent Reactive Flow in Internal Combustion Engines With an LES in a Semi-Implicit/Explicit Finite Element Projection Method
Authors: Waters Jiajia , Carrington David B.
Published: December 2016

A Finite Element Method (FEM) for the solution of turbulent reactive flow on parallel machines is being developed for engine and combustion modeling. This FEM solver is parallel (MPI), solves multi-species fluids using either Reynolds Averaged Navier-Stokes (RANS) k-ε model or dynamic LES model for turbulent reactive flow. The code provides an excellent platform for developing better in-cylinder fuel and species evolution, including sprays associated with injection. This code is more robust and more accurate than current engine simulators, with quick turn-around times required by design engineers. We’ve also developed a dynamic LES method which can transition through laminar to fully turbulent flow, and hence requires no assumptions about the turbulent sublayers near walls in bounded flows; this is ideal for engines where the turbulent wall layers are never in equilibrium and the flow is not always turbulent. Another key component of combustion modeling for engines is fuel injection. Spray modeling from KIVA is adopted in our work with the ability to solve large 3D turbulent flow by the help of the parallel technique.
Analysis of the Impact of Uncertainties in Inputs on CFD Predictions of Gasoline Compression Ignition
Authors: Kodavasal Janardhan , Ciatti Stephen , Som Sibendu
Published: December 2016

Computational fluid dynamics (CFD) is a valuable tool to gain insights into the combustion process, particularly for novel engine combustion concepts that do not have significant experimental data available. However, prediction of targets of interest from a CFD simulation can oftentimes be quite sensitive to the uncertainties in inputs to the CFD model. These uncertainties could be in the experimental boundary and initial conditions, fuel properties, CFD model constants, chemical kinetic rates, etc. In this work we isolate the effect of uncertainties in some key inputs in the form of experimental boundary conditions and CFD model parameters on combustion and emissions targets of interest for gasoline compression ignition (GCI) at two operating conditions — idle, and low-load. The uncertainties in the subset of inputs studied in this work were identified to have the greatest impact out of 34 inputs to the CFD model studied by means of a global sensitivity analysis (GSA) performed in our prior work. The goal of this study is to perform a more focused study as a follow-on to that GSA, by perturbing only a single parameter at a time.
A Comparison of Methyl Decanoate and Tripropylene Glycol Monomethyl Ether for Soot-Free Combustion in an Optical Direct-Injection Diesel Engine
Authors: Dumitrescu Cosmin E. , Cheng A. S. (Ed) , Kurtz Eric , Mueller Charles J.
Published: December 2016

Oxygenated fuels have been reported to have beneficial effects for leaner lifted-flame combustion (LLFC), a non-sooting mode of mixing-controlled combustion associated with lift-off length equivalence ratios below approximately 2. A single-cylinder heavy-duty optical compression-ignition engine was used to compare two oxygenated fuels: neat methyl decanoate (MD) and T50, a 50/50 blend by volume of tripropylene glycol monomethyl ether (TPGME) and #2 ultra-low sulfur emissions-certification diesel fuel (CF). High-speed, simultaneous imaging of natural luminosity and chemiluminescence were employed to investigate the ignition, combustion, and soot formation/oxidation processes at two injection pressures and three dilution levels. Additional Mie scattering measurements were employed to observe fuel-property effects on the liquid length of the injected spray. Results indicate that both MD and T50 reduced considerably the engine-out smoke emissions by decreasing soot formation and/or increasing soot oxidation during and after the end of fuel injection. MD further reduced soot emissions by 50–90% compared with T50, because TPGME could not completely compensate for the aromatics in the CF. Despite the low engine-out soot emissions, both fuels produced in-cylinder soot because the equivalence ratio at the lift-off length never reached the non-sooting limit. With respect to the other engine-out emissions, T50 had up to 16% higher NOx emissions compared with MD, but neither fuel showed the traditional soot-NOx trade-off associated with conventional mixing-controlled combustion. In addition, T50 had up to 15% and 26% lower unburned hydrocarbons (HC) and carbon monoxide (CO) emissions, respectively, compared with MD.
An Optimization Method of Multiple Tuned Mass Damper Systems and Application to Bridge With Moving Car
Authors: Nguyen Thuan , Miura Nanako , Sone Akira
Published: December 2016

Tuned mass damper (TMD) device has been a popular vibration control system for moderns as high-rise building, bridge to suppress excessive vibration due to environment or human loading. Moreover, multiple tuned mass dampers have received much attention in the researched. An optimal design theory for bridge implemented with multiple TMD devices is proposed in this paper. The proposed method chooses the objective function with the constraints on the peaks which are at the same heights over frequency ranges of interest. This proposed method successfully reduces vibration of bridge traveled by a car. In a future study, we will extend the optimal design theory for the cases with more than one car and the bridge under seismic loading.
Micro-Porous Coatings and Enhanced CHF for Downward Facing Boiling During Passive Emergency Reactor Cooling
Authors: Segall Albert E. , Sohag Faruk A. , Beck Faith R. , Mohanta Lokanath , Cheung Fan-Bill , Eden Timothy J. , Potter John
Published: December 2016

During a Reaction Initiated Accident (RIA) or Loss of Coolant Accident (LOCA), passive external-cooling of the reactor lower head is a viable approach for the in-vessel retention of Corium; while this concept can certainly be applied to new constructions, it may also be viable for operational systems with existing cavities below the reactor. However, a boiling crisis will inevitably develop on the reactor lower head owing to the occurrence of Critical Heat Flux or CHF that could reduce the decay heat removal capability as the vapor phase impedes continuous boiling. Fortunately, this effect can be minimized for both new and existing reactors through the use of a Cold-Spray delivered, micro-porous coating that facilitates the formation of vapor micro-jets from the reactor surface. The micro-porous coatings were created by first spraying a binary mixture with the sacrificial material then removed via etching. Subsequent quenching experiments on uncoated and coated hemispherical surfaces showed that local CHF values for the coated vessel were consistently higher relative to the bare surface. Moreover, it was observed for both coated and uncoated surfaces that the local rate of boiling and local CHF limit varied appreciably along the outer surface. Nevertheless, the results of this intriguing study clearly show that the use of Cold Spray coatings could enhance the local CHF limit for downward facing boiling by more than 88%. Moreover, the Cold-Spray process is amenable to coating the lower heads of operating reactors.
Fundamental Design of Response Control Technology for Aerogenerator Against Seismic Motion and Wind Load
Authors: Furuya Osamu , Cho Sunggook , Kurabayashi Hiroshi , Uchida Kazuma
Published: December 2016

Aerogenerators have been constructed in various countries during the recent years as one of the power generation system using environmentally friendly energy. Japan has been promoting a national project to examine constructing a wind turbine power generating station in the ocean. In general, the structure of aerogenerator is heavy at top due to the higher position of the center of gravity because a heavy nacelle is set at the top of aerogenerator. Since the dynamic response of the aerogenerator increases excessively due to the top position of heavy weight, it is further required to reduce the responses and improve the seismic and wind resistances.

This study has examined the response control system to reduce the structural responses and to upgrade the resistant performance against earthquakes and wind excitation. The paper discusses design methods and loading tests of elasto-plastic damping devices to investigate the mechanical characteristics of dampers. In order to confirm the structural seismic and wind response control effects by the damping devices, the preliminary analyses and a set of vibration tests using a 1/16 scale model of aerogenerator were performed in this study. This paper reviews the results obtained from analyses and tests.
Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 4 — Aging Properties of a Half Scale Thick Rubber Bearings Based on Breaking Test
Authors: Watakabe Tomoyoshi , Yamamoto Tomohiko , Fukasawa Tsuyoshi , Okamura Shigeki , Somaki Takahiro , Morobishi Ryota , Sakurai Yu , Kato Kouji
Published: December 2016

A seismic isolation system composed of a thick rubber bearing and an oil damper has been developed for Sodium-Cooled Fast Reactor. One of the advantages of the isolation system is the use of thick rubber bearings to ensure the longer vertical natural period of a plant, thereby mitigating seismic loads to mechanical components. Based on many previous studies, rubber bearing technology has progressed, but test data regarding the effect of aging is not sufficient. Moreover, there is no data on the limits of linear strain and breaking behavior for thick rubber bearings after aging. This paper focused on the aging properties of thick rubber bearings, such as basic mechanical properties and ultimate strength. An aging test of thick rubber bearings was conducted using 1/2-scale (800mm diameter) and 1/8-scale (200mm diameter) rubber bearings. Aging of the rubber bearings was reproduced using thermal degradation, in which the target of aging periods were 30 and 60 years. The hysteresis loops of the thick rubber bearings after aging were obtained through horizontal and vertical static loading tests, and the effects of aging were evaluated by comparison with the initial mechanical properties. In addition, for the purpose of further research, the effect of scale by aging was clarified to compare the mechanical properties between the 1/2-scale and 1/8-scale rubber bearings.
INCEFA-PLUS (Increasing Safety in Nuclear Power Plants by Covering Gaps in Environmental Fatigue Assessment)
Authors: Mottershead Kevin , Bruchhausen Matthias , Métais Thomas , Cicero Sergio , Tice David , Platts Norman
Published: December 2016

INCEFA-PLUS is a major new five year project supported by the European Commission HORIZON2020 program. The project commenced in mid 2015. 16 organizations from across Europe have combined forces to deliver new experimental data which will support the development of improved guidelines for assessment of environmental fatigue damage to ensure safe operation of nuclear power plants.

Prior to the start of INCEFA-PLUS, an in-kind study was undertaken by several European organizations with the aim of developing the current state of the art for this technical area. In addition to stress/strain amplitude, this study identified three additional experimental variables which required further study in order to support improved assessment methodology for environmental fatigue, namely the effects of mean stress/strain, hold time and surface finish. Within INCEFA-PLUS, the effects of these three variables on fatigue endurance of austenitic stainless steels in light water reactor environments are therefore being studied experimentally. The data obtained will be collected and standardized in an online environmental fatigue database. A dedicated CEN workshop will deliver a harmonized data format facilitating the exchange of data within the project but also beyond.

Based on the data generated and the resulting improvement in understanding, it is planned that INCEFA-PLUS will develop and disseminate methods for including the new data into assessment procedures for environmental fatigue degradation. This will take better account of the effects of mean stress/strain, hold time and surface finish.

This paper will describe the background to the project and will explain the expectations for it.
Calculation and Analysis for Pressure Vessel Rupture Study Under Fire in Plant
Authors: Ito Yoshiyasu , Tsuruoka Akira , Waki Yoshiyuki , Osedo Hiroko
Published: December 2016

In case of fire occurring in an Oil and Gas facility, pressurized vessels may be exposed to fire. Though the entire system will be depressurized once a fire is detected, vessels may rupture, leading to risk of flammable, toxic or cryogenic fluid being released. Therefore, pressure vessels should be designed to withstand internal pressure without rupture in fire situations, at least until the system pressure can be decreased to a safe level. A pressure vessel rupture study should be conducted in addition to design code calculation to ensure a safe design in case of fire. As part of the recent trend for safer plant design, demand for pressure vessel rupture studies is growing.

In our previous presentation (PVP2015-45260 [1]), the material data for carbon steel (SA-516 Gr.70) and stainless steel (SA240 SUS type304 and SUS type304L) at the high temperature range were obtained by material testing and presented as our study result.

For the present research, pressure vessel rupture studies were performed for carbon steel and stainless steel using FEM analysis and calculation methods in published design guidelines for various conditions (e.g. heating area and shell thickness, etc.). In conclusion, a procedure for pressure vessel rupture study is proposed.
Numerical and Experimental Study of Elastic Interaction in Bolted Flange Joints
Authors: Zhu Linbo , Bouzid Abdel-Hakim , Hong Jun
Published: December 2016

Bolted flange joints are widely used to connect pressure vessels and piping equipment together and facilitate their disassembly. Initial tightening of their bolts is a delicate operation because it is extremely difficult to achieve the target load and uniformity due to elastic interaction. The risk of failure due to leakage and fatigue under service loading is consequently increased.

This paper presents a study on the effect of elastic interaction that is present during the tightening of a bolted flange joints using three-dimensional nonlinear finite element modeling and experimentation. The nonlinear non-elastic behavior of the gasket is taken into account in the numerical simulation. The scatter in bolt preload produced during the tightening sequence is evaluated. Based on the elastic interaction coefficient method, the initial target tightening load in each bolt for every pass are determined by using the nonlinear finite element model to obtain a uniform preload after the final tightening pass. The validity of the FEA (Finite Element Analysis) is supported by experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joints using fiber and flexible graphite gaskets. This study provides guidance and enhances the safety and reliability of bolted flange joints by minimizing bolt scatter due to elastic interaction.
Ultimate Failure Criteria Evaluation of Elbow Pipe Components in Seismically Isolated NPPs
Authors: Hahm Daegi , Kim Min-Kyu
Published: December 2016

Seismic isolation system can be an effective alternative to protect the nuclear power plants (NPPs) against to the strong seismic events. Therefore, some research activities to adopt the seismic isolation concept to the design of the next generation NPPs have been progressed for last few years in Korea. If seismic isolation devices are installed in nuclear power plant for seismic stability, safety against seismic load of power plant may be improved. But in some equipment, the seismic fragility capacity may decrease because the relative displacements may become larger compared to the non-isolated case. It is well known that the interface pipes between isolated & non-isolated structures will become the most critical component when the seismic isolation system will be introduced. Therefore, seismic performance of such interface pipes should be evaluated comprehensively especially in terms of the seismic fragility capacity. To evaluate the seismic capacity of interface pipes in the isolated NPP, firstly, we should define the failure mode and failure criteria of critical pipe components. In many previous studies, the failure mode and failure criteria of pipes under severe seismic loading condition were defined in terms of the low-cycle fatigue and/or ratcheting failure. However, for the interface pipes in the seismically isolated NPPs, the failure mode may become different from the conventional failure modes of ordinary pipes because of the extremely large relative displacement between the support anchors which are located in the isolated and non-isolated structures. Hence, in this study, we performed the dynamic tests of elbow components which were installed in a seismically isolated NPP, and evaluated the ultimate failure mode and failure criteria by using the test results. To do this, we manufactured 24 critical elbow component specimens and performed cyclic loading tests under the internal pressure condition. The failure mode and failure criteria of a pipe component will be varied by the design parameters such as the internal pressure, pipe diameter, loading type, and loading amplitude. From the tests, we assessed the effects of the variation parameters onto the failure criteria. For the tests, we generated the seismic input protocol of relative displacement between the ends of elbow component. The results of ultimate failure mode and failure criteria are presented in terms of the number of cyclic loading counts, damage indices which are the functions of dissipated energy and inelastic deformation. From the results, we found that the increase of the internal pressure will slightly increase the failure criteria. Tested elbow components had a very good sustainability against to the earthquake loading since that more than 34 times of 0.5g earthquakes (40 mm relative displacement) were required to make a penetration crack at the most critical point.
Failure Analysis for Welding of Primary Loop Pipes in High-Power Pump Test Platform
Authors: Yang Bo , Huang Yi-chang , Qian Yao-zhou , Tang Xiao-ying
Published: December 2016

Welding of 15NiCuMoNb5-6-4 and austenitic stainless steel thickness pipes is necessary in the primary loop pipes installation for the platform. In the process of formulating welding procedure specification of the pipeline pre-welding between 15NiCuMoNb5-6-4 and Z3CN20-09M, some macroscopical cracks appeared repeatedly on the surface of bend-test specimens, while other performances of welding joints such as mechanical properties at room temperature, high temperature tensile properties and impact properties could meet the relevant codes requirements. Focus on present problem, chemical composition analyses, metallographic microstructures analyses and scanning electron microscope observation were adopted to find the welding failure root cause. Finally, INCONEL®152M and 52M with 30% chromium were chosen to be the welding materials because of good ductility dip cracking resistance. It was found that the performance of the welding joints could satisfy the codes and engineering requirements.
Improving Simulations for Low Cycle Fatigue and Ratcheting Responses of Elbows
Authors: Islam Nazrul , Hassan Tasnim
Published: December 2016

A rate-independent constitutive model is developed incorporating various uniaxial and multiaxial modeling features for improving the simulations of elbow low-cycle fatigue and ratcheting responses. The model development is motivated by the fact that the Chaboche model in ANSYS is unable to simulate the strain ratcheting responses of elbows subjected to internal pressure and opening-closing displacement-controlled cycles. This drawback of the existing model is traced to the isotropic and kinematic hardening modeling features. The isotropic hardening in the Chaboche model can reasonably simulate the material test stress peaks but fails to simulate the hysteresis loop shapes. Incorporation of a strain range dependent modeling feature in evolving the isotropic and kinematic hardening rule parameters improved the simulation of the hysteresis loops both at the material and component levels. The axial and circumferential strain ratcheting simulation of elbow is improved by incorporating a biaxial ratcheting parameter. A modeling feature for nonproportional loading developed by Tanaka is also incorporated in order to simulate the additional cyclic hardening under multiaxial loading. The performance of modified model developed is validated against simulating a broad set of cyclic responses both at the material and component levels. Finally, a numerical technique is developed to simulate the initial and welding residual stresses in elbows, and thereby analytically demonstrate the influence of initial residual stresses on elbow responses.
Role of Long Term Ageing on the Creep Life of Type 316H Austenitic Stainless Steel Bifurcation Weldments
Authors: Martinez-Ubeda Ana I. , Griffiths Ian , Payton Oliver D. , Younes Charles M. , Scott Tom B. , Flewitt Peter E. J.
Published: December 2016

Intergranular creep cracks have been observed in the heat affected zone of the 316H austenitic stainless steel superheater boiler tube bifurcation weldments after long term service at temperature of ∼550°C. The cracking mechanism is believed to be creep dominated. Moreover, chemical composition of defective material compared with similar uncracked components suggests that composition influences susceptibility to creep cracking. A systematic characterization of ratios number of creep cavities/grain boundary length and inter-granular precipitation length/grain boundary length has been undertaken in HAZ of three samples extracted from plants with different specific compositions. Here, the role of precipitation on creep deformation and fracture is explored. Precipitates of both ferrite and M23C6 carbide arising from long term service and associated creep cavitation have been identified using transmission electron microscopy. The creep damage and cracking, and therefore overall service life creep, is discussed by consideration of susceptibility of creep cavity nucleation and subsequently growth arising from specific differences in the chemical composition of the three boiler tube bifurcations.
Applicability of a Crack Length Correction on the RCC-M Fracture Toughness Reference Curve
Authors: Delvallée-Nunio Isabelle , Blain Christophe
Published: December 2016

The safety cases of the French 900-MWe and 1300-MWe reactor pressure vessels (RPV) have been reviewed respectively in 2010 and 2015 by the French Nuclear Safety Authority (ASN) and the Institute for Radiological Protection and Nuclear Safety (IRSN) in order to decide of the continued operation for the next ten years after their third decennial outage.

The demonstration of the RPV serviceability, based on a deterministic approach, includes an assessment of the risk of crack initiation under normal and accidental conditions. The fracture criterion defined by the French utility, takes into account a size effect on fracture toughness in the ductile-to-brittle transition of ferritic steel by the application of a correction factor to the fracture toughness estimated on the French code RCC-M fracture toughness reference curve. This correction related to the crack length is built on the observation that the failure probability follows a Weibull distribution and on the assumption that the RCC-M KIC curve can be associated to a reference crack length of 100 mm.

A first crack length correction has been judged inappropriate by ASN and IRSN in 2010. A new temperature-dependent correction has then been proposed in 2014. Nevertheless, numerous elements presented in this paper have led ASN and IRSN to the conclusion that this new correction should not be applied to the RCC-M KIC curve. In particular the RCC-M KIC curve already integrates intrinsically a size effect on fracture toughness.
Fragility Analysis of Horizontal Pressure Vessels in the Coupled and Uncoupled Case
Authors: Korndörfer Jonas , Hoffmeister Benno , Feldmann Markus
Published: December 2016

The European project “INDUSE-2-SAFETY” aims for the development of a quantitative risk assessment methodology for seismic loss prevention of “special risk” petrochemical plants and components. To demonstrate the capabilities of this approach, a representative case study containing typical components is subjected to detailed investigation. Probabilistic seismic models are used to establish a relation between seismic demand and structural performance of the components with respect to relevant limit states. The resulting fragility curves are used as input for the quantitative risk model.

The study at hand focusses on the fragility analysis of a horizontal steel pressure vessel, which represents a common component type in (petrochemical) plants. Prior to performing the fragility analysis, the dynamic characteristics as well as the pushover behaviour of the vessel are investigated in detail. In order to allow for transient dynamic analyses with reasonable computational resources, a simplified model of the pressure vessel is derived. For the probabilistic seismic demand analysis, the so-called cloud method is applied, using 26 seismic records subdivided into three different groups. The influence of different variables, in particular the liquid filling height and the coupling conditions, on the fragility is investigated in greater detail.
Analytical Study on Failure Mode Map for Lower Formed Head of Reactor Pressure Vessel Under BDBE
Authors: Ogawa Hiroshi , Machida Hideo , Kasahara Naoto
Published: December 2016

Some of the important lessons learned from Fukushima Daiichi nuclear power plant accident are that mitigation of failure consequences and prevention of catastrophic failure are essential to combat severe accidents (SA) and excessive earthquake conditions that correspond to design extension conditions (DEC). To improve mitigation measures and accident management, clarification of failure behaviors depending on locations is premised under DEC such as SA and earthquakes. Design extension conditions induce some failure modes that are different from those in design conditions. The best estimation for these failure modes is necessary in order to prepare countermeasures and management. A prerequisite for conducting best estimation is to clarify the failure modes with the ultimate structural strength under extreme loads due to very high temperatures, pressure, and great earthquakes.

The authors attempt to clarify unclear failure mechanisms caused by extreme loading under DEC using numerical simulation. In this paper, the relationships between failure modes and extreme loading were studied through numerical simulation using the cylinder and half-spherical model that assumes the bottom of the reactor pressure vessel (RPV) (e.g. Lower Formed Head, Instrument Tube, Gide Tube, Nozzle). This bottom structure of RPV is estimated to be under high temperature and pressure conditions due to the relocation of the molten corium. This heat loading causes major deformation of the bottom head due to creep, which leads to RPV failure. On the other hand, there is a possibility that structural discontinuities (e.g. Gide Tube Nozzle) may fail in advance. In order to recognize actual failure modes, the authors had to study the basic relationship between failure modes and load conditions in the failure mode map. This failure mode map is being considered for use as initial simple structural in beyond design basis events (BDBE) and DEC.
Studies on Fatigue Design Margins of Welded Steel Structures
Authors: Takanashi Masahiro
Published: December 2016

This paper discusses fatigue design margins based on large-sized specimens that are considered to be more closely related to actual components. A fatigue design curve is generally determined by applying an adequate margin to a best-fit curve obtained from laboratory tests using small-sized specimens. However, the reason and the background for the margin setting are unclear and controversial. In ASME Boiler and Pressure Vessel Codes Section III, for example, a factor of 2 on stress and a factor of 20 on life are applied to the best-fit curves. The conservatism of these factors has been the topic of discussion recently. In addition to a basic method like ASME Section III, new design concepts for welded structures, equivalent structural stress approach, has been proposed recently and adopted to design codes in Europe (EN13445) and the U.S. (ASME Section VIII Division 2). Thus, the design margins by these three methods were compared. The comparison made it clear that the ASME Sec. III method gives the most conservative margin, and the lowest value is approximately 2.
Two Different Approaches to Simulate J-Groove Joints
Authors: Terreros Iñigo , Gallee Sébastien , Robin Vincent , Gommez Florence , Lacroix Rémi , Gilles Philippe , Chanussot Jean-Michel
Published: December 2016

The large thickness of most of the heavy components in Pressurized Water Reactors often lead to use multi-pass welding processes. Distortion tolerance and maximal residual stress requirements if any are difficult to fulfill by simply adjusting welding processes with a trial-and-error procedure. This is the main reason why AREVA has developed a robust methodology to perform welding numerical simulations leading to have a better understanding of the phenomena involved during the process.

The present work details a 3D method successfully used to simulate a peripheral adapter J-Groove attachment weld in a vessel head [1] and compares the results to those obtained with a 3D simplified method.

The first method is the state of the art method use for solving Computational Welding Mechanics problems. It is a transient “step by step” 3D simulation using an equivalent moving heat source as input. The second method is a simplified one. First, an equivalent thermal cycle is obtained from a 3D stationary thermal simulation. This thermal cycle is representative of the welding parameters. This thermal cycle is then prescribed to all nodes in a given sector of the weld. This simplified method is called “prescribed thermal cycle” method.

A comparison between displacements and stresses obtained by both methods is completed in order to validate the hypothesis of the simplified approach. The results show a good agreement between the transient “step by step” method and the simplified one. Furthermore, the simplified method speeds up the calculations by a factor of 10. These performances offer the possibility to simulate a multi-pass welding of Pressurized Water Reactor components in a limited calculation time, providing an efficient decision making tool for engineering purpose.

This work is the result of a fruitful collaboration between AREVA and ESI-FRANCE. All the computations are performed with SYSWELD™ software [3].
Reduction of Strain Hardening Models After Manufacturing Simulation for Further Material Investigation and Surface Integrity Assessment
Authors: Lacroix Rémi , Brosse Alexandre , Gallée Sébastien , Bergheau Jean-Michel , Jourden Erwan , Robin Vincent
Published: December 2016

The present paper details a post-processing method to provide a local update of the material properties after a thorough manufacturing process simulation. This update degrades the hardening behavior model to fit in-service analyses requirements. It allows a drastic reduction of the level of complexity of the numerical model, while keeping the initial state of the component as accurate as necessary for service analyses. It makes the results of advanced best estimate numerical simulation available as direct inputs for regulatory analysis.
Overview of Proposed High Temperature Design Code Cases
Authors: Carter Peter , Sham T.-L. (Sam) , Jetter Robert I.
Published: December 2016

Proposals for high temperature design methods have been developed for primary loads, creep-fatigue and strain limits. The methodologies rely on a common basis and assumption, that elastic, perfectly plastic analysis based on appropriate properties reflects the ability of loads and stress to redistribute for steady and cyclic loading for high temperature as well as for conventional design. The cyclic load design analyses rely on a further key property, that a cyclic elastic-plastic solution provides an upper bound to displacements, strains and local damage rates. The primary load analysis ensures that the design load is in equilibrium with the code allowable stress, taking into account: i) The stress state dependent (multi-axial) rupture criterion, ii) The limit to stress re-distribution defined by the material creep law. The creep-fatigue analysis is focused on the cyclic creep damage calculation, and uses conventional fatigue and creep-fatigue damage calculations. It uses a temperature-dependent pseudo “yield” stress defined by the material yield and rupture data to identify cycles which will not cause creep damage > 1 for the selected life. Similarly the strain limits analysis bounds cyclic strain accumulation. It also uses a temperature-dependent pseudo “yield” stress defined by the material yield and creep strain accumulation data to identify cycles which will not cause average (membrane) inelastic strain > 1% for the design life. The paper gives an overview of the background and justification of these statements, and examples.
Applying Fracture Mechanics to Cracked Components Subjected to Unloading
Authors: Oliver Sam , Pavier Martyn , Mostafavi Mahmoud
Published: December 2016

The J-integral is widely used as a fracture parameter for elastic-plastic materials. The J-integral describes the intensity of the stress field close to the crack tip in a power-law hardening material under a set of well-known restrictions. This study investigates what happens when one of these restrictions is broken, namely the requirement for no unloading to occur.

In this work, a centre-cracked plate is subjected to a single cycle of load in which unloading occurs. A remote tensile stress is applied, then released, then applied again up to and beyond its initial magnitude. The J-integral at each step of the analysis is calculated using finite element analysis. Its validity as a fracture parameter at each step is discussed with the aid of results from a strip yield analysis of the same problem. The relevance of the results in the context of structural integrity assessment is discussed.