bluuebunny/crossref_metadata_2025 huggingface dataset:
DISFRAC Testing and Results
Authors: Erickson Marjorie , Cochran Kristine B.
Published: November 2014

A theoretical, multi-scale model to predict the fracture toughness of ferritic steels in the ductile-to-brittle fracture mode transition temperature region has been implemented into the DISlocation-based FRACture (DISFRAC) computer code to permit fracture safety assessments of ferritic structures. The theoretical basis of this model provides a means of predicting fracture behavior outside of the ranges of data currently used in deriving empirically-based models and should provide a means of improving the understanding of fracture behavior in the fracture mode transition region. Testing has been conducted to verify the model behavior as coded into DISFRAC_V2 and to validate the code predictions against trends observed in mechanical test data. Sensitivity studies were also conducted to identify the models and parameters having the greatest effect on the predicted results. The DISFRAC model was found to be most sensitive to the definition of a “specimen size” relative to the number of particles considered. Specimen size had a large effect, both on the temperature-dependence observed across the range of predicted fracture toughness as well as on the range of KJc values simulated at each test temperature. This sensitivity of KJc to specimen size needs more study to ensure definition of an appropriate specimen size based strongly on the particles most relevant to the fracture process.
Brittle Fracture Probabilistic Assessment of WWER-1000 RPVs
Authors: Orynyak Igor , Zarazovskii Maksym , Batura Anatolii , Borodii Mykhaylo , Danil’chuk Evgen
Published: November 2014

This paper presents a methodology for brittle fracture probability assessment of WWER-1000 RPVs subjected to PTS. The main attention of the study is focused on the definition of the stochastic input data: fracture toughness, CTB, size and shape of the defects.

Fracture toughness of RPV metal in the initial state is determined, separately for the base metal and the welds, as the mean curve lines of relevant experimental data. Metal embrittlement is taken into account by increasing CTB.

Based on the results of the Ukrainian surveillance specimens program, a CTB database of WWER-1000 RPVs is created. As a result of processing these data, the CTB temperature dependence on the neutron fluence and chemical composition are obtained. The probability of the fracture toughness curve position on the temperature axis is defined by the CTB standard deviation in accordance with normal distribution law.

The distribution laws of depth and shapes of defects are taken according to the NRC data and verified on the base of the statistics of the defects, which were found in the WWER-1000 RPVs of the Zaporozhye NPP.

In fact, probabilistic calculation of the RPV brittle fracture is performed similarly to the deterministic one. Fields of temperature and stresses in different RPV zones in each timepoint of considered emergency scenario are calculated by the high-effective variant of transfer matrix method in axisymmetric elastic formulation. Semielliptical axial cracks of different sizes and proportions are conservatively considered on the inner surface of RPV. SIF along the crack front is defined using the original variant of Weight Function Method. The probability of failure of a particular defect is determined as the probability that CTB of the appropriate metal reaches the maximum allowable CTB value for the scenario.

The presented method is used for the renewal of operating licenses process of Unit 2 RPV of the South Ukrainian, and Units 1 and 2 RPVs of the Zaporozhye NPPs.
CFD Modelling of a Choke Valve Under Critical Working Conditions
Authors: Malavasi Stefano , Messa Gianandrea Vittorio
Published: November 2014

Choke valves are widely used in the oil&gas industry to control the fluid flowing in the system. Some of these valves rely on a “cage and sleeve” functioning, in which an outer, sliding sleeve controls the flow rate by overlapping the holes of an inner, fixed cage. The regulation characteristic of choke valves is typically quantified by the opening curve, which is the plot of the flow coefficient versus the valve opening. Experimental tests performed on a “cage and sleeve” choke valve revealed that the orientation of the holes of the cage affects significantly the flow coefficient. This work focuses on the worst situation encountered, in which an anomalous decreasing trend in the opening curve for large valve openings is accompanied by strong vibrations of the device. CFD simulations were run to provide a physical interpretation of this unexpected result. Due to the complexity of the flow field structure at the origin of this behavior particular attention was paid in properly defining the CFD model; the turbulence model and the differencing scheme for the convective fluxes were found to be the most significant parameters. The CFD runs allowed attributing the anomalous trend of the opening curve to the peculiar interactions of the jets within the cage. At last, a modification of the trim design is suggested for avoiding the malfunctioning of the valve and the abnormal vibrations.
Local Limit Load Analytical Model for Thick-Walled Pipe With Axial Surface Defect
Authors: Ageiev Sergii , Orynyak Igor , Radchenko Sergii , Zarazovskii Maksym
Published: November 2014

Based on the previous limit load analytical modeling for cracked thin-walled pipe [1] the limit load model for thick-walled pipe had developed. There are some additional peculiarities included in proposed model. First, the radial stresses distribution and their accounting for the Tresca’s criterion. Second, the crack location and related to it the interaction of hoop stress (due to the inner pressure) and axial one (caused by local bending moment) in the limit state. Third, hoop stress redistribution with possibility of plastic hinge forming in the zone, which is opposite to the crack zone. Forth, an analysis of derived easy to use analytical formulas by comparing with results of full-scale burst test.
Hydraulic Tensioner Assembly: Load Loss Factors and Target Stress Limits
Authors: Brown Warren
Published: November 2014

This paper examines two key themes regarding the use of hydraulic tensioners to assemble pressure boundary bolted joints. The first theme is the amount of overload required to compensate for load loss that occurs due to both nut-to-tensioner mechanical interaction and, in the case of less than 100% tensioning, bolt-to-bolt mechanical interaction during assembly using hydraulic tensioners. The second theme is to examine the effect on the required assembly procedure if the target bolt stress value is close to yield. This paper has practical application for general assembly of large diameter bolts, but in particular for assembly of low strength bolting, such as A193-B8M class 1 and class 2 bolts.
Environmental Influences on the Fatigue Assessment of Austenitic and Ferritic Steel Components Including Welds
Authors: Roth Armin , Herbst Matthias , Rudolph Jürgen , Wilhelm Paul , Schuler Xaver , Herter Karl-Heinz , Kammerer Matthias , Weissenberg Thomas
Published: November 2014

The fatigue assessment of safety relevant components is of importance for ageing management with regard to safety and reliability. For cyclic stress evaluation, different country specific design codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as limiting criteria, the influence of different factors like e.g. environment, surface, temperature and data scatter must be taken into consideration in an appropriate way. In this context there is a need of consolidating and increasing the current knowledge.

In the framework of an ongoing three years German cooperative project performed by Materials Testing Institute MPA Stuttgart and AREVA GmbH (Erlangen) it is the aim to both improve the state of the art based on an experimental program on the factors mentioned above including hold-times at transient free static load and on the derivation of a practicable engineering fatigue assessment concept. Emanating from a review of the current state of the art the cooperative project is split up into three major parts:

1) Experimental investigations concerning the influence of loading parameters and environmentally assisted fatigue (EAF) effects (light water reactor environment) on the fatigue strength of ferritic steels including weldments.

2) Experimental investigations concerning the influence of long hold times and the EAF effects on the fatigue strength of austenitic and ferritic steels.

3) The results of the outlined experimental program and published results will constitute the input for the proposal of an engineering fatigue assessment concept. This concept includes the differentiation between numerous factors of influence as an essential feature. In this context the margins between mean data curves and design curves are to be discussed in detail considering the factors of influence in general and EAF in particular.

Based on a comprehensive consolidation of the state of the art and previous investigations in air and in light water reactor environment an experimental program is set up with the following key aspects:

- Strain controlled fatigue tests on welded (microstructure of the weldment excluding microscopic and macroscopic weld notch effects) and unwelded smooth laboratory specimens subjected to constant and variable strain amplitude loading in air and light water reactor environment.

- Strain controlled fatigue tests on notched specimens for the consideration of multi-axiality effects in air and light water reactor environment.

- Strain controlled fatigue tests on smooth round laboratory specimens in air and in light water reactor environment focusing on long (power plant relevant) hold time effects.
Understanding Behaviors of Bolted Flanges With Non-Axisymmetric Temperature Distribution
Authors: Jung Gong H. , Kim Minsu
Published: November 2014

It is critical to maintain uniformity of gasket stress in control against leakage in piping and heat exchangers. Many innovative bolting tools have been developed, but their benefit could be downgraded if there were sources disrupting initially achieved uniformity of gasket stress.

The characteristics behaviors of gasket stress in flanges with NATD (Non-Axisymmetric Temperature Distribution) were studied using finite element analysis on ANSI standard flanges.

It was found that change of gasket stress was independent of the magnitude of initial bolt stress and size of flange, but strongly dependent upon type of flange class. Empirical curves (curve fitting equation) were proposed to determine change of gasket stress which was function of degree of NATD and flange class (rigidity index). The change of bolt stress with NATD was relatively small compared to the change of gasket stress, which may make it difficult to assess flange integrity by monitoring bolt stress in service.
A Remaining Life Assessment of Autofrettaged Tubes From an LDPE Facility
Authors: Cochran Jeffrey D. , Panzarella Charles H.
Published: November 2014

The manufacture of low density polyethylene by radical polymerization regularly subjects components to extreme pressures exceeding 20 ksi and, possibly, to runaway reactions with fluid temperatures exceeding 2000 °F and pressures above 30 ksi. Components are often treated with autofrettage to induce a beneficial residual stress distribution that retards crack growth and increases fatigue life. This paper presents a case-study remaining life assessment of two autofrettaged tubes in accordance with API 579-1/ASME FFS-1. Measurements of the remaining residual stress after 40+ years in service agree with FEA predictions of the initial residual stress, indicating no significant stress relaxation over this time. Nevertheless, the MPC Omega creep model is calibrated to the tube material and used to estimate the potential for stress-relaxation due to creep. The model correctly predicts no stress relaxation for over 40 years of normal operation, but creep damage and stress relaxation are predicted for temperature excursions as low as 900 °F for 10.8 s. ASME FFS-1 procedures for assessing brittle fracture, fatigue, plastic collapse, and creep damage are then adapted for autofrettaged components. It is found that autofrettage increases resistance to brittle fracture and fatigue, does not affect limit load analyses, and alters creep damage distributions.
A Comparison of the Deterministic and Probabilistic Aspects of the ASME III Fatigue Evaluation Procedures
Authors: Watson Chris , Beardsmore David , Wright Keith
Published: November 2014

Fatigue is a common failure mode in mechanical components that are subject to repeated load cycles. In nuclear plants the cyclic loading is usually associated with variations of pressure and temperature. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code provide fatigue evaluation procedures in ASME III Section NB-3220. It is required to calculate a Cumulative Usage Factor (CUF). The Code criterion for acceptance is that the calculated CUF must be less than one. The ASME method is deterministic and it is assumed that uncertainties are accounted for by largely un-quantified inherent safety margins in the assessment.

The conservatism in the ASME III Code fatigue evaluation methods may come from the assessment procedure used and/or the fatigue design curve. In this paper the inputs to an ASME III fatigue assessment that is based upon a finite element determination of stresses are outlined and assessed. Based upon these inputs possible areas of conservatism within the analysis are then discussed and conclusion drawn on the inherent margins.

In addition a probabilistic model that uses Monte Carlo (MC) methods is developed. By assuming the scatter in the fatigue data, used to generate the design fatigue curve, to be the most significant random variable, the MC model was used to calculate the conditional probability of initiation associated with CUFs from a number of plant representative examples.
Implementation in VIBIC of an Improved Time-Domain Simulation Model for Fluidelastic Instability in Tube Arrays
Authors: Sawadogo Teguewinde , Han Yingke , Mureithi Njuki
Published: November 2014

VIBIC (Vibration of Beams with Intermittent Contacts) is a non-linear dynamics computer code developed and maintained by Atomic Energy of Canada Limited over the past 40 years in collaboration with universities. Its main application is the assessment of possible vibration damage to steam-generator and heat exchanger tubes. This assessment is done by performing simulations of the vibration response of beam-like structures to various flow-induced excitation mechanisms, such as turbulence buffeting, vortex shedding, and fluidelastic excitation. Fluidelastic excitation is potentially the most damaging flow-induced excitation mechanism. The fluidelastic effect has, until now, been incorporated in VIBIC using the frequency-based Connors model.

To properly perform a time-domain simulation of fluidelastic-induced vibration, a time-domain fluidelastic force model is needed. In the present work, a time-domain formulation of the fluidelastic forces based on the quasi-steady model is implemented in VIBIC. The time delay inherent to the quasi-steady model is taken into account by using a delayed displacement in the expression of the fluidelastic forces. The resulting modal equations are delay differential equations that are solved using a continuous extension of the Runge-Kutta method. Both linear and nonlinear fluid force models are incorporated. The fluidelastic instability results predicted by the models are compared to known theoretical and experimental results for validation. The predictions of the models are in good agreement with those results. The results given by the nonlinear quasi-steady fluidelastic forces are found to be more realistic than those of the linear quasi-steady fluidelastic forces. A realistic simulation of the post-instability behaviour is made possible through the use of the nonlinear fluidelastic forces.
Prediction of Margins in the TBS Seismic Considerations Analysis for Circumferential Surface-Cracked Piping Under Beyond Design Basis Seismic Loading
Authors: Uddin Mohammed , Brust Frederick , Wilkowski Gery , Zhang Tao , Betervide A. A. , Mazzantini O. , Fernandez Ricardo A.
Published: November 2014

The Transition Break Size analysis is given in Draft Regulatory Guide 1216 for assessment of ECCS requirements. There are additional analyses required for seismic considerations for beyond design basis seismic loading. The beyond design basis loading was for seismic event with a probability of occurrence of 1e−6 per year, whereas safe-shutdown earthquake loading is typically closer to a probability of 1e−4 events per year. The peak-ground accelerations for US plants are typically in the 0.1 to 0.2 g’s range for SSE loading, while the 1e−6 seismic loading may be about 3 times higher (depending on site specific seismic hazard curves).

A simplified method was created for the TBS seismic consideration analysis, which is given in Appendix A and B in the Draft Reg Guide. The technical basis is in NUREG-1903. The TBS analysis approach utilizes a simple method for scaling the seismic stresses from the SSE to 1e−6 loading, allowing for a bilinear stress correction (linear to yield of the material and an ultimate point consistent with uncracked seismic tested pipe results). A best-estimate fracture analysis is then conducted using the ASME Section XI Service Level D flaw size, but a best-estimate fracture analysis uses more realistic material properties and more accurate fracture analyses than the ASME Code.

In this paper, the TBS flaw size was calculated by the Draft Regulatory Guide approach for the Atucha II nuclear plant in Argentina that is about to start up. Additionally a full 3D FE model of the plant including the whole NSSS, containment building, and supports between the building and the NSSS components was developed. Circumferential surface cracks were put in the nonlinear time-history FE model at the highest stressed locations in the primary pipe loop to determine the depth of the flaw that would fail at the 1e−6 seismic excitation to the plant building. This was done to assess the margins in the flaw size for the TBS analysis, and also characterize the magnitude of the LOCA.

Where the TBS simplified model showed that a surface flaw of 0.709 and 0.669 of the thickness for the RPV/hot-leg and pump/cold-leg (respectively) and 270-degrees around the circumference could be tolerated, the full 3D FE analysis showed that even a surface crack of 90-percent of the thickness and 270-degrees around the circumference would not reach crack initiation for the material used in this plant with its seismic hazard curve. The information developed here may also be useful for assessing the piping integrity of a plant once it has exceeded the Service Level D limits of the ASME Code.
Development of Structural Codes for JSFR Based on the System Based Code Concept
Authors: Asayama Tai , Wakai Takashi , Ando Masanori , Okajima Satoshi , Nagae Yuji , Takaya Shigeru , Onizawa Takashi , Tsukimori Kazuyuki , Morishita Masaki
Published: November 2014

This paper overviews the current status of the ongoing research and development as well as activities for codification of structural codes for the Japan Sodium Cooled Fast Reactor (JSFR), the demonstration fast reactor which is in the phase of conceptual study. Not only the design and construction code which has been published and updated on a regular basis, codes on welding, fitness-for-service, leak-before-break evaluation as well as the guidelines for structural reliability evaluation are being developed. The basic strategy for the development is to fully take advantage of the favorable technical characteristics associated with sodium-cooled fast reactors; the codes will be developed based on the System Based Code concept, a concept that materializes code rules that are most suitable to the reactor types they are applied to. The above mentioned set of codes are planned to be published from the Japan Society of Mechanical Engineers in 2016.
Investigation on Restraint Capability of Pipe Support Used as Anchor in Piping System
Authors: Sodeyama Hiroshi , Mizuma Hiroyuki , Nakatsu Masanobu
Published: November 2014

The authors have developed a new pipe support, which is intended for use as an anchor of piping system in power plants. This anchor type support takes a pipe between two-tiered metal blocks and ideally restraints the pipe movement with six degrees of freedom, namely all directions of the piping movement. The four bolts adequately join the two-tiered metal block of the anchor type support with the pipe that is not subjected to unnecessary stress. The internal shape of the two-tiered metal block is designed to stabilize the pipe firmly by increasing area of contact between the pipe and the support. Developing the four-point support design for the internal shape of the blocks has also reduced the stress on the pipe. The restraint forces and restraint moments of the support have been investigated and the verification testing has been conducted for the restraining capability. The relaxation of the bolted joint over time and thermal influence on the relaxation has been also studied experimentally. Since no welding operation on the pipe is required for installation of this anchor support, reduction of time and labor is expected for both a combination of planning and construction of an anchor on piping system.
High Temperature Dynamics Strain Hardening Behavior in Stainless Steels and Nickel Alloys
Authors: Yu Xinghua , Qiao Dongxiao , Feng Zhili , Crooker Paul , Wang Yanli
Published: November 2014

Primary water stress corrosion cracking (PWSCC) is a major materials challenge for dissimilar metal welds (DMW) in pressurized water reactors. The reliability of structure integrity assessment of DMW is strongly dependent on the reliable determination of the weld residual stress (WRS) field, which is one of the primary driving forces for PWSCC. Recent studies have shown that WRS prediction using today’s DMW WRS models strongly depends upon the choice of strain-hardening constitutive model. The commonly used strain hardening models (isotropic, kinematic, and mixed) are all time-independent ones that are inadequate to accounting for the time-dependent (viscous) plastic deformation at the elevated temperatures during welding. Recently, a dynamics strain hardening constitutive model has been proposed and the application of such a model has resulted in improved WRS prediction when compared to the WRS measurement results by contour method and deep-hole drilling method. In this study, the dynamic strain hardening behavior, under uniaxial tensile loading conditions, of several stainless steels and nickel alloys (SS304, Alloy 600, Alloy 82 and Alloy 52) commonly used in pressure vessel nozzle DMW are experimentally determined and compared. The extent of softening due to different duration of high-temperature exposure is studied and its influence on final residual stresses is discussed. An empirical correlation combining both the time and temperature effects on dynamic strain hardening is proposed for weld residual stress modeling.
Equilibrium Mechanism Based Curve Fitting and Data Smoothing Methods for Data With Single and Multiple Failure Mechanisms
Authors: Wei Zhigang , Nikbin Kamran
Published: November 2014

A recently developed equilibrium mechanism based linear curve/surface fitting method is extended for data with nonlinear characteristics. The concept of k-th order equilibrium ‘moment’ is proposed to derive curve fitting formulae for k-th order polynomial functions. An approach based on the equilibrium concept is also proposed for data smoothing with k-th order polynomial functions, and it is found that the formulae derived are exactly the same as the well-known Savitzky-Golay filter algorithm for smoothing and differentiation. Data pattern identification and characterization are emphasized in this paper for accurate linear and nonlinear data processing. Several examples are provided to demonstrate the developed concepts and procedures for test data with single and multiple underlying failure mechanisms or modes: fatigue crack growth rate under mixed-mode loading, stress-corrosion-cracking, corrosion-fatigue life, thermal-fatigue and creep-fatigue data. A curve fit procedure is also introduced for the creep-fatigue data with a specific data pattern.
An Assessment of Branch Technical Position 5-3 to Determine Unirradiated RTNDT for SA-508 Cl. 2 Forgings
Authors: Troyer Greg , DeVan Matthew
Published: November 2014

10 CFR 50.61 and 10 CFR 50, Appendix G require the evaluation of the unirradiated nil ductility transition reference temperature (RTNDT) determined in accordance with ASME Section III, paragraph NB-2331. For extended operation, components outside of the traditional beltline may require evaluation of RTNDT per NB-2331. Many of these components do not have sufficient test data to determine RTNDT in accordance with NB-2331 due to different test requirements during fabrication. The US NRC has provided methods in Branch Technical Position (BTP) 5-3 of NUREG 0800 to estimate a bounding RTNDT for these components using available test data. This paper compares Branch Technical Position 5-3, paragraph 1.1(4) estimates of RTNDT using 10°F Charpy V-notch data to the ASME B&PV Section III, Paragraph NB-2331 values of RTNDT, for a sample of 35 SA-508 Cl. 2 reactor vessel shell forgings. The BTP 5-3, Paragraph 1.1(4) estimates underestimate NB-2331 values by an average of 13.8°F and by as much as 40°F. This non-conservatism is attributed to the use of 10°F Charpy V-notch data for the BTP 5-3, paragraph 1.1(4) estimate and the difficulty of using only Charpy V-notch data to estimate a parameter based on Charpy V-notch and dropweight data. If BTP 5-3, paragraph 1.1(4) estimates for RTNDT are to be used in 10 CFR 50.61 and 10 CFR 50 Appendix G calculations, the bias and measurement uncertainty of BTP 5-3, paragraph 1.1(4) should be accounted for, such that the estimate of RTNDT bounds the NB-2331 RTNDT with 2σ confidence, as shown in Regulatory Guide 1.99, Revision 2.
Probabilistic Seismic Hazard Assessment in Countries With Low Seismicity
Authors: Demjancukova Katerina , Prochazkova Dana
Published: November 2014

The region of the Czech Republic is mostly composed of the Bohemian Massif which is considered as a geological unit with low seismic activity. Nevertheless, all critical objects as the nuclear power plants, big dams etc. are built as aseismic structures. The nuclear installations have to satisfy the IAEA safety standards and requirements. One of important phenomena that have to be involved in the PSHA process is the diffuse seismicity.

In 2010 International Atomic Energy Agency issued a specific safety guide SSG-9 Seismic Hazards in Site Evaluation for Nuclear Installations. The key chapters are focused on general recommendations, necessary information and investigations (database), construction of a regional seismotectonic model, evaluation of the ground motion hazard, probabilistic seismic hazards analysis (PSHA), deterministic seismic hazards analysis, potential for fault displacement at the site, design basis ground motion, fault displacement and other hazards, evaluation of seismic hazards for nuclear installations other than NPPs.

In the paper a numerical example of seismic hazard assessment will be presented with emphasis on problems and particularities related to PSHA in countries with low seismic activity.
The Assessment for a New Pressure-Relief Structure in Non-Refillable Steel Welded Industry Cylinder
Authors: Jin Weiya , Li Yuebing , Gao Zengliang
Published: November 2014

The performance of a new pressure-relief structure in non-refillable steel welded industry cylinder is evaluated. Instead of a rupture disc welded on the opening of the head, this new pressure-relief structure uses a circular groove which is pressed by a special mold on the dished head. This structure not only avoids opening on the head but also reduces the manufacture cost. To ensure the safety of this pressure-relief structure, the study includes the material tests, tensile tests, hardness tests and burst tests, the limited pressure prediction are carried on. Based on the experimental data and finite element analysis results, an empirical correlation between the limited pressure and the groove pressure is proposed. Furthermore, a probabilistic analysis is performed for the limited pressure.
Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities: Part 11 — Improvement of the Seismic Isolator Design Method
Authors: Aikawa Yuji , Hibino Hiroshi , Takeuchi Yoshitaka , Asahara Shingo , Hirai Hideo , Kosugi Shinji , Matsuoka Shinji , Umeki Yoshito
Published: November 2014

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows improvements of seismic isolator design method applied to nuclear power facilities. The proposed improvement design methods consist of the following two items.

One is an improvement of design method for axial stress in a laminated rubber bearing. Largely different natural frequency in vertical and horizontal direction of the seismic isolator may need a special consideration to combine the design seismic loads in different directions. Therefore isolator’s behavior under multiple direction earthquake is studied, and an improved design method is proposed in the axial stress in a laminated rubber bearing.

The other is a reasonable design method for seismic isolator joints. A seismic isolator joint is considered to be one of the key factors for assuring seismic integrity of the seismic isolation system for nuclear power facilities. As a series of design method of seismic isolators, evaluation method of axial force of anchor bolts, among various parts of joints, under design level seismic load is studied and improved method is proposed to confirm the structural behavior for a better performance of the system.
Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities: Part 8 — Fundamental Properties of Full-Scale Lead Rubber Bearings Based on Breaking Test
Authors: Sato Nobuhisa , Nakayama Takashi , Kaneko Takashi , Nagata Seiji , Imaoka Tetsuo , Kurihara Keisuke , Hirai Hideo , Mizutani Ko , Umeki Yoshito
Published: November 2014

This paper provides a part of the series “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities.” This part shows the fundamental properties of full-scale lead rubber bearings with 1600 mm diameter based on break tests. The following results are mainly obtained.

One: The deformations and the acting loads of the full-scale specimens were accurately obtained up to break by the measurement system for the break tests.

Two: The fundamental properties for the full-scale lead rubber bearings with a large-diameter lead plug were obtained by the basic property tests. The load-displacement relations were stable and similar basic properties were obtained among the specimens.

Three: The result of shear break tests showed that the hardening property of the specimens had a certain harmony with the hardening stiffness model which was used in the seismic response analysis to investigate the safety margin for severe earthquakes beyond design basis earthquakes of nuclear power facilities. The effect of axial pressure on hardening property was not specifically observed. The evaluated linear strain limit was larger than 250% for every specimen.

Four: The softening property of the specimens was obtained from the tensile break tests. The axial stress of tensile yield was approx. 1.4 MPa and the axial stress did not show any negative gradient at least up to approx. 10% axial strain after the tensile yield even with offset shear strains.

Five: The tensile force acting on the bolts which secure the specimen to the testing machine was lower than the estimated tensile force at shear break, which indicates tensile force was conservatively calculated to maintain safety in the design for foundation of lead rubber bearings.
SILER Project: Design of the Seismic Isolators
Authors: Poggianti Alessandro , Forni Massimo , Ferrucci Barbara , Scipinotti Riccardo , De Bruyn Didier , Yoo Bong , De Grandis Silvia , Castellano Maria Gabriella , Dusi Alberto , Manzoni Elena
Published: November 2014

This paper describes the SILER (Seismic-Initiated event risk mitigation in LEad-cooled Reactors) Project results obtained so far in the design of the seismic isolation system of two nuclear power plants: the ELSY configuration for the LFR (Lead-Cooled Fast Reactor) design and the MYRRHA configuration for the accelerator-driven systems (ADS).

The seismic protection of the nuclear buildings by means of seismic isolation has been chosen in order to minimize changes to the standard design of the civil works and internal components of the Nuclear Power Plant. The work led to the identification of the optimal design solution, in terms of type and location of seismic devices, to achieve compliance to the floor response acceleration spectra in horizontal and vertical direction, with levels of horizontal displacements not exceeding the maximum acceptable values for structural and non-structural elements.

The isolators studied in the project are of the type elastomeric, both High Damping Rubber Bearings and Lead Rubber Bearings; moreover the adoption of a fail-safe system to limit the horizontal isolator deformation in case of beyond design earthquakes is studied.
Creep Analysis of Hemisphere Shell Structure Under High Temperature Gradient
Authors: Zhu Jianwei , Bao Shiyi , Li Yuebing , Gao Zengliang
Published: November 2014

The In-Vessel Retention (IVR) of molten core debris has been part of the severe accident management strategy for advanced pressurized water reactor (PWR) plant. Generally, the pressure is supposed to successfully be released, and the externally cooled lower head wall mainly experiences the temperature difference which may be more than 1000°C. However, the Fukushima accident shows that a certain pressure (up to 8.0MPa) still exists inside the reactor pressure vessel (RPV). Therefore, in order to make the IVR succeed, it is necessary to investigate the structural integrity of the RPV under the combined internal pressure and the thermal load on the lower head.

Therefore, it is supposed that the lower head of RPV is a Hemisphere Shell Structure (HSS) with 2150mm external radius and 25mm wall thickness. Similarly, the outer wall temperature is supposed to be 127°C, the wall temperature difference 1200°C, and the material properties (i.e., thermal conductivity, specific heat capacity, yield strength, and so on) are dependent on the temperature. In this paper, the main subjects discussed are as below.

First, the heat transfer analysis is carried out to obtain the temperature distribution of the HSS wall. Due to the high temperature gradient, there may present different failure modes along the HSS wall thickness, i.e., plastic failure and creep failure. Then, the stress and strain distributions along the wall thickness are analyzed by ANSYS finite element method where the Norton-Bailey type creep law is adopted. The result shows that the stress in the lower temperature part (LTP) whose temperature is lower than 405°C is lower than the yield stress of the material with the corresponding temperature. That is to say, the LTP still can bear a certain internal pressure. At last, to consider the combined impact of internal pressure and temperature difference on the HSS, the finite element analysis is carried out by adopting the isochronous stress-strain curves of the Chinese RPV material. The relationship between the stress in the LTP at 100 hours and the internal pressure is discussed, and the limit internal pressure is determined. It is concluded that HSS still can maintain its integrity under IVR, even if there exists a certain internal pressure.
License Renewal Environmental Fatigue Screening Application
Authors: Kupper Christopher T. , Gray Mark A.
Published: November 2014

In NUREG-1801 (GALL) Revision 0 and Revision 1, the US Nuclear Regulatory Commission (NRC) defined the locations evaluated in NUREG/CR-6260 as a minimum acceptable set for evaluation of environmentally assisted fatigue (EAF), in addressing license renewal for nuclear plant components. Within GALL Revision 2, the NRC revised the expectation, so that plants also investigate the possibility of other locations being more limiting. To address GALL Revision 2 and NUREG-1800 Revision 2, an EAF screening methodology was developed that considers all Safety Class 1 reactor coolant pressure boundary components in major equipment and piping systems that are susceptible to EAF, including those locations listed in NUREG/CR-6260. While the overall screening process steps are similar to those published by EPRI, elements of the detailed application of some steps were performed using alternative techniques. The screening process utilized the comprehensive database of plant component fatigue qualifications available in NSSS vendor documentation, and yielded a comprehensive list of lead indicator locations for EAF consideration. This paper describes the overall process and alternate methods in the context of a specific plant license renewal application.
Evaluation of Constraint Effect on Creep Crack Growth by Advanced Creep Modeling and Damage Mechanics
Authors: Dichiaro Simone , Esposito Luca , Bonora Nicola
Published: November 2014

Effects of constraint induced by crack depth and sample geometry on creep crack behavior of high chromium steels was investigated by numerical simulation. An advanced mechanism-based creep model formulation, which accounts for primary and secondary creep stage was used. Here, the transient creep rate is modeled considering the evolution of the internal stress with the activation energy while the steady state creep rate is modelled considering both diffusional and dislocation creep mechanisms. This formulation allows one to predict accurately creep strain accumulation over a wide range of stress and temperature. Model parameters were identified on constant load creep tests and their transferability to the multiaxial state of stress was verified comparing predicted creep life with data obtained on notched bar samples. Continuum damage mechanics was used to predict the occurrence of tertiary creep stage and crack advance. To this purpose, a non-linear damage law, as proposed in Bonora and Esposito [1] was used. The effect of the geometry constrain on creep crack growth was investigated in different sample geometries (C(T), SEN(T), SEN(B), DEN(T) and CCP(T)) for a given crack depth values, and the same biaxiality ratio for SEN(T), SEN(B) and DEN(T). Numerical simulation results were validated by comparison with available experimental data for P91 steels.
Effect of Reflection Waves on Water Hammer Loads
Authors: Rovagnati Beniamino , Gray John H.
Published: November 2014

In power plants, engineering analysis is used to design piping systems for steam and water hammer events. A simple and effective approach based on hand calculation was proposed by E.C. Goodling1 which has been widely used in the industry to estimate fluid loads for pipe stress analysis and design of piping restraints. His approach provides a conceptual understanding of many factors that control fluid loads, which can be used both to perform approximate checks of more detailed computer solutions, and to identify parameters that can be changed to optimize system designs. In Goodling’s work, the possibility of reflection waves affecting fluid loading is mentioned. However, this effect was not explored and is often neglected when simple hand estimates of fluid loads are made. This paper looks at the effects reflection waves from pressure vessels or large headers may have on steam/ water hammer loads. A few sample problems are solved with the aid of a Method of Characteristic (MOC) computer program and compared to solutions found using the Goodling approach. It is shown that neglecting reflection waves may lead to non-conservative loads (by up to a factor of two). The effects of other critical parameters (e.g., pressure pulse rise rate) are also discussed.
Etching of Ag and Au films in CH4-based plasmas at low temperature
Authors: Choi Tae-Seop , Hess Dennis W.
Published: November 2014

Plasma-assisted Ag and Au subtractive etching was investigated in CH4 plasmas at 10 °C. The etch rate of Ag (29 ± 2 nm/min) was higher than that observed for Cu (17 nm/min), while the Au etch rate (12 nm/min) was lower than that for both Ag and Cu. Etch rates of Ag and Au due to pressure variation decreased as pressure increased, analogous to Cu etch results. However, the specific plasma conditions under which hydrocarbon formation occurred on Cu, Ag, and Au depended upon the metal being etched as a result of variation in surface chemical reactivities. Comparison of etch results using glass slides and Si wafers as etch masks, confirmed the formation of volatile etch products for Cu and Au. Etch product removal for Au and Cu was enhanced by UV photons, while Ag etching showed no effect at wavelengths > 300 nm. These studies demonstrated that in CH4 plasmas, chemical components in the etch process are most important for Cu while Ag and Au etching is more dependent upon physical sputtering.
Training Periodization of Professional Australian Football Players During an Entire Australian Football League Season
Authors: Moreira Alexandre , Bilsborough Johann C. , Sullivan Courtney J. , Cianciosi Michael , Aoki Marcelo Saldanha , Coutts Aaron J.
Published: November 2014

Purpose:

To examine the training periodization of an elite Australian Football team during different phases of the season.

Methods:

Training-load data were collected during 22 wk of preseason and 23 wk of in-season training. Training load was measured using the session rating of perceived exertion (session-RPE) for all training sessions and matches from 44 professional Australian Football players from the same team. Training intensity was divided into 3 zones based on session-RPE (low, <4; moderate, >4 AU and <7 AU; and high, >7 AU). Training load and intensity were analyzed according to the type of training session completed.

Results:

Higher training load and session duration were undertaken for all types of training sessions during the preseason than in-season (P < .05), with the exception of “other” training (ie, re/prehabilitation training, cross-training, and recovery activities). Training load and intensity were higher during the preseason, with the exception of games, where greater load and intensity were observed during the in-season. The overall distribution of training intensity was similar between phases with the majority of training performed at moderate or high intensity.

Conclusions:

The current findings may allow coaches and scientists to better understand the characteristics of Australian Football periodization, which in turn may aid in developing optimal training programs. The results also indicate that a polarized training-intensity distribution that has been reported in elite endurance athletes does not occur in professional Australian Football.
The Blood-Brain Barrier’s Gut Check
Authors: Bien-Ly Nga , Watts Ryan J.
Published: November 2014

The gut microbiota may influence blood-brain barrier permeability during embryonic development, and this effect may be maintained into adulthood.
Structural Variations of the Cell Wall Precursor Lipid II and Their Influence on Binding and Activity of the Lipoglycopeptide Antibiotic Oritavancin
Authors: Münch Daniela , Engels Ina , Müller Anna , Reder-Christ Katrin , Falkenstein-Paul Hildegard , Bierbaum Gabriele , Grein Fabian , Bendas Gerd , Sahl Hans-Georg , Schneider Tanja
Published: November 2014

Oritavancin is a semisynthetic derivative of the glycopeptide antibiotic chloroeremomycin with activity against Gram-positive pathogens, including vancomycin-resistant staphylococci and enterococci. Compared to vancomycin, oritavancin is characterized by the presence of two additional residues, a hydrophobic 4′-chlorobiphenyl methyl moiety and a 4-epi-vancosamine substituent, which is also present in chloroeremomycin. Here, we show that oritavancin and its des-
N
-methylleucyl variant (des-oritavancin) effectively inhibit lipid I- and lipid II-consuming peptidoglycan biosynthesis reactions
in vitro
. In contrast to that for vancomycin, the binding affinity of oritavancin to the cell wall precursor lipid II appears to involve, in addition to the
d
-Ala-
d
-Ala terminus, other species-specific binding sites of the lipid II molecule, i.e., the crossbridge and
d
-isoglutamine in position 2 of the lipid II stem peptide, both characteristic for a number of Gram-positive pathogens, including staphylococci and enterococci. Using purified lipid II and modified lipid II variants, we studied the impact of these modifications on the binding of oritavancin and compared it to those of vancomycin, chloroeremomycin, and des-oritavancin. Analysis of the binding parameters revealed that additional intramolecular interactions of oritavancin with the peptidoglycan precursor appear to compensate for the loss of a crucial hydrogen bond in vancomycin-resistant strains, resulting in enhanced binding affinity. Augmenting previous findings, we show that amidation of the lipid II stem peptide predominantly accounts for the increased binding of oritavancin to the modified intermediates ending in
d
-Ala-
d
-Lac. Corroborating our conclusions, we further provide biochemical evidence for the phenomenon of the antagonistic effects of
mecA
and
vanA
resistance determinants in
Staphylococcus aureus
, thus partially explaining the low frequency of methicillin-resistant
S. aureus
(MRSA) acquiring high-level vancomycin resistance.
Correlation betweenIn VitroComplement Deposition and Passive Mouse Protection of Anti-Pneumococcal Surface Protein A Monoclonal Antibodies
Authors: Khan Naeem , Qadri Raies Ahmad , Sehgal Devinder
Published: November 2014

The shortcomings of the licensed polysaccharide-based pneumococcal vaccine are driving efforts toward development of a protein-based vaccine that is serotype independent and effective in all age groups. An opsonophagocytic killing assay (OPKA) is used to evaluate the antibody response against polysaccharide-based pneumococcal vaccines. However, the OPKA is not reliable for noncapsular antigens. Thus, there is a need to develop anin vitrosurrogate for protection for protein vaccine candidates like pneumococcal surface antigen A (PspA). PspA is a serologically variable cell surface virulence factor. Based on its sequence, PspA has been classified into families 1 (clade 1 and 2), 2 (clades 3, 4 and 5), and 3 (clade 6). Here, we report the characterization of 18 IgG anti-PspA monoclonal antibodies (anti-PspAhkR36AMAbs) generated from mice immunized with heat-killed strain R36A (clade 2). An enzyme-linked immunosorbent assay (ELISA)-based analysis of the reactivity of the MAbs with recombinant PspAs from the 6 clades indicated that they were family 1 specific. This was confirmed by flow cytometry using a hyperimmune serum generated against PspA from R36A. Eight MAbs that bind at least one clade 1- and clade 2-expressing strain were evaluated for complement deposition, bactericidal activity, and passive protection. The anti-PspAhkR36AMAb-dependent deposition of complement on pneumococci showed a positive correlation with passive protection against strain WU2 (r= 0.8783,P= 0.0041). All of our protective MAbs showed bactericidal activity; however, not all MAbs that exhibited bactericidal activity conferred protectionin vivo. The protective MAbs described here can be used to identify conserved protection eliciting B cell epitopes for engineering a superior PspA-based vaccine.