bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Axial Thermal Expansion for a 1000MW Nuclear Steam Turbine HIP Casing
Authors: Mei Ziyue , Zhang Hengliang , Xie Danmei , Guo Yanan , Hou Xiuqun , Xiong Yangheng
Published: October 2017

Steam turbine casing axial thermal expansion is of great significance to the safe operation for nuclear units.

Taking a certain 1000MW nuclear steam turbine’s HIP casing as an object, this paper calculates the HIP casing absolute axial thermal expansions under such conditions as: steady-state, startup and load shedding.

Firstly, a 3D model of the nuclear steam turbine HIP casing is this established by using Pro/E software. Secondly, the heat transfer coefficients of every surface of HIP casing are calculated. Finally, the HIP casing temperature field and the absolute axial thermal expansions under three conditions are calculated and analyzed by using finite element analysis software.

The result shows that, the HIP casing axial thermal expansions are 22.642mm and 22.529mm under steady-state condition and startup condition respectively. While, under load shedding condition, minimum axial expansion is 16.202mm and it increases to 22.491mm at rated load.
Fracture Mechanics Analysis of Clad Subsea Equipment in Sour HPHT Conditions
Authors: Holtam Colum , Saraswat Rajil , Thodla Ramgopal
Published: October 2017

High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. This paper presents the results of a fatigue based fracture mechanics assessment case study conducted on a fully clad subsea HPHT component. The component was assumed to be constructed from F22 low alloy steel internally clad with alloy 625 and exposed to 20ksi (137.8MPa) and 400°F (204°C) internal pressure and temperature.

A number of different assessment methods were evaluated as part of this study, including standard failure assessment diagram (FAD) based assessment methods, such as those found in API 579-1/ASME FFS-1 and BS 7910, as well as finite element (i.e. crack mesh) methods.

A detailed description of the finite element analysis (FEA) of the uncracked and cracked component is provided. An internal surface flaw assumed to be exposed to sour production fluids was evaluated. The results of the fatigue and fracture assessments are summarized along with the key differences between the assessment methods adopted. The sensitivity of the assessment results to other variables such as welding residual stresses is also discussed.
A Fracture Mechanics-Based Approach to Establish Minimum Pressurization Temperature Envelopes
Authors: Prueter Phillip E. , Kummari Seetha Ramudu , Osage David A.
Published: October 2017

Preventing brittle fracture is an essential part of instituting life-cycle management strategies for fixed pressure equipment. Using fracture mechanics principles to establish permissible minimum pressurization temperature (MPT) envelopes for components is one way to mitigate the potential for unstable flaw growth. In the refining industry, heavy-walled, low-alloy hydroprocessing reactors are designed to operate at elevated temperatures and high hydrogen partial pressures. Components that operate in high-pressure hydrogen environments require special treatment and necessitate guidance that falls outside the bounds of current pressure vessel construction codes. This operating environment results in two factors that affect the MPT envelope: long-term temper embrittlement and hydrogen embrittlement. Additionally, hydrogen charging can manifest damage in two ways: fast (brittle) fracture due to a reduction in fracture toughness and slow (subcritical) hydrogen-assisted crack growth. When developing a MPT envelope for a given component, both failure modes need to be considered in addition to residual stress effects from weld overlay or cladding. MPT envelopes provide insight into the permissible pressure-temperature combinations for specific locations and for chosen reference flaw sizes. From a reliability standpoint, understanding the risk of brittle fracture associated with heavy-walled reactors for all operating scenarios is crucial. Furthermore, taking the appropriate life-cycle management steps, such as establishing MPT envelopes, coupling MPT analysis predictions with targeted inspection, optimizing process operating conditions, and developing a flaw acceptance criteria to mitigate the risk of crack propagation and ultimately, brittle fracture is essential.

In this study, a fracture-mechanics based methodology is summarized that is fully documented in upcoming Welding Research Council (WRC) Bulletin 562 [1] to determine MPT envelopes for all components (in any service environment) based on fast fracture with supplemental MPT requirements based on slow fracture for equipment that operates in high-pressure hydrogen environments. Finally, a finite element analysis-based case study of a 2-1/4-Cr-1-Mo hydrotreater reactor is summarized and practical life cycle-management guidance is offered based on analysis results. This example highlights how evaluation of start-up and shut-down procedures for heavy-walled reactors has the potential to save significant time and related cost per unit shut-down cycle, while maintaining an acceptable risk tolerance against subcritical crack growth and brittle fracture.
Investigation of Smooth Pipe Bends Under the Effect of In-Plane Bending
Authors: Abdulhameed Diana , Martens Michael , Cheng J. J. Roger , Adeeb Samer
Published: October 2017

Pipe bends are frequently used to change the direction in pipeline systems and they are considered one of the critical components as well. Bending moments acting on the pipe bends result from the surrounding environment, such as thermal expansions, soil deformations, and external loads. As a result of these bending moments, the initially circular cross-section of the pipe bend deforms into an oval shape. This consequently changes the pipe bend’s flexibility leading to higher stresses compared to straight pipes. Past studies considered the case of a closing in-plane bending moment on 90-degree pipe bends and proposed factors that account for the increased flexibility and high-stress levels. These factors are currently presented in the design codes and known as the flexibility and stress intensification factors (SIF). This paper covers the behaviour of an initially circular cross-sectional smooth pipe bend of uniform thickness subjected to in-plane opening/closing bending moment. ABAQUS FEA software is used in this study to model pipe bends with different nominal pipe sizes, bend angles, and various bend radius to cross-sectional pipe radius ratios. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the currently used SIF factor presented in the design code for different loading cases. The study showed that the in-plane bending moment direction acting on the pipe has a significant effect on the stress distribution and the flexibility of the pipe bend. The variation of bend angle and bend radius showed that it affects the maximum stress drastically and should be considered as a parameter in the flexibility and SIF factors. Moreover, the CSA results are found to be un-conservative in some cases depending on the bend angle and direction of the applied bending moment.
Susceptibility of Carbon Steel Pipe, Fittings and Flanges to Brittle Fracture
Authors: Messer Barry , Soltaninia Shahab , Hamre Ted
Published: October 2017

Brittle fractures in parent material carbon steel pipe, fittings, and flanges are surfacing in recent ASME B31.3 refinery and gas plant construction and facility start-ups with unexpected low toughness of 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −10°C (14°F) to −29°C (−20°F). The issue is becoming wide-spread globally, affecting up to 30 percent of materials tested, although many manufacturers are not experiencing this issue. The issue creates a new brittle fracture risk that needs to be addressed as the uncertainty of not knowing suitability for service at temperatures down to −29°C (−20°F) is concerning for reliability and safety.

These components are considered by ASME VIII Div I and ASME B31.3 Code as being inherently ductile, and brittle fracture resistant without any Charpy impact testing requirements. Testing showed brittle transgranular cleavage cracks. The components were deemed to be unsuitable and not safe for use at low temperatures even though they complied with the applicable ASME Codes [1, 2] and ASTM material standards. Low toughness can result in brittle fracture of the material during hydrostatic tests, cold start-ups, or upset conditions that result in low temperature operations. Additionally, some ASTM A350 LF2 CL1 [3] forged flanges certified to −46°C (−50°F) exhibited the same 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −46°C (−50°F).

This paper discusses historical literature, metallurgical investigations, findings, and factors that contribute to susceptibility to brittle fracture including chemistry, grain size, heat treatment and forming techniques and also issues of ductile to brittle temperature transition shift, and fracture mechanical assumptions. This paper provides guidance to ensure the components are suitable for service and proposes options in addition to the current minimum Codes requirements to mitigate risks of in-service brittle fracture.
Creep-Fatigue Damage Evaluation of Modified Grade 91 Headers Using Damage Coupled Unified Viscoplastic Model
Authors: Islam Nazrul , Dewees David J. , Cooch Michael , Hassan Tasnim
Published: October 2017

A case study for life prediction of Grade 91 heat recovery steam generator (HRSG) superheater outlet header of typical combined cycle power plants (CCPP) is presented in this paper. The effect of high cycling and fast startup along with elevated design temperature and pressure on the creep life is studied. A consistent material model based on MPC Omega is used to evaluate the creep damage of HRSG header components. In addition, a robust unified constitutive model (UCM) based on continuum damage mechanics (CDM) (see [1]) is used for creep-fatigue damage evaluation of the header components. The performance of the UCM is compared against creep and damage focused models in predicting the life of HRSG header components subjected to steady operation condition with low cycle fatigue scenario.
Use of Mini-CT Specimens for Fracture Toughness Characterization of Low Upper-Shelf Linde 80 Weld
Authors: Sokolov Mikhail A.
Published: October 2017

Any fracture toughness specimen that can be made out of the broken halves of standard Charpy specimens may have exceptional utility for evaluation of reactor pressure vessels since it would allow one to determine and monitor directly actual fracture toughness instead of requiring indirect predictions using correlations established with impact data. The Charpy V-notch specimen is the most commonly used specimen geometry in surveillance programs and most likely to be used in advanced reactors as per ASME code. The advantage of the Mini-CT specimen technique is that multiple specimens can be machined from one half of a broken Charpy specimen, used in a standard surveillance capsule of a reactor pressure vessel. Up to now, most of the work on validation of this type of the specimens has been performed on base metal. In this study, Mini-CT specimens were used to perform fracture toughness characterization of low upper-shelf Linde 80 weld, designated WF-70. This weld was utilized in the Midland beltline weld and has been previously well characterized at ORNL with various types and sizes of fracture toughness specimens. The Mini-CT specimens were machined from broken previously tested Charpy V-notch specimens. Despite very small size and relatively small number of Mini-CT specimen tested, the transition fracture toughness temperature, To, derived from these Mini-CT specimens is in very good correspondence with To reported from analysis of a large number of larger fracture toughness specimens.
Numerical and Experimental Research on Pipeline Magnetic Flux Leakage Testing With Inspection Device of Variable Diameters
Authors: Yanlei Liu , Hong Wang , Xiangyue Yang , Chengdai He , Xinhua Wei , Tao Chen , Xiaoling Liao
Published: October 2017

Finite element analysis model of magnetic flux leakage testing outside pipeline was established with analysis software in this paper. The leakage magnetic field characteristic curves of defects were obtained using this model. Also, the simulation on different diameter and depth of the cylindrical defects was carried out. And influence on flux leakage field, such as depth of defects corrosion defects was gotten. Then, detection device which can do inspection on pipeline with different diameters was manufactured based on the theory and finite element calculation results. The experiments with this device were carried out on the wall thickness of 8 mm and 6 mm pipeline with artificial defects above or under. And the results showed good agreement with simulation which meets engineering application of pipeline inspection.
Comparative Creep Life Evaluation of HR3C Using Creep Damage Models
Authors: Kang Seok-Jun , Lee Hoomin , Kim Moon-Ki , Choi Jae-Boong
Published: October 2017

Recently, due to both environmental and energy efficiency, the designed life cycle of many power plant have been extended and also their operating temperature increased. When a material is exposed to high temperature over 50% of its melting temperature, it often shows unusual creep behavior in which the long time exposure of high temperature causes a microstructural degradation in the material and leads to creep rupture at a stress much lower than yield. Thus, there is a great significance in evaluating the creep life of high temperature components in power plant. In this study, accelerated uniaxial creep tests have been conducted to obtain material properties of HR3C at high temperature.

The material properties of three damage models were derived from the accelerated short term creep tests in different stress conditions and the constitutive equation was the form of a power-law for the Kachanov and Liu-Murakami damage models and a hyperbolic sine function for the Dyson model, respectively. Based on these three damage models, the long term creep life was also evaluated. Using the creep rupture envelope, a modified grain boundary constrained cavitation coefficient function is proposed to resolve the constant failure strain problem. Also another modifications is made to the aging coefficient calculation by suggesting a new type of optimization function. By this, the classical problem of rupture time underestimation in the original Dyson model has been resolved. Consequently, the suggested creep life evaluation technique with a simple uniaxial creep example can be extended to more complicated engineering components at high temperature.
Recent Developments of Fracture Mechanics Tools for Nozzle Corners
Authors: Blouin Arnaud , Chapuliot Stéphane , Marie Stéphane , Jaubert André , Courtin Stephan
Published: October 2017

A recent effort was performed within AREVA-NP in order to develop and validate specific tools dedicated to the Fracture Mechanics Assessment of nozzle and penetration corners. This work is motivated by the need to perform accurate defect assessments for this geometry potentially submitted to a high level of stress. It includes:

• The development of a specific compendium for the calculation of the Stress Intensity Factor under various types of loading like internal pressure or cold thermal shocks;

• The evaluation of the effect of plasticity through simplified analytical schemes;

• The validation through the comparison to existing solutions.

One important target of those tools being the Fatigue Crack Growth evaluation under cyclic thermal shock loading situations, a validation of the fully analytical evaluation scheme was performed by a comparison to a complex 3D Finite Element Modelling of a defect propagating at a flange corner. This comparison is presented in the paper and illustrates the large benefit in terms of time and simplicity of the analytical scheme for such evaluation.
Large SA-508 Class 2 Nozzle Forging Near-Surface Fracture Toughness
Authors: Hall J. Brian , Mays Benjamin E. , DeVan Matthew
Published: October 2017

The current approach in evaluating the Pressurized Water Reactor (PWR) inlet and outlet nozzle corner regions with respect to plant heat-up and cool-down pressure-temperature limit curves contains a number of conservatisms. These conservatisms include postulation of a large ¼ thickness flaw at the nozzle corner region and use of RTNDT (reference nil-ductility temperature) or an estimation of RTNDT. The paper herein discusses generic fracture toughness of nozzle forging material SA-508 Class 2 for use with postulated smaller surface flaws in developing pressure-temperature limit curves for nozzle corners for nuclear power plant operations.

ASME Appendix G uses the lower bound KIC curve, which has inherent margin since RTNDT is a conservative method for locating the KIC curve. RTNDT is based on the drop weight test, which is a crack arrest transition temperature measurement, and the Charpy impact test, which is a blunt notch impact test. These data are conservatively bounded by the KIC curve, which is a lower bound crack initiation toughness curve. In contrast, the master curve method is based on an initiation transition temperature fracture toughness test technique per ASTM E1921. The master curve index temperature (T0) provides a more accurate measure of the material fracture toughness than KIC indexed with RTNDT. Since many of the nuclear pressure vessels were fabricated to ASME Code editions prior to 1972, RTNDT was not measured for the nozzles. In many cases, RTNDT has been estimated. Therefore, for this work, the fracture toughness was generically established based on conservative T0 measurements of 22 representative forgings with a margin of two standard deviations to ensure a conservative lower bound toughness using ASME Appendix G, G-2110.

The properties of a forging are better near the surface due to the faster cooling rate during heat treatment. The difference in reactor pressure vessel fracture toughness was established for forgings near the surface at the postulated flaw location as allowed by ASME Section III, NB-2223.2 relative to the traditional ¼ thickness location. The near-surface forging toughness was conservatively determined through evaluation of 31 near-surface and approximate ¼ thickness location fracture toughness measurements.
Leak Detection Assessment of a Through Wall Crack in a Circumferential Weld
Authors: Gill Peter , Madew Colin , Booth Steve
Published: October 2017

A leak detection assessment at a circumferential weld has been carried out to support a Leak-before-Break argument. This was performed using detailed finite element analysis (FEA) of the component to determine limiting defect sizes and crack opening areas. Leak rates of CO2 were then calculated and were found to be at an acceptable level.

The loading on the component were complex, including thermal, pressure and weld residual stresses. The thermal field originated from both a steady state operating condition and hold point during start up plant state. Computational Fluid Dynamics (CFD) was used to generate the thermal fields for this component and the crack was postulated to occur at the region of highest opening stress along the weld. In addition to the thermal field, the weld was also subjected to a residual stress, which was applied in the model via a novel application method that is described in the paper.

The FEA incorporated temperature dependent Ramberg-Osgood stress strain data that was generated from tensile data. For the limiting defect size calculation, lower bound material properties were used, and for the crack opening area, mean properties were used.

Various crack sizes were considered and J-integrals were calculated and compared against the material toughness of the weld. This enabled the calculation of a limiting defect size, and crack opening area, so that a leakage rate could then be calculated. Contour independence was observed for the J-integral evaluation giving confidence that the finite element meshes were fit for purpose.
Coupled Pump and Pipe System Analysis for Optimum Design of District Heating System
Authors: Jonsson Magnus Thor , Magnusdottir Lilja
Published: October 2017

This paper describes a novel approach for optimizing a district heating distribution network under various flow rate conditions. For district heating systems, the demand or the flow and pressure at each node varies over the time of year. The flow control that affects the operational cost can be based on the variable speed and the on/off control on serial pumping or pressure controlled valves. In the pipe system design, the topology, or the pipe layout, and the pipe diameter is optimized using genetic algorithms. Standardized methods are used for calculating the pipe thickness, supports, anchors and the thermal expansion loops. The interconnection between the pipe system and the pump station design is discussed. The objective is to minimize the total or life cycle cost (capital maintenance and operational cost), subject to ensuring demands or constraints at all points. The results are compared to classical methods where the pump station and the pipe system are designed separately and the improvements are discussed.

The problem is formulated by developing an objective function where the optimization parameters define the pump arrangement, pipe system topology, and pipe diameters. The pump station and pipe system optimization consist of selecting components from a pre-defined set of elements and is implemented with discrete decision variables. Optimization of pipe elements consists of optimizing the diameter, after the topology has been defined, and is implemented with discrete variables. Flow distribution and pressure analysis is performed. Thicknesses, pressure classes, supports, expansion loops and anchors are not part of the optimization parameters, but are determined during the evaluation of the objective function. Each time the objective function is evaluated, the pipe system is designed in a sub-optimization according to given loads. The pressure head constraints are used to design the pumping curves. The method is tested on a district heating system in Reykjavik, Iceland.
Experimental Study of the Dynamic Response of Partially Filled Pipes Focused on Natural Frequencies and Mode Shapes
Authors: de la Torre Oscar , Escaler Xavier , Goggins Jamie
Published: October 2017

The presence of air in piping systems is a major concern in the industry. Problems like flow disruption, reduction of hydraulic machinery efficiencies or a significant drop in pipe capacity are many times related to this fact. The present paper aims to find a simple and non-intrusive experimental method to detect air in piping systems. The method, based on the dynamic properties of fluid-structure systems and underpinned by a novel low computational cost numerical simulation, accurately predicts the volume of water present in a pipe. Good agreement between numerical and experimental solutions has been obtained using much less computational effort than traditional fully coupled Fluid Structure Interaction with CFD analysis. From the numerical and experimental data, two different mathematical expressions relating the system natural frequencies, both vertically and horizontally, and the area occupied by the water have been obtained. These expressions account for the pipe geometry which theoretically would make them suitable for other diameter and wall thickness values. The paper is combined with a preliminary study of the system’s mode shapes for the different volumes of water.
Acoustic Emission Entropy for Evaluation of Fracture Toughness of HSLA Steel Welded Joint
Authors: Chai Mengyu , Wu Weijie , Zhang Zaoxiao , Cheng Guangxu , Duan Quan
Published: October 2017

In this investigation, fracture toughness behavior of high strength low alloy (HSLA) steel welded joint was studied using acoustic emission (AE) monitoring. For the design of new structures and for the safety and reliability analyses of operating components, fracture toughness (KIC) values of materials play an essential role. Acoustic emission technique (AET) has been used for determination of fracture toughness based on some observable changes of AE evolutions. However, the occurrence of appreciable plasticity in materials, the friction between the crack surfaces and mechanical noise could generate high emission and may result in some difficulties in precise determination of fracture toughness. Thus, the objective of this study is to propose a new approach to evaluate fracture toughness values and to characterize the fracture process based on AE entropy. Specimens were selected from 2.25Cr-1Mo-0.25V steel welded joint which were thermally aged at 978 K for 8 h. The AE signals generated during fracture processes were recorded and the corresponding AE entropy was calculated based on the probability amplitude distribution from each original AE waveform. The point of crack initiation was identified by the occurrence of sudden rise of AE entropy and the corresponding critical load was used to estimate fracture toughness value. The estimated values obtained from the proposed new approach were compared with those determined by the methodology proposed by compact tension specimen testing according to ASTM standard E399. The results showed that the estimated values were in close agreement with those gained from ASTM standard. It was concluded that AE entropy was an effective parameter to estimate fracture characteristics and fracture toughness values.
Structural Health Monitoring for Conventional Power Plants: Solutions for Operational Challenges
Authors: Rudolph Jürgen , Bergholz Steffen
Published: October 2017

The load follow operation of thermal power plants in the context of the German “Energiewende” is a big challenge for those power plants. In this context TMF/SHM methods gain increasingly in importance. Most existing power plants do not actually work any more according to the load profile which was originally specified. Load monitoring with the potential of optimization of operational modes combined with highly qualified fatigue and creep-fatigue assessment modules is a central concern. A lot of new methods were developed for getting appropriate information about the structural health situation of loaded components and prevent premature damage. In this context, it is essential to process both design load data as well as information of the real operational load situation and combine this with a highly qualified assessment method based on the relevant design codes for conventional power plant components such as EN 12952-3 and EN 13445-3. In the case of thermal power plants both fatigue due to cyclic loading and creep due to high temperatures (and their combination) play an important role. Note that there is a change of dominating damage mechanisms and dominating damage locations (from creep towards low cycle fatigue) due to new (load follow) operating modes. This implies the qualified assessment of fatigue damage respectively combined creep-fatigue phenomena. Due to the detailed knowledge of stress histories, temperatures and the duration of hold times a best forecast can be given. A staged concept is envisaged consisting of a simplified estimation according to conventional design codes (EN 12952-3 / EN 13445-3) and a detailed solution based on the application of a non-linear material model.
Qualification of the Notch Stress Approach for the Fatigue Assessment of Welded Pressure Equipment and Power Plant Components
Authors: Rudolph Jürgen , Trieglaff Ralf , Stößlein René , Hauser Fabian
Published: October 2017

The fatigue assessment of welded joints in different engineering disciplines is usually based on nominal, structural or notch stresses on one hand (elastic concept using component fatigue curves of load controlled test data) and local strains on the other hand (elasto-plastic concept using material fatigue curves of strain-controlled push-pull test data of un-notched and polished standard specimens). The concepts of the first mentioned group are implemented in widespread standards and recommendations such as [1] to [3]. The fatigue assessment procedure of the European standard for unfired pressure vessels (EN 13445-3, Clause 17 & 18 and related annexes) [4] is currently under revision with one focus on the elaboration of user friendly fatigue assessment options for welded components [5]. The current state of the art focuses on the application of an adapted structural hot spot stress approach to the fatigue assessment of welded pressure equipment [5]. Although this is a significant step forward, the implementation of a notch stress approach can furtherly increase the fatigue assessment options by detailed weld seam analysis. The paper focuses on respective methodological proposals and application examples of typical welded joints. The finite element analysis as part of the procedure has to be harmonized with the requirements of the assessment procedure. Of course, the compatibility of the hot spot stress approach and a notch stress approach has to be guaranteed for individual examples. The direct comparison of the different approaches allows for a qualitative evaluation of methods. The application of an appropriate master fatigue curve FAT100 and the limitations with regard of stress/strain ranges in the low cycle fatigue (LCF) regime as well as the fatigue assessment of welded joints with mild weld toe notches is the subject of special considerations. The latest recommendations of German Welding Society (DVS) [6] constitute a reference for the last two subjects raised.
Numerical Simulation of Tornado Missile Impact on Steel Stack
Authors: Antaki George , Gilada Ramiz , Pease Derrick
Published: October 2017

This paper describes the methods and criteria for the numerical analysis of damage caused by tornado missiles to steel stacks. The paper will describe the range of classic design-basis tornado missiles, the target steel stacks, and the key parameters that affect the analysis. The models of missile and targets will be addressed, as well as the benchmark of calculated damage compared to experimental data. Strain-based material models and strain-based criteria will be described, to predict the various failure modes and the structural and functional damage criteria.
Reliability Based Design Optimization of Primary Shield Structure Consisting of Steel-Plate Composite (SC) Walls Under Seismic Load
Authors: Chakraborty Arindam , Krishnasamy Radha Satish , Sener Kadir C. , Varma Amit H.
Published: October 2017

This paper presents a reliability based design optimization (RBDO) of a primary shield wall (PSW) specimen consisting of steel-plate composite (SC) walls scaled from a typical pressurized water reactor (PWR) nuclear power plant under seismic loads. The PSW structure consists of thick SC wall segments with complex and irregular geometry that surround the central reactor vessel’s cavity. Previously, researchers at Purdue University have developed a 3D finite element model (FEM) model of the well-established experimental test setup of a 1/6th scale PSW specimen and the seismic load-deformation behavior was simulated. This paper extends the efforts of the researchers at Purdue University, through RBDO, thereby using the same 3D FEM model. For the simplicity of RBDO, only monotonic loading is considered and response surface method (RSM) is used for approximating the response of the 3D FEM model. Yielding of steel due to tension and/or shear is being considered as a milestone failure mode. The thicknesses of steel plate thicknesses are being considered as the objective to be optimized. The yield stress of steel, applied displacement and steel plate thicknesses are considered to be normal random variables. General purpose finite element software Abaqus (FEA) along with process automation and design exploration software Isight, both developed by Dassault Systèmes Simulia, are being used for the RBDO.
A Review of Welding Research Within the New Nuclear Manufacturing (NNUMAN) Programme
Authors: Smith Mike C. , Vasileiou Anastasia N. , Rathod Dinesh W. , Francis John , Irvine Neil M. , Sun Yongle
Published: October 2017

The New Nuclear Manufacturing (NNUMAN) Programme is a five year UK research project developing manufacturing technologies for next generation nuclear power plants. One of its research themes is advanced joining. Within this theme NNUMAN has manufactured, characterised, and modelled benchmark narrow groove weldments in SA508 Gr 3 Cl 1 low alloy steel over a range of thicknesses up to 130 mm thick using four welding processes: submerged arc (SAW), gas-tungsten arc (GTAW), Electron beam (EB) and cold wire laser (CWL). This paper describes the manufacture and characterisation of the weldments, including diverse residual stress measurements both before and after post weld heat treatment (PWHT).
Improved Engineering Process-Zone Model for Evaluation of Structural Strength of Annulus Spacers in CANDU Nuclear Reactors
Authors: Liu Cheng , Gutkin Leonid , Scarth Douglas
Published: October 2017

The core of a CANDU®(1) pressurized heavy water reactor consists of a lattice of either 390 or 480 horizontal Zr-Nb pressure tubes, depending on the reactor design, which contain the nuclear fuel. Each pressure tube is surrounded by a Zircaloy calandria tube that operates at a significantly lower temperature. Fuel channel annulus spacers maintain the annular gap between the pressure tube and the calandria tube throughout the reactor operating life. To meet this design requirement, the annulus spacers must have adequate structural strength to carry the interaction loads between the pressure tube and the calandria tube. Crush tests performed on specimens from Inconel X-750 spacers, both non-irradiated and ex-service, have demonstrated that their structural strength had degraded with operating time due to irradiation damage. An engineering process-zone model was developed and used to analyze the spacer crush test results, and to predict the maximum load carrying capacities of the Inconel X-750 spacer coils, as described in the companion paper “Engineering Process-Zone Model for Evaluation of Structural Strength of Fuel Channel Annulus Spacers in CANDU Nuclear Reactors” presented at the PVP2017 Conference. The developed model is based on the strip-yield approach of a process zone with a uniform restraining stress that represents the fracture region surrounded by elastic material. This baseline process-zone model has been improved by allowing the restraining stress to evolve with the variation in the opening displacement in accordance with a traction-separation constitutive relation. The development of this improved engineering process-zone model incorporating a non-trivial traction-separation constitutive relation is described in this paper.
Technical Basis of Fatigue Crack Growth Threshold for Stainless Steel in Air Environment for ASME Code Section XI
Authors: Hasegawa Kunio , Usami Saburo
Published: October 2017

The fatigue crack growth threshold is an important characteristic of crack growth assessment for the integrity of structural components. However, threshold values for austenitic stainless steels in air environment are not well provided in many fitness-for-service (FFS) codes, although extensive amount of fatigue crack growth tests data has been published. This paper focuses on fatigue crack growth threshold values for austenitic stainless steel in air environment at room and high temperatures. The paper introduces the current fatigue crack growth rates provided by the ASME (American Society of Mechanical Engineers) Code Section XI and summarizes the available test data of fatigue crack growth thresholds based on the literature survey. The paper then discusses the applicability of the existing fatigue crack growth thresholds for stainless steels and proposes a new relation as a function of the stress ratio for use by the ASME Code Section XI.
Large Dataset Assessment of the Upper Shelf Master Curve Model
Authors: Kirk Mark , Erickson Marjorie , Link Richard
Published: October 2017

In 2006, EricksonKirk and EricksonKirk proposed a model describing a temperature dependence for upper shelf fracture toughness (JIc), based on the Zerilli-Armstrong (ZA) temperature dependence of the flow stress, that was common to the large number of ferritic steel datasets studied. The equation describing the temperature dependence of JIc was found to be a simple scalar multiple of the temperature dependence predicted by ZA for flow stress. Since that time a large dataset has been developed containing many experimental measurements of JIc for the purpose assessing and refining the previously proposed model. The new data, reported herein, validates the previously proposed model of JIc temperature dependence but suggests that revisions of the previously proposed model of JIc uncertainty are needed to ensure the applicability of the model to both low and high fracture toughness steels.
Nuclear Power Plant Fires and Explosions: Part III — Hamaoka Piping Explosion
Authors: Leishear Robert A.
Published: October 2017

An explosion that burst a steel pipe like a paper fire cracker at the Hamaoka Nuclear Power Station, Unit-1 is investigated in this paper, which is one of a series of papers investigating fires and explosions in nuclear power plants. The accumulation of flammable hydrogen and oxygen due to radiolysis has long been recognized as a potential problem in nuclear reactors, where radiolysis is the process that decomposes water into hydrogen and oxygen by radiation exposure in the reactor core. Hydrogen ignition and explosion has long been considered the cause of this Hamaoka piping explosion, but the cause of ignition was considered to be a minor fluid transient, or water hammer, that ignited flammable gasses in the piping, which was made possible by the presence of catalytic noble metals inside the piping. The theory presented here is that a much larger pressure surge occurred due to water hammer during operations. In fact, calculations presented here serve as proof of principle that this explosion mechanism may be present in many operating nuclear power plants.

Chubu Electric, the operator of the Hamaoka plant, took appropriate actions to prevent this type of explosion in their plants in the future. In fact, this accident indicates one potential preventive action from explosions for other operating plants. Ensure that a system high point is available, where mixed hydrogen and oxygen may be removed during routine operations and during off-normal accident conditions, such as nuclear reactor meltdowns and loss of coolant accidents.
Proposal of alternative sensitive region for MOS based radiation sensors: Yb2O3
Authors: Kahraman Aysegul , Yilmaz Ercan
Published: October 2017

The purpose of this study is to investigate the usability of ytterbium oxide (Yb2O3) as a sensitive region/gate oxide in metal oxide semiconductor (MOS) based dosimeters and to determine the advantages and disadvantages of this device relative to its alternatives. For this purpose, amorphous Yb2O3 films were grown on p type Si by radio-frequency magnetron sputtering and aluminum (Al) was used as front and back ohmic contacts of the capacitor. Yb2O3 MOS devices were irradiated incrementally to the total dose of 70 Gy by 60Co radioactive source. The capacitance–voltage measurements were performed at low (100 kHz) and high (1 MHz) frequencies to examine the behavior of the traps. The sensitivity of the device for 70 Gy was obtained using flat band voltage shifts as 27.5 ± 1.1 and 28.1 ± 1.3 mV/Gy for 100 kHz and 1 MHz, respectively. The changes in the oxide trap charge densities in the studied dose between 0.5 and 70 Gy are in the ranges of (1.09 ± 0.04)× 1011–(1.23 ± 0.05) × 1012 cm−2 for 100 kHz and (−3.26 ± 0.08) × 1010–(8.16 ± 0.35) × 1011 cm−2 for 1 MHz. For both frequencies, there was no significant change in the interface trap charge densities over the applied dose and the density of these traps remained in order of 1011 cm−2 after each applied dose. The percentage fading were measured at only 1 MHz for evaluation of the device's dose storage capacity and the results varied from 4% (5 min) to −19% (50 min). An almost constant fading value was obtained after 20 min from irradiation. The capacitor's sensitivity was found to be higher than those of similar devices composed of HfO2, La2O3, SiO2, Sm2O3, and Y2O3. Yb2O3 would be a promising candidate for a new generation of MOS based radiation sensors.
Extending Wheeler’s delayed-choice experiment to space
Authors: Vedovato Francesco , Agnesi Costantino , Schiavon Matteo , Dequal Daniele , Calderaro Luca , Tomasin Marco , Marangon Davide G. , Stanco Andrea , Luceri Vincenza , Bianco Giuseppe , Vallone Giuseppe , Villoresi Paolo
Published: October 2017

The quantum wave-particle duality of light is confirmed at the unprecedented distance of low-Earth-orbit satellites.
Echoes of Ebola as plague hits Madagascar
Authors: Roberts Leslie
Published: October 2017

Fast-spreading pneumonic form reaches the cities, drawing international response.
Neandertals gave ‘lost’ African DNA back tomoderns
Authors: Gibbons Ann
Published: October 2017

Eurasians acquired genes linked to smoking and waist size.
‘Base editors’ open new way to fixmutations
Authors: Cohen Jon
Published: October 2017

Novel CRISPR-derived technologies surgically alter a single DNA or RNA base.
Medicine's future?
Authors: Trivedi Bijal P.
Published: October 2017

In an ambitious experiment, a rural U.S. health system is trying to integrate genomic screening into routine care.
AAAS adopts scientific freedom and responsibility statement
Authors: Jarvis Michaela
Published: October 2017

Related online resources offer guidance, support, and information to scientists
Webinar | Unlocking the elusive mind: The role of protein biomarkers in understanding neurodegenerative disease
Authors: Galasko Douglas R. , Zetterberg Henrik , Blennow Kaj
Published: October 2017

Neurological disorders affect millions of patients worldwide. The inaccessibility of the brain to physical examination and the complexity of clinical evaluation for such conditions represent major challenges. Subjective symptoms such as chronic pain, for example, can be difficult to confirm, while cognitive impairment can result from a range of different pathologies. In the absence of clear biological markers indicating a particular pathology, it can be difficult to provide a rapid, definitive diagnosis. These challenges are particularly pertinent in neurodegenerative diseases, as few effective treatments for slowing or stopping such conditions are currently available. This situation is confounded by the relative scarcity of blood- or cerebrospinal fluid (CSF)–based biomarkers that can increase our understanding of disease pathology, and might also serve as effective differential diagnostic or prognostic tools. New protein biomarkers would ideally show specific brain pathologies and act as early indicators of disease. There is also an urgent need for biomarkers to stratify patients into subtypes of neurodegenerative disorders and facilitate selection of the most effective and appropriate treatments. Our panelists will discuss how the ability to analyze multiple protein biomarkers is beginning to address some of these challenges, providing potentially important new insights into neurological disorders.

View the Webinar
A multistage antimalarial targets the plasmepsins IX and X essential for invasion and egress
Authors: Pino Paco , Caldelari Reto , Mukherjee Budhaditya , Vahokoski Juha , Klages Natacha , Maco Bohumil , Collins Christine R. , Blackman Michael J. , Kursula Inari , Heussler Volker , Brochet Mathieu , Soldati-Favre Dominique
Published: October 2017

Plasmodium
parasite entrance and exit

Sweats and fever are the hallmarks of malaria. Red blood cells are the replication factories for malaria parasites. Fever occurs when the parasites' merozoite stages burst en masse from red blood cells into the circulation. Nasamu
et al.
and Pino
et al.
discovered that two parasite proteases, plasmepsin IX and X, are essential for mass cell exit (see the Perspective by Boddey). Plasmepsin X is also used by the merozoites to enter a fresh red blood cell to continue the replicative cycle. These two plasmepsins act by regulating the maturation of enzymes required to disrupt host cell membranes. Because these functions are essential for the parasite, the authors used protease inhibitors to show that plasmepsins provide potential drug targets.

Science
, this issue p.
518
, p.
522
; see also p.
445
Atomic structure of sensitive battery materials and interfaces revealed by cryo–electron microscopy
Authors: Li Yuzhang , Li Yanbin , Pei Allen , Yan Kai , Sun Yongming , Wu Chun-Lan , Joubert Lydia-Marie , Chin Richard , Koh Ai Leen , Yu Yi , Perrino John , Butz Benjamin , Chu Steven , Cui Yi
Published: October 2017

Frozen in time

The electrochemical processes occurring in a battery are highly dynamic. To
understand the complexities of the charge and discharge cycles, you need to be
able to watch the processes in situ or to freeze the battery rapidly for ex situ
analysis. Li
et al.
applied cryo–electron microscopy
techniques commonly used for studying biological samples to examine batteries.
They identified the solid electrolyte interphase that forms, observed the
interactions of Li with the interphase, and captured the formation of dendrites
that can be detrimental to the lifetime of a battery.

Science
, this issue p.
506
Plasmepsins IX and X are essential and druggable mediators of malaria parasite egress and invasion
Authors: Nasamu Armiyaw S. , Glushakova Svetlana , Russo Ilaria , Vaupel Barbara , Oksman Anna , Kim Arthur S. , Fremont Daved H. , Tolia Niraj , Beck Josh R. , Meyers Marvin J. , Niles Jacquin C. , Zimmerberg Joshua , Goldberg Daniel E.
Published: October 2017

Plasmodium
parasite entrance and exit

Sweats and fever are the hallmarks of malaria. Red blood cells are the replication factories for malaria parasites. Fever occurs when the parasites' merozoite stages burst en masse from red blood cells into the circulation. Nasamu
et al.
and Pino
et al.
discovered that two parasite proteases, plasmepsin IX and X, are essential for mass cell exit (see the Perspective by Boddey). Plasmepsin X is also used by the merozoites to enter a fresh red blood cell to continue the replicative cycle. These two plasmepsins act by regulating the maturation of enzymes required to disrupt host cell membranes. Because these functions are essential for the parasite, the authors used protease inhibitors to show that plasmepsins provide potential drug targets.

Science
, this issue p.
518
, p.
522
; see also p.
445
Size effect in ion transport through angstrom-scale slits
Authors: Esfandiar A. , Radha B. , Wang F. C. , Yang Q. , Hu S. , Garaj S. , Nair R. R. , Geim A. K. , Gopinadhan K.
Published: October 2017

Squeezing through a hole

Transport of an ion is usually directly related to its hydrated radius and assumed to be nonflexible. Either a hydrated ion fits through an aperture or it does not, and shape should play a dominant role rather than charge. Esfandiar
et al.
created nanofluidic devices by stacking structured bulk materials, including graphite, boron nitride, and molybdenum disulfide. They investigated the transport of ions in aqueous solutions through the nanochannels in the devices. Unexpectedly, they observed different behavior for ions of similar hydrated size but opposite charge.

Science
, this issue p.
511