bluuebunny/crossref_metadata_2025 huggingface dataset:
Long Term Operation of Nuclear Power Plants: Status in the U.S.
Authors: Young Garry G.
Published: January 2014

As of January 2013, the U.S. Nuclear Regulatory Commission (NRC) has renewed the operating licenses of 73 nuclear units out of a total of 104 licensed units, allowing for up to 60 years of safe operation. In addition, the NRC has license renewal applications under review for 15 units and more than 13 additional units have announced plans to submit applications over the next few years [1]. This brings the total of renewed licenses and plans for renewal to over 97% of the 104 operating nuclear units in the U.S.

This paper presents the status of the U.S. license renewal process and issues being raised for possible applications for subsequent renewals for up to 80 years of operation. By the end of 2013 there will be 26 nuclear plants in the U.S. (or 25% of the 104 units) that will be eligible to seek a second license renewal and by the end of 2016 this number will increase to about 50% of the 104 licensed units. Although some nuclear plant owners have announced plans to shutdown before reaching 60 years, the majority are keeping the option open for long term operation beyond 60 years. The factors that impact decisions for both the first license renewals and subsequent renewals for 80 years of safe operation are presented and discussed in this paper.
Prediction of the Crack Growth Rate Under Creep and Neutron Irradiation for Austenitic Stainless Steels in Initial, Aged and Irradiated Conditions
Authors: Buchatsky Andrey , Margolin Boris , Gulenko Alexander , Kashtanov Alexander
Published: January 2014

This work is aimed at investigating the crack growth rate in austenitic steels under creep and neutron irradiation for a material in initial and aged conditions.

The crack growth rate under creep is studied for 18Cr-9Ni steel and its welds. This steel and its welds are the base structural materials for manufacturing BN-600 fast reactor components. Experimental investigations of crack growth rate have been performed for the base metal, weld metal and heat-affected zone which were subjected to thermal ageing during operation. It is shown that the fastest crack growth rate is observed for specimens from the base metal.

The crack growth rates are compared for the base metal in initial and aged conditions. The initial condition of metal is modeled by annealing thermally aged metal taken from the components after its operation. The investigations show that the crack growth rate for the initial condition is faster than for the aged condition.

A method for predicting the crack growth rate under creep and irradiation has been developed on the basis of a physical-and-mechanical intergranular fracture model proposed before [1]. The crack growth rate for the material in initial condition is used as input data to calculate this rate under creep and irradiation according to the developed method.
International Harmonisation: A Key Challenge for Mechanical Components Codes and Standards
Authors: Faidy Claude
Published: January 2014

Many Code Comparisons have been done by different organizations. The differences are better and better known by Code Development Organizations like ASME, AFCEN, JSME, KEPIC, CSA and NIKIET.

This paper uses the last MDEP (Multinational Design Evaluation Program) comparison for class 1 components to classify differences in different aspects:

- National regulatory requirements

- Technical differences

- Scope differences.

Few examples are selected to confirm needs of harmonization in different areas like: documentation, design rules, materials, product specifications, welding and non destructive examination personal qualifications.

The paper concludes on selected topics proposed for harmonization by AFCEN.

The objectives of this paper is to discuss technical harmonization of Nuclear Codes and Standards, based on French long experience in Codes and Standards used for design-fabrication and operation of nuclear components (mainly pressure retaining components).

After a long period of use of ASME Section III code, during the Westinghouse licensing process, AFCEN (AREVA, EDF and the major manufacturers) decided to develop their own AFCEN French Codes. The 1st version has been issued in 1980 and the last one in 2007, completed by annual addendum. During more than 20 years the 2 Codes, RCC-M and ASME Section III, have leave separately, with different constraints like industrial history, localisation of fabrication, more new plants in France than in USA, different R&D programs to support Code improvement…

Recently a detailed review of differences for class 1 vessel has showed under a “general global quality equivalence”, a lot of differences in the Code development process, in the Code organization, in the scopes, in the State of the Art fulfillment, in ageing consideration at the design stage, in relation with national or international regulations, in term of standards used or complementary specification needs…

The harmonization of Codes and Standards is possible under an important effort to move toward new ideas, more international rules and with a strong support of national safety authorities.
A Study of the Effect of Long-Term Thermal Aging on the Creep-Rupture Properties of 18Cr-9Ni Steel
Authors: Gulenko A. G. , Margolin B. Z. , Buchatsky A. A. , Kashtanov A. D.
Published: January 2014

Experimental investigations of the creep-rupture properties of metal of intermediate heat exchangers (IHX) from fast breeder reactor BN-600 after its operation during ∼ 170 thousands hours over temperature range of 500–550°C were carried out. IHX was produced from 18Cr-9Ni steel. To study the role of thermal aging part of the IHX metal was annealed at 1000–1050°C for 0.5 hours. Comparison of experimental results of aging metal and annealed metal was carried out and the microstructure and fractography of both materials examined. The effect of aging on the creep-rupture properties of 18Cr-9Ni steel was revealed and described by the physical and mechanical model of intergranular fracture.

On the basis of experimental and calculative results an explanation of the effect of long-term aging on the mechanical short-term and creep-rupture properties of 18Cr-9Ni steel has been provided.
Acoustic Damping in Smooth and Corrugated Pipes With and Without Liquid Injection
Authors: Golliard J. , Belfroid S. P. C. , Vijlbrief O.
Published: January 2014

From previous experiments, it was shown that small quantities of liquids reduce or eliminate the singing phenomenon in corrugated tubes. The singing mitigation was attributed to filling up of the corrugations, interference with the boundary layer or due to the increased acoustic damping.

To evaluate the influence of the presence of liquids on the acoustic damping, this damping was measured in a smooth and a corrugated tube (internal diameter 49 mm). The damping was measured using an active source (loudspeaker) and measuring amplitude of sound waves on both sides of the pipe. This was done at different gas velocities (U = 0, 15, 30 m/s) and different liquid injection rates (0, 150, 250 350 ml/min) for a frequency range between 0–2200 Hz.

The smooth pipe results compared well with literature models such as the Kirchhoff model. In the presence of liquid, the acoustic damping increased linearly with the liquid rate. This increase was higher than expected based on the assumptions of mist flow or overall pressure drop. In case of the corrugated tube, the measured damping is dominated by a large fluctuation due to the source behavior (negative damping) at flowing conditions. At low velocities a decrease in source strength was measured with increasing liquid. At higher gas velocities, it was observed that liquid has almost no effect on the damping.
Influence of Hand Disc Grinding on Surface Integrity of Nickel-Based Alloys: Numerical Approach
Authors: Youssef Sawsen , Calonne Olivier , Hamdi Hédi
Published: January 2014

For complex part geometry, hand grinding is one of finishing and super finishing process the most used in mechanical industry. Surface integrity is today one major concern for industrials. The surface integrity is defined by a set of important characteristics of ground surface as surface geometric parameters (roughness, …), mechanical behaviour of the subsurface (hardness, residual stress, …) and structural changes of the material in the near surface. High heat and pressure, high strain and strain rate observed during hand grinding process, strongly influence surface integrity. Therefore, the surface behaviour, in terms of resistance to corrosion and crack initiation depends on how the process was conducted. The purpose of this study is to understand the effects of thermal and mechanical plastic deformation induced on the surface of components. The action of the disc-grinding wheel on the workpiece is modelled by a moving heat flux on the surface. The challenge is to be able to find the shape and intensity of thermomechanical load entering the workpiece in accordance with the hand disc grinding process and taking into account specific parameters of the process. In a first part, a mechanical description of the action of the disc-wheel on the surface is proposed in order to develop an analytic formulation of the grinding power and the heat flux density. They are function of the disc-grinding wheel velocity, the feed speed and the applied forces. This expression is then used in a finite element modelling to perform thermomechanical simulations of the hand disc-grinding process. In a first stage, heating and cooling are computed. They give maximum temperature reached, temperature gradients and cooling kinematic. In a second stage, thermomechanical computation is conducted in order to compute residual stresses induced by this abrasion process. A discussion based on experimental results obtained by XRD method is then proposed and some local explanation are given on the way the material structure has changed leading to a structural hardening in the 50 first microns beneath the ground surface.
Chained Welding and Finish Turning Simulations of Austenitic Stainless Steel Components
Authors: Valiorgue Frédéric , Brosse Alexandre , Robin Vincent , Gilles Philippe , Rech Joel , Bergheau Jean Michel
Published: January 2014

The chaining of manufacturing processes is a major issue for industrials who want to understand and control the quality of their products in order to ensure their in-service integrity (surface integrity, residual stresses, microstructure, metallurgical changes, distortions,…). Historically, welding and machining are among the most studied processes and dedicated approaches of simulation have been developed to provide reliable and relevant results in a industrial context with safety requirements. As the simulation of these two processes seems to be at an operational level, the virtual chaining of both must now be applied with a lifetime prediction prospect. This paper will first present a robust method to simulate multipass welding processes that has been validated through an international round robin. Then the dedicated “hybrid method”, specifically set up to simulate finish turning, will be subsequently applied to the welding simulation so as to reproduce the final state of the pipe manufacturing and its interaction with previous operations. Final residual stress fields will be presented and compared to intermediary results obtained after welding. The influence of each step on the final results will be highlighted regarding surface integrity and finally ongoing validation works and numerical modeling enhancements will be discussed.
Experience With Using Code Case 2564 to Design and Certify an Impulsively Loaded Vessel
Authors: Haroldsen Brent , Stofleth Jerome , Yip Mien , Caplan Allan
Published: January 2014

Code Case 2564 for the design of impulsively loaded vessels was approved in January 2008. In 2010 the US Army Non-Stockpile Chemical Materiel Program, with support from Sandia National Laboratories, procured a vessel per this Code Case for use on the Explosive Destruction System (EDS). The vessel was delivered to the Army in August of 2010 and approved for use by the DoD Explosives Safety Board in 2012. Although others have used the methodology and design limits of the Code Case to analyze vessels, to our knowledge, this was the first vessel to receive an ASME explosive rating with a U3 stamp. This paper discusses lessons learned in the process. Of particular interest were issues related to defining the design basis in the User Design Specification and explosive qualification testing required for regulatory approval. Specifying and testing an impulsively loaded vessel is more complicated than a static pressure vessel because the loads depend on the size, shape, and location of the explosive charges in the vessel and on the kind of explosives used and the point of detonation. Historically the US Department of Defense and Department of Energy have required an explosive test. Currently the Code Case does not address testing requirements, but it would be beneficial if it did since having vetted, third party standards for explosive qualification testing would simplify the process for regulatory approval.
High Temperature, Low Cycle Fatigue Characterisation of P91 Weld and Heat Affected Zone Material
Authors: Farragher T. P. , Scully S. , O’Dowd N. P. , Leen S. B.
Published: January 2014

The high temperature low cycle fatigue behaviour of P91 weld metal (WM) and weld joints (cross-weld) is presented. Strain-controlled tests have been carried out at 400 °C and 500 °C. The cyclic behaviour of the weld material (WM) and cross-weld (CW) specimens are compared with previously published base material (BM) tests. The weld material is shown to give a significantly harder and stiffer stress-strain response than both the base material and the cross-weld material. The cross-weld tests exhibited a cyclic stress-strain response which was similar to that of the base material. All specimen types exhibited cyclic softening but the rate of softening exhibited by the CW specimens was lower than that of the base and all-weld tests. Finite element models of the base metal, weld metal and CW test specimens are developed and employed for identification of the cyclic viscoplasticity material parameters. HAZ cracking was the primary mode of failure for the cross-weld tests.
Design Basis of an Impulsively Loaded Vessel for Specific Loading Configurations
Authors: Yip Mien , Haroldsen Brent
Published: January 2014

For an impulsively loaded containment vessel, such as the Sandia Explosive Destruction System (EDS), the traditional notion of a single-value explosive rating may not be sufficient to qualify the vessel for many real-life loading situations, such as those involving multiple munitions placed in various geometric configurations. Other significant factors, including detonation timing, geometry of explosive(s), and standoff distances, need to be considered for a more accurate assessment of the vessel integrity. It is obvious that the vessel structural response from an explosive charge detonated at the geometric center of the vessel will be very different from the structural response from the same explosive charge detonated next to the vessel wall. It is, however, less obvious that the same explosive can produce vastly different vessel response if it is detonated at one end versus at the middle versus from both ends. The goal of this paper is to identify some of the effects that non-trivial loading situations have on the vessel structural integrity. The metric for determining vessel integrity is based on Code Case 2564 of the ASME Boiler and Pressure Vessel Code. Based on the findings of this work, it may be necessary to qualify impulsively loaded containment vessels for specific explosive configurations, which should include the quantity, geometry and location of the explosives, as well as the detonation points.
Mesh Convergence Studies for Hexahedral Elements Developed by the ASME Special Working Group on Computational Modeling
Authors: Tso Chi-Fung , Molitoris David P. , Yaksh Michael , Snow Spencer , Ammerman Doug , Bjorkman Gordon S.
Published: January 2014

The ASME Special Working Group on Computational Modeling for Explicit Dynamics was founded in August 2008 for the purpose of creating a quantitative guidance document for the development of finite element models used to analyze energy-limited events using explicit dynamics software. This document will be referenced in the ASME Code Section III, Division 3 and the next revision of NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged. One portion of the document will be devoted to a series of element convergence studies that can aid designers in establishing the mesh refinement requirements necessary to achieve accurate results for a variety of different element types in regions of high plastic strain. These convergence studies will also aid reviewers in evaluating the quality of a finite element model and the apparent accuracy of its results.

In this paper, the authors present the results of a convergence study for an impulsively loaded propped cantilever beam constructed of LS-DYNA hexahedral elements using both reduced and selectively reduced integration. Three loading levels are considered; the first maintains strains within the elastic range, the second induces moderate plastic strains, and the third produces large deformations and large plastic strains.
Mechanical Testing of Component Size Specimen Under Impact Conditions
Authors: Müller Karsten , Scheidemann Robert , Auster Jürgen
Published: January 2014

For validation of structural integrity under normal and hypothetical accident conditions during transport and storage of radioactive material the Federal Institute for Materials Research and Testing (BAM) focuses its safety related scientific research on advanced mechanical safety assessment methods including simulation of high rate impact of model components and structures. A drop and crash test facility with an unyielding target and a load capacity of 1.200 kg was designed for materials testing of component size specimen under impact conditions at elevated and higher loading rates. The maximum drop height is 12 meters which enables impact velocities up to 15 m/s. An exactly falling test object or drop weight allows impact, bending, compression as well as crash and crush tests with maximum input energy of 118 kJ. An arresting unit has been developed to avoid multiple impacts during instrumented drop tests. The paper presents experimental techniques and examples of various measurement methods and advancements in order to assess assumption of materials and components behavior by definite displacement and stresses within mechanical testing. Instrumented drop weight tests are performed to complete materials data base and energy absorption of shock-absorbing materials and structures as well as to implement materials and structural parameters into FEA of reference structures. Furthermore, fracture mechanics parameters of thick walled DCI containers by means of dynamic bending tests are characterized by crack initiation and crack resistance behavior at the lowest operational temperature depending on the strain rate.
A Unified Viscoplastic Model for High Temperature Low Cycle Fatigue of Service-Aged P91 Steel
Authors: Barrett R. A. , O’Donoghue P. E. , Leen S. B.
Published: January 2014

The finite element (FE) implementation of a hyperbolic sine unified cyclic viscoplasticity model is presented. The hyperbolic sine flow rule facilitates the identification of strain-rate independent material parameters for high temperature applications. This is important for the thermo-mechanical fatigue of power plant where a significant stress range is experienced during operational cycles and at stress concentration features, such as welds and branch connections. The material model is successfully applied to the characterisation of the high temperature low cycle fatigue behaviour of a service-aged P91 material, including isotropic (cyclic) softening and non-linear kinematic hardening effects, across a range of temperatures and strain-rates.
Crack Opening Displacement Model for Through-Wall Axial Cracks in Cylinders
Authors: Benson Michael L. , Young Bruce A. , Shim Do-Jun , Brust Frederick W.
Published: January 2014

For piping systems, leak-before-break calculations rely on estimates of leak rates when postulated cracks grow through the pipe wall. The leak rate, in turn, depends on the crack opening dimensions. Previous work on crack opening displacement (COD) includes recent advances in COD estimates for circumferentially-oriented cracks in cylinders under tension, bending, and internal pressure loading conditions. This paper summarizes previous work in this area and reports on new solutions for COD in the case of axially-oriented cracks under internal pressure. The results reported here include COD solutions at three locations through the wall thickness for axial cracks.
Guidelines for Managing the Integrity of Bolted Joints: Developments in European Standards
Authors: Noble Robert
Published: January 2014

The Energy Institute Guidelines for the Management of Integrity of Bolted Joints in pressurized systems [1] was first introduced in 2002 in response to a drive to reduce Hydrocarbon leakage in the UK Offshore Industry. This was a successful initiative and the guidelines were updated in 2007 assisting with a further push to reduce Hydrocarbon leakage — at that time the guidelines were extended to the onshore industry.

The guidelines are now under review again with a target publication in 2013 to ensure they remain current best practice, which has a high relevance in 2013 the 25th Anniversary Year of the Piper Alpha disaster.

This paper will give an overview of the Guidelines — and discuss the key changes on the previous versions and alignment with ASME PCC-1-2010.[2]

The paper will also discuss developments in other key bolted joint standards in Europe including: En1591-1[3] and En1591-4[4].
Study of Crack Extension Effects on a Weld-Induced Residual Stress Field
Authors: Hong Jeong K. , Forte Thomas P.
Published: January 2014

For many applications, welding is the best manufacturing process for joining two separate components. However, the welding process with its highly localized heating and cooling results in the residual stresses both along the surface and through the thickness of the joint. These residual stresses will affect the rate of growth of a fatigue crack as it propagates through the joint and therefore will affect the service life. Therefore, service life predictions must consider the residual stresses as well as their redistribution that occurs as the crack grows.

Analytical approaches to assess fitness-for-service such as API 579 are available to evaluate the effect of weld-induced residual stresses. However, current industry practices calculate stress intensity factors (SIFs) for fracture and fatigue crack growth life estimates without considering the redistribution of the residual stresses as the crack propagates, and thus tend to be very conservative.

In this paper, Battelle’s weld residual stress modeling methods are combined with a procedure for calculating the SIF using local crack tip displacements that accounts for the redistribution of the residual stresses due to crack extension. In addition, the finite element model used to determine the weld residual stresses is also used to determine the SIF. Therefore, the complete mechanical response to the welding, including residual stress, deformed geometry, elastic and plastic strains, etc. are available for the crack growth analysis. This new unified procedure is demonstrated for simple joints and is compared to a “simplified” crack growth analysis that uses stress mapping. The unified procedure clearly characterizes mixed mode crack behavior at the crack tip. In this paper the procedure is presented in terms of how the crack affects the weld-induced residual stress field; it is equally well suited for practical design use to assess structural integrity in the presence of a weld-induced residual stress field with or without external service loading.
Effects of Side-Grooves and 3-D Geometries on Compliance Solutions and Crack Size Estimations Applicable to C(T), SE(B) and Clamped SE(T) Specimens
Authors: Donato Gustavo Henrique B. , Moreira Felipe Cavalheiro
Published: January 2014

Engineering procedures for design and integrity assessment of structural components containing crack-like defects are highly dependent on accurate fracture toughness and Fatigue Crack Growth (FCG) experimental data. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical measurement, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain-modulus vary between E (plane stress) and E/(1−ν2) (plane strain); ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Results from Shen et al. and from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W = 0.1 and a/W = 0.7 on 1/2T, 1T and 2T geometries. The 1T geometry is taken as the reference and presents width to thickness ratio W/B = 2. Side-grooves of 5%, 10% and 20% are considered. The results include compliance solutions incorporating 3D and side-groove effects to provide accurate crack size estimation during laboratory fracture and FCG testing. The proposals were verified against current standardized solutions and deviations were strongly reduced.
Residual Stress Modelling in a Thick-Sectioned Electron Beam Weld
Authors: Pellereau Ben , Gill Chris , Hurrell Paul , Kingston Ed
Published: January 2014

Previous work presented residual stress measurements in an electron beam weld in a thick section ferritic forging [1]; this weld was also modelled using finite element analysis. Due to the tool used to model the heat source, the mesh density in the region of the weld was limited. This work improves on the previous work by using a DFLUX subroutine to provide a mesh-independent heat source input, allowing a better mesh in the region of the weld. The modelling was carried out in Abaqus[2] using the VFT[3] user material model to allow phase transformation effects to be included. This however does not include creep properties and so the as-welded stresses were seeded on to a model that used Abaqus built-in material properties in order to model the heat treatment. The results of this analysis have been compared with analyses run using just the VFT material model (with no creep) and using just the Abaqus properties (with no phase transformation) in order to investigate the sensitivity of the stresses predicted to the material model used. The results of all three analyses have also been compared to the results of the original analysis and with the deep hole drilling residual stress measurements.
Effect of Explosion Source Type on Blast Wave Shielding
Authors: Geng Jihui , Thomas J. Kelly
Published: January 2014

A key component of explosion hazard evaluations is the determination of standoffs to given blast overpressure values. Many such evaluations use a simplified methodology that assumes that the blast wave propagates from the explosion source to the target location without interacting with intervening buildings or structures (i.e., without blast wave shielding). This is obviously a perfectly acceptable approach for a screening study, but blast wave shielding effects can be significant in certain circumstances (e.g., within a building group). A methodology was proposed by the UK Health & Safety Laboratory (HSL) in 2001 to account for blast shielding due to buildings/structures between the explosion source and target location. The HSL methodology is based on the blast waves generated by high explosives (HE). This paper extends the blast shielding evaluation to blast waves generated from pressure vessel bursts (PVB) and vapor cloud explosions (VCE). The influences of blast wave shape parameters (overpressure, duration and rise time) on blast wave shielding are examined. The results indicate that the degree of blast shielding is strongly dependent on the source of the blast wave (i.e., on the blast wave shape parameters) and that the shielding factors obtained with HE blast waves are not always directly applicable for PVB and VCE blast waves.
Standards, Specifications, Test Methods and Technical Reports for GRP Water, Drainage and Sewerage Piping
Authors: Marques António Torres
Published: January 2014

Many end-users, specifiers, governmental agencies and testing facilities, are not fully aware of the wealth of standards available for GRP piping products and the continuing work being done in CEN &ISO and other standards developing organizations. As a result the introduction of Ad-Hoc test methods, standards and obsolete requirements is, unfortunately, not uncommon.

The paper will list and comment available GRP Standards that has been prepared as a reference guide to assist in the proper specification and use of GRP piping products. The primary focus is on EN and ISO standards. The work being done in CEN and ISO is closely linked, with ISO taking the lead in test method development and ISO test methods being referenced in EN standards. The work in CEN is conducted in CEN TC 155 WG14 and the work in ISO in ISO TC138 SC6. However, important standards are issued by other standards organizations and these will be also covered in the paper.
Determining Optimum Temperature Changes During Heating of Pressure Vessels With Holes
Authors: Taler Jan , Dzierwa Piotr , Taler Dawid
Published: January 2014

A method for determining time-optimum medium temperature changes is presented. The heating of the pressure elements will be conducted so that the circumferential stress caused by pressure and fluid temperature variations at the edge of the opening at the point of stress concentration, does not exceed the allowable value. In contrast to present standards, two points at the edge of the opening are taken into consideration. The first point P1 is located at the cross section and the second P2 at the longitudinal section of the vessel. It will be shown that the optimum temperature courses should be determined with respect to the total circumferential stress at the point P2, and not, as in the existing standards due to the stress at the point P1. Optimum fluid temperature changes are assumed in the form of simple time functions. For practical reasons the optimum temperature in the ramp form is preferred. It is possible to increase the fluid temperature stepwise at the beginning of the heating process and then the fluid temperature can be increased with a constant rate. By the stepwise increase in fluid temperature heating time of a thick-walled component is shorter than heating time resulting from the calculations according to EN 12952-3 European Standard.
ASME Codes Support Small Modular Reactor Development and Use: Unique Designs Require a Robust Code
Authors: Bianchini Delfo , Demoss Dennis , Peebles William R.
Published: January 2014

Authors: Sargent & Lundy, LLC: Delfo Bianchini, Dennis Demoss and William Peebles. Focus: Operations, Applications & Components. This paper will review new Small Modular Reactor (SMR) designs and implications on the ASME Section III Code. Four SMR technologies will be discussed: B&W mPower (TVA Clinch River site), Westinghouse SMR (Ameren Callaway site), NuScale/Fluor SMR (Pacific NW lab site) and Holtec SMR (Savannah River site). SMR reactor designs vary from 45 to approximately 225 MWe. SMR goals include significantly reducing plant capital cost requirements and enabling multi-reactor module construction and addition over time providing greater utility flexibility. A primary SMR advantage includes its installation in smaller grids typical of electrical power systems in developing countries. Unique aspects of the SMR technologies include integral reactor and steam generator vessel, integral pressurizer and internal piping, below grade containment vessel, helical-coil integral steam generators, integral decay heat removal systems, modular plant construction and arrangement, in-service inspection unique requirements, special materials and welding. Current ASME code design rules and requirements may require expansion and clarification; Section XI testing requirements and frequencies may require revision.
Criteria for High Frequency Cutoff Based on ABWR Reactor Building Vibratory Loads
Authors: Ulku Evren , Ozgur Cagri , Ozkan Mustafa Kemal , Vaidya Nish , Srivastava Hari , Tanoue Tetsuharu
Published: January 2014

In the seismic analysis practice, the calculation of modal response has traditionally been limited to a cutoff frequency of about 33 Hz based on United States Nuclear Regulatory Commission (US NRC) Regulatory Guide (RG) 1.60 [1] response spectra. The structural response in higher modes is calculated as a missing mass correction by static analysis.

Seismic ground motions at several sites (such as Central and Eastern United States) exhibit high frequency content, up to about 100 Hz. Additionally, the reactor building vibratory (RBV) loads that result from the suppression pool hydrodynamic loads due to loss of coolant accident (LOCA), and the annulus pressurization (AP) load from a postulated pipe break at the reactor pressure vessel (RPV) safe ends and shield wall generate peaks at frequencies in excess of 100 Hz. The qualification of safety equipment supported in the reactor building needs to reflect these high frequency motions. Extracting frequencies and mode shapes up to zero period acceleration (ZPA) frequencies in these cases may not be practical or economical. Therefore, the cutoff frequency criteria for these types of high frequency loads need to be evaluated so that the analysis produces a representative and a reasonably conservative response.

In this study, the equipment response is described in terms of stress quantities, member forces, and moments resulting from the solution up to a cutoff frequency. The responses are compared to the full solution up to the ZPA frequency under hydrodynamic and AP loads using the Response Spectrum Method. The cutoff frequency is deemed adequate if the ratio of the truncated response considering missing mass to the full response is 90% or greater. The internal strain energy (or its surrogate kinetic energy) for all modes with frequencies below the cutoff is also studied to assess the missing strain energy in modes in excess of the cutoff. The evaluation presented also examines how well the strain energy correlates with calculated stresses.
Flaw Size Acceptance Limits for a Stainless Steel Pressure Vessel
Authors: Guzman-Leong Consuelo E. , Gosselin Stephen R. , Simonen Frederic A.
Published: January 2014

The ASME Boiler and Pressure Vessel Code Section XI provides flaw size acceptance standards for ferritic steel pressure vessels. Section XI Table IWB-3510-1 presents allowable flaw size limits in terms of flaw depth, length and vessel thickness. These flaw size limits are based on linear elastic fracture mechanics calculations that assume a brittle fracture failure mode. As yet, no allowable flaw size standards are provided in Section XI for stainless steel reactor or non-reactor pressure vessels. This paper presents allowable flaw size limits for a stainless steel pressure vessel. These limits were based on elastic plastic fracture mechanics analyses that considered limit load and ductile tearing failure modes. Although the flaw acceptance levels were developed for a specific stainless steel vessel, insights gained from this work may be useful in a general methodology for ASME Code purposes. Tabulated flaw size acceptance levels, for several aspect ratios and inspection intervals, are presented for the axial shell welds. Results show the axial seam welds were the most flaw sensitive of the various welds analyzed. The acceptable flaw sizes were limited by the ductile tearing failure mode.
Comparison of Through-Wall and Complex Crack Behaviors in Dissimilar Metal Weld Pipe Using Cohesive Zone Modeling
Authors: Shim Do-Jun , Rudland David , Brust Frederick
Published: January 2014

Cohesive zone modeling has been shown to be a convenient and effective method to simulate and analyze the ductile crack growth behavior in fracture specimens and structures. Recently, authors have applied the cohesive zone model to simulate the ductile fracture behavior of a through-wall cracked pipe test consisting of a single material. In this paper, cohesive zone modeling has been applied to simulate the ductile crack growth in dissimilar metal weld pipe tests that was recently conducted by the U.S. NRC. Two crack types, i.e. through-wall and complex cracks, were simulated in the work. This paper describes how the cohesive parameters were determined and discusses in detail about the finite element modeling of the cohesive zone model. Various fracture parameters were compared between the finite element analyses and the experiments to validate the model. The results of the cohesive zone models showed good agreement with the pipe test results. Furthermore, the results of the cohesive zone model demonstrate that the fracture toughness (J at crack initiation, Jinit.) of the complex cracked pipe can be significantly lower (factor of 0.41) than that of the through-wall cracked pipe.
Probabilistic Assessment of Axial Crack-Like Flaws and Remaining Life in Onshore Pipelines
Authors: Polasik Steven J. , Maier Clifford , Jaske Carl , Lee David
Published: January 2014

The predicted failure pressure and estimated remaining life of axial crack-like flaws are two key parameters pipeline operators use to develop excavation programs and set re-assessment intervals following an assessment (in-line inspection or hydrostatic pressure test, for example). Deterministic approaches routinely use conservative input values, such as specified minimum or worst-case conditions, leading to potentially overly conservative conclusions. Probabilistic approaches, on the other hand, can account for inherent variability and provide probabilities of failure; however, there are no current approaches to define an acceptance threshold in the onshore pipeline industry. This paper discusses the probabilistic approach Det Norske Veritas (USA), Inc., (DNV) uses to assess axial crack-like flaws. DNV’s approach incorporates an inelastic fracture mechanics model in combination with Monte Carlo simulations and Paris Law fatigue crack growth to estimate the cumulative probability of failure over time. Topics include the application of this methodology for two primary cases: (1) the defect population can be described with a certain degree of confidence (in-line inspection) and (2) the defect population cannot (hydrostatic pressure test). The potential for using the methodology for determining a case-by-case acceptance threshold will also be explored.
Existing Methods in Ductile Fracture Propagation Control for High-Strength Gas Transmission Pipelines
Authors: Zhu Xian-Kui
Published: January 2014

Ductile fracture propagation control is one of the most important technologies adopted in engineering design for high-pressure, high-strength gas transmission pipelines. In the early 1970s, Battelle Memorial Institute developed a two-curve model that is now commonly referred to as BTCM for dynamic ductile fracture control analysis. The BTCM has been applied successfully for determining the minimum fracture toughness required to arrest a running ductile fracture in a gas transmission pipeline in terms of Charpy vee-notched (CVN) impact energy. Practice showed that BTCM is accurate only for pipeline grades up to X65, and becomes invalid for high strength pipeline steels like X70, X80 and X100. Since 1990s, different correction methods for improving the BTCM have been proposed. However, a commonly accepted method is not available yet for the high strength pipeline steels in grades X80 and above. This paper reviews and evaluates the primary existing methods in determination of fracture arrest toughness for ductile pipeline steels. These include the CVN energy-based methods, the drop-weight tear test (DWTT) energy-based methods, the crack-tip opening angle (CTOA) method, and finite element numerical analysis methods. The purpose is to identify a method to be used in engineering design or to be investigated further for determining the minimum fracture toughness to arrest a ductile running crack in a modern high-pressure, high-strength gas pipeline.
Stress-Based Environmental Fatigue Monitoring of PWR Charging Nozzle
Authors: Gilman Timothy , Chinthapalli Archana , Hoehn Michael
Published: January 2014

This paper describes the techniques utilized to perform a stress-based environmentally-assisted fatigue evaluation of Westinghouse-designed charging branch nozzles on the reactor coolant loop of the Callaway Energy Center nuclear power plant. Analysis results from using idealized, design transient definitions are compared to those resulting from analysis of the actual plant data. Benchmarking analyses, performed to address Nuclear Regulatory Commission (NRC) concerns about simplified methodologies, are described. The simplified results are also compared to those produced using an advanced, multiaxial stress-based fatigue methodology defined in a recent EPRI technical report [3]. This paper concludes that stress-based fatigue monitoring using actual plant data is an effective way for a plant to manage environmentally-assisted fatigue of charging nozzles in pressurized water reactors (PWRs).
Environmentally-Assisted Fatigue Management of PWR Pressurizer Using Nonlinear Strain-Based Analysis
Authors: Gilman Timothy , Gillis Jay , Hiremagalur Jagannath , Rodamaker Scott , Weitze William , Hoehn Michael
Published: January 2014

This paper describes the techniques utilized to perform a nonlinear, strain-based, environmentally-assisted fatigue evaluation of a pressurizer vessel in a nuclear power plant. Significant differences between the strain-based and more traditional fatigue analysis results are demonstrated. This paper concludes that leveraging today’s computer power with the use of more detailed, nonlinear analysis is an effective tool for nuclear power plants to meet license renewal commitments related to the management of environmentally-assisted fatigue.
Inelastic Response of a SDOF Structure to Earthquake Motions Synthesized in Wavelet Domain
Authors: Masuda Arata , Sone Akira
Published: January 2014

This study presents the estimation of the ductility responses of inelastic SDOF structures to an earthquake motion from the velocity responses of elastic SDOF structures. Based on the energy balance equation, the ductility response and the baseline drift of the inelastic structure can reasonably be estimated from the extrema of the elastic velocity response. Then, the estimation of the maximum ductility is derived by accumulating them. Illustrative examples are presented to show the performance of the proposed ductility estimation. Because the velocity responses of the elastic SDOF structure are correlated with the time-frequency characteristics of the earthquake motion via the velocity response wavelet transform (VRWT), which was previously proposed by the authors, in which the latter are represented in the wavelet-domain using former as time-frequency building blocks, the proposed estimation method may have a potential to help to obtain an in-depth understanding of time-frequency characteristics of the earthquake motion that impacts the ductility responses of the inelastic structure.
Effect of Seal Welding Conditions on Residual Stress Field and Fracture Mechanics Parameter Around Remaining Crack
Authors: Mochizuki Masahito , Okano Shigetaka , Torigata Keisuke
Published: January 2014

In this study, the effects of seal welding conditions, such as welding heat input, depth of crack, plate thickness, and weld sequence, on the welding-induced residual stress and the stress intensity factor (SIF) around the remaining crack were investigated by finite element analysis. In addition, the parameter Q√a (Q: welding heat input, a: depth of crack) was theoretically derived from welding thermal conduction theory as representative of the temperature distribution along the crack direction. As the results, it was clarified that the residual stress at the downside crack tip is governed largely by the parameter Q/√a. Similarly, the SIF depends on the parameter Q/√a. When the range of Q/√a is smaller than approximately 1.5, the residual stress at the downside crack tip becomes compressive and the SIF becomes 0. An appropriate seal welding condition corresponding to crack size helps to ensure higher structural soundness and reliability of seal welds. Next, the effect of the weld pass sequence on the residual stress around the remaining crack was investigated. As the results, an appropriate weld pass sequence to more effectively reduce the residual stress was clarified. Finally, the effect of seal welding conditions on the residual stress and SIF after seal welding was investigated. It was concluded that the appropriate seal welding conditions was evaluated for reducing the welding-induced residual stress and SIF at seal welds.
Latest Developments in Optimizing Reformer Tube Life Through Advanced Inspection and Remaining Life Assessment
Authors: Shannon Brian , Jaske Carl E.
Published: January 2014

Steam methane reformer tubes must withstand high temperature and pressures during operation and are made from centrifugally cast austenitic materials, typically HK-40, HP Modified, and Micro-Alloy materials. Since operating conditions can result in various forms of damage, the identification and quantification of damage is of vital importance if tube life is to be predicted accurately.

This paper describes the recent developments in an integrated inspection system which uses multiple NDT techniques to provide a most comprehensive assessment of current tube condition. This system is coupled with a sophisticated remaining life assessment software model which predicts the remaining life of each tube in a furnace.
Load Definition on BWR Steam Dryer due to Turbine Stop Valve Closer
Authors: Faal-Amiri Asgar , Srivastava Hari , Moody Frederick J.
Published: January 2014

In the boiling water reactor (BWR), closure of a turbine stop valve (TSV) on the main steam piping system, hereafter called main steam (MS) line, will reduce the steam flow velocity to zero in about 100 msec (0.1 Sec) and create a pressure disturbance that propagates backward through the MS line toward the reactor pressure vessel (RPV). When the compression wave reaches the RPV, it expands into a region at lower pressure, transmitting a compression wave at acoustic speed from the pipe geometry into a complex geometric region at reactor pressure, bounded by the steam dryer and RPV inner wall surfaces. The arriving compression wave expands on the dryer surface, creating a pressure force, while simultaneously steam in the steam line, compressed from the valve closure to a pressure higher than that in the reactor, flows backwards into the RPV, creating a jet impingement, or “backflow” force on the dryer. Simplified, conservative modeling is applied in this study to obtain reasonable bounding loads which allow for the dryer curvature and other complexities of the dryer-vessel geometry.