bluuebunny/crossref_metadata_2025_split huggingface dataset:
Behavior of Wood Filled Impact Limiters During the IAEA Thermal Test
Authors: Feldkamp Martin , Erenberg Marina , Nehrig Marko , Bletzer Claus , Musolff André , Schönfelder Thorsten , Wille Frank 
Published: October 2017

Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood, encapsulated by steel sheets. These impact limiters shall ensure that transport casks meet the IAEA safety requirements. After damage caused by the mechanical tests the package has to withstand a severe fire scenario. It is required that the mechanical tests have to produce maximum damage, taking into account the thermal test. Furthermore, any damage, which would give rise to increased radiation or loss of containment or affect the confinement system after the thermal test, should be considered. Concerning the thermal test, the IAEA safety requirements state that during and following the fire test, the specimen shall not be artificially cooled and any combustion of materials of the package shall be permitted to proceed naturally.
Different works from the French Institute for Radiological Protection and Nuclear Safety (IRSN) and BAM show that additional energy supply from a pre-damaged impact limiter to the cask could occur caused by smoldering of the wood. This effect should be considered within the safety assessment of the package. A heat wave from the fire could overlap with the additional energy from the impact limiter in the sealing system. In 2015 BAM conducted small scale fire tests with wood filled metal drums showing continuing combustion processes during the cooling down phase. As not much is known about smoldering processes in wood filled impact limiters, it is highly complex to define pre-damage of impact limiters, which are conservative, regarding the most damaging energy flow from the impact limiter to the containment system in dependence of time. More research has to be done to develop models to examine the effects of smoldering impact limiters on the containment of packages for the assessment. The process of smoldering is described with regard to the requirements in the thermal safety assessment. Parameters influencing the smoldering process are identified.
BAM operates test facilities to examine the issue of mechanical damage, combustion and heat transfer of packages for transport of radioactive material. A thermal test will take place with a wood filled test specimen with a diameter of about 2.3 meters. The aim is to understand the phenomena of smoldering under the consideration of relevant regulatory boundary conditions.
Acoustical Characteristics of Single and Two-Phase Horizontal Pipe Flow Through an Orifice
Authors: Belfroid S. P. C. 
Published: October 2017

In this work, the acoustic effects of horizontal air-water flow through an orifice are investigated experimentally. Single phase flow (air) and two-phase flow (air and water) tests are performed for two sets of orifices. One set of straight edged and one set of upstream rounded orifices. For each set, the diameters of the orifices were 2, 5, and 10mm, with a thickness of 5 mm. The two-phase flow is generated by injecting water at a rate of 0 to 40 g/s to air in a pipe with diameter of 25 mm. The air rate is fixed in the range from 5.8 to 14 g/s, where the upstream pressure varies from 1.5 to 4 bar at ambient temperature. Unsteady pressure fluctuations are recorded at two upstream and two downstream position.
The valve noise standard NEN-EN-IEC (60534-8-3, 2011) for dry gas is assessed by means of experimental data in dry conditions at fixed air mass flow rate. Predictions of sound power spectra by means of the standard are found to be more accurate compared to those obtained following Reethof & Ward (1986), also in conditions of a choked orifice.
In case of multiphase flow already at very low liquid fractions of much less than 1%, the standard is no longer valid. The frequency spectrum is no longer determined by the jet noise but starts to be dominated by low frequency general multiphase flow. The Strouhal number based on the jet conditions is an order lower than Sr = 0.2 indicating process variations rather than jet noise. Furthermore, at choking conditions the further expansion which occurs in single phase flow is likely different at multiphase flow. For non-choked flow, the standard can be adapted using multiphase mixture properties. This does lead to a good prediction. However at choked conditions, this method fails.
A Numerical Study on Fracture Toughness of CANDU Pressure Tube
Authors: Keim Elisabeth , Nicak Tomas , Wasiluk Bogdan 
Published: October 2017

CANDU pressure tubes carry nuclear fuel and belong to the primary heat transport system. They are fabricated from cold-worked Zr-2.5Nb alloy prone to deuterium ingress under normal operating conditions. Increased hydrogen equivalent concentration and reactor pressure-temperature transients result in development of a brittle phase, hydride, changing mechanical behavior. The hydride downgrades fracture toughness properties in the transition region and reduces material ductility.
Canadian Nuclear Safety Commission founded a two-phase project to improve understanding of the parameters governing fracture toughness properties and load carrying capacity of Zr-2.5Nb pressure tubes with elevated hydrogen equivalent concentrations. This paper presents preliminary results obtained in the first phase. The fracture behavior of a curved compact tension specimen (CCTS) and a pressure tube burst specimen (PT) with axial through-wall crack used in destructive burst test were studied in details. The intention was to identify any differences between fracture behavior of the CCTS and the PT potentially affecting fracture toughness estimates.
The stress and deformation states ahead of the crack front, calculated fracture toughness parameters including J-integral and crack tip opening displacement (CTOD), as well as fracture constraint by means of elastic T-stress have been discussed.
Component Testing and Numerical Calculation of a Bolted High Temperature Power Plant Pipe Flange Connection Under Complex, Near-Service Loads
Authors: Leibing Benjamin , Klenk Andreas , Seidenfuss Michael 
Published: October 2017

To ensure a reliable power supply with a minimum environmental impact in the future, further increases in efficiency and flexibility of fossil-fired power plants are major challenges to address in recent R&D activities. In order to counterbalance substantial fluctuations in the electricity grid due to the rising share of renewable resources, frequent start-ups and shutdowns of turbomachinery accompanied by quick and heavy load changes will be claimed by the market. Hence, along with the development of advanced materials for elevated steam parameters, contemplations with respect to altered boundary conditions of currently used materials, e.g. for bolted pipe flange connections, are required.
In this paper, a selection of results from a recently finished research project on stress relaxation will be presented. Together with European power plant component manufacturers, a newly developed test rig comprising a scaled IP steam turbine pipe flange now allows investigations under near-service conditions. Before, throughout and after performance of the experiments, an extensive measurement setup enables the examination of effects that cannot be studied in standardized relaxation tests. For example, deformation of the flange plates caused by the interaction of creep and stress relaxation can be considered as such an effect. Within this project, a loss in bolt pretension of up to almost 50% over a comparatively short period of experimental time was observed. By means of numerical calculations, creep deformation in the transition areas between pipe and flange plate sections was identified to be a major originator of these pretension drops. Particularly, good correlations between experiments and FEM-simulations could be achieved through the implementation of enhancements concerning the fitting process of the Graham-Walles-type creep model which was used.
Design and Analysis of Vertical Vessels for Lifting in Fully Dressed Condition
Authors: Doctor Christopher , Stefanovic Radoslav 
Published: October 2017

Depending on plant/site location, it may be advantageous to dress a vertical vessel, in horizontal position, prior to erection. Dressing refers to the installation of items attached to the vessel such as internals, insulation, piping, ladders, platforms, electrical cable trays, lighting, etc. The decision to dress a vessel may be due to safety, schedule or economic reasons. Dressing a vessel results in higher lifting loads.
Vessel Codes address loadings to be considered when designing a vessel in its operating position and not necessarily for lifting. Since the Codes do not address erection loadings, engineering judgment must be used in their consideration and analysis in order to avoid overstressing the vessel. In some cases, erection loads govern the design thickness of the vessel.
Lifting analysis in the context of this paper is the evaluation of stresses in the vessel when it is initially picked up from the horizontal position. This paper discusses the compressive stresses which usually govern in the lifting analysis of thin-walled vessels. Different methods used in literature and industry are presented in the paper. Some Owners/Users, engineering firms, and fabricators use the Factor B in ASME Section II, Part D, Subpart 3 as the limiting criterion for compressive stresses. In some cases, this criterion is too conservative. This paper presents the application of alternative buckling criteria for lifting analysis.
Swelling of VVER-1000 Core Baffle: Numerical Modeling and Direct Measurement of its Geometrical Dimensions
Authors: Oryniak Andrii , Orynyak Igor 
Published: October 2017

Traditionally, the brittle strength evaluation of reactor pressure vessel was the central issue in lifetime assessment of Ukrainian nuclear power plants (NPPs). The problem of swelling of the reactor core baffle only recently got due attention from the side of operator.
Here the most efforts were given on numerical modeling of austenitic steel 08Kh18N10T swelling and its effect on induced stresses in core baffle and distortion of its geometry. The calculation shows that essential changing of core baffle dimensions is expected after 35–40 years of operation. Eventually this can lead to the contact with the core barrel. Yet, these predictions contain the big number of uncertainties related to the input data used in analysis: fluence distribution; temperature variation due to heat release induced by neutron and gamma radiation; thermal-hydraulic boundary condition between the baffle and coolant; and, especially, the adopted law of swelling in dependence with above factors as well as mechanical stresses.
So, the second task was to measure the real geometry of baffle after 27 years of operation, to determine its change and compare these results with the numerically calculated data with accounting for the design tolerances. Thus, the spatial measurement system (SMS) equipped with ultrasonic gages was designed. It contains the central vertical beam which can move in vertical direction and rotate. To the lower end of the beam four horizontal levels are attached, which are equipped with device resistant to the hot water and radiation. The gages are used to measure the shortest distances to the edges of baffle. Two types of results were obtained. The first one are the measurements in the different horizontal planes obtained by rotation the SMS around the vertical axis with angular steps equal to 1 degree. These results were difficult to handle with and required a special mathematical treatment due to the possible shift of the centre of measurement. The second set of measurements was performed by moving the SMS in vertical direction. These data demonstrate the change of distance with the height.
The results clearly show that problem of swelling do exists, and, in general, the measured patterns of the distortions along the vertical and angular coordinates correspond to numerically obtained results. Further work on baffle integrity is however needed.
Hybrid Welding vs Conventional Welding: A Solution to Residual Stress and Distortion Mitigation?
Authors: Gallee Sébastien , Lacroix Rémi , Robin Vincent , Gommez Florence , Jourden Erwan 
Published: October 2017

The present paper deals with the hybrid laser/MIG welding process, which allows to assembly high thickness steel sheets. The laser heat source added to the MIG torch improves the process productivity while respecting quality standard.
The multi-pass welding simulation of a plate is presented in this paper and numerical results are compared to experimental measurements (temperature and stresses).
Water Hammer Caused by Fast Closing Valves
Authors: Koirala Shesh R. , Telci Ilker T. 
Published: October 2017

Operation of fast closing valves in piping systems can create an overpressure condition, resulting in permanent deformation, joint damage, leakage, or rupture. Fast closing valves are used in many piping systems to protect personnel, equipment and the environment from the danger of overpressure. When there is a sudden closure of a piping system valve, the change in the flow velocity produces a transient increase in pipe pressure. This increased pressure is commonly known as transient, fluid hammer waterhammer, or surge pressure. In a very simplistic system, the excess pressure created by this sudden closure of valves can be computed using a simple hand calculation using Joukowsky method. The method is applicable only for the initial pressure wave generated. In complex systems, where there are dead legs (e.g. closed by-pass valves) or branches, there is more chance of the pressure waves being reflected, transmitted and superimposed. The overpressure problem is even more severe if a liquid column separation and re-joining occurs during the transient conditions. The magnitude of the pressure in the system due to these effects may be higher than that estimated by Joukowsky method. Hence a transient analysis needs to be performed to estimate the overpressure in the system.
In this case study, the transient conditions initiated due to closure of buckling pin valves (BPVs) are modeled using a proprietary software CE099. The objectives are to calculate the maximum surge pressures, dynamic loads, and to recommend mitigations to reduce transient pressures and loads. The results showed that pressures could be reduced by increasing the pipe size of few segments or adding expansion loops. The most sensitive parameter for transient pressure was pipe size and that for dynamic load was valve closure time. It is recommended that this kind of study be performed in the early phase of engineering design, so that any identified overpressures can be mitigated with simple, cost effective options such as increasing pipe size, altering valve closure times, and adding expansion loops.
Fitness-for-Service Creep Life Evaluation of a Hot Reheat Piping System at 400,000 Operating Hours
Authors: Cohn Marvin J. 
Published: October 2017

This paper discusses a fitness-for-service (FFS) evaluation of a hot reheat (HRH) piping system with about 400,000 hours of operation. It discusses significant differences between the as-designed and simulation as-found piping stress analyses. The significant range of stresses in the piping system illustrates that the few lead-the-fleet girth welds should have significant creep damage decades before many other girth welds.
Since the weldment examination intervals will correspond to scheduled outages, the creep life uncertainties can be grouped into high, medium, and low priorities (e.g., 0–10 years, 10–20 years, and beyond 20 years) with high confidence of rankings among the selected groups.
There are 14 girth welds in this HRH piping system. In this case study, only 2 girth welds were evaluated as high priority nondestructive examination (NDE) locations and 1 girth weld was evaluated as a medium priority location for the next set of NDE reexaminations. Many of the low priority girth welds have predicted creep rupture lives substantially beyond 1,000,000 operating hours.
An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array
Authors: Elhelaly Amro , Hassan Marwan , Mohany Atef , Moussa Soha 
Published: October 2017

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure.
This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.
Creep Life Prediction of HR3C Steel Using Creep Damage Models
Authors: Lee Hoomin , Kang Seok-Jun , Choi Jae-Boong , Kim Moon-Ki 
Published: October 2017

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions.
In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.
Simulation of Fatigue Crack Initiation in Heat Affected Zone Microstructure Using Crystal-Plasticity Finite Element Method
Authors: Hiraide Takashi , Igi Satoshi , Tagawa Tetsuya , Ikeda Rinsei , Tsutsumi Seiichiro 
Published: October 2017

It is well known that fatigue fracture of welded joints can depend on many factors such as residual stress, stress concentration and an inhomogeneous microstructure in the HAZ (Heat Affected Zone). Some solutions to improve fatigue properties, for example, hammer peening (1), have been developed to mitigate effects related to stress. Improvement from mechanical view point is not only applied, but optimized microstructure design of the base metal and HAZ should be also considered. However, microstructural effects on fatigue crack initiation behavior have not been fully understood because systematic experimental evaluation of them takes much efforts with difficulty. An analytical method is a useful idea to specify the optimum microstructure against fatigue crack initiation before experimental examinations. CP-FEM (Crystal-Plasticity Finite Element Method) is expected to describe fatigue crack initiation behavior, because it can express strain localizations caused by an inhomogeneous microstructure.
In the present study, a simulation model using CP-FEM is developed to describe strain localizations under cyclic loading. Microstructural effects on plastic strain localization and accumulation were investigated by changing microstructural factors.
Modified GTAW Orbital Tube-to-Tubesheet Welding Technique, and the Effect of a Copper Weld Retainer During Welding of Alloy 825
Authors: Krustev Angel , Alexandrov Boian , Kovacich Jerry 
Published: October 2017

Tube-to-tubesheet welds are an essential part of the design of heat exchangers used in power generation, petro-chemical, chemical processing, pharmaceutical, and food processing industries. The tube-to-tubesheet welds are typically produced using gas tungsten arc welding (GTAW) with or without the addition of filler wire, and involve carbon steels and various creep and corrosion resistant alloys. The weld heat input in tube-to-tubesheet welds is an essential parameter that controls the productivity and weld quality, in terms of weld bead geometry and heat affected zone microstructure and properties.
A modified GTAW tube-to-tubesheet orbital welding head that utilizes a copper weld retainer is described in this paper. The copper weld retainer provides a heat sink during welding, and supports the molten weld metal. This permits the use of a relatively high heat input, required for a single pass welding with filler wire addition. Furthermore, the copper retainer limits the amount of weld overlap into the tube bore.
The application of the modified orbital welding technique, which helped for resolving a suspected liquation cracking problem in Alloy 825 tube to 316L stainless steel tubesheet welds, is presented.
Proposed Approach of Scenario Analysis Using a Probabilistic Code
Authors: Sallaberry Cédric J. , Kurth Robert E. , Brust Frederick W. , Kurth Elizabeth A. 
Published: October 2017

The following paper presents a global methodology to analyze the set of results generated by a probabilistic analysis. The approach regroups traditional analyses such as Sensitivity Analysis (SA), Uncertainty Analysis (UA), and stability analysis as well as sensitivity studies (both deterministic and probabilistic) with enhanced sampling techniques (double loop to separate aleatory from epistemic uncertainty, importance sampling, adaptive sampling) in an incremental set of steps, with the goal to give the analyst and decision maker the most comprehensive and defensible collection of results.
An example using the xLPR code and a selected scenario is used to illustrate each step of the approach.