bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Diesel/CNG Dual-Fuel Combustion on Exhaust Soot Characteristics
Authors: Nithyanandan Karthik , Lin Yilu , Donahue Robert , Meng Xiangyu , Li Yuanxu , Lee Chia-Fon F.
Published: December 2016

This paper presents the chemical composition, oxidation reactivity and nanostructural characteristics of particulate matter (PM) produced by a diesel engine operating with diesel/compressed natural gas (CNG) dual-fuel combustion. Raw, undiluted soot samples from pure diesel, 40% CNG, and 70% CNG (energy-based substitution rate) combustion were collected from the exhaust pipe. Engine operating conditions were held at 1200 RPM and 20 mg/cycle baseline load. For dual-fuel operation, split diesel injection (two injections) was used as the pilot, and CNG was injected into the intake manifold. First, soot oxidation reactivity was characterized using thermogravimetric analysis (TGA). Carbon, hydrogen, and nitrogen weight fractions were obtained using elemental analysis to measure soot aging. Transmission electron microscopy (TEM) was then used to determine the diameter of the spherules, and the morphology of soot agglomerates. It was found that soot reactivity increased with increasing CNG content. TEM images revealed a higher variation in particle diameter with increasing CNG substitution. High resolution TEM (HRTEM) images showed that CNG70 soot displayed features of immature soot particles. The enhanced reactivity could also be due to more active sites available in CNG soot, as well as the CNG soot being immature. Under this test condition and engine configuration, it can be concluded that the use of CNG affects the morphology and nanostructure of PM, and hence the oxidation reactivity of the soot.
Fitness for Service Evaluation of Class 1 Piping Component
Authors: Abdelsalam Usama , Vijay Dk , Glover Andrew
Published: December 2016

This paper summarizes the methodology, procedure, and results of a fitness for service assessment performed for one CANDU outlet feeder in accordance with the COG FFSG Appendix E (Evaluation of Thinned Regions) ‘Level 3’. A wall thickness of 80% of the pressure-based thickness of the corresponding straight pipe is conservatively considered uniformly distributed along both tight radius bends. Plastic collapse load analyses are performed to address the pressure loading alone (E-6) and the bending moment plus coincident pressure loading (E-9). The crack initiation potential (E-10) is addressed by calculating the cumulative fatigue usage factor (Thermal & Seismic).

This paper highlights the major modelling and analysis details with particular emphasis on the challenges that cut feeder models would face when dealing with the seismic load. These challenges are handled using a full length feeder model and the results from both approaches are compared. It is demonstrated that the cut feeder model for this particular feeder is more conservative compared to the corresponding full length feeder model. As such, it is expected that the full length feeder model would have a significant potential in handling the seismic issues with CANDU feeder pipes. However, more analysis work is needed to confirm and support the findings of this paper in a more general sense.
Creep Rupture Life Prediction of Grade 91 Circumferential Welded Tube Under Combined Internal Pressure With Axial Load
Authors: Ogata Takashi , Mitsueda Toshiki , Sakai Hiroshi
Published: December 2016

Grade 91 steels are widely used for high temperature pipes in ultra-super-critical thermal power plants. It was recently reported that the creep damage was detected in the fine grain region within the heat affected zone (HAZ) in the welded pipes, so called “Type IV” damage. So far, studies on creep damage and life assessment methods for welded joints of the Grade 91 steel were concentrated on longitudinal welded pipes. Circumferential welded joints are also susceptible to Type IV damage due to the increase of axial thermal stress superimposed with pipe weight. In this study, the effect of additional axial stress to the axial stress produced by the internal pressure on damage and rupture property is discussed based on internal pressure creep tests adding different levels of the axial loads using the Grade 91 circumferential welded tubes. Rupture time of the circumferential welded tube decreases with increasing additional axial load level. Longitudinal cracking in the weld metal was observed in the specimens tested under lower additional load level, and Type IV cracking was observed in the specimens under higher additional load level. The stress analysis results indicate that the longitudinal stress in the HAZ increases with the axial load. Type IV cracking occurs at a certain value of a ratio of the total longitudinal stress to the circumferential stress. Under the test condition where Type IV cracking occurs, the rupture time is significantly shorter than the predicted rupture time based on the creep rupture data of the longitudinal welded tubes. The limited creep strain concept is introduced to predict the rupture time of the circumferential welded tubes by considering the effect of stress multiaxiality. Eventually, the rupture times caused by Type IV cracking of both the longitudinal and the circumferential welded tubes were accurately predicted by the limited creep strain concept.
Fatigue Usage Life and Gradient Factors for ASME Class 1 Piping Fatigue Analyses
Authors: Gosselin Stephen R. , Nunez Daniel , Esselman Thomas C. , Palm Nathan
Published: December 2016

This paper examines conservatisms associated with two aspects of piping fatigue life as applied in NB 3600 fatigue calculations. First, piping component allowable cyclic life is defined by stress-life (S-N) curves based on constant displacement push-pull test results of small diameter (≤ 0.375 inch (≤ 9.5 mm)) smooth test specimens in air at room temperature. These life estimates are subsequently applied to all Class 1 piping components regardless of their actual size or thickness. Secondly, all component cyclic stresses are treated as uniform through-thickness membrane stresses when most transients induce stresses that vary across the thickness of the pipe.

The application of fatigue usage correction factors that account for: 1) increased cyclic life associated with the growth of engineering size fatigue cracks in thicker components and 2) the presence of actual through-thickness stress gradients is considered. An example case study indicates that, depending on the nature of the applied cyclic loading and pipe section thickness, considerable reductions in design fatigue usage can be obtained.
Presentation of the New Edition of RCC-M Code in 2016
Authors: Malouines Philippe , Wintle John
Published: December 2016

The paper describes the general approach followed by AFCEN, the French Society for Design, Construction and In-Service Inspection Rules for Nuclear Island Components, in developing the RCC-M code from the technical and organizational points of views. The changes that the RCC-M Subcommittee has introduced into the 2016 Edition of RCC-M code are explained and commented upon. The main activities of the RCC-M Subcommittee have been in achieving and demonstrating conformity of the code with French regulation and making comparisons with other codes and standards. The paper highlights how industrial experience is being integrated into the RCC-M code and how conformity with the essential safety requirements of the European Pressure Equipment Directive has been demonstrated. The processes for updates, interpretations or inquiries are also addressed.
Seismic Responses of Isolated Buildings With Supplemental Devices Subjected to Near-Fault Earthquake
Authors: Liao Wen-I , Wang Sheng-Qing
Published: December 2016

Near-fault ground motions, which caused much of the damage in recent major earthquakes (Kobe 1995, Chi-Chi 1999), are characterized by a pulse-like motion that exposes the structure to high input energy at the beginning of the record. The first objective of this research is to compare the dynamic response of seismic isolated and non-isolated building structures subjected to near-fault ground motions with large velocity pulse. Two typical building structures with three stories and eight stories designed by Taiwan seismic design specifications of buildings are adopted for this study. Numerical results show that the seismic performance of isolated buildings is not definitely better than the no-isolated one under some near-fault ground motions with large velocity pulse. Secondly, the isolated building structures retrofitted with supplemental elastic device (SED) or supplemental viscous damper device are analyzed. Parametric studies for the dynamic response of seismic isolated buildings with and without supplemental devices are developed. Analyzed results show that the parameters PGV/PGA ratio and spectral velocity may govern the isolated building response characteristic for input near-fault pulse-like ground motions.
A Linear Flow Resistance Model of a Multi-Governing Steam Valve System Using Computational Fluid Dynamics
Authors: Wang Peng , Liu Yingzheng , He Jin , Xu Sihua
Published: December 2016

A linear flow resistance model (LFRM) of multi-governing valve system performance was built using computational fluid dynamics to determine the distribution of flow rate through all parallel-placed steam valves at different opening ratios. A four-valve configuration connected to a water-feed pump turbine was systematically separated into three sections: valve chambers, diffuser passages and governing stages. The steam flow through each individual section was computationally modeled, and revealed that pressure drops were dependent on the flow rate. A numerical simulation strategy based on shear stress transport (SST) turbulence modeling was validated by the experimental measurements from a single valve test rig, which showed favorable agreement with the measured pressure drop at different flow rates. Subsequently, an LFRM was built to consider the geometric topology. Here, the pressure drop’s dependency on the flow rate along each section in an individual valve passage was regarded as a transfer function module. A performance map of the multi-governing valve system was obtained to predict the flow rate distribution under the opening conditions of different valves. Finally, the three-dimensional steam flow of the full multi-governing-valve system was numerically simulated to obtain the steam flow rate through different valves, and found to be in good agreement with the prediction gained using the LFRM. The proposed model can potentially be used in planning operation control strategies.
Flexibility Analysis of Piping Systems With Discontinuities in Displacement
Authors: Choudhury Birendra N.
Published: December 2016

The class of piping flexibility analysis problems discussed in this paper arises when a new piping system at ambient temperature is connected to a piping system that is in operation. At the time of tie-in, the new piping has no thermal expansion and no elastic deformation. Therefore, displacement at the tie-points in the new piping system is zero. On the other hand, the operating piping systems would have undergone some displacements at this point before the tie-in. So there is a discontinuity in displacement at the tie point. This paper discusses how the equations for piping flexibility analysis can be modified to accurately obtain the redundant restraint forces for such cases and their use with current stress analysis programs for some piping configurations.
Fracture Mechanics and Inspection Qualification Issues Related to UK Licensing Aspects for Nuclear Reactors
Authors: Sharples John , Toft Adam , Turner Nick
Published: December 2016

With plans for new nuclear build being prominent in the UK in recent years, the licensing aspects have obviously been of paramount importance for the requesting parties. It has been particularly important for the requesting parties to properly understand the overall UK licensing framework and the detailed differences with respect to that of their country of origin. One of the main detailed differences is in the areas of fracture mechanics and Inspection Qualification and how the information relating to these two technical disciplines is linked in order to evaluate the defect tolerance of relevant plant components.
The Effect of Carbon Diffusion on Creep Behaviours for a Dissimilar Joint Between P91 and 12Cr1MoV Steels
Authors: Zhao Yanping , Gong Jianming , Jiang Yong
Published: December 2016

Dissimilar joints have been widely used in many applications, especially for steam piping in the superheater and reheater of power plants. However, these dissimilar metal welds tend to fail less than half of their design life, and carbon diffusion is the main cause of the premature failure. Dissimilar joints operated at high temperature or after post-weld heat treatment (PWHT) exhibit carbon-enriched zone (CEZ) in the high alloy part and carbon-depleted zone (CDZ) in the low alloy part, causing by the chemical potential gradients across the weld interface. The carbides dissolute in the low alloy part while precipitate in the high alloy part. At the same time, a consequent of strength gradients are generated between the CEZ and CDE. The CDZ results in a loss of creep strength due to the carbides dissolution while an increase of strength due to the carbides precipitation.

In this work, welding consumable of GTR-2CM was used to join P91 and 12Cr1MoV metals together. The stable phases and carbon activities of these metals are calculated by THERMO-CALC software. Carbon diffusion between P91/GTR-2CM/12Cr1MoV dissimilar joint after aging at 550 °C for varying time are predicted by employing dispersed multiphase model in DICTRA software. Volume fractions of carbides varying with distance from both sides of the weld interfaces were also investigated, showing that the formation of CDZs and CEZs is related to the dissolution and precipitation of M23C6 and M7C3 carbides. The dissolution and coarsening of M7C3 and M23C6 particles in the CDZ and CEZ were also modelled by DICTRA software.

The creep properties of base metals, weld metal and the dissimilar joint were investigated at 550 °C. The stress dependence of minimum creep rate and rupture life obeyed the Norton’s power law, and the stress exponents can be used to identify the creep mechanism. Monkman-Grant (MG) relations were also used to study the creep rupture data.

The simulation results of carbon diffusion can be used to study the creep properties of CDZ and CEZ for the P91/GTR-2CM/12Cr1MoV dissimilar joint. The threshold stress concept can be incorporated into the analysis of creep power law. The magnitudes of threshold stress within CEZ and CDZ can be calculated according to the volume fraction and average diameter of carbides from carbon diffusion.
Pressurization Analysis for Flame Heating of a Screw Top Utility Can Loaded With Plutonium Oxide Powder
Authors: Laurinat James E. , Kesterson Matthew R. , Hensel Steve J.
Published: December 2016

The documented safety analysis for the Savannah River Site (SRS) evaluates the consequences of a postulated 1000 °C (1273 K) fire in a glovebox. The radiological dose consequences for a pressurized release of plutonium oxide powder during such a fire depend on the maximum pressure that is attained inside the oxide storage containers. To enable evaluation of the dose consequences, temperature and pressure transients have been calculated for exposure of a typical set of storage containers to the fire. The oxide storage configuration selected for analysis is can/bag/can, comprised of oxide powder inside an 8.38E−6 m3 stainless steel B vial inside 0.006 kg of polyethylene bagging inside a one-quart screw top utility can of the type commonly used to package solvents or rubber cements.

The analysis accounts for pressurization from gases generated by pyrolysis of the polyethylene bagging and evaporation of moisture adsorbed onto the oxide powder. Results were obtained for different can orientations and different surface fire exposures, with and without initial pressurization of the B vial by hydrogen from the radiolysis of moisture. Based on the results of hydrogen back pressure tests for plutonium oxide powders loaded with moisture, the initial gauge pressure from radiolytic hydrogen was set at a bounding value of 82 psig (5.65E5 Pa). The pressurization analysis credits venting to and from the B vial but does not credit venting or leakage from the can.

Calculated maximum gauge pressures inside the utility can range from 1.98E5 Pa for an upright can exposed to fire on only one side, to 7.78E5 Pa for an upright can engulfed by fire. Maximum gauge pressures inside the B vial vary from 1.36E5 to 1.43E6 Pa. Due to the low rate of venting from the B vial into the can gas space, the can pressure is nearly independent of the B vial pressure.

Calculated maximum pressures are compared to the utility can burst pressure. In lieu of an analytic structural analysis of the utility cans, burst pressures and leakage rates were measured using compressed nitrogen gas. Leakage of gas through the can lid thread and seams prevented the test apparatus from reaching the burst pressure. To achieve the burst pressure, it was necessary to seal the can lid threads and seams by brazing. The measured gauge burst pressure was 2.50E5 +/− 0.43E5 Pa. The measured burst pressures are lower than the calculated maximum pressure due to fire exposure, indicating that the utility cans could burst during exposure to a 1000 °C (1273 K) fire.

Leakage rates were measured for cans initially pressurized to a gauge pressure of 1.24E5 Pa. The measured leakage rates were found to be proportional to the gauge pressure inside the can, with a time constant for leakage of 0.424 +/− 0.010 reciprocal seconds. The leakage time constants follow a threshold Weibull distribution.
Reconstruction by Data Assimilation of the Inner Temperature Field From Outer Measurement in Thick Pipe
Authors: Argaud Jean-Philippe , Bouriquet Bertrand , Courtois Mathieu , Le Roux Jean-Christophe
Published: December 2016

The detailed knowledge of the inner skin temperature behavior is very important to evaluate and manage the aging of large pipes in cooling systems. We describe here a method to obtain this information as a function of outer skin temperature measurements, in space and time. This goal is achieved by mixing fine simulations and numerical methods such as impulse response and data assimilation. Demonstration is done on loads representing extreme transient stratification or thermal shocks. From a numerical point of view, the results of the reconstruction are outstanding, with a mean accuracy of the order of less than a half percent of the temperature value of the thermal transient.
An Improved Design of Threaded Closures for Screw Plug (Breech Lock) Heat Exchangers
Authors: Sippy Haresh K. , Chandiramani Dipak K.
Published: December 2016

Threaded closures for pressure vessels have been in use for decades. Much work has been done to develop convenient, safe and economical threaded closures. Threaded closures are used when there is a need for opening the vessel either for maintenance or as part of its operation.

Heat Exchangers are a typical application where there is a need for opening the vessel and cleaning the tubes at regular intervals to maintain the heat transfer efficiency. These are known as Breech Lock or Screw Plug Exchangers. These are basically U-tube exchangers. The channel side operates at high temperature and pressure and it has a threaded end closure. In some designs, the shell side may also be at high pressure. The tube bundle is removable without having to dismantle the channel or disconnect the nozzles from the pipeline. Thus screw plug exchangers help to reduce fabrication cost and reduce time for in-service maintenance.

The major problem encountered with the use of such end closures are 1) Jamming of the threaded plug, due to deformation of the channel barrel. Thus the opening of the end closure by unscrewing becomes a difficult task. With the increase in operating temperatures and pressures, the problems become more severe, due to which, users are not inclined to use these type of end closures.

A study was undertaken to assess the reasons for bulging of the end of the channel which caused jamming of the screw threads and also for leakage through the gasket.

By shrink fitting a ring over the end of the channel, the deformation was reduced, enabling easy opening of the cover.

2) The leakage through the gasket between the shell and tubesheet, causing the intermixing of shell and tube-side fluids. This on analysing was found that the additional forces were acting on the gasket due to thermal expansion of the internals. This led to changing to a gasket that could withstand the forces and pressure.

Leakage through the gasket was prevented by analysing the additional forces acting on the gasket due to thermal expansion of the internals and changing to a gasket that could withstand the forces and pressure.
Sliding and Rocking Motion Mitigation of a Rigid Body Subjected to Seismic Excitation due to High-Viscous Liquid
Authors: Ito Tomohiro , Sakurai Hideki , Shintani Atsuhiko , Nakagawa Chihiro
Published: December 2016

After the accident at the Fukushima Daiichi Nuclear Power Plant in Japan, it has steadily become more important to ensure the structural integrity of cask systems containing spent fuels or radioactive debris during seismic events. These cask systems are free-standing cylindrical structures and are believed to show rocking and sliding motions at huge seismic excitations. In the worst case, these cask systems can possibly overturn or collide with each other. Therefore, it is very important to reduce the sliding and rocking motions of the cask system in order to avoid subsequent contamination due to radioactive substances.

To date, the authors have been studying the response behaviors of these motions, and have developed some types of methods that are effective at mitigating sliding or rocking motions, and confirmed the effectiveness of these methods. A system utilizing coaxial circular cylinders and high-viscosity liquid filled into the annular spaces was developed for the suppression of sliding motion. This system was installed at the bottom end of the rigid body. Previous studies show that liquids with high-viscosity provide a very large added damping effect that causes sliding motion to be suppressed significantly. For the suppression of rocking motion, the authors developed a system that utilizes a gyro system, and confirmed it’s effectiveness both analytically and experimentally.

However, the gyro system is slightly complex and requires electric power even during a seismic event. Thus, some passive suppression method is required. On the other hand, the above-mentioned coaxial circular cylindrical system filled with high-viscosity liquid is thought to have a high damping effect on rocking motion, along with suppression of sliding motion.

This study investigated the effect of rocking motion suppression due to the above-mentioned coaxial circular cylindrical system that is utilized for the suppression of sliding motion. First, an analytical model that can account for the coupled rocking and sliding motion was established, and then the rocking behavior of a rigid structure coupled with its sliding motion was studied. Next, shaking table tests were conducted by using a fundamental test model. By comparing the analytically obtained rocking motion with that obtained by the test results, the validity of the analytical model was confirmed. Finally, the analytical model was modified for cask systems equipped with a rocking suppression system, and the rocking motion was analyzed to evaluate its effectiveness.

The proposed rocking suppression system was found to be very effective in suppressing the rocking motion of the rigid body when subjected to base excitations.
Experimental Study on Ultimate Strength of Single and Double Type Bellows Under Internal Pressure
Authors: Ando Masanori , Yada Hiroki , Tsukimori Kazuyuki , Ichimiya Masakazu , Anoda Yoshinari
Published: December 2016

Containment vessel is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. Namely, the safety margins due to the relationship of the ultimate toughness of containment vessel structures and maximum design pressure is not clear. Indeed, to clarify the progress of the events under the beyond design basis events (BDBE) and to design the BDBE countermeasure equipment, it is necessary to evaluate the pressure toughness of containment vessel adequately. The containment vessel of fast reactor is composed of the various structures, and one of the thinnest boundary structures is bellows structure to absorb the thermal expansion of the coolant piping penetrating the containment vessel. In addition to the containment vessel boundary, evaluating the pressure toughness of reactor coolant and gas boundary is also important because of same reason of that in the containment vessel boundary. In the primary coolant and gas boundary, the cover gas bellows of the intermediate heat exchanger in fast reactor is one of the thinnest structures and has important role when the progress of the BDBE is considered. Therefore, in order to develop the evaluation method of the pressure toughness of bellows structure under the BDBE, the pressure failure tests and finite element analysis of the bellows structure subjected to internal pressure were performed in this study.
Constraint Solutions for Cracked Plates and Cylinders
Authors: Meek Caroline , Gintalas Marius , Sherry Andrew H. , Ainsworth Robert A.
Published: December 2016

There is little advice in fitness for service procedures for assessing constraint parameters T (elastic) and Q (elastic plastic) for biaxially loaded plates and cylinders.

This paper presents the analytical determination of T stresses for biaxially loaded plates and the determination of Q for plates and cylinders using finite element analyses. It demonstrates the extent to which T can be used to conservatively predict Q and how, near collapse, Q can be estimated from the stress field corresponding to plastic collapse, enabling a significant reduction in computing effort.

The effect of biaxial loading of plates and cylinders on these parameters is discussed as well as the differences found when comparing the values for plates and cylinders.
Development of a New Thermo-Mechanical Environmental Fatigue Testing Facility to Investigate the Impact of Thermal Strain Gradients on Fatigue Initiation
Authors: Platts N. , Brown P. , Gill P. J. , Smith R. D. , Stairmand J. W.
Published: December 2016

Light water reactor coolant environments are known to significantly reduce the fatigue life of austenitic stainless steels. However, most available data are derived from isothermal testing of membrane loaded tensile specimens, whereas the majority of plant loading transients result from thermal transients and involve significant through-wall strain gradients. This paper describes the development of a high temperature water facility to enable both thin and thick wall hollow fatigue endurance specimens to be subjected to thermal and mechanical loading for a wide range of thermal cycles including rapid shock loading.

Thermal shock loading from 300°C to between 40 and 150°C has been achieved and Finite Element Analysis, FEA, has been used to calculate the thermally induced strain profiles through a 12mm thick-wall specimen. This indicates peak surface thermal strain ranges of up to 0.8% for a transient between 300 and 40°C. Testing is underway to investigate the impact of the strain gradient and thermal waveform on the fatigue life of this specimen where significantly longer lives may be expected compared to membrane loaded specimens.

The ability within the same facility to apply simulated thermal shock profiles to both thick-wall specimens and mechanically loaded thin wall specimens provides a powerful tool to assess the impact of thermal fatigue loading and thermal strain gradients on component life.
FeCrAl Alloys for Accident Tolerant Fuel Cladding in Light Water Reactors
Authors: Rebak Raul B. , Terrani Kurt A. , Fawcett Russ M.
Published: December 2016

The goal of the U.S. Department of Energy (DOE) Accident Tolerant Fuel Program (ATF) for light water reactors (LWR) is to identify alternative fuel system technologies to further enhance the safety of commercial nuclear power plants. An ATF fuel system would endure loss of cooling in the reactor for a considerably longer period of time than the current systems. The General Electric (GE) and Oak Ridge National Laboratory (ORNL) ATF design concept utilizes an iron-chromium-aluminum (FeCrAl) alloy material as fuel rod cladding in combination with uranium dioxide (UO2) fuel pellets currently in use, resulting in a fuel assembly that leverages the performance of existing/current LWR fuel assembly designs and infrastructure with improved accident tolerance. Significant testing was performed in the last three years to characterize FeCrAl alloys for cladding applications, both under normal operation conditions of the reactor and under accident conditions. This article is a state of the art description of the concept.
ASME B16 Cases 1 and 2, and Their Implications for ASME B16.34 Valves
Authors: Cheta Ayman
Published: December 2016

Similar to ASME Boilers and Pressure Vessel Code Cases, ASME B16 Standards Committee has recently begun to issue B16 Cases to address urgent needs for rules on materials and constructions not covered by existing B16 standards. Case 1[3], approved on December 16, 2013, provides alternative rules for establishing pressure-temperature ratings for ASME B16.34 [1] valves made of Group 3 (high nickel alloys) materials. Case 2[4], approved on February 13, 2014, provides rules for use of unlisted materials for construction of ASME B16.34 valves. In this paper, the author provides an overview of both Cases and discusses their potential implications for ASME B16.34 valves.
Traditional Versus New Technology Boiler Drum Water Level Instruments
Authors: Liu Zhelin , Harris John Michael , Liu Jichuan , Han Dong , Liu Lei
Published: December 2016

The art and science of boiler drum water level measurement has long been the source of questionable results. A low-tech examination of the boiler drum reveals where the drum level has been controlling — there is a water mark inside the drum. The problem is obvious; the mark in the drum and that in the control system do not agree. The level is off by a wide margin. This paper seeks to explain how poor assumptions are the source of the error. Then two design approaches are considered to eliminate the sources of error. Consider that boiler drum water is not saturated; feedwater entering from the economizer is below saturation. Also consider the constant head chamber. Typically, the reference leg is considered to be at ambient temperature, but it is really a gradient starting at near drum temperature. The effect of these two poor assumptions is a relatively large error such that the true level is different from indicated level.

Once this situation is understood, it is possible to redesign instruments which take the actual situation into account. One such instrument is nearly the same as the original DP-type instrument, but the constant head chamber is located inside the drum. This design change deals with both errors. It eliminates the differences in temperature and density between the constant head leg and the water inside the drum. It also exposes the constant head leg to the exact same temperature as the boiler water, thus eliminating the need for complicated (and incorrect) formulae to compensate for the differences in density. A second design approach is to “steam jacket” an instrument located outside the drum, thus eliminating the differences in temperature and density. This is an appropriate way to deal with the Conductivity Probe and the Boiler Water gauge glass. By steam jacketing these instruments, we can make the water temperature between the indicator and the drum almost the same.
Stress Analysis and Structural Integrity Evaluations of Pressure Vessel in Molten Salt Reactor
Authors: Wang Xiaoyan , Zhu Shifeng , Wang Xiao , Cao Yun
Published: December 2016

To guarantee the safety of nuclear reactor, the stress analysis and structural integrity evaluations of the reactor pressure vessel (RPV) are very important for Thorium-based Molten Salt Reactor (TMSR), whose design temperature and design pressure are 700 °C and 0.5MPa respectively. In this paper, the structural analysis is firstly carried out by using a 3D coarse model of the RPV. Secondly, the reactor core support are recalculated by a sub-model with a fine mesh and the analysis results are evaluated according to ASME NH code, including stress evaluation, strain and deformation evaluation and creep-fatigue evaluation. It was found that the initial structural did not meet the requirements of creep-fatigue limits. Finally, structural optimization designs are proposed, such as T-shaped modified structure and fillet design, whose results can satisfy the requirements of creep-fatigue limits. These analysis methods and results provide some practical engineering guidance to the structural design and safety evaluation of the RPV in TMSR.
Reactor Cavity Analysis Under Steam Explosive Conditions by TNT Model
Authors: Kim Seung-Huyn , Chang Yoon-Suk , Cho Yong-Jin
Published: December 2016

Steam explosion may occur in nuclear power plants by fuel-coolant interactions when the external reactor vessel cooling strategy is failed. This phenomenon can cause shock wave that endangers surrounding reactor cavity wall due to resulting dynamic effects. Even though extensive researches have been performed to predict influences of the steam explosion, due to complexity of physical phenomena and thermal-hydraulic conditions, it is remained as one of possible hazards. The object of this study is to examine characteristics of reactor cavity and nuclear components under representative steam explosion conditions. In this context, an assembled finite element mesh was generated and evaluated by the trinitrotoluene model. As a result, stresses, strains and displacements of the reactor cavity and nuclear components were calculated. Subsequently, crack evaluation of reinforced concrete was performed and their results were discussed.
Safety Evaluation of the Hydrogen Flaking Damage in the Doel 3 and Tihange 2 Reactor Pressure Vessels
Authors: Roussel Guy
Published: December 2016

In the summer of 2012, the detection of a large number of quasi-laminar flaw indications in the reactor vessel beltline ring forgings of two Belgian pressurized water reactors (Doel Unit 3 and Tihange Unit 2) posed a significant safety threat that led the licensee to shutdown both plants. Those indications were identified by the licensee as hydrogen flakes that developed during the fabrication of the forgings. As a prerequisite for a potential restart of the units, the Belgian Nuclear Safety Regulator, the Federal Agency for Nuclear Control (FANC), requested the licensee to provide, for each unit, a safety case demonstrating the acceptability of the reactor pressure vessel for continued operation. As the technical subsidiary of the FANC, Bel V performed a safety evaluation of the condition of the reactor pressure vessels. The paper documents the approach Bel V used in his safety evaluation and the criteria he defined to evaluate the acceptability of the hydrogen flaking damage in the reactor pressure vessels.
Analysis of Fatigue Crack Growth in Standard Endurance Test Specimens in Support of Total Life Approaches to Fatigue Assessment
Authors: Mann Jonathan , Twite Marius , Burke M. Grace
Published: December 2016

The ASME Boiler & Pressure Vessel Code Section III method for the evaluation of fatigue in nuclear plant components uses a fatigue design curve derived from the testing of standard cylindrical specimens to describe the fatigue endurance of austenitic stainless steel components. The test results describe the number of cycles to achieve a 25% total load drop within a standard specimen (approximately equal to a 3 mm crack) under membrane loading conditions and the design curve is commonly associated with fatigue initiation. However, for non-standard loading conditions, such as the case of a thermal gradient within a component where a crack may be growing into a decreasing stress field, this description of initiation may be overly conservative.

Alternative approaches, such as the total life approach, may provide better representations of fatigue life in real plant components. By separating out quantifiable portions of long crack growth (Stage II) from the current design curve, alternative definitions of initiation can be derived and subsequently used in conjunction with standard fracture mechanics in order to model fatigue more accurately.

In this paper numerical methods are used to model the fatigue crack growth between starting crack depths of 0.25 mm, and the depth associated with a 25% load drop in a standard cylindrical specimen. The numerical predictions are compared with striation spacings measured at a range of crack depths on the fracture surfaces of austenitic stainless steel specimens tested in both air and water environments, under strain control. A good correlation between numerical predictions and the measured striation spacings was obtained and the results are used to characterise different stages of fatigue cracking.

Based upon the methods developed in this paper, modified fatigue design curves, using alternative definitions of crack initiation, are proposed and their applications in total life approaches to fatigue assessment are discussed, based on a worked example of a thermally fatigued stepped pipe experiment.
Evaluation of Repair Welding Influence on GH3535 Superalloy Microstructure and Mechanical Properties
Authors: Li Chaowen , Chen Shuangjian , Yu Kun , Li Zhijun
Published: December 2016

GH3535 supperalloy, whose grade of ASME is UNS N10003, is currently considered as a candidate material for solid-fuel and fluid-fuel molten salt reactor in china. During the development of procedures for welding GH3535 superalloy, consideration should always be given to the possibility that repair welding may be necessary. This paper presents weld repairs of GH3535 alloy rolled plates using gas tungsten arc welding with filler metal. The purpose of this work is to evaluate the low heat input process for weld repair of GH3535 alloy plates about the microstructure features and mechanical properties. The results demonstrated that sound joints without defects could be obtained after weld repairs. Due to repair thermal cycles on the original weld seam, the size of carbide precipitate became large, but repair welding is found to cause no decrease in short-term time-independent strength.
Comparison of a One-Dimensional Pursuit Model With Experimental Data for Rarefaction Pressure Wave Catch-Up and Diminishment of a Pressure Shock Within Two-Phase Media
Authors: Pellman Abby M. , Jones Ryan E. , Minichiello John C.
Published: December 2016

The Waste Treatment Plant (WTP), located at the U.S. Department of Energy’s Hanford Site, will process waste slurries capable of retaining a dispersed non-condensable gas phase while in a quiescent state. Under postulated conditions, a pressure pulse generated from a deflagration or detonation within a flammable gas pocket may be transmitted into piping systems that contain the gas-liquid slurry. It is necessary to understand how a pressure pulse diminishes as it propagates through the system in order to properly quantify the structural loading on the piping and its associated supports. Earlier work presented a set of conservation equations and discussed the dynamics of individual bubble oscillations but still required discretization within a numerical CFD solver (Reference PVP2015-45972). To simplify the computation requirements, a one-dimensional pursuit model that calculated the rarefaction wave catch-up was developed and compared to experimental data.

This paper presents a one-dimensional model that utilizes the difference in speeds of the shock and acoustic rarefaction waves in the two-phase media to model the propagation and diminishment of a traveling pressure shock wave. The rarefaction waves overtake the shock front which is then rapidly diminished and decreases speed accordingly. Results of the pursuit model are compared to experimental data and shown to accurately capture the diminishment behavior and shock propagation.
Re-Evaluation of Long-Term Creep Strength of Welded Joint of ASME Grade 91 Type Steel
Authors: Yaguchi Masatsugu , Nakamura Kaoru , Nakahashi Sosuke
Published: December 2016

Creep rupture data of welded joints of ASME Grade 91 type steel have been collected from Japanese plants, milling companies and institutes, and the long-term creep rupture strength of the material has been evaluated. This evaluation of welded joints of Grade 91 steel is the third one in Japan as similar studies were conducted in 2004 and 2010. The re-evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained since the previous study, with durations of the new data of up to about 60000h. The new long-term data exhibited lower creep strength than that obtained from the master creep life equation for welded joints of Grade 91 steel determined in 2010, then the master creep life equation was again reviewed on the basis of the new data using the same regression method as that used in 2010. Furthermore, the weld strength reduction factors obtained from 100000h creep strength of welded joints and the base metals are given as a function of temperature, where the master creep equations of the base metals are also redetermined in this study.
Fatigue Life Properties and Anomalous Macroscopic Fatigue Fracture Surfaces of Low Carbon Steel JIS-SM490B in High-Pressure Hydrogen Gas Environment
Authors: Ogawa Yuhei , Matsunaga Hisao , Yoshikawa Michio , Yamabe Junichiro , Matsuoka Saburo
Published: December 2016

Tension-compression fatigue tests using smooth specimens of low carbon steel JIS-SM490B were carried out in air and hydrogen gas environment under the pressure of 0.7 and 115 MPa at room temperature. In 0.7 MPa hydrogen gas, fatigue life curve was nearly equivalent to that in air. On the other hand, in 115 MPa hydrogen gas, fatigue life was significantly degraded in the relatively short fatigue life regime (e.g. Nf < 105). To clarify the effect of hydrogen environment on fracture process, fracture surfaces of these specimens were observed. In general, fatigue fracture process of steels with low or moderate strength is macroscopically divided into 3 stages. In the first stage (stage I), fatigue cracks initiate in some crystalline grains. In the second stage (stage II), the cracks propagate stably on a cycle-by-cycle basis. In the final stage (stage III), a tilted fracture surface, shear-lip, is formed by ductile tearing. In SM490B steel, this general fracture process was confirmed in air and 0.7 MPa hydrogen gas. In contrast, in 115 MPa hydrogen gas, there was no tilted portion in the stage III region, and the fracture surface was totally flat. Observation with scanning electron microscope revealed that dimples were formed by ductile tearing in the tilted fracture region in air and 0.7 MPa hydrogen gas. On the other hand, only a quasi-cleavage fracture surface existed in the final fracture region in 115 MPa hydrogen gas. To understand the cause of this peculiar fracture morphology, we conducted elasto-plastic fracture toughness tests in each environment, and investigated the fracture morphology.

As a result of fracture toughness tests, crack growth rate in air and 0.7 MPa hydrogen gas was approximately equal to each other, and both the fracture surfaces were covered by dimples. This fracture morphology was in accordance with that of stage III morphology in fatigue specimen tested in air and 0.7 MPa hydrogen gas. However, in 115 MPa hydrogen gas, the crack growth was significantly accelerated, and the whole fracture surface was covered by quasi-cleavage.

In this paper, firstly, the similarity of fracture surface between two test methods, i.e. fatigue test and fracture toughness test, is investigated. And then, the formation mechanism of the flat fracture surface is discussed by paying attention to the crack-growth acceleration in high-pressure hydrogen gas.
Residual Stress State of X65 Pipeline Girth Welds Before and After Local and Furnace Post Weld Heat Treatment
Authors: Ren Yao , Paradowska Anna , Wang Bin , Eren Elvin
Published: December 2016

This research investigated the effects of global (in other words, furnace-based) and local post weld heat treatment (PWHT) on residual stress (RS) relaxation in API 5L X65 pipe girth welds. Two pipe spools were fabricated using identical pipeline production procedures for manufacturing multi-pass narrow gap welds. Non-destructive neutron diffraction strain scanning was carried out on girth welded pipe spools and stress-free comb samples and also thin slices for the determination of lattice spacing. All residual stress measurements were carried out at the KOWARI strain scanning instrument at the Australian Nuclear Science and Technology Organization (ANSTO).

Residual stresses of two pipe spools (in the as-welded condition) were measured through the thickness in the weld material and adjacent parent metal starting from the weld toe. Three line-scans were completed 3mm below outer surface, at mid thickness and 3mm above the inner surface. PWHT was adopted for stress relaxation; one pipe was conventionally heat treated entirely in an enclosed furnace and the other was locally heated by a flexible ceramic heating pad. Residual stresses were measured after PWHT at exactly the same locations as those used for the as-welded condition. Residual stress states of the two pipe spools in as-welded condition and after PWHT were compared and the results were presented in full stress maps. Additionally, through thickness residual stress profiles and the results of one line scan (3mm below outer surface) were compared with the respective residual stress profiles advised in British Standard BS 7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the UK nuclear industry’s R6 procedure. The residual stress states of the two pipe spools measured in the as-welded condition were similar. With the given parameters, local PWHT has effectively reduced residual stresses in the pipe spool to such a level that it prompted the thought that local PWHT can be considered a substitute for global PWHT.