bluuebunny/crossref_metadata_2025 huggingface dataset:
Fitness for Service Assessments on Cracked Heavy Wall Reactors
Authors: Keltjens Jan , Van Zyl Gys , Mudhayeq Fahad
Published: November 2018

A number of large heavy wall reactors showed severe stress corrosion cracking in the high strength low alloy steel shells. The stress corrosion was mainly caused by the fact that no PWHT was performed which resulted in very high hardness of the Heat Affected Zone; this made the HAZ extremely sensitive for stress corrosion cracking in the feed water environment. The extent of the cracking was such that replacement of all reactors was unavoidable. The redesign and fabrication of the new reactors would take over a year. Fitness for Service methodologies were used keep the reactors running safely until the replacements were installed with minimized down time. This resulted in large economic benefits over several years. The paper covers the FFS assessments performed, the special NDT methods required to get the necessary crack size information at operating conditions as well as failure mode and repair options. It demonstrates an application and the benefits of Fitness for Service assessments on key equipment.
Application of JSME Seismic Code Case by Elastic-Plastic Response Analysis to Practical Piping System
Authors: Otani Akihito , Kai Satoru , Kaneko Naoaki , Watakabe Tomoyoshi , Ando Masanori , Tsukimori Kazuyuki
Published: November 2018

A Code Case in the framework of JSME Nuclear Codes and Standards is being developed to incorporate a seismic design evaluation methodology for piping by means of advanced elastic-plastic response analysis methods and strain-based fatigue criteria. The Code Case as an alternative seismic design rule over the current rule will provide a more rational seismic design evaluation than the current criteria.

This paper demonstrates an application result of the JSME Seismic Code Case to an actual complex piping system. The secondary coolant piping system of Japanese Fast Breeder Reactor, Monju, was selected as a representative of the complex piping systems. The elastic-plastic time history analysis for the piping system was performed and the piping system has been evaluated according to the JSME Seismic Code Case. The evaluation by the Code Case provides a reasonable result in terms of the piping fatigue evaluation that governs seismic integrity of piping systems. Moreover, it is found that the supporting forces and the response accelerations of the piping system obtained by the elastic-plastic response analysis also become more rational results than those with the current elastic response analysis. The contradiction of two requirements in piping design, flexibility for thermal expansion and rigidity for seismic response, can be effectively relaxed by use of the Code Case being developed.
Optimization of Reactor’s Start-Up and Shutdown Procedures by Transient Thermo-Mechanical Finite Element Analysis
Authors: Lee Sang-Mo , Kwon Ohgeon , Garcia Vitor Lopes
Published: November 2018

Efficient refinery start-up and shutdown durations are vital in establishing prolonged productivity in refineries operating hydrotreating reactors. The benefits of efficient start up and shutdown cycles are extensive, and include considerable operational and cost reduction. Reduced start-up and shutdown cycles, however, require increased heating and cooling rates, which cause higher temperature gradients throughout the reactor vessel, consequently leading to higher thermal stresses, which may affect damage mechanisms and limit reactor’s life. The equipment’s OEM has defined guidelines for the reactor heating and cooling during start-up and shutdown cycles and any attempt to reduce the start-up and shutdown duration is usually limited by these guidelines. It is therefore necessary to carry out an engineering assessment to determine the effect of changing the start-up and shutdown procedures beyond the OEM guidelines on reactor’s life.

Multiple thermo-mechanical Finite Element analyses for a series of different start-up/ shutdown procedures, including the current procedure, were carried out to determine the through-wall thermal gradient and stresses, and identify the most critical locations. In order to estimate convective heat transfer coefficients, Computational Fluid Dynamic (CFD) analysis was utilized to describe the complex fluid flow behavior of the feedstock in the presence of catalysts and internal geometry features. Low Cycle Fatigue (LCF) was adopted as a main damage mechanism to quantify the damage as a result of the changed operating conditions. It was determined that the LCF life calculated in the reactor vessel’s critical damage locations was found to be sufficiently long with respect to the frequency of start/shutdown cycles, even with operating conditions exceeding the OEM limit. Therefore, alternative guidelines were suggested to achieve the time reduction in startup/shutdown operation by increasing ramp rates without compromising structural integrity of the vessel.
Development of High Temperature Semiconductor Strain Gages for Thermal Power Plant Applications
Authors: Suprock Christopher A. , Christian Joseph J. , Rosinski Stan T.
Published: November 2018

This paper discusses a specially developed semiconductor strain cell that allows sensitive measurement of surface strain in environments with temperatures up to 1050F (566C). There is an unmet industry-wide need in the manufacturing and power generation fields for monitoring material mechanics and component degradation at temperatures exceeding the maximum working temperature of traditional strain gage technologies. This technology advances attachment methodology of the semiconductor gage to allow field deployment and a physically reliable interface with structural strain. Measuring strain at these temperatures is useful both in the laboratory and in practical monitoring applications. The technology provides a way to monitor changes in materials exposed to heat and stress and give plant engineers tools to predict and avoid critical failures.
Discussion on Rules of Inspection and Type Test for Imported Pressure Piping Valves in China
Authors: Zhou Lu-yun , Fu Ming-hai , Xu Wei-pu
Published: November 2018

In recent years, the number of imported Chinese pressure pipeline valves has been increasing, and the Administration of Quality Supervision Inspection and Quarantine (AQSIQ) issued Circular No. 151 in 2012 to clarify that the imported pressure piping valves need to have type test by the bodies approved by the type testing administration verified by AQSIQ. This paper makes a comparative study on the differences of the valve test and the test standard commonly used in China and in the foreign countries, as well as on the relevant requirements of the valve manufacturing standards involved in the imported valve type test. Through the comparison on above test standards and type test requirements, the foreign manufacturers will understand the standard differences, inspection requirements and precautions when importing China’s pressure pipeline valve. Combined with imported valve inspection and type test case analysis to help foreign enterprises fully understand our laws and regulations to ensure that when they import Chinese valve, they can meet our requirements to ensure the use security.
Seismic Test Result of Motor-Operated Butterfly Valve Actuators for Nuclear Power Plant
Authors: Kojima Nobuo , Tsutsumi Yoshitaka , Yonekura Kazuyoshi , Nishino Koji , Watanabe Yukio , Kumagai Shin , Kamino Hiroyuki
Published: November 2018

Seismic tests were carried out to confirm the operability limit acceleration for a standard motor-operated butterfly valve actuator in three excitation directions. Based on the results, seismic brackets that can operate valves even in three directions at 20 × 9.8 m/s2 or more were designed in three representative models. For the model subjected to the seismic test, we mounted the designed seismic bracket and confirmed the operability of the butterfly valve actuator by carrying out vibration tests in three directions at 20 × 9.8 m/s2. We used these results and previously reported motor-operated valve actuator seismic test results to creat a revision (draft) of the earthquake resistance evaluation methods.
Estimation Accuracy of Absolute Maximum Elasto-Plastic Displacements of MDOF Oscillators Based on a Modal Combination Rule With Post-Yielding Modal Properties and Linear Response Spectrum Values
Authors: Taniguchi Tomoyo , Toda Yoshihiko , Ono Yusuke , Mukaibo Kyosuke
Published: November 2018

Taniguchi, et al. [1] developed an analytical method for evaluating the absolute maximum elasto-plastic displacements of multi-degree-of-freedom (MDOF) oscillators under the action of base excitation based on a modal combination. Its essence is that 1) modal frequencies, shapes and damping during yielding of any member of the MDOF oscillators are readily specified by the modal analysis with the secondary stiffness of the members being yielded, 2) assuming that a bilinear hysteresis may describe the force-displacement relationship of each mode, an equivalently linearized system consisting of a single-degree-of-freedom (SDOF) oscillator is introduced to approximate the absolute maximum elasto-plastic displacement of each mode, 3) the absolute maximum elasto-plastic displacement of the MDOF oscillator is evaluated by the Square Root of Sum of Squares rule (SRSS-rule) by combining the maximum elasto-plastic displacement of each mode approximated by the proposed equivalently linearized system. This study first provides small modification in the equivalently linearized system. Then, employing a couple of MDOF oscillators whose spring at arbitrary storey may yield and an accelerogram, the maximum elasto-plastic displacement of the MDOF oscillator is calculated by the proposed method and is compared with that computed by the time history analysis. Their comparison suggests that the proposed method can reasonably evaluate the absolute maximum elasto-plastic displacement of the MDOF oscillator subjected to earthquake excitation as the conventional SRSS-rule does that for the linear MDOF oscillators.
Applicability of the Simplified Analysis and Relevant Calculations to Evaluating Uplift Displacement of Unanchored Tanks
Authors: Taniguchi Tomoyo , Yoshida Yuichi , Hatayama Ken
Published: November 2018

Evaluation of the rocking motion of unanchored cylindrical tanks subjected to the ground acceleration is a main topic in the framework of the seismic vulnerability assessment of this particular kind of structures. However, despite the anchored or unanchored tanks, any calculation that attempts fully evaluate tank uplift has not been presented, while many of the analyses of the tank rocking motion and the deformation of the tank bottom plate have been respectively presented. This paper carries out a thought experiment of applicability of these analyses to evaluating uplift of the unanchored tanks. First, this paper focuses on an anchored tank at a chemical plant whose anchor bolts were pulled-out during the 2011 off the pacific coast of Tohoku Earthquake. Second, combine a few analyses of uplift of the unanchored tanks being available to date; then, calculate the uplift displacement of an anchored tank of interest as if it were an unanchored tank. Next, infer the pulling-out length of anchor bolt of the anchored tank of interest from a photo in a reconnaissance report; then, compare it with the uplift displacement calculated. Since the uplift displacement calculated is larger than that inferred. Since a discrepancy between them would be responsible for the constraint effects of anchors that have not been clearly quantified, the present analyses of the tank rocking motion and the deformation of the tank bottom plate may have a potential to give an appropriate uplift of unanchored tanks.
Experimental Results and Numerical Analyses of Tests Conducted on Large Alloy 600 Centre Cracked Tensile Specimens
Authors: Le Delliou Patrick , Dahl Anna , Sonnefraud Christophe , Vincent Willy
Published: November 2018

Some components of the main primary circuit of PWR nuclear power plants contain nickel-base alloy 600 parts (steam generator (SG) tubes, steam generator partition plates, lower internal radial supports). It is well known that this alloy is prone to stress corrosion cracking in the primary water environment. In 2002, surface cracks were discovered for the first time in SG partition plates of EDF 900 MWe NPP. The integrity of the SG containing these cracks must be demonstrated for all operating conditions, including accidental conditions. Due to the high tensile consolidation rate and the high fracture toughness of alloy 600, this was proved using limit load analysis. However, for a thorough demonstration, an experimental program was launched at EDF/R&D to better understand the behaviour of cracks in this high fracture toughness material. Centre Cracked Tensile (CCT) specimens were selected for this experimental program, being closer to the industrial case than conventional CT specimens.

Two tests have been conducted at room temperature on large CCT specimens containing a semi-elliptical crack. The paper presents the design of the CCT tests, the material characterisation, the main results of the tests and their numerical interpretation.
Drag Loads From Vapor Cloud Explosions
Authors: Geng Jihui , Lowry William , Thomas Kelly
Published: November 2018

Drag loads due to the gas flows generated by vapor cloud explosions (VCEs) can damage piping and vessels, particularly near or in the flammable cloud. There is little guidance available to the piping and vessel designer regarding the magnitude of such drag loads, beyond evaluating drag loads on a case-by-case basis [e.g., using computational fluid dynamics (CFD)]. This paper presents a newly developed set of drag loads vs standoff distance for a range of flame speeds and vapor cloud sizes. Nine flame speeds were evaluated, up to and including supersonic flame speeds. Cloud sizes are characterized using energy scaled standoff distances (i.e., Sachs scaling). The purpose of this work is to provide a database of drag loads that can be used to evaluate the structural response of piping, vessels, equipment, and supporting structures. The database presentation is similar to that used for existing VCE blast load charts, such as those used in the Baker-Strehlow-Tang (BST) and TNO MEM (Multi-Energy Model) methods.
Creep Evaluation for a PWR Reactor Pressure Vessel Lower Head Under Severe Accident Conditions Considering Sustained Internal Pressure
Authors: Gao YongJian , Cao Ming , He YinBiao
Published: November 2018

In-Vessel Retention (IVR) is one of appropriate severe accident mitigation strategies for AP1000 Nuclear Power Plant (NPP), and assurance of prevention against to thermal failure and structural failure of Reactor Pressure Vessels (RPV) is the prerequisite of IVR. A Finite Element Model fora RPV considering lower head melting was established, the creep calculation was carried out after the temperature field analysis, and the stress-strain responses for different times were obtained. By means of choosing representative evaluation sections and applying the Accumulative Damage Theory based on Larson-Miller Parameter, the Creep Damage calculations and evaluations were conducted. The results showed that the failure modes associated with creep rupture would not happen under IVR condition when a certain amount of internal pressure sustained. The approaches employed in this paper could be utilized in structural integrity evaluation of RPV under IVR for other new type NPPs.
Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation
Authors: Scano Lorenzo , Esposito Luca
Published: November 2018

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).
Study on the Predictive Evaluation Method of Nonlinear Sloshing Wave Height of Cylindrical Tanks: Part 2 — Proposal and Examination of Applicability of the Predictive Evaluation Method
Authors: Sago Hiromi , Morita Hideyuki , Takata Tomoshige , Madokoro Hideki , Murakami Hisatomo , Yokoi Shinobu , Yamamoto Tomohiko
Published: November 2018

When cylindrical tanks installed on the ground, such as oil tanks and liquid storage tanks, receive strong seismic waves, including the long-period component, motion of the free liquid surface inside the tank called sloshing may occur. If high-amplitude sloshing occurs and the waves collide with the tank roof, it may lead to accidents such as damage to the tank roof or outflow of internal liquid. Therefore, it is important to predict the wave height of sloshing generated by an earthquake input.

Sloshing is vibration of the free liquid surface, and when the sloshing wave height is small, it can be approximated with a linear vibration model. In that case, the velocity-response-spectrum method using velocity potential can estimate the sloshing wave height under an earthquake input. However, when the sloshing wave height increases and the sloshing becomes nonlinear, it is necessary to evaluate the wave height using other methods such as numerical analysis.

Taking into consideration that design earthquake levels tend to increase and the use of seismic isolation mechanisms has continued to spread in recent years, the amplitude of the long-period components of an earthquake input which act on cylindrical tanks may also increase. Therefore, although the evaluation of nonlinear sloshing wave height is important, there are few examples which quantitatively evaluate the wave height of nonlinear sloshing.

The purpose of this study is to construct a simple evaluation technique of a nonlinear sloshing wave height of cylindrical tanks. In this study, the simple evaluation technique of the nonlinear sloshing wave height was proposed based on the study result shown by the 1st report (PVP2018-84416). Moreover, in order to verify the applicability of the proposed evaluation technique, the shaking table test and flow analysis which used the small cylindrical tank were carried out. As a result, the applicability of the proposed evaluation technique has been verified.
Development of New Design Fatigue Curves in Japan: Proposal of a New Fatigue Evaluation Method
Authors: Asada Seiji , Hirano Akihiko , Saito Toshiyuki , Takada Yasukazu , Kobayashi Hideo
Published: November 2018

In order to develop new design fatigue curves for carbon steels & low-alloy steels and austenitic stainless steels and a new design fatigue evaluation method that are rational and have clear design basis, Design Fatigue Curve (DFC) Phase 1 subcommittee and Phase 2 subcommittee were established in the Atomic Energy Research Committee in the Japan Welding Engineering Society (JWES). The study on design fatigue curves was actively performed in the subcommittees.

In the subcommittees, domestic and foreign fatigue data of small test specimens in air were collected and a comprehensive fatigue database (≈6000 data) was constructed and the accurate best-fit curves of carbon steels & low-alloy steels and austenitic stainless steels were developed. Design factors were investigated. Also, a Japanese utility collaborative project performed large scale fatigue tests using austenitic stainless steel piping and low-alloy steel flat plates as well as fatigue tests using small specimens to obtain not only basic data but also fatigue data of mean stress effect, surface finish effect and size effect. Those test results were provided to the subcommittee and utilized the above studies.

Based on the above studies, a new fatigue evaluation method has been developed.
Verification of the Relation Between the Directions of Control Force and Responses in Active Seismic Isolation Device
Authors: Nakamura Keigo , Miura Nanako , Sone Akira
Published: November 2018

In this research, the focus is on the energy problem in active vibration control of a seismic isolation device using self-powered active control that regenerates electric power from kinetic energy of vibration system and uses it as control power. In recent years, it is proposed to install semi-active control or active control in an isolated structure to deal with seismic waves of various periods. However, since energy is required for control, there is a problem that the desired response reduction performance cannot be achieved when energy supply is interrupted at the time of a power outage. In our previous device, power is always given to the motor to control, thus power consumption is high. Therefore, the purpose of this research is to propose input method of control force that can reduce control power while keeping base isolation performance by classifying the role of the control force for each control phase and considering various combinations of input control force.
Fast Reactor Core Seismic Experiment and Analysis Under Strong Excitation
Authors: Yamamoto Tomohiko , Iwasaki Akihisa , Kawamura Kazuteru , Matsubara Shinichiro , Harada Hidenori
Published: November 2018

In design of fast reactor (FR) core components, seismic response must be evaluated in order to ensure the structural integrity. Thus, a core seismic analysis method has been developed to evaluate 3D core vibration behavior considering fluid structure interaction and vertical displacement (upward).

Thirty seven 1/1.5 scale core element models which shape hexagonal-arrangement were used to validate the core element vibration analysis code in three dimensions (REVIAN-3D). Based on the test data, the newly incorporated analysis model has been verified to respond to strong excitation.
Fast Reactor Core Seismic Experiment of Full Scale Single Model of Control Rod
Authors: Iwasaki Akihisa , Matsubara Shinichiro , Kawamura Kazuteru , Harada Hidenori , Yamamoto Tomohiko
Published: November 2018

The control rod guide tube self-stands on the core support plate. The control rod is inserted in the control rod guide tube, and the control rod hangs from the upper structure of the reactor. At scrum in case of an earthquake, the control rod is detached and it sits on the seating structure in the control rod guide tube. The control rod guide tube is raised more easily than the fuel assembly by the vertical differential pressure of the core during operation, because the control rod guide tube is lighter than the fuel assembly. Therefore, it is necessary to restrain the rising of the control rod guide tube. The sleeve dashpot structure, in which a sleeve is attached on the upper surface of the receptacle tube, is employed. Moreover, the control rod guide tube is equipped with the control rod dashpot in order to restrain the vertical movement of the control rod. In case of an earthquake, horizontal vibrational behavior also arises. The horizontal vibration generates friction force in the vertical direction and it restrains the rising. In this seismic evaluation of the control rod guide tube and the control rod, only the vertical motion is taken into consideration because it becomes conservative side against the rising displacement.

The seismic evaluation of the control rod guide tube is performed in operating condition (the coolant is flowing upward); that of the control rod assembly (the control rod guide tube and the control rod) is performed in shutdown condition (the coolant is not flowing).

Seismic experiments were performed using a full-scale model of the control rod guide tube and the control rod, vertical excitation and water instead of liquid sodium in the actual plant, to verify the analysis method and to demonstrate the rising restraining effect of the sleeve dashpot and the control rod dashpot. In this study, the rising behavior of the control rod guide tube and the control rod was investigated. The effect of restraining rising by the sleeve dashpot and by the control rod dashpot was confirmed.
Fast Reactor Core Seismic Analysis for Verification of Assessment Model of Control Rod
Authors: Iwasaki Akihisa , Matsubara Shinichiro , Kawamura Kazuteru , Harada Hidenori , Yamamoto Tomohiko
Published: November 2018

The control rod guide tube self-stands on the core support plate. The control rod is inserted in the control rod guide tube, and the control rod hangs from the upper structure of the reactor. At scrum in case of an earthquake, the control rod is detached and it sits on the seating structure in the control rod guide tube (Fig.1). In a vertical earthquake, the control rod guide tube is raised from the core support plate, and the control rod is also raised from the control rod guide tube. Therefore, drawing out may arise. During the earthquake after scrum, the rising behavior is different from the other core elements because the control rod and the control rod guide tube rise interfering each other.

The control rod guide tube is raised more easily than the fuel assembly by the vertical differential pressure of the core during operation, because the control rod guide tube is lighter than the fuel assembly. Therefore, it is necessary to restrain the rising of the control rod guide tube. The sleeve dashpot structure, in which a sleeve is attached on the upper surface of the receptacle tube, is employed. Moreover, the control rod guide tube is equipped with the control rod dashpot in order to restrain the rising displacement of the control rod.

This paper summarizes the analysis method of the rising behavior of the single control rod guide tube and the rising behavior of the control rod and the control guide tube after the control rod is inserted.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 5 — Influence of Damper Properties on Lifetime
Authors: Aida Kiyoshi , Minagawa Keisuke , Tanaka Go , Fujita Satoshi
Published: November 2018

In 2011, Great East Japan Earthquake that is the largest earthquake ever observed in Japan occurred. The earthquake had large energy, long duration and many aftershocks, and coal-fired thermal power plants were damaged by the earthquake [1]. Boiler structures in coal-fired thermal power plants are generally high-rise structures, and boilers are simply suspended from the top of the support structures in order to allow thermal expansion, so boilers easily vibrate [2]. In order to suppress vibration of boilers during earthquakes, stoppers are generally set between boilers and support structures. The stoppers are made of steel, and dissipate vibration energy by plastic deformation. However aseismic requirements for thermal power plants have been increased as a result of the Great East Japan Earthquake. Thus authors have developed a vibration control damper for coal-fired power plants. The damper is set instead of conventional stopper. Construction of the damper is similar to oil dampers, but inner fluid is viscous fluid. In PVP 2017, the basic performance of the proposed damper was presented [3–5]. In this paper, influence of damper properties on lifetime of the damper was investigated by seismic response analyses. In addition, lifetime of dampers for long period and long duration earthquake waves were investigated by seismic response analyses.
A Study on the Magnetic Distribution of Nd-Fe-B Permanent Magnets in Pipeline in Line Inspection Tool
Authors: Song Pan , Tang Xiaoying , Wang ShaoJun , Ren Bin , Zuo Yantian , Wang Jielu
Published: November 2018

The pressure pipeline in line inspection technology is the most effective nondestructive testing method to detect the quality of buried oil and gas pipelines at present. In line inspection tool usually uses magnetic flux leakage (MFL) technology to detect the change of leakage magnetic field to detect pipeline defects. Permanent magnets magnetize the wall of the pipeline as an excitation. During the detection process, the magnetic field performance of permanent magnets is required to be high. At the same time, the magnetic performance of the permanent magnet in the magnetic cleaning pipe also determine the cleaning effect inside the pipeline. In this paper, the magnetic distribution of permanent magnets is studied and the Nd-Fe-B permanent magnets with the best magnetic properties are taken as the objects. The finite element simulation is used to optimize the shape of the permanent magnets with better magnetic distribution, and the magnetic intensity factors of the preferred cylindrical permanent magnets are analyzed. In addition, three experiments of the influence of temperature, the influence of the ferromagnetic combination, and the influence of the environment medium are conducted.

As a result, the relationship between the magnetic intensity of the Nd-Fe-B permanent magnets and the factors is obtained. The conclusion is of great significance to the design and research of permanent magnetic circuit in line inspection magnetization device.
Large-Scale Simulation for Particle Damping
Authors: Saeki Masato , Bitoh Mika
Published: November 2018

Particle damping is an effective method of passive vibration control. Although it has been widely used in various structural damping applications, there are some points to be examined. Few studies have focused on the difference in the effectiveness of particle dampers for systems with different natural frequencies. Also, a computational scheme for conducting large-scale simulations has not been established. The authors previously presented some computational methods for predicting large-scale particle damping. The calculations are performed using equivalent large particles instead of the original-size particles. However, the range of the radius of the equivalent large particles for which these methods are effective is still incompletely understood. The objective of this study is to experimentally examine the difference in the effectiveness of particle dampers for systems with different natural frequencies and to investigate the relationship between the radius of the equivalent large particles and the validity of the computational methods.
Investigation of the Time and Temperature Dependent Behavior of Metal Seals in Radioactive Waste Containers
Authors: Grelle Tobias , Wolff Dietmar , Probst Ulrich , Jaunich Matthias , Völzke Holger
Published: November 2018

The Bundesanstalt für Materialforschung und –prüfung (BAM) runs an investigation program on the long-term behavior of multi-component metal seals. Such seals are used in a wide area of applications including transport and storage casks for spent nuclear fuel and high level radioactive waste. The seal function is mainly based on the compression of the inner helical spring, which generates the necessary seal force to keep the sealing surfaces in close contact. This in turn leads to a plastic deformation of the outer jacket of the seal, comprised of highly ductile aluminum or silver that adapts to the sealing surfaces of cask body and bolted lid, thus providing high level leak tightness. In Germany, those casks are licensed for interim storage periods of up to 40 years or more if extended interim storage would become necessary before a final repository is available. Thus, the sealing performance has to be evaluated, including factors like elevated temperature due to decay heat or mechanical loads due to transport under normal as well as accident conditions. Long-term investigations at BAM have been running over the last nine years to identify and evaluate the seal performance by measuring the remaining seal force, the useable resilience and the leakage rate after various time intervals at temperatures ranging from room temperature up to 150 °C. It was found that the seal force and useable resilience decrease with time and temperature, caused by creep deformation of the outer jacket. In order to obtain an analytical description for the seal behavior and to achieve more information on the material behavior under application conditions a comprehensive investigation program with focus on aluminum as outer jacket material was launched. The program includes material investigations such as compression and tension creep tests with representative basic materials. An additional test setup allows for the continuous measurement of the remaining seal force at temperatures of up to 150 °C. Furthermore, seal segments are compressed and stored in heating chambers, thus producing segments at different stages of the aging process. The segments are investigated regarding the development of the contact area width, jacket thickness and microstructural changes. This data will be used to develop material models and an analytical description of the time and temperature dependent long-term sealing behavior. This paper explains the current status of gained test results and modelling approaches and closes with an outlook to the future project plans.
Local Mesh Refinement for Correlation of FEA Estimated Plastic Strain to Tests in Areas of High Plastic Strain
Authors: Liu Katharine , Xiao Emma , Westwater Gregory , Johnson Christopher R. , Mann J. Adin
Published: November 2018

The total strain, elastic plus plastic, was measured with strain gages on valve bodies with internal pressure that caused surface yielding. The correlation of the simulated maximum principal strain was compared to strain gage data. A mesh sensitivity study shows that in regions of large plastic strain, mesh elements are required that are an order of magnitude smaller than what is used for linear elastic stress analysis for the same structure. A local mesh refinement was adequate to resolve the local high strain values. Both the location and magnitude of the maximum strain changed with a local mesh refinement. The local mesh refinement requirement was consistent over several structures that were tested. The test and simulation work will be presented along with the mesh sensitivity study. Some results on using an energy stabilization technique to aid convergence will be presented in terms of the impact on the predicted plastic strain.
Evaluation of Strength of Pipe With Metal-Loss due to CUI by FFS and FEA Which Considered the Fracture Ductility
Authors: Yamaguchi Atsushi , Yoshida Nobuyuki
Published: November 2018

Corrosion under insulation (CUI) is an aging degradation issue in long-term service vessels and pipes made of carbon steel and low-alloy steel. One of the problems in managing CUI is an equivocal evaluation technique of thinning detected by inspection. A replacement period with more accuracy can be evaluated more appropriately by performing fitness-for-service (FFS) assessment in this equipment. It is important to verify the validity of the FFS assessment using actually corroded pipes in order to promote the spread of FFS assessment in the domestic industry. In the present paper, pipes with complicated metal-loss due to CUI that were used in a chemical plant are burst in burst tests. An estimated burst pressure, which is calculated based on the assessment of metal-loss and through finite element analysis (FEA) based on FFS assessment, is compared with experimentally obtained burst pressures in order to validate the integrity evaluation. The burst pressure is then estimated by FEA, in which the ductile fracture under the multiaxial stress condition is considered. The burst pressure estimated by FFS approximately matched the burst pressure obtained based on experimental results. Fitness-for-service is sufficiently valid for investigating the remaining strength or burst pressure of corroded pipe. In addition, the burst pressure estimated by FEA that considered the ductile fracture under the multiaxial stress condition agreed with the experimental results and is valid so long as the remaining strength factor (RSF) is less than 0.6.
A Case Study: Balanced Globe Valves Failure, Root Cause, and Recovery
Authors: Farrell Ronald , Laney Matthew , Vock Preston , Garcia Andrew
Published: November 2018

During the pre-operational blowdown testing of the AP1000® Automatic Depressurization System (ADS), it was observed that several ADS Stage 1-3 balanced globe valves did not fully open; however, the valves did sufficiently open to provide adequate ADS flow to meet the ADS System depressurization safety function. Since the Main Control Room did not receive a full-open signal indicating that the ADS valves fully completed the valve stroke, the valves were disassembled to determine the potential cause and scoring was observed on the valve disk and valve body guide surfaces. A technical design review team was formed and determined that the primary cause was unequal thermal expansion between the thin walled valve disk and the thicker valve body resulting in interference during valve stroking. Classical thermal and CFD analyses were used to confirm that, once a normally closed globe valve received its signal to open, there was not sufficient “soak time” for the thicker valve body to reach thermal equilibrium with the thinner valve disk; thus, as the valve disk stroked open as it moved along the guide surfaces, there was not sufficient clearance resulting in scoring between the disk and the guides preventing the disk from stroking fully open. The solution was to maximize the clearance between the disk and body guides to allow for thermal growth during the ADS blowdown event. However, changing the clearances between the body guides and disk may compensate for thermal growth but may also impact the valve’s “balancing” function; therefore. disk piston rings were added to restore the tight clearance needed for “balancing” yet sufficiently provide relief from the effects of thermal growth. A prototype valve was retrofitted, and small scale validation tests were performed using air to challenge the changes. The preliminary performance test results were utilized by system designers to better understand the valve function in the event of an ADS blowdown. Although no full-scale retrofit testing was practical using high temperature saturated steam, as no suitable test facility was available within the plant operational test schedule time frame, the quality of the recovery effort yielded a high degree of confidence that the system retest would be successful. The project came to a successful conclusion upon two successful operational ADS blowdown tests with the retrofits installed.
Application of the CEL Approach to Consider FSI for the Assessment of Leak Tightness for Elastomeric Seals
Authors: Gorash Yevgen , Bickley Alan , Gozalo Francisco
Published: November 2018

Swellable elastomeric seal is a type of specifically engineered packer that swell upon contact with wellbore fluids. Assessment of leakage tightness is a fundamental aspect in the design of swellable packers, since they should guarantee a reliable sealing under extreme pressures of the downhole fluids. Numerical capability of the leakage pressure prediction would facilitate improvement in the packer design methodology. Previous work was focused on investigation of the non-parametric optimisation capability seeking for an optimal external shape with a goal to maximise the grip of a packer with a borehole. The verification of an optimised design was done with a dynamic FE-simulation of packer’s failure by extrusion under an excessive pressure. The downside of that verification analysis was that Abaqus/Explicit solver couldn’t implement a realistic adaptive pressure application due to changing packer disposition and contact conditions. This simulation challenge is addressed in this paper by application of the Coupled Eulerian-Lagrangian (CEL) approach in Abaqus/Explicit, which provides the ability to simulate a class of problems where the fluid-structure interaction is important.
Estimation of Weibull Life Distributions From Expert Categorical Estimates of Failure Probabilities
Authors: Cluever Joseph , Esselman Thomas , Harvey Sam
Published: November 2018

The Electric Power Research Institute (EPRI) with Électricité de France (EDF) developed the Integrated Life Cycle Management (ILCM) computer code to provide a standard methodology to support effective decision making for the long-term management of selected nuclear station components. In 2016, a Likelihood of Replacement (LoR) expert elicitation was developed to provide reliability curves for determination of replacement options for components that were not initially included in ILCM. The LoR methodology required expert’s to estimate future replacement probabilities which were then combined with historical failures using Bayesian analysis. Although this methodology was effective, parts of the industry were accustomed to providing a High/Medium/Low (HML) probability categorization for selected periods of operation. This paper presents an approach for calculating Weibull replacement probability curves from HML categorical replacement probability estimates. Additional questions beyond the initial HML categorization were developed. These focused on the timing of category transitions to refine parameter likelihood functions, reduce parameter uncertainty, and offset the significant Weibull parameter uncertainty introduced by using categorical estimates.
Value-Based Bayesian Optimization of Preventive Maintenance Programs
Authors: Cluever Joseph , Esselman Thomas , Harvey Sam
Published: November 2018

The EPRI Preventive Maintenance Basis Database (PMBD) has become a standard in the industry to develop, validate, or examine the impact of custom changes to maintenance strategies for common power plant equipment. The PMBD provides failure modes and an indication of frequency of occurrence. Recent feedback from PMBD users has made it clear that including a “Cost Module” to work with PMBD data would be a useful addition to the PMBD program and allow users to view the cost impacts associated with alternate custom maintenance strategies. This paper presents a methodology for the merging of maintenance information extracted from PMBD with cost estimates and additional expert-provided reliability data to estimate a maintenance cost distribution. Additional expert information includes missing data and PM type: monitoring, wear-rate reducing (e.g. oil change), or life-restoring (e.g. refurbishment). The cost distribution is calculated via Monte Carlo simulation and is dependent on the PM plan currently considered. Value-based optimization of the PM plan is performed through Bayesian optimization of the mean PM cost by varying the various PM frequencies. Bayesian optimization iteratively uses Gaussian Process Regression (GPR) to fit a non-parametric meta-model to a noisy objective function. As a part of GPR it is necessary to fit a covariance function that describes the spatial correlation or smoothness of the objective cost function. The meta-model with the covariance function effectively produces a built-in sensitivity analysis for the optimization as well.
Seismic Response of a Cylindrical Water Storage Tank of Nuclear Power Plant
Authors: Matsuura Shinichi , Tamura Ichiro
Published: November 2018

It is important in the confirmation of the safety of the nuclear power plant to clarify the response behavior of a vertical cylindrical water storage tank under seismic motion. When a vertical cylindrical tank is shaken by a large earthquake, deformation of side shell due to the elephant foot buckling, the oval vibration etc. may occur. The occurrence of those deformations depends on materials, shapes, stored water level and time history of seismic motion. Then, response behavior was obtained for a condensate storage tank (CST) model under large seismic motion such as standard earthquake Ss multiplied by 2 with the elastic-plastic finite element calculation. In this calculation, dynamic water pressure and elastic-plastic characteristics of the material were taken into account. In this case, the elephant foot bulge did not occur but the oval vibration of side shell became dominant. Based on the result, we estimated the structural integrity of the tank.
Approximate Formulas for Cylindrical Shell Free Vibration Based on Vlasov’s and Enhanced Vlasov’s Semi-Momentless Theory
Authors: Orynyak Igor , Dubyk Yaroslav
Published: November 2018

Simple approximate formulas for the natural frequencies of circular cylindrical shells are presented for modes in which transverse deflection dominates. Based on the Donnell-Mushtari thin shell theory the equations of motion of the circular cylindrical shell are introduced, using Vlasov assumptions and Fourier series for the circumferential direction, an exact solution in the axial direction is obtained. To improve the results assumptions of Vlasov’s semimomentless theory are enhanced, i.e. we have used only the hypothesis of middle surface inextensibility to obtain a solution in axial direction. Nonlinear characteristic equations and natural mode shapes, are derived for all type of boundary conditions. Good agreement with experimental data and FEM is shown and advantage over the existing formulas for a variety of boundary conditions is presented.