bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Two-Phase Flow in Packed Bed Systems
Authors: Yasugi Noriaki , Fujitsu Akito , Odaira Naoya , Ito Daisuke , Ito Kei , Saito Yasushi
Published: October 2021

Two-phase pressure drop in the debris has been studied by many researchers in relation to the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established well to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow pattern on interfacial drag and pressure drop. Normally it would be very difficult to visualize such two-phase flow behavior in an ordinary packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates two-dimensional network of porous structures, was fabricated to avoid the overlapping bubbles. By using a high-speed imaging of the two-dimensional network model, two-phase flow pattern in the porous structure have been identified. From the experimental results, it was suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model.
Tritium Transport Modeling and Analysis for HCCB Blanket of CFETR
Authors: Zhang Baorui , Xia Zhaoyang , Zhou Zhiwei
Published: October 2021

China Fusion Engineering Test Reactor (CFETR) is aimed to meet the technical gaps between International Thermonuclear Experimental Reactor (ITER) and future fusion DEMO reactors, tritium self-sufficiency must be guaranteed for the operation of fusion reactors. Helium Cooled Ceramic Breeder (HCCB) blanket is one of the promising candidate blanket schemes for CFETR. Tritium generated in Li4SiO4 pebble bed is carried out by purge gas, it is crucial to study the tritium behavior in the blanket from the tritium fuel cycle point of view. In this paper, the effective diffusivity of tritium in purge gas is conducted based on Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) coupled simulation considering the influence of the pebble bed structure. The flow characters analysis of purge gas is carried out by CFD simulation as well, which includes velocity field distribution, pressure field distribution and pressure drop. Based on the macro parameters conducted above, the tritium transport process in blanket including tritium permeation into coolant, tritium inventory in blanket and tritium carried out by purge gas is simulated based on a 2D model set up in COMSOL Multiphysics, the results can be the reference for the design of Tritium Extraction System (TES) and Coolant Purification System (CPS).
Estimation of the Amount of I-129 in the Environment Generated Due to the Decay of Te-129m Discharged by the Fukushima NPS Accident
Authors: Sato Haruo
Published: October 2021

The accident at the Fukushima Daiichi Nuclear Power Station (1F-NPS) occurred following the Great East Japan Earthquake in March 2011, and led to the release of volatile radionuclides, which were deposited on the environment such as soils, forests, residential land, etc. in the Fukushima prefecture and the neighbouring areas. From immediately after the accident, air dose rate monitoring and analyses of radionuclides in soil, etc. were conducted in a wide range of area. Consequently, volatile radionuclides such as I-131, Cs-134, Cs-137, Te-129m, and Ag-110m were detected in a wide range of area, where was distant over 60km from 1F-NPS. Since I-131 is short-lived, it approximately disappeared after a few months. After the decay of short-lived I-131, Radiocaesium (Cs-134 and Cs-137) are the main contributors to radiation dose rate.

On the other hand, Te-129m, of which amount was approximately the same level as both Radiocaesium, was also detected although its half-life is short about 1 month. Since very long-lived I-129 is generated due to the decay of Te-129m, the accumulation of I-129 in the environment by accident is worried. Te-129m decays to I-129 by the following 2 decay series; Te-129m → Te-129 (half-life: 69.6min) → I-129 (64%), Te-129m → I-129 (36%). Since the half-lives of Te-129m and Te-129 are 33.6d and 69.6min, respectively, radioactive equilibrium is established between both nuclides, but it is not established between Te-129 and I-129 and between Te-129m and I-129. In this case, the amount of I-129 increases due to the decay of Te-129m, but also the maximum value of the amount theoretically exists.

In this study, the amount of I-129 in the environment generated due to the decay of Te-129m discharged by the 1F-NPS accident was estimated based on the analysed data of Te-129m in soil. The analysis was conducted for 3 investigation locations (Okuma Town, ca. 2.7km from 1F-NPS, Naraha Town, ca. 19km from 1F-NPS, and Fukushima City, ca. 60km from 1F-NPS) among the analysed data (as of 14 June 2011) of soil samples obtained at about 2,200 investigation locations in the Fukushima prefecture and the neighbouring prefectures. The maximum amount of I-129 was estimated 1.03 × 10−1 (Bq/m2) after about 1,000d even for the maximum deposition amount of Te-129m (2.7 (MBq/m2) as of 14 June 2011). This is approximately the same level as radioactivity concentration in the environment (5.75 × 10−3 ∼ 2.96 × 10−1 (Bq/m2)). Additionally, the results of field investigation around 1F-NPS also support this conclusion.
Comparison on HAPPY200 Reactor With Different Type Fuel Assembly
Authors: Sun Canhui , Zhou Tao , Chen Yaodong , Meng Zhaocan
Published: October 2021

In order to meet the new challenges on the energy and environment, a new conceptual design of nuclear heating reactor (HAPPY200) is developed. HAPPY200 is a two-loop low pressure water reactor with low thermal parameters and passive safety systems. The outlet temperature is 120 °C, the inlet temperature is 80 °C, and the operating pressure is 0.6MPa. In this study, the thermal performance problems of big and small fuel assemblies are discussed for HAPPY200. Under the same total power condition, the small assembly core is better considering thermal performance. And under the same average rod power condition, the small assembly core condition 2 is better considering thermal performance. Considering maturity and economic factor comprehensively, the big assembly core is chosen in the near term.
Research on the Air-Water Flow Regime and Characteristics in Rectangular Channel
Authors: He Qingche , Pan Liangming , Zhang Luteng , Yan Meiyue , Xu Wangtao
Published: October 2021

Two-phase Flow is widely involved in reactor design and is directly relevant to reactor safety. However, the flow regime in narrow rectangular channels still needs further study because it has a considerable difference from tube and bundle channels. To investigate the two-phase flow regime and interfacial structure characteristics, the air-water experiment with an adiabatic vertical channel of 4 × 66 × 1800, 6 × 66 × 1800 mm have been conducted under atmosphere pressure condition. The impedance void meter was used to measure the global void fraction in narrow rectangular channels. A high-speed camera was used to record the profiles of the flow regime. The flow regime was identified by the random forest clustering algorithm based on a training sample. The profiles of different parameters, including void fraction, pressure loss at Z/D = 150, were analyzed in this paper. Furthermore, based on the parameters’ distribution, the regime transition criteria in narrow rectangular channels were discussed. It is shown that the transition from bubble to slug flow always occurred when the average void fraction is 0.17–0.2. The transition value is 0.57–0.62 when the slug Flow changes to the churn-turbulent Flow and 0.78–0.8 from churn-turbulent to annular Flow. The constant used in the Lockhart-Martinelli correlation is found to calculate the frictional pressure drop in a rectangular channel. Furthermore, the drift-model applied to the rectangular channel is verified.
Study on PSA Application in VVER NPP Design Extension Condition Identification
Authors: Ma Chao , Ma Yuan , Du Jinyan
Published: October 2021

After the Fukushima accident, the safety requirements of nuclear power plants have been further improved. As an important design requirement, the design extension conditions need to be fully considered in the design of advanced nuclear power plants. Design extension condition list is an important aspect. The VVER nuclear power plant has also made many design improvements on the basis of practice. According to the requirements of design extension condition analysis, combining the design characteristics of VVER nuclear power plants, through carrying out PSA analysis of VVER nuclear power plants, PSA insights are used to systematically analyze the design extension conditions without significant fuel degradation (DEC-A). Such as SBO, ATWS, total loss of feedwater, total loss of heat sink, etc, have been analyzed and quantified to support design extension condition determination. Due to the need to identify important event sequences, the selection of the probability screening value of DEC-A is discussed and suggestions are given. In the probability screening value determination, the safety goal of nuclear power plant is considered, and also the accident sequences in PSA. In addition, the containment bypass event sequence has always been an important radioactive release scenario, which has a greater impact on safety, and is also discussed in the DEC-A analysis.
Validation of Computational Fluid Dynamics Models for Industrial Applications
Authors: Dzodzo Milorad B.
Published: October 2021

Validation of Computational Fluid Dynamics (CFD) models for industrial applications is more challenging due to the complex geometry and long duration and complexity of various postulated accident scenarios, resulting in different and wide ranges of length and time scales. Thus, CFD models for industrial applications are restricted to the smaller subdomains and short periods of postulated accident scenarios.

Validation is most often based on the comparisons with experimental results obtained with the scaled down test facilities. Thus, the effect of scaling needs to be considered and incorporated in the validation process.

During validation, valuable experience is gained related to geometry simplifications, needed mesh size, turbulence and heat transfer modeling, effects of initial and boundary conditions, different fluid thermophysical properties and interaction with other phenomena and processes. Based on the gained experience the validated CFD models are adjusted and used to simulate prototypical domains and conditions.

Several examples of validations of CFD models for industrial applications are presented.
Dedicated CT Tests and Numerical Simulations to Assess Crack Arrest by Quasi-Laminar Flaws
Authors: Dulieu Pierre , Lacroix Valéry , Gérard Robert , Brynk Tomasz , Uytdenhouwen Inge , Chaouadi Rachid
Published: October 2021

Following the detection of a large number of quasi-laminar flaw indications in the core shells of two Belgian Reactor Pressure Vessels (RPV), an extensive Safety Case demonstrating the Fitness-for-Service for continued operation of both reactors was elaborated. These indications were attributed to hydrogen flaking induced during the component manufacturing process. The conservative Flaw Acceptability Assessment demonstrated that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. However, beyond this specific case, the need to better understand the behavior of quasi-laminar flaws has been brought to light.

In that framework and as a defense-in-depth investigation, the question of quasi-laminar flaws subsequent behavior in case of fracture initiation is raised. In the hypothetical case of brittle failure initiation, it is expected that the presence of quasi-laminar flaws in the propagation path can stop the flaw propagation. To illustrate this statement, exploratory compact tension (CT) tests are designed such as a mode I pre-crack, from which initiation occurs, subsequently interacts with quasi-laminar flaws in the propagation path. In each of the CT tests, the measured load-displacement curve shows evidence of crack arrest. Besides these experimental results, 3D extended finite element analyses (XFEM) are conducted to confirm and provide additional insights about this phenomenon, in particular the link with the mixed-mode fracture toughness. Moreover, the simulations allow defining an additional test matrix aiming at evaluating the relation between the mixed-mode fracture toughness and the ratio between mode II and mode I stress intensity factors.

The present paper presents the experimental results and describes the numerical simulations that are performed to illustrate the capacity of quasi-laminar flaws to induce a crack arrest phenomenon.
Development of New Design Fatigue Curves in Japan – Treatment of Variable Loading Amplitude Effect
Authors: Asada Seiji , Nomura Yuichiro
Published: October 2021

Design fatigue curves of new concept were developed in the Subcommittee on Design Fatigue Curve in the Atomic Energy Research Committee in the Japan Welding Engineering Society (JWES). Also, Working Group on Design Fatigue Curves (WG DFC) in the JSME is studying the validity and the applicability of the design fatigue curves developed in the JWES to incorporate into the JSME Environmental Fatigue Evaluation Method.

The developed design fatigue curve consists of the best-fit curves using tensile strength as a parameter, correction of mean stress effect employed the Smith-Watson-Topper approach, surface finish effect and variable loading amplitude effect. This paper discusses the treatment of variable loading amplitude effect in the improved design fatigue curves.

The developed design fatigue curves have employed the method of variable loading amplitude effect in EN 13445. This method uses a fatigue life exponent of −0.1 from N = 2 × 106. Research Group on Fatigue Strength in the JSME performed a series of fatigue tests for variable loading amplitude and the test data showed the fatigue life exponent was −0.07. This outcome of the JSME Research Group can support the fatigue life exponent of −0.1 in EN 13445.

A survey of the procedure of variable loading effect has been performed on a thermal fluctuation transient at mixed zone of T-junction piping of nuclear power plants for which UF is significantly affected by variable loading effect. Based on this study, the design fatigue curve for variable loading effect that starts from 2 × 106 with the slope of 1/10, which comes from EN 13445-3, can be considered to be applicable to the developed design fatigue curves. Also, the difference of UF between up to 1 × 108 and extension with no limit is relatively small, and the maximum number of cycles of 1 × 108 can be employed for the engineering fatigue analysis.
Investigation of the Internal Impact During a 9 M Drop Test of an Accident-Safe Waste Package
Authors: Nehrig Marko , Scheidemann Robert , Wille Frank , Ballheimer Viktor
Published: October 2021

The safety assessment of packages for the transport of radioactive material follows the IAEA regulations and guidance. The specified regulatory tests cover severe accidents and demonstrate the package containment system integrity. Special attention must be drawn to the behaviour of the content which could move inside the package due to unpreventable gaps caused by the loading procedure and the structure of the content. A possible internal impact of the content which occurs during the drop tests onto the lid system is investigated. The IAEA regulations SSR-6 and the Guidance SSG-26, revised recently, consider input from Germany and France related to the significance of internal gaps.

In the context of a waste package design assessment, a model was equipped with a representative content to conduct a drop test with an internal impact. The weight and kinetic impact of this content covered all possible real contents. The objective of the test was to maximize the load onto the lid system and to prove the mechanical integrity by complying with the required leak tightness. The test was conducted conservatively at a package temperature lower than −40 °C at the BAM Test Site Technical Safety.

This paper gives an overview of efforts to address internal gaps and their consequences, and the BAM efforts with the implementation of this topic into IAEA regulations and guidance material. The paper then focuses on the conduction of a drop test and investigation of internal component impact.
Numerical Study on the Strain Capacity of Girth-Weld Pipes With Unequal Wall Thickness Transition Joints
Authors: Wang Xu , Shuai Jian , Zhang Shengzhu
Published: October 2021

Girth-weld pipes with unequal wall thickness transition joints result in the misalignment of geometry, and the mismatched welding and heat-affected zone (HAZ) softening prompt inhomogeneity of material in the local area of girth weld. The misalignment of geometry and inhomogeneity of material are the main causes of local strain concentration in the girth weld, which greatly increases the possibility of crack initiation and propagation. In this paper, the numerical models of girth-welded pipe with cracks on the fusion line have been accurately constructed, referring to the crack size and location of the actual accident pipe. The influences such as the ratio of unequal wall thicknesses, the mis-matched coefficients and load conditions on the crack driving force curves have been investigated. The critical apparent fracture toughness has been selected as a failure criterion of girth welded pipe. Results show that an increase in the thickness ratio and a decrease in the weld strength will reduce the strain capacity of girth welded pipes, and the increase in internal pressure will weaken the strain capacity of girth welded pipes. The application of unequal wall thicknesses and low matching welding in the girth-weld pipes in engineering should be avoided or reduced.
Quantitative Risk Assessment of Densely Populated High Consequence Area of Gas Transmission Pipeline
Authors: Zhou Li-Guo , Wang Xiao-Lin , Li Ming , Shi Lei , Wang Yong , Yang Jing
Published: October 2021

In view of the importance of densely populated high consequence area in the management of buried gas pipelines, a special quantitative risk assessment method was proposed in order to clarify the key points of control, optimize resource allocation and refine emergency plans. Firstly, the general failure probability was determined under different pipe diameters based on the pipeline failure statistics. According to the uncertainty of pipeline management and pipeline damage, the calculation models of management correction factor and damage correction factor were constructed. And the pipeline failure probability was obtained by correcting the general failure probability. Then, combining with the theories of explosion shock intensity and fire heat radiation intensity, the probability variable of personnel death was calculated by taking personnel death as the main failure consequence of densely populated high consequence area. Finally, the individual risk and social risk of the gas pipeline accident were analyzed to determine the risk acceptability of the densely populated high consequence area. Method was applicated by taking a buried gas pipeline as an example, the case analysis shows that the risk acceptability can be effectively evaluated through the special quantitative risk assessment, which provides the basis for the formulation of risk control measures, and measures to shorten the response time can reduce the risk level of the pipeline.
Thermodynamic Characteristics of Gas Cylinder During the Process of Hydrogen Filling and Discharging of High Pressure Cycle
Authors: Guo Xiaolu , Fan Zhichao , Liu Xiaoliang , Xu Shuangqing
Published: October 2021

Hydrogen fuel cell vehicle has become the main direction of hydrogen energy utilization because of its advantages of zero emission, short hydrogenation time, long driving range and high efficiency. High pressure hydrogen storage cylinder is one of the key components of hydrogen fuel cell system. Because the temperature of the gas cylinder increases sharply during the rapid hydrogen filling process, and the temperature drops sharply during the hydrogen release process, the drastic temperature change will reduce the fatigue life of the cylinder, which has an important impact on the safety and stability of the whole system. At present, it is necessary to further study the thermodynamic characteristics of gas cylinders in the process of hydrogen filling and discharging. According to the filling and discharging process of high pressure hydrogen cycle, the change and distribution of pressure and temperature and the streamline change in the high pressure cylinder during the process of hydrogen filling and discharging are studied. The pressure and temperature control strategy of high-pressure tank, precooler, test cylinder and low-pressure tank in the process of hydrogen filling and discharging were discussed, and a more safe and effective hydrogen filling and discharging optimization control measure was put forward. This study is of great significance for the stability and safe operation of high pressure hydrogen storage system in the field of hydrogen energy.
Numerical Study on the Re-Rounding Process of Dented Pipelines
Authors: Zhao Pengcheng , Shuai Jian
Published: October 2021

A dent is a common type of pipeline defect that causes a local stress and strain concentrations, which can threaten the safety and integrity of the pipeline. In actual engineering, unconstrained dents tend to re-round as the internal pressure of the pipeline increases. In this paper, the process of re-rounding of a dented pipeline was investigated by numerical study. A 3D numerical model was established. The strain variation of the re-rounding process was analyzed in detail. The effect of various factors (loading depth, indenter diameter, pipe diameter-thickness ratio, initial internal pressure and material) on the re-rounding coefficient were analyzed. The results show that the elastic recovery occurs in the re-rounding process. And no secondary plastic damage occurred in the dented pipeline. The coefficient of re-rounding increases with the increase of the dent depth and initial internal pressure; while the diameter-thickness ratio and indenter diameter display a negative effect. Based on the finite element results, an engineering calculation equation of the re-rounding coefficient was fitted by the nonlinear regression method.
Analytical Limit Load Formula and Procedure for Strength Calculation of Axial Complex Shaped Defect in Pipe
Authors: Orynyak Igor , Bai Julia , Mazuryk Roman
Published: October 2021

This paper describes the analytical model for complex shaped axial defects. The model is based on classical lower bound limit load theorem of theory of plasticity, and consists in construction of statically admissible solution (distribution of stress which satisfies to equilibrium equations). Its main advantage is the possibility to explicitly take into account a lot of geometrical (complex shape) and physical parameters (additional axial loading, variance of material properties along the axis), — while still retaining its relatively simple application and appearance. So, contrary to other approaches, the formula for rectangular defect here is only a particular case of application of the general procedure. The main focus of the paper is description and justification of numeric algorithm of this general procedure (named here as O-procedure) for axial complex defect in pipe under internal pressure, which in fact is an optimization process to get the most favorable stress distribution.

Four different approaches for complex shaped defect are compared. First, ASME (named here as A-) rectangular defect formula combined with RSTRENG (named here as R) procedure, i.e., A-R approach. Second, PCORRC (P-) formula with R-procedure, P-R approach. Third, Orynyak (O-) rectangular formula with R-procedure, O-R approach. Fourth, our universal procedure (as goal of the paper), O-procedure. The comparison is performed as for some artificial complex defects, for example, two interacting rectangular defects, as well as for known full scale test performed in Waterloo University. Further considerations as to enhancing of the theory and its experimental verification are made.
CFD Simulation of Cavitation Erosion Behavior in an Impeller of Industrial Lean Amine Liquid Pump
Authors: Liu Juanbo , Lin Haitao , Duan Linlin , Sun Li , He Meng , Chen Sheng
Published: October 2021

Multistage pump of lean amine liquid is crucial rotating equipment in an industrial refining catalytic reforming unit. Cavitation often causes the damage of impeller in the pump to affect the long-term safe operation of unit. The formation of cavitation on impeller is 3D simulated by using Zwart-Gerber-Belamri model in accord with the actual position under the industrial operating condition. The discrepancies of cavitation range between different volume flux (400 to 800 m3/s. operating pressure (0.4 to 2.0 MPa) and vapor pressure of lean amine liquid (0.05 to 0.5 MPa) in terms of the industrial running conditions every stage impeller are investigated to guide design and safety operation of pump. The simulation results indicate that the impeller cavitation often starts from the forward-curved groove of the blade. and then gradually expands along the flow path of the blade and the two side walls of the forward bend. When the volume flux exceeds critical value of cavitation. the impellers appear cavitation and those ranges enlarge and expend along the flow direction of the blade with the increase of volume flux. With the cavitation pressure increasing. the cavitation ranges of impeller lesson even to disappear. especially at 2.0 MPa. Bigger vapor pressure of lean amine liquid leads easily to erosion.
Numerical Study of Detection of Crack on Corroded Rough Surface Using EMAT-Generated Surface Wave
Authors: Wang Zhe , Chen Xuedong , Fan Zhichao , Chen Wei , Cheng Jingwei , Su Yuanlian
Published: October 2021

Electromagnetic acoustic transducer (EMAT) gradually becomes the main excitation method for surface wave, which is suitably used in periodic inspection or long-term monitoring of pressure equipment. However, the corroded surfaces appearing on the pressure pipes and vessels can cause an increase of background noise and remarkable attenuation of the echo wave, which restrict the improvement of detection accuracy of surface crack. In this paper, a finite element model of EMAT-Generated surface wave inspection for steel plate with rough surface is established based on the constitutive equation of ferromagnetic materials. Considering the Lorentz force and magnetostrictive effect, the influences of rough surface on energy conversion of multiple fields in the excitation and propagation process of electromagnetic acoustic surface wave are separately investigated. The surface wave responses of cracks characterized by rectangular groove on corroded rough surface have been analyzed further. The numerical results indicate that the rough surface of the excitation region below the transducer with a center frequency of 330 kHz has a slight effect on the surface wave energy, while the surface roughness of the propagation region attenuates echo signal of crack significantly. The reflection coefficients of echo signals can be utilized to quantitatively characterize the depth of crack on the corroded surface with roughness less than λ/15 (λ is wavelength of surface wave).
Modeling and Sensitivity Analysis of the TN-32 UNF Cask: Comparison With the HBU Project Data
Authors: Higley Megan , Hadj-Nacer Mustafa , Greiner Miles
Published: October 2021

In this work, a 3D, one-eighth homogenous fuel CFD model of the TN-32 UNF cask is constructed, and simulations are performed as part of the Extended Storage Collaboration Program (ESCP). The simulations are carried out using ANSYS/FLUENT1 package with geometry and boundary conditions recommended by ESCP. Simulation results, including external and internal cask temperatures, are compared with experimental data from the High-Burnup (HBU) project. A preliminary sensitivity analysis is conducted to determine the effect the different assumptions/simplification proposed by ESCP on the cask temperatures. This sensitivity analysis indicates that the cask internal natural convection has a significant effect on the prediction of internal temperatures when the drain holes at the base of the basket are modeled. Additionally, the results indicate that a small variation in the thickness of the peripheral basket-rail gap has a significant effect on the internal temperatures. The best simulation model is shown to include modeling of the drain holes, natural convection, a peripheral basket-rail gap of 4.78 mm (0.188 inch), and omission of the base inner liner-gamma shield gap.
Effect of Shape Modeling on FEM Analysis Results of Equal Tee Pipe
Authors: Nakamura Izumi , Shibutani Tadahiro
Published: October 2021

To understand the properties of the shape of the actual tee pipe and the effect of shape modeling on finite element method (FEM) analysis results, the authors measured the 3D shape of a 150A equal tee pipe and conducted inelastic static and modal analysis on a specimen including the equal tee pipe. The tee pipe joint used in this investigation was a “steel butt-welding type” carbon steel. In the inelastic analysis, the material property was modeled using bi-linear kinematic hardening. The data for two kinds of shapes were prepared for the FEM analysis: based on the measured configuration; based on the nominal dimension.

The 3D shape measurement showed that the actual wall thickness of the tee pipe joint was greater than the nominal value, and it was unevenly distributed in the pipe. The maximum measured wall thickness of the pipe was up to 47% thicker than the nominal value. The analysis showed that the model based on the nominal dimension reduces the collapse load by 25%–30% compared to that based on the actual shape. The distribution of cumulative equivalent plastic strain was also affected by the shape modeling; the model based on the nominal dimension predicts the point of strain concentration to be closer to the center of the tee. Though the natural frequencies of these models were different, which is attributed to the difference of elastic stiffness of each model, the mode shapes were similar.
Creep Damage Predictions Under Multiaxial Conditions for 316L Stainless Steel Samples Manufactured by Laser Powder Bed Fusion
Authors: Burridge D. J. , Davies C. M.
Published: October 2021

316L stainless steel, often used for high-temperature applications, can be manufactured by laser powder bed fusion (LPBF). However, the LFBF manufacturing process can lead to undesirable multiaxial residual stresses (RS), which may require relaxation by heat treatments. The high residual stresses combined with high operating temperatures will induce creep deformation and damage processes. Therefore, the creep behaviour of LPBF 316L under multiaxial stress conditions must be understood, and models are available to predict the creep deformation and damage processes.

In this work, a FE modelling methodology has been developed and validated by simulating the creep deformation and damage accumulation in notched bar tests on samples with two different notched acuities, denoted large and medium notches. Notched bar creep tests were simulated for samples built in both the horizontal and vertical orientations (i.e. parallel and perpendicular to the build direction). A new progressive creep damage modelling approach was applied, based on the creep ductility exhaustion approach, enabling the progressive deterioration of material properties as creep damage accumulates. A sensitivity study was performed to account for the significant variabilities in creep deformation rates and creep ductility in LPBF samples. It was generally found that accurate predictions of the creep deformation and failure behaviour could be obtained using a specific combination of creep strain rate and ductility bounds; however, some tests results, particularly for vertically built samples, were not predictable. This has been attributed to the deleterious effects of porosity resulting from the build process.
NuScale Pressure and Temperature Limits Methodology Using Finite Element Analysis
Authors: Xu Heqin , Remic Joe , Xu Hongqing
Published: October 2021

Per 10 CFR 50 Appendix G, the pressure-temperature (P-T) limit curves and minimum temperature must be established to provide adequate margins for ferritic pressure-retaining components of the reactor coolant pressure boundary; this is to protect against brittle failure during any normal operating conditions, including anticipated operational occurrences and system hydrostatic tests, to which the pressure boundary may be subjected over its service lifetime. Specifically, the American Society of Mechanical Engineers (ASME) Code Section XI Appendix G procedures must be used for P-T limit calculations considering the pressure and temperature at various operating transient conditions. However, the elastic fracture mechanics solutions in Section XI are only suitable for cylindrical reactor pressure vessel (RPV) beltline without geometric discontinuities. Hence, these solutions are not suitable for postulated flaws near the core support blocks attached to the NuScale RPV inside surface, which is part of the beltline. As a result, NuScale has used finite element analysis to calculate thermal stress and stress intensity factors for the postulated flaws. The solutions using finite-element analysis have been validated using the formulations for straight cylinders for both axial and circumferential flaws. In addition, special considerations are given to the RPV beltline nil-ductility transition temperature (RTNDT) due to neutron irradiation occurring at lower temperatures than conventional plants. This paper summarizes the methodology and finite-element models used to develop P-T limit curves for the NuScale RPV at the end of its 60-year design life.
Application of Risk-Based Design Methodology to Tuned Mass Damper
Authors: Corritore Daniele , Minagawa Keisuke , Paolacci Fabrizio
Published: October 2021

Suppressing earthquake damage in chemical plants has great benefits not only to a business continuity of a company but also to surrounding areas and social activities. For example, chemical plants have a lot of slender structures such as distillation columns and chimneys, which may be damaged by large earthquakes. Tuned mass dampers (TMDs) are one of the effective approaches to suppress seismic response of slender structures. The TMD consists of a mass, a spring and a damper, and it is generally installed at the top of a target structure. The damping effect depends on the mass, natural frequency, damping ratio of the TMD. In general, its natural frequency and damping ratio can be determined by the optimum tuning theory and a TMD having large mass has good performance of vibration control. However, the cost of TMD depends on the mass. In addition, since the optimum tuning theory assumes that the target structure is a simple single degree of freedom system, application of the optimum tuning theory to the TMD for a slender structure is not easy. Therefore, this study proposes a risk-based design methodology for TMDs. The proposed method considers a seismic hazard of a site where a target structure located and a damage state of the target structure. Then the mean annual frequency of exceeding the damage state can be calculated as function of the mass of the TMD.
Example Proposals of Fracture Controlled Vessels and Piping for Failure Mitigations
Authors: Kasahara Naoto , Wakai Takashi , Nakamura Izumi , Sato Takuya , Ichimiya Masakazu
Published: October 2021

As a lesson learned from the Fukushima nuclear power plant accident, the industry recognized the importance of mitigating accident consequences after Beyond Design Basis Events (BDBE). We propose the concept of applying fracture control to mitigate failure consequences of nuclear components under BDBE. This paper discusses example applications of our proposed method to vessels and piping.

As an example for vessels, the fracture controlled method of a fast reactor vessel was proposed to maintain coolant under high pressure and high temperature conditions. One of the important accidents to consider is fuel criticality upon a core meltdown. This accident will cause high temperature and high pressure conditions in the vessel.

To maintain coolant to cover the fuel under above conditions, strength of the upper part of a vessel is controlled to be weaker than the lower part. When the upper parts fail, internal pressure will be released and the lower part will be protected. Coolant of fast reactors is liquid metal with a high boiling point. Therefore, there is no boiling when the pressure drops. As a result, the coolant stays within the vessel for continuous cooling after accidents. If nozzles penetrate only the upper part of a vessel, controlling strengths at the structural discontinuities can realize the proposed method.

As a piping example, the fracture controlled method of main steam piping of a BWR was proposed to avoid collapse and break under excessive earthquake. The piping is constrained by supports to the building. Strength of piping supports should be weaker than that of the piping. If piping supports break before the piping, natural frequencies of piping decrease increasing the frequency ratios. When their frequency ratios are larger than one, the seismic energy hardly transfers to the piping and the piping will not collapse or break. When the primary stresses from dead weight are not negligible, simple supports by wire are enough to protect piping against dead weight.
Numerical Investigation of Ductile Fracture in Pipelines Under Complex Loading Using a Phenomenological Damage Model
Authors: Santos Iago S. , Sarzosa Diego F. B.
Published: October 2021

This paper presents a numerical study on pipes ductile fracture mechanical response using a phenomenological computational damage model. The damage is controlled by an initiation criterion dependent on the stress triaxiality and the Lode angle parameter, and a post-initiation damage law to eliminate each finite element from the mesh. Experimental tests were carried out to calibrate the elastoplastic response, damage parameters and validate the FEM models. The tested geometries were round bars having smooth and notched cross-section, flat notched specimens under axial tensile loads, and fracture toughness tests in deeply cracked bending specimens SE(B) and compact tension samples C(T). The calibrated numerical procedure was applied to execute a parametric study in pipes with circumferential surface cracks subjected to tensile and internal pressure loads simultaneously. The effects of the variation of geometric parameters and the load applications on the pipes strain capacity were investigated. The influence of longitudinal misalignment between adjacent pipes was also investigated.
The Influence of Low Melting Point Elements on Hot-Cracking of 310 Austenitic Stainless Steel
Authors: Almomani Abdulla Fawzi , Alhaj Hazem , Ismail Mourad Abdel-Hamid
Published: October 2021

This work highlights the influence of the low melting point elements such as sulfur, phosphorus, and silicon together with the delta (δ) ferrite content on the susceptibility of austenitic stainless-steel grade 310S welding to hot cracking. Defected weld seams from a vessel component were analyzed in this work. Transverse linear cracks on both the circumferential and longitudinal welding seams, with excess bleeding, were revealed during the examination of the defected welding joints through Dye Penetrant Testing (DPT). The ferrite number (FN), i.e., a description of the ferrite content, was found to be less than 1.0 FN on the weld metal (WM) and 1.5 FN on the parent metal (PM). Hardness testing showed high values (295 HB max.) on the parent material PM while it was found within the range (211 HB max.) at the WM. The chemical composition of the WM, with the use of X-Ray Fluorescence (XRF) spectrometer, revealed 0.09% S, 0.09% P and 2.27% Si which are deemed to be in critical range against the susceptibility of 310S to solidification cracking. The microstructure of the weld material WM displayed extensive cracking at the austenite grain boundaries of the cellular dendrites, in which film-like features were observed on the crack surfaces along the interdentric interfaces. It is suggested that sulfur S and phosphorus P combine with iron to form low-melting compounds, which as a result can form low melting eutectics with impact to segregate at the austenitic grain boundaries during solidification. Hence and in line with the literature, adequate control of S and P to less than 0.002%, and Si away from 1.5–2.5% was found key in minimizing the susceptibility of 310S welding joints to hot cracking.
Application of the Williams-Wittrick Algorithm for Thin Shell Vibrations Problems
Authors: Dubyk Yaroslav , Ishchenko Oleksii
Published: October 2021

This article presents adaptation of the Wittrick-Williams algorithm to calculate the natural vibration frequencies of cylindrical shells. Initially, the “algorithm” was proposed and used to find the natural frequencies of branched piping systems (trusses) in structural mechanics problems. We expanded it for shells, where a more difficult system of main differential equations is solved, with increasing calculation effort. The Wittrick-Williams algorithm was chosen to find vibration frequencies, because it is the only one exact solution for the transcendental eigenvalue problem. The “algorithm” gives the number of natural frequencies below a trial value of frequency, therefore, using bisection method, as the simplest, it is possible to find frequencies with sufficient accuracy. It can been used, for example, in a dynamic analysis, where it is important to find accurately the lower frequencies, and to distinguish between coupled frequencies. For solution the shell must been divided into a certain number of parts; convergence graphs are given, according to which the optimal number of partitions is selected. Obtained results show good convergence with experimental and literature data for different boundary conditions. Several special cases have been considered for shells with different values of elastic boundary conditions. The method has proven to be practical and can been used for modal, harmonic and seismic analysis.
A Newly Developed Measuring Principle for Precise Measurement of Forces in Test Autoclaves
Authors: Oßwald Alexandra , Werz Martin , Weihe Stefan
Published: October 2021

For material testing under environmental conditions like pressure, test medium and temperature, testing machines are extended with autoclave units in which controlled ambient conditions are set. The load is applied to the specimen placed inside the autoclave from the outside via rods. Thepressure of the testing environment is sealed by the autoclave system. The challenge of this setup is the correct measurement of the specimen force due to the frictional forces on the gasket. The most current problem in this field, on which we focus our work, is the precise determination of material properties under high-pressure hydrogen atmosphere.

At the Materials Testing Institute (MPA) University of Stuttgart, a new measurement principle was developed which solves the conflicting objectives of precise force measurement and reusability of strain gauges. This is achieved by applying the strain gauges on the inside of the load rod which transfers the force onto the specimen inside the autoclave. The newly developed measuring principle was integrated into an existing testing machine. The applicability of the measuring setup was validated in experimental tests under cyclic load and with the test environment of highly pressurized hydrogen. With the help of the new test setup, it is possible to measure the actual specimen force, i.e. without the influence of the frictional force of the gasket.
Gasket Design for Alkylation Units & Other Possible Dangerous Liquid Media
Authors: Norman Dale , Navarrete Gustavo
Published: October 2021

The design and testing of gaskets for severe, possibly life threatening, liquid media, like hydrofluoric acid, is critical and difficult. This paper shows the relationship between basic gasket stress calculations, of applied load over the gasket sealing area, actual gasket stress test results, and dye penetrant test results. The gasket designs evaluated will be from across the industry and follow the typical design of having expanded PTFE (ePTFE) as the inner sealing element for the harsh media and a redundant flexible graphite sealing element that will seal the media as well as give an expected fire test rating.

The gaskets tested had different structural designs for sealing the media as well as providing corrosive protection for the clamping flanges. There was both supported and unsupported ePTFE sealing elements. Some designs are new, and one has been in service for years. The basic calculations typically used to determine adequate gasket stress showed that all the gaskets should seal effectively. The question is: Would they all equally help protect the flange face from corrosive damage?

The data from the actual applied gasket stress correlates nearly perfectly to the dye penetrant results but varies from expected stress distribution of the typical gasket stress calculation. The paper will cover the theoretical calculation approach, the test methodology for the actual applied gasket stress, the methods for ensuring applicable dye penetrant testing and comparing the results to each other. The results show that under equal clamping loads, the different structural designs directly impact the ability for fluid to penetrate the ePTFE section of the gaskets.
Study on Flow-Induced Vibration of Self-Regulation Check Valve During Opening
Authors: Liu Shuai , Huang Xuan , Feng ZhiPeng , Jiang XiaoZhou , Wang BiHao , Wu WanJun
Published: October 2021

Pump-Valve-Pipeline is an important part of the power plant. It plays a key role in the normal operation of the reactor. The vibration of the system can bring harm to itself and also lead to the safety troubles and noise of other parts. As an important over-flow component, the structure and the adjustment method of check valve is complex, which can lead to pressure fluctuation and result in oscillation problems seriously. The study is to explore the characteristics of the internal flow field and pressure fluctuation of the check valve. Especially, the characteristics of internal flow field and the abnormal fluctuations are concerned during the moving process of the valve core and valve stem. There are many researches focusing on flow vibration under fixed opening of the valve, which can not reflect the real opening process of the valve. In this paper, the abnormal fluctuation of internal flow-field for the check valve is studied. Based on the UDF dynamic grid technology, the transient motion law equation of the moving parts is established as the moving boundary of the fluid. The transient motion analysis model of the check valve is constructed to simulate the dynamic opening process of the valve. The vibration characteristics of the valve with different spring stiffness are studied, which can provide guidance for the regulation of the valve in the system.