bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Particle Transfer Behavior in Fuel Rod Bundles Using CFD Lagrangian Particle Tracking Method
Authors: Xu Yiban , Krammen Michael A. , Wang Guoqiang , Fisher Jesse S. , Karoutas Zeses
Published: October 2021

Crud has been observed on the fuel rod surfaces in a variety of fuel designs around the world, and in some limited situations fuel performance was compromised due to crud-induced power shift (CIPS) and/or crud-induced localized corrosion (CILC). It is generally believed that crud deposition depends on fuel rod surface sub-cooled nucleate boiling, coolant chemistry and the availability of particles from component corrosion or from reinserted fuel. The formation, release, and accumulation of crud on the fuel and its influence on CIPS and/or CILC is a complicated process involving multi-physics phenomena. This study uses Computational Fluid Dynamics (CFD) Lagrangian Particle Tracking (LPT) techniques in analysis of particle transfer behavior in fuel rod bundles focusing on flow swirl and turbulence impacts. It is hoped that high fidelity CFD results can provide insights into particle transfer behaviors in the bulk coolant as well as near the fuel rods, which may provide guidance for model development of lumped or integrated analysis methods.

The CFD model was built based on the best practices learned from previous single-phase analyses. The LPT options, including particle injectors, forces on particles, and solver settings, were verified by comparing the simulated results to the test data from simple geometry with various particle sizes, covering deposition mechanisms in diffusion-, turbulent- and inertial-dominated regimes. The tested model then was applied to Westinghouse fuel designs with and without Intermediate Flow Mixing (IFM) grids. Particle concentration and size distributions in the coolant around fuel rods were obtained and the effects of grid induced swirl flow on particle transfer were identified. The analysis results may be included in lumped or integrated crud formation/release analysis methods. Limitations and potential improvements of this analysis method are also discussed.
Considering Hydrotest Pressure Loading in the Calculation of MAWP of a Pressure Vessel
Authors: Nawandar Suresh K.
Published: October 2021

As defined in UG-98 of the Code, the Maximum Allowable Working Pressure (MAWP), is the maximum pressure permissible at the top of the vessel in its normal operating position. It is the least of the values calculated for each of the vessel part adjusted for the static head and by including the effect of any combination of loadings listed in UG-22 of the Code.

Conventional method of calculating the MAWP is to consider only the main pressure parts viz., the shells and the heads and the significant UG-22 loading viz., the wind and the seismic. Once the MAWP is determined, the rest of the vessel design is completed considering this value of MAWP as design pressure combined with any other applicable UG-22 loading. At the end, the vessel is verified for its adequacy to the test condition.

It is noted that, the MAWP obtained through this method is often higher than the design pressure thus leading to the overdesign of the vessel. Moreover, higher MAWP results in higher test pressure, which might have a considerable impact of its own on the design of the vessel.

The objective of this paper is to propose a design approach in which the test pressure itself is included as one of the governing loads in the determination of the MAWP so that the impact on vessel design, as explained above, is minimized.
Natural Frequency of Oval-Type Vibration of an Aboveground Storage Tank Installed With Wind Girders
Authors: Yoshida Shoichi
Published: October 2021

The current seismic design codes of aboveground storage tanks (ASTs) for oil storage are conducted based on the beam-type vibration with circumferential wave number m = 1. The oval-type vibration with m ≥ 2 in which shell plate vibrates like a petal shape occurs in ASTs. The causes are local mass/stiffness, initial imperfections or nonlinear strong vibration. The initial stress due to hydrostatic pressure was reported to increase the natural frequency in high m range by several studies. The circumferential tensile stress on shell plates due to hydrostatic pressure increases the stiffness and as a result, the natural frequency is also increased. Wind girders are installed to the shell plates of ASTs for the prevention of buckling due to wind pressure. The wind girder which is a ring stiffener increases the stiffness of the shell plate. In this paper, the natural frequency of the oval-type vibration in a large-sized AST is analyzed and the effect of the wind girder on natural frequency is studied. The method is the free vibration analysis of axisymmetric shell finite element method considering vibration coupled with fluid motion.
Post-Test Analysis of a Large Scale Mock-Up Test Performed in the European Project ATLAS+
Authors: Nicak Tomas , Rempel Alexey
Published: October 2021

The safety and reliability of all systems has to be maintained throughout the lifetime of a nuclear power plant (NPP). This requires a systematic ageing management procedure for justifying their safe long term operation. One fundamental part in this process is to demonstrate the integrity of the nuclear power plant components. The European project ATLAS+ aims to develop and validate advanced methods of structural integrity assessment applicable in the ageing and lifetime management of primary circuit components.

To support development and validation of those methods a large scale test programme was developed with the aim to investigate fracture behavior of relevant piping material at the component level.

Three of the planned large scale experiments focus on the fracture behavior of flawed ferritic pipe segments made of material WB 36 (15 NiCuMoNb 5); this material is representative of secondary feedwater lines installed in German NPPs.

In order to improve understanding of test results post-test simulations and fractographic examination of all large scale tests are planned, some of them have been already performed.

In this paper the post-test simulation of the mock-up FP2 (ferritic pipe with outer semi-elliptical circumferential crack) is presented and discussed. This mock-up was selected because it experienced an unexpected brittle fracture during the test, which occurred after limited ductile crack propagation.

To investigate both the ductile and the brittle crack propagation phases of the test detailed ductile tearing analysis and brittle fracture assessment have been performed. In addition, relevant results of fractographic examination of the mock-up FP2 are presented and discussed.
A Study on Residual Stresses on Autofrettaged LDPE Tubing Including the Bauschinger Effect and Strain Aging
Authors: Nyquist Taylor , Warren Kraig
Published: October 2021

This paper compares and discusses the change to the residual stresses and strains on four tubes of SA-723 Gr 1 Cl 2 (Timken HS 220) tubing material that were autofrettaged at different Overstrain ratios (20% and 40%). The four tubes were autofrettaged with strain gages to obtain actual OD strain. The effect on the residual stress and strain of the material is reviewed after a single autofrettage and after a low temperature heat treat followed by a second autofrettage. The low temperature heat treat was performed on two of the four tubes to create comparable data. Any strain aging effect from the low temperature heat treat is examined on the measured residual stress and strains. The effect and possible benefits of strain aging and re-autofrettage on tubes with different Overstrain ratios is discussed. To obtain the residual stress values in the tube wall after the autofrettage cycles, the sample tube pieces were tested by X-ray diffraction. The actual residual stresses after autofrettage were then compared with the calculated theoretical residual stresses including Bauschinger effect correction factors from ASME Section VIII Div. 3 KD-5. The residual stress and strain data between one and two rounds of autofrettage is also studied to see if the Bauschinger effect is present.
Structural Integrity Assessment of Refractory Lined Component With Thermal Hot Spot Subjected to Steam Cooling
Authors: Yoo Eui Jong , Choi Capjoo
Published: October 2021

The refractory lined components could be damaged during operation due to various causes such as thermal expansion and contraction from changes of the temperature in service fluids, vibration caused by internal flow, or improper refractory construction. The damaged refractory causes thermal hot spot because a hot service fluid contacts to the inside surface of the component directly and this situation leads temperature increases in the skin of the component. This temperature increases from thermal hot spot does not causes immediate failure of the component, but creep phenomenon can cause structural rupture in the long term. As one of the countermeasures against thermal hot spot, the steam cooling is used as a field practice of maintenance works to reduce elevated temperature by spraying steam onto the area of thermal hot spot. However, when steam cooling is applied, it is designed and installed based on experiences without performing proper engineering. After steam cooling is applied, it is observed that thermal hot spot is locally cooled only in the area where the steam touches, which also raises concerns about unexpected damage due to local temperature gradient from localized cooling. This paper provides the evaluation of structural integrity of an actual case of thermal hot spot subjected to steam cooling in the FCC unit and discusses the appropriate steam cooling method as a countermeasure for thermal hot spot to ensure more effective structural integrity.
Valve Failures and Suggested Remedies
Authors: Ezekoye L. Ike , Josodipuro Irawan
Published: October 2021

Valves are one of the most used products in the power industry. The subject of valves is broad. They come in various configurations to meet end-user requirements. Because of their uniqueness, valves are designed to meet specific industry standards such as the American Petroleum Institute (API), the American Society of Mechanical Engineers, the Manufacturers Standardization Society, the British Standards Institute, the International Organization for Standardization, and many others. Compliance with these standards assures the valve end-users that their purchased valves will provide them with long term service. In most cases they do. However, there is no guarantee that newly installed valves in plants will last forever as nothing mechanical lasts forever. In this paper, the authors present survey results where the newly installed valves did not last long in service and where they did. In another survey, the authors will show some examples of valves that failed in service and what actions were taken to address the failures. Additionally, the authors will present examples of installed valves that provided long term services and the reasons for their good performance. Finally, the paper will cover remedies that valve end-users should consider adopting to ensure that their valves will provide long term service in operation.
Study on the Predictive Evaluation Method for Loads Acting on Roof and Sidewall of Cylindrical Tank in Nonlinear Sloshing Based on Simplified Equations
Authors: Ikesue Shunichi , Morita Hideyuki , Ishii Hidekazu , Sago Hiromi , Yokoi Shinobu , Yamamoto Tomohiko
Published: October 2021

When a cylindrical tank installed on the ground, such as an oil tank or a liquid storage tank, receives strong seismic waves, including a long-period component, motion of free liquid surface inside a tank called sloshing may occur. If high-amplitude sloshing occurs and waves of free liquid surface collide with tank roof, it may lead to accidents such as damage to tank roof or outflow of internal liquid. There is also a possibility that tank sidewall may be damaged due to fluid force generated by high liquid surface level of sloshing.

When sloshing wave height is small, liquid surface level and velocity can be calculated based on the linear velocity potential theory. When sloshing wave height increases, sloshing becomes nonlinear, and the difference between actual value and calculated value based on the linear velocity potential theory increases. Sloshing loads acting on roof and sidewall should be evaluated in consideration of nonlinear sloshing. In the previous study, simplified equations of nonlinear liquid surface shape and nonlinear liquid surface velocity distribution were proposed, as input parameters of evaluating sloshing loads.

In this paper, a new method is proposed for nonlinear sloshing condition of cylindrical tanks, which can evaluate the vertical load acting on roof and the horizontal load acting on sidewall. In the proposed method, new pressure models modified from existing models are combined with simplified equations of nonlinear liquid surface shape and nonlinear liquid surface velocity distribution proposed in the previous study. A long calculation time as CFD analysis is not needed, because the proposed method is consisted of simplified equations.
Designing and Optimising Duplex/Superduplex Compact Flanges to Negate HISC in Subsea Applications
Authors: Lutkiewicz Przemyslaw
Published: October 2021

Hydrogen Induced Stress Cracking (HISC) is a phenomena related with metals, with potentially severe consequences when utilizing Duplex / Super Duplex stainless steels in subsea equipment exposed to Cathodic Protection (CP). In general, the three conditions need to be present: hydrogen source (CP), susceptible material (Duplex/Super Duplex stainless steel) and high stresses/strains. The third one can be related with loads, calculation promises and parts design in general (for example risers). The designing rules to minimize the risk of HISC failure are still in development and the latest state of art is presented in DNVGL-RP-F112 June 2018 edition. The Compact Flange (CF) is much lighter and more robust connection than standard ASME or API types as the CF design methodology is based on plastic capacity which is presented in the ISO-27509 code. However, ISO standardization covers only topside applications (with IX seal ring type), pressure class range up to CL2500 and simplified face angles methodology. The ISO-27509 flanges are not HISC proven. Therefore, to deal with HISC requirements and subsea conditions the SPO-S (Subsea) flange series with HX seal ring type was defined and type approved by DNVGL based on extensive FEA documentation, testing and field experience. The SPO-S range has, currently, only HISC compliant designs for the 5K, 7.5K, 10K and 15K flange ranges. For the projects where the Duplex / Super Duplex flanges are used subsea with CP, consideration for HISC still must be addressed. For such cases, the process is not straight forward and often many FEA rounds are needed depending on the engineer’s experience and project related restrictions. The process is time consuming and every decision reflects many aspects to finalize the design. Genetic Algorithms (GA) are a good optimization tools to use in such situations, because at the end, the engineer will only get few design propositions to choose from, and the process itself, is highly automated. In the following paper the results for HISC optimized CF flange connection will be presented and compared with standard ISO-27509 flange design. The GA optimization steps and designing process will also be presented in the same example. Commercial FEA code ANSYS will be used for calculations based on parametrical model and GA implemented by APDL scripting. The following optimization method is already in use for HISC related projects.
Research on Characterization Method of Pressure Equipment Accident
Authors: Fang Zhou , Huan Zhibo , Wang Zhe , Fu Junjie , Shi Puan , Liu Qia , Wu Gang
Published: October 2021

The description of pressure equipment accidents has always been expressed in large paragraphs. It was difficult for readers to grasp the contents of the whole accident and analyze the objective laws of the accident. The representation method based on chart can show the accident context of pressure equipment intuitively and clearly, so that readers can quickly grasp the causes and consequences and development law of the accident. In this paper, the research framework of pressure equipment accident characterization method was established. Three characterization methods: fault tree, fishbone diagram and radar chart were used to analyze a typical pressure equipment accident. The advantages and disadvantages and application scope of the three characterization methods were obtained by comparing the analysis process and results. The results show that fault tree and fishbone diagram can not represent the weight of each factor, but radar chart method can do it directly. Radar chart method is suitable to analyze the primary and secondary causes of pressure equipment accidents. Since the radar chart has never been used in the accident analysis of pressure equipment before, a new characterization method of pressure equipment accident was established based on radar chart in this paper.
Modified Response Spectrum Accounting for Seismic Load Categorization as Primary or Secondary in Multi-Modal Piping Systems
Authors: Labbé Pierre , Nguyen Thuong-Anh
Published: October 2021

This paper presents practical implementation of a theoretical approach that was introduced at PVP 2020 conference. Analysis of the seismically induced ductility demand in elastic-plastic oscillators of variable frequencies and hardening slope is carried out by running time response analyses. The input motion consists of 1000 stochastic process samples of central frequency fc. Oscillators of natural frequencies, f0, (0.1 fc ≤ f0 ≤ 10 fc) are submitted to a wide range of ductility demand, up to 20. It turns out that seismic loads should be regarded as secondary for flexible oscillators (f0 < fc) and primary for very stiff oscillators (f > fcut, cut-off frequency of the input motion), with intermediate situations. On this basis, we derive a strongly f0/fc dependent evaluation of the seismically induced inertial stresses primary part. In the frame of the conventional linear modal analysis method, practical implementation consists of reducing the input response spectrum: spectral ordinates are minimized in the low frequency domain by a factor that depends on the ductile capacity and hardening slope, unchanged at the ZPA frequency and vary linearly in the medium frequency domain. This approach is tested against nonlinear time-response analysis of a multimodal piping system.
A New Stress-Intensity Factor Solution for an External Surface Crack in Spheres
Authors: Sobotka James C. , Lee Yi-Der , Cardinal Joseph W. , McClung R. Craig
Published: October 2021

This paper describes a new stress-intensity factor (SIF) solution for an external surface crack in a sphere that expands capabilities previously available for this common pressure vessel geometry. The SIF solution employs the weight function (WF) methodology that enables rapid calculations of SIF values. The WF methodology determines SIF values from the nonlinear stress variations computed for the uncracked geometry, e.g., from service stresses and/or residual stresses. The current approach supports two degrees of freedom that denote the two crack tips located normal to the surface and the surface of the sphere. The geometric formulation of this solution enforces an elliptical crack front, maintains normality of the crack front with the free surface, and supports two degrees of freedom for fatigue crack growth from an internal crack tip and a surface crack tip. The new SIF solution accommodates spherical geometries with an exterior diameter greater than or equal to four times the thickness. This WF SIF solution has been combined with stress variations common for spherical pressure vessels: uniform internal pressure on the interior surface, uniform tension on the crack plane, and uniform bending on the crack plane.

This paper provides a complete overview of this solution. We present for the first time the geometric formulation of the crack front that enables the new functionality and set the geometric limits of the solution, e.g., the maximum size and shape of the crack front. The paper discusses the bivariant WF formulation used to define the SIF solution and details the finite element analyses employed to calibrate terms in the WF formulation. A summary of preliminary verification efforts demonstrates the credibility of this solution against independent results from finite element analyses. We also compare results of this new solution against independent SIFs computed by finite element analyses, legacy SIF solutions, API 579, and FITNET. These comparisons indicate that the new WF solution compares favorably with results from finite element analyses. This paper summarizes ongoing efforts to improve and extend this solution, including formal verification and development of an internal surface crack model. Finally, we discuss the capabilities of this solution’s implementation in NASGRO® v10.0.
Crack Propagation Calculation for Axial Cracks in Hollow Cylinders Subjected to Thermal Shock
Authors: Mora M. Diego F. , Niffenegger Markus
Published: October 2021

The core region of the RPV can be considered a hollow circular cylinder disregarding the geometrical details due to nozzles. This contribution investigates the prediction capabilities for crack initiation, crack growth and arrest by means of a rather simple method based on the closed-weight function formula for the stress intensity factor (SIF) for axial cracks in hollow cylinders subjected to thermal shock. The method is explained together with some illustrative examples for real low allow steel used in nuclear applications. In order to obtain the temperature and stress distribution in the cylinder during the thermal shock, a finite element (FE) model is defined to obtain the uncoupled solution of these two fields needed for the closed-weight function. Since the material exhibits a ductile-brittle transition fracture behavior, the temperature-dependent fracture toughness for initiation and for arrest are described using the ASME model. The solution for the SIF is based on linear elastic fracture mechanics (LEFM) and therefore only elastic material is assumed and the crack can propagate in brittle manner. The crack initiates propagation if the SIF value at the crack tip reaches the fracture toughness (for initiation) and propagates unstably in mode I unless the fracture arrest toughness is reached. The quality of the solution is checked by comparing the obtained solution for a “stationary” crack with the calculated extended finite element method (XFEM) solution for the same loading transient. The results show that for some geometries of the cylinder, the crack stops and in some other cases the crack propagates until the cylinder fails. The combined closed-weight function-initiation-growth-arrest (WFF-IGA) algorithm does not require expensive computational resources and gives fast reliable results. The WFF-IGA method provides a powerful and economical way to predict the crack propagation and arrest of the initial crack. This is an advantage when an optimization of the structure is needed.
Study on Fracture Behavior and Assessment for Dissimilar Metal Weld of Low Alloy Steel and Ni-Base Alloy Weld Using a BWR Reactor Pressure Vessel Material
Authors: Hayashi Takahiro , Ogawa Takuya , Yoshida Shuichi , Itatani Masao , Hattori Yasuhiro , Yamaoka Tetsushi , Tanaka Shigeaki , Saito Toshiyuki
Published: October 2021

Cases of stress corrosion cracking (SCC) in Ni-base alloy weld metals welded to low alloy steel (LAS) of reactor pressure vessel (RPV) components have led to discussions on the possibility of SCC propagating into the RPV. However, the fracture behavior and the assessment methodology have not been sufficiently studied for such dissimilar metal weld (DMW) components where embrittlement due to neutron irradiation damage is negligible and the operating temperature is above the upper shelf temperature range.

In this study, the fracture mode of the DMW of LAS and Ni-base alloy weld was investigated by using a large, heavy forged steel part, called the bottom head ring, of a RPV, manufactured for a recent BWR. In addition to fracture toughness tests with compact tension specimens, fracture tests using plates cut from a DMW material with a semi-elliptical surface crack were conducted. The initial crack tip locations were designed and controlled to be in the heat affected zone (HAZ) in LAS, at varying distances from the weld fusion line. All the mechanical tests conducted showed highly ductile fracture behaviors and properties; the evaluated elastic-plastic fracture toughness was more than 400 kJ/m2 in the fracture toughness tests. The fracture loads evaluated using the elastic-plastic fracture mechanics (EPFM) methodology showed fairly good agreement with the maximum loads in the fracture test. The results confirmed that the fracture assessment methodology based on EPFM is reasonably applicable to the DMW of RPV components where the operating temperature is above the upper shelf temperature range and the embrittlement is not a concerned mechanism of degradation.
In-Plane Flexibility Factor of 90 Degree Long Radius Elbows With Large Diameter
Authors: Haji Mohammad Karim Milad
Published: October 2021

Bend flexibility factor is defined as the ratio of rotation of a pipe bend to that of a straight pipe of the same diameter, wall thickness and length under the action of the same bending moment. In stress analysis of piping systems with the beam method, this factor is of great importance and plays a direct role in the formation of the stiffness matrix of a system. The exact calculation of this coefficient results in the precise amount of force and moment being obtained on anchor points (i.e., equipment nozzles) and also in stopper and guide restraints. Different codes such as ASME B31.3 and B31.1 present a formula for this factor without consideration of the end effect (constraint of bend ends by the adjacent straight pipe). Another limitation is that these formulas are valid only within the range of D/T ≤ 100 (diameter to thickness). In this paper the effect of adjacent straight pipes on in-plane flexibility factor of long radius 90-degree elbows has been investigated and it has also been demonstrated that the equation presented in ASME B31J-2017 as the minimum required length for the attached straight pipe is highly accurate and greater values do not have much effect on elbow flexibility. Finite element analysis (FEA) studies have been carried out on 31 models with various diameters and thicknesses for both D/T ≤ 100 and D/T > 100 and in all cases the high precision of the given equation in B31J-2017 is indicated. Also, a new formula of in-plane flexibility factor (with consideration of the end effect) for long radius-90degree elbows is presented that has acceptable accuracy in all ranges of D/T. The new formula reveals that the B31 equation also has an acceptable accuracy even for D/T > 100.
Effect of the Third Body Layer on Fretting Wear Behavior of 316 Stainless Steel
Authors: Zhang Shengzan , Liu Liyan , Ma Xu , Tan Wei , Zhu Guorui
Published: October 2021

It is very important to evaluate the fretting wear damage of heat exchanger tube in steam generator. In this study, the self-designed high-temperature fretting wear experimental equipment was used to conduct experimental studies on 316 stainless steel, commonly used as steam generator tube in nuclear power plants, at 95 °C for 24h, 48h, 72h and 120h, respectively. The effect of TBL on fretting wear behavior was analyzed. The results show that due to the formation of the third body layer, fretting wear damage does not increase significantly before 72 h. With the accumulation of damage, the third body layer was worn out and the damage continued to increase. The influence of the third body layer on the fretting wear behavior cannot be ignored.
An Application of the Brittle Fracture Criterion Gp Method to a RPV Type Geometry – Towards the Industrialization of the Method
Authors: Zheng Bin , Liu Han , Jules Samuel , Xie Hai , Shi Kaikai
Published: October 2021

With the life extension of Nuclear Power Plants worldwide, new challenges have emerged in engineering calculations. These challenges often stem from the difficulty to demonstrate an adequate margin for some key components, which have gradually been ageing during the operation of the plant. In particular, the Reactor Pressure Vessel (RPV) is impacted by the irradiation, and the risk of brittle fracture under severe cold shocks must be assessed.

In parallel to conventional approaches, a significant amount work has been performed over the past 20 years in France to adapt the historic Griffith energy release-rate approach to engineering space. The work was initiated by Francfort and Marigo[1]who set up a new elastic fracture theory, extended from the Griffith approach. Lorentz and Wadier[2][3] have since then improved the model which is based on several ingredients including the application of an energy minimization principle, the definition of a specific damage model and the use of a notch to represent the crack.

Among other advantages, the Cleavage brittle fracture energy approach parameter (Gp) method has been developed as a true engineering approach and hence is relatively easy to implement in a FEA software: it has already been implemented into code_aster developed by EDF R&D [4]. Recently, CEA also implemented the method in Cast3M [5].

Beyond the application in France, and in the wake of a simple comparison benchmark launched in 2018 with CNNC/NPIC from China on a CT specimen [6], a calculation on a RPV type geometry was initiated. This is the second step of a larger effort aiming at working together on establishing a strong industrial basis to demonstrate applicability in engineering and structural integrity space.

The paper provides the progress achieved in the benchmark work and the results obtained in the frame of the work jointly led with company B in the field.
Application of 3D Constraint-Based Fracture Mechanics for the Determination of R-Curves of Thermal Aged 16MND5 Steel
Authors: Liu Zheng , Wang Xin , Miller Ronald E. , Shen Yueyin , Chen Xu
Published: October 2021

In the current work, the comprehensive combined effects of thermal aging, and three-dimensional (3D) in-plane and out-of-plane constraints on the fracture resistance curves (J-R) of reactor pressure vessel (RPV) steel, 16MND5 were investigated. First, the fracture experiments of RPV steel with different thermal aging durations using variously sized clamped single edge notched tension (SENT) specimens, were summarized. Then, 3D finite element method (FEM) was used to determine the constraint parameters for the tested specimens. From the analysis results, it was shown that the normalized T11, and the independent portion of T33 can accurately quantify the in-plane and out-of-plane constraint levels, respectively. Next, the in-plane and out-of-plane constraint-quantified R-curves were developed. Results showed that the effects of thermal aging, in-plane and out of-plane constraints on fracture toughness present significant interactions. The specific characteristics observed are: the influence of constraints on fracture toughness decreases with the increase of thermal aging duration, especially the in-plane constraint effect; the effect of thermal aging on fracture behavior is more significant under low constraint conditions. Further, the current in-plane and out-of-plane constraint dependent R-curves can easily reproduce all tested R-curves determined by clamped SENT specimens. It was also shown that they can accurately predict R-curves of pin-loaded SENT specimens or real RPV cracked structures under different thermal aging durations.
Reactive CFD Simulation of Fixed Coke Formation in an Industrial RFCC Riser Reactor
Authors: Chen Sheng , Kang Haoyuan , Wang Mengke , Liu Cenfan , Lin Haitao , Liu Juanbo
Published: October 2021

Severe fixed Coke in the industrial residue fluid catalytic cracking (RFCC) riser reactor often results in the reduction of product yield and unplanned unit shutdown. It is difficult to simultaneously depict physical and chemical formation of fixed coke near wall due to no approach and coking model. In this paper, the complex gas-solid-liquid three phase flow, mixing and cracking reaction are in agreement with the industrial data by 3D reactive simulation with multiphase Eulerian granular model coupling with the vaporization empirical correlation and the energy-minimization multi-scale (EMMS) drag and mass transfer models. A new coking index is developed to predict the formation possibility of fixed coke based on the 3D accurate simulation. The variations of coking profiles at different diameter of oil droplet are investigated. The results indicate that the fixed coke formation can be well depicted by the coking index. The predicted of fixed coke in the feed injection zone is same with the actual positions in industrial unit, which mainly located near the walls of the 0.5∼3.0m height above the feed nozzles and the circumferential between adjacent nozzles. The feed oil droplet size can improve the formation possibility of fixed coke.
Research and Application of Safety Valves Inspection Method Based on Failure and Risk Big Data
Authors: Xing Jian , Ai Shuping , Han Zhiyuan
Published: October 2021

Inspection interval of safety valves is generally at least once a year specified by the Safety Technical Supervision Regulations for Safety Valves (TSG ZF001-2006) in China, while the maintenance interval of production equipment in oil refining and chemical enterprises is usually 3–5 years. There is a prominent problem that inspection interval and maintenance interval is not consistent. This paper reveals the main failure modes, opening rate as well as maintenance replacement rate by analyzing the operation condition of 24720 safety valves of 322 typical units in oil refining and chemical industry. Moreover, the engineering application data of 44692 safety valves carried out with Risk-Based Inspection (RBI) method in the past eight years are statistically analyzed to reveal the risk distribution and risk level of safety valves. Based on the failure and risk level big data of safety valves, this paper proposes the safety valves inspection method to solve the contradiction between inspection interval and maintenance interval, which maybe further promote the legal compliance and long-term safe operation of production units in oil refining and chemical enterprises. The advantages and limitations of this method are summarized by sharing the engineering application cases in a petrochemical company about Safety valves inspection based on big data of failure and risk.
Research and Examination of Seismic Safety Evaluation and Function Maintenance for Important Equipment in Nuclear Facilities
Authors: Furuya Osamu , Fujita Satoshi , Muta Hitoshi , Ohtori Yasuki , Itoi Tatsuya , Okamura Shigeki , Minagawa Keisuke , Nakamura Izumi , Fujimoto Shigeru , Otani Akihito , Nishida Akemi , Watakabe Tomoyoshi
Published: October 2021

Since the Fukushima accident, with the higher safety requirements of nuclear facilities in Japan, suppliers, manufacturers and academic societies have been actively considering the reconstruction of the safety of nuclear facilities from various perspectives. The Nuclear Regulation Authority has formulated new regulatory standards and is in operation. The new regulatory standards are based on defense in depth, and have significantly raised the levels of natural hazards and have requested to strengthen the countermeasures from the perspective of preventing the simultaneous loss of safety functions due to common factors. Facilities for dealing with specific serious accidents are required to have robustness to ensure functions against earthquakes that exceed the design standards to a certain extent. In addition, since the probabilistic risk assessment (PRA) and the safety margin evaluation are performed to include the range beyond the design assumption in the safety improvement evaluation, it is very important to extent the special knowledge in the strength of important equipment for seismic safety. This paper summarizes the research and examination results of specialized knowledge on the concept of maintaining the functions of important seismic facilities and the damage index to be considered by severe earthquakes. In the other paper, the study on reliability of seismic capacity analysis for important equipment in nuclear facilities will be reported.
The Creep Crack Growth Behavior of GH3535 Superalloy at 650°C
Authors: Guangcheng Fan , Wanxia Wang , Jianping Tan , Kexian Shi , Songlin Wang , Yanling Lu
Published: October 2021

GH3535 alloy is a kind of Ni-Mo-Cr based structural material independently developed by China especially for thorium molten salt reactor (TMSR) that is the only liquid fueled reactor among the six fourth-generation advanced fission reactors. GH3535 alloy has good high temperature mechanical properties and the purpose of this work is to evaluate the creep crack growth (CCG) performance of it. The CCG tests on GH3535 alloy were conducted with the compact tension (CT) specimen under different effective stress intensity factors Kn at 650°C. Based on this, the relationship between creep crack initiation time ti, creep crack growth rate da/dt and fracture parameter C* were obtained and compared with the result predicted by Nikbin-Simth-Webster (NSW) model. The microstructural degradation at creep rupture was characterized using scanning electron microscopy (SEM). The results show that in the double logarithmic coordinate system, the fracture parameter C* has a linear relationship with the crack growth rate da/dt and the crack initiation time ti which show C* can correlate well with the crack growth rate and crack initiation time. The NSW model under plane stress can better predict creep crack growth behavior. The crack propagates in two ways: firstly, it propagates along the grain boundary, and then enters the rapid propagation stage, where the ductile dimple fracture occurs.
Failure Analysis and Intelligent Prevention and Control Technology of High Pressure Air Cooler in Hydrogen Environment
Authors: Ou Guofu , Jin Haozhe , Gu Yong , Liu Xiaofei , Yu Chenyang
Published: October 2021

The failure anatomy and simulation of high pressure air cooler bundle in hydrogenation unit are analyzed. Based on the typical working condition data, DCS and Lims data during the calibration period of the unit, the process simulation of the hydrogenation effluent system was carried out in Aspen Plus, and the cooling separation process of the hydrogenation effluent was simulated by using the material reverse sequence backward pushing method. According to the distribution of oil, gas and water multiphase flow in the air cooler, the temperature of ammonium salt crystallization, the content of liquid water, the concentration of ammonium sulphate hydrogenation, the corrosion factor and the pH value were calculated. The results showed that there were corrosion risks of ammonium salt crystallization and erosion corrosion in the air cooler. At the same time, according to the state and physical parameters, the erosion risk of air cooler inlet pipe and air cooler is predicted and analyzed, and the characteristic parameters such as shear stress, mass transfer coefficient and water phase fraction are used to represent the erosion risk. The anatomic analysis results of the failed bundle are verified by the process and fluid mechanics simulation. In view of corrosion analysis, corrosion prevention and control are carried out by means of technological protection, mainly by adjusting the water injection volume and water injection location. Based on the design of resistance to flow corrosion, the compound liner of air cooler tube bundle was modified. A corrosion expert supervision system was developed to monitor the running state of the hydrogenation effluent system in real time. The process calculation model and fluid dynamics simulation prediction model are embedded into the system to calculate each characteristic parameter and present the corrosion status of the current device to the enterprise, so that the enterprise can timely take measures to avoid safety accidents.
Thermal Analysis Evaluations Using the Dry Cask Simulator
Authors: Suffield S. R. , Richmond D. J. , Fort J. A.
Published: October 2021

Different thermal analysis models were developed to simulate the dry cask simulator (DCS). The DCS is an experiment designed to simulate dry storage of a single boiling water reactor fuel assembly under a variety of heat loads and internal pressures. The DCS was set up and tested in both a vertical and horizontal configuration to determine cladding temperatures in vertical and horizontal dry cask storage systems. The models included a detailed STAR-CCM+ model with the fuel assembly geometry explicitly modeled, a porous STAR-CCM+ model with the fuel assembly geometry modeled as a porous media region with calculated effective properties, and a COBRA-SFS model. COBRA-SFS is a thermal-hydraulic code developed for steady-state and transient analysis of multi assembly spent-fuel storage and transportation systems. STAR-CCM+ is a commercial computational fluid dynamics (CFD) code. Both a detailed and porous STAR-CCM+ model were developed to look at the effective thermal conductivity (keff) approach to modeling a fuel assembly. A keff fuel model is typically modeled in CFD thermal analyses due to its significantly lower computational costs. The models were run for a combination of low and high canister pressures (100 kPa and 800 kPa) and low and high internal heat loads (0.5 kW and 5 kW). Results from all three models were compared against experimental data taken from the DCS for the peak cladding temperature (PCT) and inlet air mass flow.
Proposal of Simulation Material Test Technique for Clarifying the Structure Failure Mechanisms Under Excessive Seismic Loads
Authors: Hashidate Ryuta , Kato Shoichi , Onizawa Takashi , Wakai Takashi , Kasahara Naoto
Published: October 2021

This paper proposes simulation material test technique using 99% lead - 1% antimony alloy instead of actual structural material. It is very essential to clarify the structure failure mechanisms under excessive seismic loads. However, structural tests using actual structural materials are very difficult and expensive. Therefore, the authors have proposed the structure test approach using lead alloys in order to simulate the structure failure mechanisms under the excessive seismic loads. Because the strength of such alloys is much inferior to that of the actual structural materials, failure phenomena can be observed by much small load. For demonstration of qualitative analogy between the failure mechanisms of the structures made of lead alloys under small loads and those of the actual structural materials under the actual loads, numerical analyses are required. In this study, the authors conducted material tests using lead alloy and verified the effectiveness of the simulated material tests. Moreover, the authors formulated inelastic constitutive equations (best fit fatigue curve equation and cyclic stress range – strain range relationship equation) of lead alloy based on the results of a series of material tests. Nonlinear numerical analyses, e.g. finite element analyses, can be performed using the proposed equations. A series of simulation material test technique enables structural tests and analyses using lead alloy to simulate the structure failure phenomena under excessive seismic loads. It is important to note that while mechanical behavior can be simulated by structural tests using such alloys, metallurgical evolutions cannot be simulated.
Dynamic Behavior of a Simplified Cantilever With Progressive Static Loading due to Ratchet Deformation
Authors: Kai Satoru , Kasahara Naoto , Ichimiya Masakazu
Published: October 2021

The importance of the severe accident mitigation under beyond design-basis events (BDBEs) was realized to achieve the nuclear safety through the Fukushima accident. Failure mode estimation of essential components in nuclear facilities is necessary to take appropriate measures against the severe accident conditions. The failure mode of piping systems exposed to excessive seismic loading was found to be ratchet deformation followed by fatigue failure through many experimental tests in the past, whereas the failure of Test #37 of Pipe-fitting dynamic reliability program (PFDRP) conducted by EPRI was unexpected and its failure mechanism remains unclear, as it was often suspected to have been failed in plastic collapse. In the past research, the constant stress on the structure such as a dead-weight was revealed to significantly affect the failure mode and failure level of structures under seismic excitation. In this study, the constant stress components which can increase due to the ratchet deformation during a seismic excitation is focused and is analytically examined to clarify the effects on the failure mode of structures by using a cantilever structure with various dead-weight conditions and a constant cycles of sinusoidal waves which essentially represents the seismic loading with specific frequency ratios to establish the failure estimation of a structure exposed to seismic loading.
Fracture Toughness in Postulated Crack Area of PTS Evaluation in Highly-Neutron Irradiated RPV Steel
Authors: Ha Yoosung , Shimodaira Masaki , Takamizawa Hisashi , Tobita Tohru , Katsuyama Jinya , Nishiyama Yutaka
Published: October 2021

The Japanese Electric Association Code 4206-2016 requires that the semi-elliptical crack sized 10 mm in depth × 60 mm in length shall be postulated near the inner surface of a reactor pressure vessel (RPV) in pressurized thermal shock events. The fracture toughness distribution was investigated in the postulated crack area under the PTS events of unirradiated and highly-neutron irradiated RPV steels. Vickers hardness in heat-affected zone (HAZ) due to stainless overlay cladding and 10 mm from the cladding were higher than that of a quarter thickness position, where the surveillance specimens are machined, for both unirradiated (E1) and irradiated (up to 1 × 1020 n/cm2, WIM) materials. Fracture toughness of HAZ and 10 mm from the cladding was higher for the above highly-neutron irradiated material. The same result was obtained in the unirradiated material. Therefore, it was confirmed that fracture toughness obtained from surveillance specimens can provide conservative assessment of structural integrity of RPV.
Assessment of Residual Stress for Thick Butt-Welded Plate of a Reactor Pressure Vessel Steel
Authors: Ha Yoosung , Okano Shigetaka , Takamizawa Hisashi , Katsuyama Jinya , Mochizuki Masahito
Published: October 2021

Residual stress is one of the most important influence factors in the structural integrity assessment of the nuclear components. However, at the present, there are few examples of residual stress measurements for thick butt-welded plates such as the reactor pressure vessels (RPVs). In this study, the residual stresses generated by butt-welding of thick plates of RPV steel, which have almost the same thickness of 140 mm as actual boiling water reactor RPV, were measured for post-welded heat-treated condition using the deep-hole-drilling technique. In addition, thermo–elastic–plastic creep analyses with or without considering the phase transformation in the heat-affected zone using the finite element analyses (FEAs) were performed to evaluate the residual stress produced by butt-welding and post-weld heat treatment. In the analysis considering phase transformation using the commercial FEM analysis code Abaqus, the fractions of the phases, such as martensite, bainite and ferrite, are calculated based on the kinetics of phase transformation. By comparing the analytical results with the experimentally determined values, we found good agreements for the residual stress distributions within the weld and the base material near the welded part. In the presentation, the effect of phase transformation on residual stress distribution of butt-weldment of thick plate will be discussed.