bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of Linear Elastic Fracture Mechanics in Predicting the Fracture Toughness of Polyethylene Pipe Materials
Authors: El-Bagory Tarek M. A. A. , Sallam Hossam E. M. , Younan Maher Y. A.
Published: November 2015

The main purpose of the present paper is to compare between the fracture toughness based on linear elastic fracture mechanics (GIC), and that based on nonlinear fracture mechanics (JIC). The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in natural gas piping systems. The welds at the pipe junction are produced by butt-fusion (BF), welding. Curved three-point bend (CTPB), fracture specimens are used. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature Ta, equal 23°C. The study reveals that the crosshead speed has a significant effect on the fracture toughness of both welded and unwelded specimens. The results of GIC for different specimen thickness and crosshead speed found previously by the authors [1] have been compared with JIC under the same operating conditions [2]. The comparison between welded and unwelded specimens revealed that in the welded specimens there is a marginal difference between fracture toughness measured using linear elastic fracture mechanics LEFM and elastic plastic fracture mechanics EPFM, for both crosshead speeds.
Characterization of Advanced Steels as Accident Tolerant Cladding for Light Water Reactor Nuclear Fuel
Authors: Rebak Raul B.
Published: November 2015

After the tsunami incident in Fukushima in March 2011, the international community is set to identify appropriate nuclear materials with increased accident tolerance with respect to the traditional UO2-zirconium alloy fuel system permitting loss of active cooling for a considerably longer time period, while maintaining or improving the fuel performance during normal operations. The researched safety characteristics of these advanced fuels are mainly: (a) Improved reaction kinetics with steam; (b) Slower hydrogen production rate; and (c) Enhanced retention of fission products. In the US the Department of Energy is supporting the development of an improved cladding using advanced steels such as the iron-chromium-aluminum (FeCrAl) alloy system. Environmental test results show that FeCrAl alloys are highly resistant to corrosion and environmental cracking under normal operation conditions and extremely resistant to attack by steam under accident conditions. That is, the replacement of a zirconium alloy using a ferritic material containing chromium and aluminum appears to be the most near term implementation for accident tolerant fuels.
Pressurized Water Reactor Environment Effect on 316 Stainless Steel Stress Hardening/Softening: An Experimental Study
Authors: Mohanty Subhasish , Soppet William K. , Majumdar Saurindranath , Natesan Krishnamurti
Published: November 2015

In USA there are approximately 100 operating light water reactors (LWR) consisting fleet of both pressurized water reactors (PWR) and boiling water reactors (BWR). Most of these reactors were built before 1970 and the design lives of most of these reactors are 40 years. It is expected that by 2030, even those reactors that have received 20 year life extension license from the US nuclear regulatory commission (NRC) will begin to reach the end of their licensed periods of operation. For economical reason it is be beneficial to extend the license beyond 60 to perhaps 80 years that would enable existing plants to continue providing safe, clean and economic electricity without significant green house gas emissions. However, environmental fatigue is one of the major aging related issues for these reactors, and may create hurdles in long term sustainability of these reactors. To address some of the environmental fatigue related issues, Argonne National Laboratory (ANL) with the sponsorship of Department of Energy’s Light Water Reactor Sustainability (LWRS) program trying to develop mechanistic approach for more accurate life estimation of LWR components. In this context ANL conducted many fatigue experiments under different test and environment conditions on 316 stainless steel (316SS) material that is or similar grade steels are widely used in US reactors. Contrary to the conventional S∼N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to understand material ageing more mechanistically (e.g. time dependent hardening and softening) under different test and environmental conditions. Better mechanistic understanding will help to develop computer based advanced modeling tools to better extrapolate stress-strain evolution of reactor component under multi-axial stress states and hence to help predicting their fatigue life more accurately. In this paper (part-I) the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed. In another paper (part-II) the related evolutionary cyclic plasticity material modeling techniques and results are discussed.
Multiaxial Fatigue of Preloaded Threaded Fasteners
Authors: Kazemi Amir , Wu Zhijun , Nassar Sayed A.
Published: November 2015

This experimental study investigates the effect of cyclic multiaxial loading on the High Cycle Fatigue (HCF) life of preloaded threaded fasteners. A special fixture is used for orienting test bolts at different angles relative to the direction of the cyclic load applied by an MTS fatigue testing system. The orientation angle converts the external cyclic load to a combined cyclic axial and shear loading on test bolts. Test data is used for creating the S-N curves for various multiaxial load combinations. The effect of cyclic stress amplitude and mean stress level are investigated.
The Prediction of Size Effect on J-R Curve for Eurofer97 Steel by Simplified Mechanical Model
Authors: Stratil Ludek , Siska Filip , Hadraba Hynek , Dlouhy Ivo
Published: November 2015

The possibilities to derive fracture toughness from small specimens are naturally limited due to constraint requirements which are especially restrictive in toughness testing. The loss of constraint at the crack tip is more likely to occur as specimen size decreases. Application of miniature specimens in fracture toughness testing thus requires a suitable methodology or correction procedure to deal with phenomenon of the constraint loss. Schindler et al. have proposed a simplified mechanical model that can be used to scale-up the key test characteristics from miniature specimen to the larger one. The model is applied to the miniature bending specimens to describe size effect on J-R curve of the Eurofer97 steel. The examined steel exhibits quite high toughness values at upper shelf region of fracture toughness. As a result, experimentally determined J-R curves of three different sizes of pre-cracked bending specimens showed high values of J-integral, which were significantly different each other. Using semi-empirical definition of the exponent of the power law function of J-R curve the performance of the Schindler’s model was quite successful. It was shown that the model is able to handle with size effect of tested pre-cracked three-point-bend specimens.
The Application of Miniaturized Three-Point-Bend Specimens for Determination of the Reference Temperature of JRQ Steel
Authors: Stratil Ludek , Siska Filip , Dlouhy Ivo , Serrano Marta
Published: November 2015

This contribution deals with determination of the reference temperature of JRQ steel using miniaturized specimens. The dimensions of used miniaturized specimens were 3 × 4 × 27 mm (thickness × width × length). This specimen type offers the utilization of limited amount of test material or broken halves of precracked Charpy and larger specimens. The test material comes from the broken halves of 0.5T SEB specimens previously tested for purposes of the reference temperature determination in Ciemat, Madrid. The fracture toughness tests of specimens were performed in the transition region of the steel according to the recommendations of standard ASTM E1921 and according Wallin’s recommended temperature range for miniaturized specimens. The determined reference temperature of the Master Curve was very similar to the determined ones from three-point-bend specimen of sizes 0.2T, 0.4T and 0.5T. The obtained results confirm a necessity of conduct of tests at low temperatures and testing sufficient number of specimens in order to generate enough valid data for determination of the reference temperature.
A Probability-Based Leak-Before-Break Application for Small Modular Reactors
Authors: Xu Heqin , Liszkai Tamas
Published: November 2015

The leak-before-break (LBB) applicability is stated in General Design Criterion 4 (GDC-4) of Title 10 of the Code of Federal Regulation Part 50 (10 CFR 50). GDC-4 requires that analyses reviewed and approved by the U.S. Nuclear Regulatory Commission (NRC) demonstrate that the probability of fluid system piping rupture is extremely low under conditions consistent with the design basis for the piping, in order that dynamic effects associated with postulated pipe ruptures in nuclear power units may be excluded from the design basis. Standard review plan 3.6.3 (SRP-3.6.3) further requires a simultaneous safety margin of two and ten on the flaw size and leak rate detectability, respectively, for deterministic analyses, believing that the very conservative and restrictive safety margins would lead to extremely low probability of fluid system piping rupture. The technology advancements of recent years make it possible to numerically quantify the probability of rupture with confidence.

In this study, we are going to utilize a simplified methodology based on the Univariate Dimension-Reduction (UDR) method to investigate the probability of piping rupture for postulated circumferential through-wall cracks in piping systems of small modular reactors (SMRs) inside the metal containment vessel, which typically range from 5” to 8” nominal diameter for feedwater and main steam lines. The unique design of the vacuumed metal CNV in an advanced SMR offers improved leak detection capability, which makes the LBB qualification possible even for piping with much smaller diameters than piping systems in the traditional large reactors, which typically range from 18” to 40” for LBB-qualified piping systems such as surge lines, cold legs, hot legs and main steam lines.

The conditional probability that a piping with postulated crack would fail by large break, when multiplied by the probability of having a circumferential through-wall crack during the life time of plant service, produces an overall probability of piping rupture. The major quantifiable uncertainties, such as the uncertainties associated with the material properties, and flow-path crack face morphology parameters will be modeled as correlated random variables in this paper. Efficient Dimension-Reduction methods will be applied to predict the conditional probability. As sample applications of the proposed method, the relationship between the conditional probabilities and the loading factor will be established for SMR piping systems.
Safety Factor for Flaw Evaluation of a Pipe Having a Circumferential Surface Flaw
Authors: Machida Hideo , Arakawa Manabu
Published: November 2015

This paper describes the safety factors used for fracture assessments of pipes having circumferential surface flaws. The “Fitness-For-Services Codes (the FFS Codes)” of the Japan Society of Mechanical Engineers (JSME) restrict the depths of flaws according to their angles to prevent pipes with flaws from being fracture. Past restrictions were determined based on deterministic evaluations. In fracture assessments of pipes having flaws, however, the effects of measurement errors in flaw dimensions and of variations on material strength must be taken into account. Thus, we evaluated the effects of such variations on fracture assessments of pipes having flaws, and examined safety factors for giving failure probability (or reliability) equal, irrespective of the cracking angles. We found out that failure probability is heavily dependent on the measurement accuracy of flaw depths and material strength (flow stress). In view of this finding, we examined and proposed a simple approach which meets the target reliability without conducting complex evaluations by the Monte Carlo method and reliability evaluation methods (e.g., first-order second-moment method (FOSM)).
Inverse Thermal Analysis of a Coke Drum Using a Bayesian Probabilistic Approach
Authors: Gassama Edrissa , Panzarella Charles , Cochran Jeffrey
Published: November 2015

There is much interest in predicting the optimal operating conditions of a coke drum in order to extend its life and optimize both maintenance and repair. Typically, only temperature measurements on the outer surface of the wall are available from monitoring. In order to predict damage due to thermal stresses and other mechanisms, the temperature distribution through the wall is required. This could be determined if the heat flux on the inner surface of the wall were known, but this is difficult to obtain directly. In this paper, the heat flux distribution on the inner wall is determined solely from thermocouple measurements taken on the outside of the wall by solving a stochastic inverse heat conduction problem (IHCP). A finite element analysis is used to solve the forward thermal problem, and a Bayesian inference approach is used to model the posterior probability distribution of the heat flux. A newly developed probabilistic sampling technique known as the Particle Raking Algorithm (PRA) is found to be quite effective at solving this inverse problem. Once determined, the heat flux distribution is then applied as a boundary condition for the finite element model to determine the through-wall temperature distribution.
Rayleigh Scattering of Supercritical Carbon Dioxide in Dynamic Phase Transition
Authors: Ushifusa Hiroyuki , Sugasawa Konosuke , Inaba Kazuaki
Published: November 2015

A new experimental device was developed to observe and measure the dynamic generation of supercritical CO2 (scCO2) in a closed chamber. The temperature and pressure were measured locally using a thin thermocouple and a pressure transducer, respectively. The Rayleigh scattering in the chamber was visualized using a high-speed video camera. The liquid CO2 was heated by a ceramic heater located at the top or bottom of the chamber. Using this new experimental device, the color variation due to Rayleigh scattering was observed. The temperature profile was stable and scCO2 was generated slowly within a few seconds when heating occurred at the top. For heating at the bottom, scCO2 was created faster within 1 s. Additionally, natural convection, turbulence, and a phenomenon resembling boiling were observed. Numerical simulations of the scCO2 creation in a chamber were also performed using the COMSOL Multiphysics application along with the PROPATH package to obtain the thermophysical properties of CO2. The simulation results showed that scCO2 creation for heating at the top was stable due to the gas-like properties of the scCO2 near the heater. For heating at the bottom, the density distribution initially depended on the temperature distribution. However, as natural convection developed, the flow in the chamber was perturbed and the density distribution depended on both the temperature distribution and the density fluctuation caused by the convection vortices. The same tendency was observed in the experimental results. Using PROPATH, the density variation in the scCO2 generation was estimated from the measured temperature and pressure. The P-T diagram and density variation were compared in each experiment.
Wave Propagation Across Solid-Fluid Interface With Fluid-Structure Interaction
Authors: Kojima Tomohisa , Inaba Kazuaki , Takahashi Kosuke
Published: November 2015

This paper reports on investigations conducted with a view towards developing a theoretical model for wave propagation across solid-fluid interfaces with fluid-structure interaction. Although many studies have been conducted, the mechanism of wave propagation close to the solid-fluid interface remains unclear. Consequently, our aim is to clarify the mechanism of wave propagation across the solid-fluid interface with fluid-structure interaction and develop a theoretical model to explain this phenomenon. In experiments conducted to develop the theory, a free-falling steel projectile is used to impact the top of a solid buffer placed immediately above the surface of water within a polycarbonate tube. The stress waves created as a result of the impact of the projectile propagated through the buffer and reached the interface of the buffer and water (fluid) in the tube. Two different buffers (polycarbonate and aluminum) were used to examine the interaction effects. The results of the experiments indicated that the amplitude of the interface pressure increased in accordance with the characteristic impedance of the solid medium. This cannot be explained by the classical theory of wave reflection and transmission. Thus, it is clear that on the solid-fluid interface with fluid-structure interaction, classical theories alone cannot precisely predict the generated pressure.
Ultrasonic Inspection and Analysis Using the Synthetic Aperture Focusing Technique (SAFT) on Dissimilar Metal Welds With Inter-Granular Stress Corrosion Cracks
Authors: Dugan Sandra , Wagner Sabine , Rieder Hans , Spies Martin
Published: November 2015

Cases of inter-granular stress corrosion cracking (IGSCC) in dissimilar metal welds have led to an increased interest in the reliability of non-destructive testing of these welds and this crack type. The challenges related to ultrasonic testing of dissimilar metal welds (DMW) result from the elastic anisotropy of the material in combination with the grain structure of the weld. The inhomogeneous, anisotropic structure of the weld affects ultrasound propagation and leads to a decrease in the signal-to-noise ratio, thus complicating the interpretation of ultrasonic signals. As a result, cracks located exclusively in the weld material are usually harder to detect. Detection of cracks inside the weld material is particularly important in the case of a circumferential crack in a pipe weld, which could otherwise grow to a critical size before being detected. Studies have shown that the reflected ultrasonic amplitude is considerably smaller for IGSCC than it is for artificial reference flaws. In this paper, we will present the results of ultrasonic inspection and analysis using the Synthetic Aperture Focusing Technique (SAFT) on dissimilar metal welds with IGSCC.
Demonstration of Fatigue for LTO License of NPP Borssele
Authors: Hannink M. H. C. , Blom F. J. , Quist P. W. B. , de Jong A. E. , Besuijen W.
Published: November 2015

Long Term Operation (LTO) of nuclear power plants (NPPs) requires an ageing management review and a revalidation of Time Limited Ageing Analyses (TLAAs) of structures and components important for nuclear safety. An important ageing effect to manage is fatigue. Generally, the basis for this is formed by the fatigue analyses of the safety relevant components. In this paper, the methodology for the revalidation of fatigue TLAAs is demonstrated for LTO of NPP Borssele in the Netherlands.

The LTO demonstration starts with a scoping survey to determine the components and locations having relevant fatigue loadings. The scope was defined by assessment against international practice and guidelines and engineering judgment. Next, a methodical review was performed of all existing fatigue TLAAs. This also includes the latest international developments regarding environmental effects. In order to reduce conservatism, a comparison was made between the number of cycles in the analyses and the number of cycles projected to the end of the intended LTO period. The projected number of cycles is based on transient counting. The loading conditions used in the analyses were assessed by means of temperature measurements by the fatigue monitoring system (FAMOS). As a result of the review, further fatigue assessment or assessment of environmental effects was necessary for certain locations. New analyses were performed using state-of-the-art calculation and assessment methods. The methodology is demonstrated by means of an example of the surge line. The model includes the piping, as well as the nozzles on the pressurizer and the main coolant line. The thermal loadings for the fatigue analysis are based on temperature measurements. Fatigue management of the NPP is ensured by means of the fatigue concept where load monitoring, transient counting and fatigue assessment are coupled through an integrated approach during the entire period of LTO.
Development of a Testing System for Piezoelectric Wafer Active Sensors Exposed to Extreme Temperatures
Authors: Roth William , Poddar Banibrata , Bao Jingjing
Published: November 2015

Piezoelectric Wafer Active Sensors (PWAS) are a viable option for monitoring the structural integrity of pressure vessels and piping systems. They are inexpensive, small and unobtrusive sensors which can be permanently attached to structures for long term monitoring without interfering with operations, such as operating in areas with limited head space. PWAS are used to inspect the structure through several methods which include; pitch catch or pulse echo wave propagation, and electromechanical impedance spectroscopy. Since the PWAS could be exposed to a range of environmental and/or operating conditions while attached to the structure, the change in the properties and electromechanical characteristics of the sensor must be known at a given condition. Accordingly, there is a need for a testing system which can measure the PWAS properties while exposing the sensor to a wide range of temperatures.

The focus in this paper is on elevated temperatures, but the same methodology could be used for low temperature or environmental testing. The requirements which were imposed on the design include: providing an electrical connection from each electrode to the exterior of an industrial oven; allow the sensor to expand and contract both in plane and out of plane; withstand an extended duration at elevated temperatures; the equipment must not influence the measured quantities. The challenges include how to place the sensor in an oven and make electrical contact while allowing free motion, how to implement wiring and electrical connections at elevated temperatures, how to allow the thermal expansion of components and account for thermal mismatching, and how to maintain electrical isolation of the two electrodes. This paper discusses how these requirements were met and challenges overcome, as well as experimental validation of the system.
A Rational Basis for Deterministic Margins in CUF-Based Fatigue Evaluation With Uncertainty
Authors: Garud Y. S. , Steininger David A.
Published: November 2015

One of the aging issues of concern in the light-water reactor power plants is the fatigue degradation due to cyclic loads for which the updated regulatory guidelines have factored in the water environment effects that were not in the original design basis analyses. These guidelines are also applicable to newer plant designs not yet in operation. In both these cases, notably, the design/analysis is deterministic with several factors conservatively used as an engineering judgment to address various sources of uncertainty in the cumulative usage factor (CUF) based fatigue evaluation. The use of deterministic approach to an inherently statistical issue with large and unspecified uncertainty of analysis does not provide a consistent or quantifiable measure of actual safety margin, nor does it lend itself well to assess the impact of various conservative assumptions, or their potential reductions, on the gain/loss in the margin. While a probabilistic methodology is expected to be pertinent and useful it is also recognized that the deterministic approach has the simplicity and familiarity to its credit. These aspects of significance to the long-term assessment and management of fatigue degradation are addressed in this paper with a new approach focused on its engineering application.

Presented in this paper is a rational basis that relates the results of a probabilistic assessment of CUF to the common notion of deterministic margins. The objective is to account for major sources of uncertainty in the evaluation of CUF and its allowable or performance criterion, with the goal of allowing for a more realistic assessment of fatigue damage and a consistent quantification of fatigue margins. The basis itself is developed using the stress–strength (or load–resistance) interference methodology that is probabilistic. The results of application of this methodology are expressed in the form of suitable margins that can be treated in the usual deterministic manner. The relation between application dependent acceptable risk level and the quantified fatigue margin is examined to further utilize the results of proposed approach in a simplified engineering manner. Limitations of the key assumptions in the development of this basis/approach, and their expected practical significance, are discussed with suggestions for further enhancements from the application point of view.
Onsite Transportation of Radioactive Materials at the Savannah River Site
Authors: Watkins Robert W. , Opperman Erich K.
Published: November 2015

The Savannah River Site (SRS) Transportation Safety Document (TSD) defines the onsite packaging and transportation safety program at SRS and demonstrates its compliance with Department of Energy (DOE) transportation safety requirements, to include DOE Order 460.1C, Packaging and Transportation Safety, DOE Order 461.2, Onsite Packaging and Transfer of Materials of National Security Interest, and 10 CFR 830, Nuclear Safety Management (Subpart B).
Computational Aspect of Nonlinear Fracture Mechanics Application
Authors: Orynyak Igor , Oryniak Andrii
Published: November 2015

The development of powerful commercial computer programs made the concept of J-integral as computational parameter of fracture mechanics to be a very attractive one. It is equivalent to SIF in linear case, it converges in numerical calculation and the same results are obtained by different codes (programs). Besides, it is widely thought that elastic-plastic analysis gives bigger values than elastic SIF ones what is good from regulatory point of view. Such stand was reflected in the recommended by IAEA TECDOC 1627 (February 2010) devoted to pressurized thermal shock analysis of reactor pressure vessels, where the embedded crack in FEM mesh, elastic-plastic analysis with simultaneous determination of J-integral was stated as the best option of analysis.

But at that time all the most widely used software were not able to treat the residual stresses, the thermal stresses in case of two different materials. Such a contradiction between requirements and the possibilities made a lot of problems for honest contractors especially in countries where the regulator had no own experience in calculation and completely relied on the authority of international documents. This means that at that time the said recommendations were harmful. The main reason of such a situation was the absence of the carefully elaborated examples.

Now the capabilities and accuracy of such software are increasing. Nevertheless, some principal ambiguities and divergences of computations results in various J-integral contours around the crack tip still exist. They are exhibited when the large plastic zone emerges at the crack tip. Other problem is influence of the history of loading and the specification of the time of crack insertion in the mesh including the time of emergence of residual stress.

This paper is invitation for discussion of the accuracy and restriction of computational J-integral. With this aim the detailed analysis of some simplified 2D examples of calculation of elastic -plastic J-integral for surface crack with accounting for residual stress, thermal stress and inner pressure are performed and commented.

The attainment of consensus among the engineering society for treating the outcome results is the prerequisite for practical application of computational elastic plastic J-integral.
Phase Lag Model for Fluidelastic Instability in Square Cylinder Arrangement
Authors: Benaouicha Mustapha , Longatte Elisabeth , Baj Franck
Published: November 2015

In this paper, a phase lag model is proposed in order to predict the fluid velocity threshold for fluidelastic dynamic instability of a square cylinder arrangement under cross flow. A theoretical formulation of a total damping, including the added damping in still fluid, the damping due to fluid flow and the damping derived from the phase shift between the fluid force and tube displacement, is given. A function of fluid and structure parameters, such as reduced velocity, pitch ratio and Scruton number, is thus obtained. It is shown that this function, taken as function of the reduced velocity variable, vanishes at the critical reduced velocity from which the fluidelastic dynamic instability of the tube occurs. Obviously, the value of the critical velocity is depending on other fluid-structure parameters. The obtained results are compared to experimental ones and those obtained from other theoretical models.
Non-Contact Gas Accumulation Detection in Water Loaded Pipes Using Guided Waves
Authors: Tian Zhenhua , Sun Xiaoyi , Ma Linlin , Yu Lingyu
Published: November 2015

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter 2008-01 due to the safety concern associated with gas accumulation events in emergency core cooling pipes of nuclear power plants. Since the gas accumulation may critically damage pipes, pumps, and valves, and affect the safety operation of nuclear power plants, the gas accumulation needs to be detected as well as quantified.

This paper presents a quantitative gas accumulation detection method for water loaded pipes by using guided waves. To establish the detection method, we investigated the differences between guided waves in a free pipe and those in a water loaded pipe. The guided waves in both cases were measured by using a scanning laser Doppler vibrometer, and analyzed by using frequency wavenumber analysis. Analysis results show that guided wave characteristics such as wavenumbers and wave speeds are different between the free and water loaded pipes. Based on those findings, we developed a gas accumulation detection method that can also provide quantitative information of the gas accumulation. Through a proof-of-concept test, the quantitative gas accumulation detection method was verified.
A Bayesian-Probabilistic Framework for Real-Time Fatigue Usage Factor Monitoring of Nuclear Reactor Components
Authors: Mohanty Subhasish , Iverson William , Soppet William K. , Majumdar Saurindranath , Natesan Krishnamurti
Published: November 2015

Real-time estimation of the fatigue usage factor of nuclear reactor components are helpful tools for on-demand assessment of component structural integrity. Real-time measurements of field variables, such as stress and strain, along with the use of historic/available stress/strain versus fatigue life data and a Bayesian-probabilistic framework can not only help to estimate the fatigue usage factor of reactor components in real time but also can help to estimate the associated confidence bounds. In this paper, a Gaussian Process based Bayesian-probabilistic framework is proposed for real-time estimation of mean fatigue usages factor and associated probabilistic bounds. The preliminary proof of concept was demonstrated through fatigue experiments with 316 stainless steel specimens under different conditions: a) under 300 °C and pressurized water reactor (PWR) water chemistry, and b) room temperature and in-air condition. At present the proposed probabilistic monitoring approach is not part of any code requirements, however the proposed framework is output of a futuristic basic research work, which requires more advancement. Also the results discussed in the paper are part of very preliminary basic research and requires advance validation such as under realistic nuclear reactor conditions.
Online Stress Corrosion Crack Monitoring in Nuclear Reactor Components Using Active Ultrasonic Sensor Networks and Nonlinear System Identification: Data Fusion Based Big Data Analytics Approach
Authors: Mohanty Subhasish , Jagielo Bryan , Bahn Chi Bum , Majumdar Saurindranath , Natesan Krishnamurti
Published: November 2015

The current state of the art nondestructive evaluation (NDE) techniques used in nuclear reactor structural inspection are manual labor intensive, time consuming, and only used when the reactor has been shut down. Also, despite periodic inspection of plant components, a failure mode such as stress corrosion crack can initiate in between two scheduled inspections and can become critical before the next scheduled inspection. In this context, real time monitoring of nuclear reactor components is necessary for continuous and autonomous monitoring of component structural health. In this research, an active ultrasonic based on-line monitoring (OLM) framework is developed which can be used for real-time monitoring of degradation of nuclear power plant systems, structures, and components. Nonlinear system identification technique such as Bayesian Gaussian Process technique method is investigated to estimate the structural degradation in real-time. Active broadband ultrasound input is used for damage interrogation and a multi-sensor configuration is implemented to improve spatial resolution of state estimation. The damage index at any particular time is computed using nonlinear techniques such as Gaussian Process probabilistic modeling and the necessity of sensor data fusion is evaluated. The framework was demonstrated through the monitoring of an anomaly trend in a nuclear reactor steam generator tube undergoing stress corrosion cracking (SCC) testing.
Simulation of Ductile Fracture in Pipeline Steels Under Varying Constraint Conditions Using Cohesive Zone Modeling
Authors: Parmar Shreya , Wang Xin , Tyson Bill (W. R.) , Xu Su
Published: November 2015

Fracture propagation toughness is important to pipeline steels. In this study, the effect of non-singular T-stress (a measure of constraint) on crack growth resistance curves (R-curves) and crack tip opening angle (CTOA) was investigated using modified boundary layer (MBL) models of pipeline steels. Two sets of steel types: 1) TH (a typical high strength steel) and 2) C4 (X100 steel) were used in this work. Surface-based cohesive zone models with four sets of bilinear traction-separation (TS) laws were used for TH steel. The models of C4 steel were computed using element-based cohesive zone modeling with one bilinear TS law. All finite element simulations were conducted using the finite element (FE) program ABAQUS. It was assumed in these simulations that there was no effect of T-stress on the TS laws per se. With this assumption, it was found that the T-stress does not have a significant effect on the CTOA for the two materials studied.
Fatigue Crack Growth Calculations for Pipes Considering Subsurface to Surface Flaw Proximity Rules
Authors: Katsumata Genshichiro , Li Yinsheng , Hasegawa Kunio , Lacroix Valery
Published: November 2015

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the specific criteria of the re-characterizations are different among the FFS codes. Recently, the authors have proposed a new subsurface-to-surface flaw proximity rule based on experimental data and equivalent fatigue crack growth rates. In this study, fatigue crack growth calculations were carried out for pipes with subsurface flaws, using the proposed subsurface-to-surface flaw proximity rule and the current proximity rule provided in the current JSME and ASME Section XI. Different pipe sizes, flaw aspect ratios and ligament distances from subsurface flaws to inner surface of pipes were taken into account. As the results, the current proximity rule gives less conservative fatigue lives, when the aspect ratios of the subsurface flaws are small.
The Effect of Torsion on Moment Capacity in Piping Bends
Authors: Azadi-Borujemi Bijan , Asadkarami Ali , Reinhardt Wolf
Published: November 2015

Piping analysis according to NB-3600 treats bending and torsion loads as equivalent. Piping sections are generally subjected to loading that includes a combination of bending and torsion. Such loading results in a biaxial stress state in the pipe wall. Although NB-3600 would still assign a single bounding stress index to the resultant moment vector in bends and elbows, detailed analysis shows that bending moments of different orientations and torsion loading have a different effect on the calculated stresses.

This paper shows the effect of applied moment direction on the bounding bend limit load that would be evaluated in a detailed (e.g. NB-3200) piping primary stress analysis. This gives the analyst some guidance regarding the potential benefit of a detailed analysis. Further, it is shown that pure bending is not necessarily the worst loading mode in an elbow or bend. The addition of a torsion component could increase the bend stress and lead to a more severe loading condition even if the magnitude of the resultant applied moment vector remains the same.
Fatigue Evaluation for Section III, Class 1 Components Using Flaw Tolerance Method to Consider Environmental Effects
Authors: Roarty David , Reinhardt Wolf , Dewees David
Published: November 2015

An ASME Section III Task Group (TG) was formed in 2012 to develop alternate rules for the design assessment of Section III Class 1 nuclear components subject to fatigue service with environmental effects. A Section III Code Case has been proposed with the purpose of providing a method for performing fatigue evaluations of Class 1 components when the effects of a light water reactor environment on fatigue life are judged to be significant and cumulative usage factor (CUF) limits may not be satisfied. The Code Case implements a flaw tolerance approach by postulating that a fatigue crack initiates at the beginning of life and is subjected to fatigue crack growth under the specified design cycles. It must be demonstrated that the crack would remain stable with set margin throughout the design life of the component or part under consideration, and would remain confined to an acceptable fraction of the wall thickness. At this time, the application is limited to type 304/304L and 316/316L austenitic steel. This paper discusses the methodology and technical background of the proposed Code Case.
Rules for Temporary Repair Techniques in JSME Fitness-for-Service Code and Their Challenges
Authors: Dozaki Koji , Kobayashi Hiroyuki , Adachi Hiroyuki , Muraoka Katsuhide , Kono Yusuke
Published: November 2015

Chapter of Repair, Replacement Activities (RRA) in Fitness-For-Service (FFS) Code of the Japanese Society of Mechanical Engineers (JSME) includes rules of article RB-3000 for temporary repair techniques in the use of covering leakage during operation of a Nuclear Power Plant (NPP). Temporary repair techniques are RB-3010 Plating, RB-3020 Adhesion and RB-3030 Infill. In this paper, rules of these temporary repair techniques are summarized as well as the meaning of ‘temporary’, intention and benefit of them.

On the other hand, these rules of temporary repair techniques were provided by Thermal and Nuclear Power Engineering Society (TENPES) at first in 1986, about thirty years ago. “Plant Operation and Maintenance Standards (POMS) Plan” developed by Japan Power Engineering and Inspection Corporation (JAPEIC) in 1996 incorporated those rules of temporary repair techniques, then JSME FFS Code has taken over them from POMS. Because the design rules of these temporary repair techniques have had much margin since origin, it may result in excessive design, or time-consuming procurement of parts. Especially, since these temporary repair techniques are often applied to the leakage around valve gland and flange, simpler and more practical modified rules could provide more benefit for effective repair activities. In this paper, an orientation of possible revision is described on temporary repair techniques rules in JSME FFS Code.
A Monte Carlo Implementation of the James-Ford-Jivkov Micro-Structurally Informed Local Approach Applied to Predict Fracture Toughness Including Low Constraint Conditions
Authors: Ford Michael , James Peter
Published: November 2015

The need to predict changes in fracture toughness for materials where the tensile properties change through life, such as with irradiation, whilst accounting for geometric constraint effects, such as crack size, are clearly important. Currently one of the most likely approaches by which to develop such ability are through application of local approach models. These approaches appear to be sufficient in predicting lower shelf toughness under high constraint conditions, but may fail when attempting to predict toughness in the transition region or for low constraint geometries when using the same parameters, making predictions impossible. Cleavage toughness predictions in the transition regime that are then extended to low constraint conditions are here made with a stochastic, Monte Carlo implementation of the recently proposed James-Ford-Jivkov model. This implementation is based around the creation of individual initiators following the experimentally observed distribution for specific RPV steel, and determining if these initiators form voids or cause cleavage failure using the model’s improved criterion for particle failure. The model has shown to predict experimentally measured locations of cleavage initiators. Further, initial results from the Monte Carlo implementation of the model predicts the fracture toughness in a large part of the transition region, demonstrates an ability to predict the constraint shift and shows a level of scatter similar to that observed experimentally. All results presented, for a given material, are obtained without changes in the model parameters. This suggests that the model can be used predicatively for assessing toughness changes due to constraint- and temperature-driven plasticity changes.
Performance of Bolted Closure Joint Elastomers Under Cask Aging Conditions
Authors: Verst Christopher , Sindelar Robert L. , Skidmore T. Eric , Daugherty William L.
Published: November 2015

The bolted closure joint of a bare spent fuel cask is susceptible to age-related degradation and potential loss of confinement function under long-term storage conditions. Elastomeric seals, components of the joints typically used to facilitate leak testing of the primary seals that include the metallic seal and bolting, are susceptible to degradation over time by several mechanisms, principally thermo-oxidation, stress-relaxation, and radiolytic degradation. Irradiation and thermal exposure testing and evaluation of an ethylene-propylene diene monomer (EPDM) elastomeric seal material similar to that used in the CASTOR®1 V/21 cask. Testing covers a matrix of temperature and radiation exposure conditions relevant to extended storage of the cask. Semi-empirical models are being developed to predict loss of sealing force. A special insert was developed to allow Compressive Stress Relaxation (CSR) measurements before and after the irradiation and/or thermal exposure without unloading the elastomer. A condition of the loss of sealing force for the onset of leakage was suggested. The experimentation and modeling being performed could enable acquisition of extensive coupled aging data as well as an estimation of the time when loss of sealing under aging (temperature/radiation) conditions may occur.
A Method to Derive the JC Value of a 1T SE(B) Using Charpy Impact Energy in the Lower Ductile to Brittle Transition
Authors: Smith Robin J. , Sherry Andrew H. , Horn Anthony J. , Bannister Adam C.
Published: November 2015

This paper describes a method by which the elastic-plastic crack driving force, J, of a 1T SE(B) may be calculated using Charpy V-notch absorbed impact energy, Uel+pl,LLD. The method is applicable in the lower ductile-to-brittle transition regime of fracture behaviour and permits the calculation of equivalent critical J-integral values, Jc, using Uel+pl,LLD data. The method is demonstrated using a ferritic steel study material. Comparisons are made between the predictions of a Uel+pl,LLD scaling approach, which was derived using a Weibull stress model, and experimental test data for a ferritic steel. The approach was evaluated using experimental test data composed of instrumented Charpy impact test results and SE(B) fracture toughness test results.

The probabilistic predictions were found to be in good agreement with experimental values. Extension of the methodology is recommended to include other material flow properties. Further work is required to ascertain the accuracy of the approach at higher temperatures in the ductile-to-brittle transition temperature range. A practical method for applying the methodology in practice to allow description of the behaviour of a wide range of ferritic steel materials has been outlined.
Constraint Based Assessments of Large-Scale Cracked Straight Pipes and Elbows
Authors: Gintalas Marius , Ainsworth Robert A.
Published: November 2015

The paper presents T-stress solutions developed to characterize constraint levels in large-scale cracked pipes and elbows. Stress intensity factor, KI, solutions for pipes and elbows are normalised by material fracture toughness to define the Kr parameter in fitness-for-service procedures, such as R6. Adding knowledge on levels of T-stress allows more advanced analysis through a normalised constraint parameter βT.

The paper presents analyses for 6 pipes and 8 elbows. Values of the normalised constraint parameter βT are calculated for each pipe and elbow at the experimentally measured crack initiation point. Comparison of constraint levels in the pipes and elbows with those in various types of fracture toughness specimen are used to predict the initiation loads using the R6 method and to provide guidelines for transferability.
Probabilistic Pressurized Thermal Shocks Analysis for a Reactor Pressure Vessel by Considering Plume Effect
Authors: Qian Guian , González-Albuixech V. F. , Niffenegger Markus , Sharabi Medhat
Published: November 2015

The inner surface of a reactor pressure vessel (RPV) is assumed to be subjected to pressurized thermal shocks (PTSs) caused by the downstream of emergency cooling water. The downstream is not homogeneous but typically in a plume shape coming from the inlet nozzles.

In this paper, both deterministic and probabilistic methods are used to assess the integrity of a model RPV subjected to PTS. The FAVOR code is used to calculate the probabilities for crack initiation and failure of the RPV considering crack distributions based on cracks observed in the Shoreham and PVRUF RPVs.

The study shows that peak KI of the cracks inside the plume increases about 33% compared with that outside. The conditional probability inside the plume is more than eight orders of magnitude higher than outside the plume. In order to be conservative, it is necessary to consider the plume effect in the integrity assessment.