Download or read book Modeling Zirconium Hydride Precipitation and Dissolution in Zirconium Alloys written by Evrard Lacroix and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nuclear fuel cladding undergoes waterside corrosion during normal operating conditions in pressurized water reactors, whereby the zirconium (Zr) in the fuel cladding reacts with the oxygen present in water, creating zirconia (ZrO) and releasing hydrogen. Part of the hydrogen created by the corrosion reaction can be absorbed into the fuel cladding. Once in the cladding, hydrogen redistributes by solid state diffusion in the metal, in response to gradients of concentration, temperature and stress. Once the local hydrogen solubility is exceeded, zirconium hydride precipitates are formed.The precipitation of hydrides may impact the integrity of zirconium-based nuclear fuel cladding, both during normal operation and during extended dry storage. It is important to model hydrogen behavior accurately, so as to assess cladding properties both in reactor and during dry storage. This is because the cladding is the first containment barrier, which prevents fission products to be released into the primary circuit. For this reason, this study aims to first understand hydride precipitation and dissolution and then implement this understanding into a hydride precipitation and dissolution model. To this end, differential scanning calorimetry (DSC) and in-situ synchrotron X-ray diffraction experiments were used to study the precipitation and dissolution of hydrides in Zircaloy-4 under different thermo-mechanical conditions.Results showed that when hydrided samples were cooled at cooling rates above 1C/min the hydrogen content in solid solution decreased, following the Terminal Solid Solubility for Precipitation (TSSP) curve. However, when the samples were held at a fixed temperature for a long anneal, the hydrogen content in solid solution continued to decrease below the TSSP and approached the Terminal Solid Solubility for Dissolution (TSSD). This result suggests that TSSP is a kinetic limit and that a unique solubility limit, i.e. TSSD governs the equilibrium hydrogen concentration in solid solution. DSC was used to perform isothermal precipitation experiments, from which the hydride precipitation rate and the degree of precipitation completion were quantified between 280 and 350C for the first time. The data obtained was used to generate a TTT diagram for hydride precipitation in Zircaloy-4 showing that hydride precipitation is diffusion-controlled at low temperatures and reaction-controlled at high temperatures. The experimental precipitation rate was fitted using the Johnson-Mehl-Avrami-Kolmogorov model to obtain a value of the Avrami parameter of 2.56 (2.5 is the theoretical value for the growth of platelet-shaped precipitates). It was also possible to derive the precipitation activation energy of for each process. Because it was possible to separate hydride nucleation and hydride growth, it was possible to ascertain that if the hydrogen content in solid solution is greater than TSSP, precipitation occurs by hydride nucleation. In contrast, precipitation occurs by hydride growth as long as hydride platelets are present and the hydrogen content in solid solution is above TSSD. Hydride dissolution will take place if hydrides are present and the hydrogen content in solid solution is below TSSP. Using this new understanding of hydrogen precipitation and dissolution mechanisms, experiments were conducted at the Advanced Photon Source (APS) using high temperature change rates to measure hydride nucleation and dissolution kinetics. These observations and measurements were combined to existing theory to a model, entitled Hydride Growth, Nucleation, and Dissolution model (HNGD model) that can accurately simulate hydrogen behavior in Zircaloy fuel cladding and that shows a significant improvement on the model used in BISON.The development of such a model is the first step towards obtaining a model for the impact of the development of hydride microstructure on nuclear fuel cladding mechanical properties during normal operation and to address concerns over fuel handling during dry storage. The use and benchmarking of such a code can be used to justify a safe burnup extension of nuclear fuel, which would reduce the cost of nuclear energy in an increasingly competitive market.

Download or read book Hydrogen Migration and Mechanical Behavior of Hydrided Zirconium Alloys written by Soyoung Kang and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zirconium alloys have been widely used for nuclear fuel cladding materials in light-water nuclear reactors. The cladding corrodes as a result of exposure to the coolant water and produces hydrogen as a result of the corrosion reaction. A fraction of this hydrogen can be picked up into the cladding material. Once the hydrogen content reaches the terminal solid solubility, zirconium hydride particles start to precipitate. The cladding suffers waterside corrosion in service, leading to hydrogen ingress, which can redistribute in the cladding and form hydrides. Because these zirconium hydrides are more brittle than the zirconium matrix, they can deteriorate the ductility of the cladding. Therefore, understanding hydrogen behavior in cladding is important to maintain cladding integrity. This study aims to investigate hydrogen migration under a temperature gradient and mechanical behavior of hydrided zirconium alloys. The hydrogen transport and hydride precipitation /dissolution model HNGD was implemented in the fuel performance code BISON to predict hydrogen behavior. The hydrogen is distributed inhomogeneously in the cladding as a result of Fick's law and Soret effect. The hydrogen tends to move from higher to lower concentration governed by Fick's law and higher to lower temperature based on the Soret effect. Hydrogen migration tests were designed to determine the heat of transport value (Q*) of hydrogen in Zr, a parameter needed to evaluate the Soret effect. Hydrided samples were subjected to a long annealing schedule in a temperature gradient to re-distribute the hydrogen. The annealed samples were cut into several pieces along the temperature gradient, and the hydrogen contents were analyzed using hot vacuum extraction. The hydrogen distribution along the temperature gradient was observed in this experiment, and from this data, the heat of transport value (Q*) was determined. Further, the mechanical behavior of zirconium alloys was assessed using ring compression tests. The zirconium alloy tubes were characterized by electron backscatter diffraction (EBSD) to identify the microstructure of materials. Stress relieved anneal ZIRLO (SRA) and low Sn Partially recrystallized anneal LT ZIRLO (PRXA) show different grain shapes and sizes. After characterization, the zirconium alloy tubes were hydrogen charged and cut into 8 mm length rings. The ring samples were subjected to compression at 12 o'clock following a specified thermomechanical cycle. This thermomechanical treatment caused partial precipitation of radial hydrides in certain positions of the ring samples. The radial hydride fractions were characterized and showed a difference between ZIRLO and LT ZIRLO because of their different microstructures. Finite element modeling conducted using ABAQUS could then determine the threshold stress for two materials by comparing simulation results (stress state) and hydride morphologies. In addition, the ring compression tests for assessing hydrided cladding ductility for various hydride morphologies were conducted at room temperature. Ring samples with different radial hydride continuity factors (RHCF) were tested to determine their load-displacement curves. The 1% permanent strain and 2 % offset strain criteria were chosen to assess the ductility of samples. The ductility degrades with increasing RHCF.

Download or read book Characterization of Zirconium Hydrides and Phase Field Approach to a Mesoscopic Scale Modeling of Their Precipitation written by Z. Zhao and published by . This book was released on 2008 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zirconium alloys are currently used in nuclear power plants where they are submitted to hydrogen pick-up. Hydrogen in solid solution or hydride precipitation can affect the behavior of zirconium alloys during service but also in long term storage and in accidental conditions. Numerical modeling at mesoscopic scale using a "phase field" approach has been launched to describe hydride precipitation and its consequences on the mechanical properties of zirconium alloys. To obtain realistic results, it should take into account an accurate kinetic, thermodynamic, and structural database in order to properly describe hydride nucleation, growth, and coalescence as well as hydride interaction with external stresses. Therefore, an accurate structural characterization was performed on Zircaloy-4 plates and it allowed us to identify a new zirconium hydride phase called ?. The ? phase has a trigonal symmetry and is fully coherent with hcp ?Zr. The consequences of this new zirconium hydride phase on hydride transformation process and stress-reorientation phenomenon are discussed. A first attempt to numerically model the precipitation of this new zirconium hydride phase has been undertaken using the phase field approach.

Download or read book Phase Field Modeling and Quantification of Zirconium Hydride Morphology written by Pierre Clement Simon and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In light water nuclear reactors, waterside corrosion of the cladding material leads to the production of hydrogen, a fraction of which is picked up by the zirconium cladding. Once the hydrogen concentration reaches its solid solubility limit in zirconium, it precipitates into brittle hydride particles. These nanoscale hydride particles aggregate into mesoscale hydride clusters. Depending on the material's texture and the thermomechanical treatment imposed on the cladding, these mesoscale hydride clusters exhibit different morphologies. In particular, the principal orientation of the hydride platelets in the cladding tube can be circumferential or radial. Because hydrides are usually more brittle than the zirconium matrix, the morphology of the mesoscale hydride clusters can affect cladding integrity. This is in part because radial hydrides can ease crack propagation through the cladding thickness and because the concentration of hydrides in specific locations driven by temperature, hydrogen concentration, and stress gradients can create local weak points in the cladding. This dissertation work investigates the link between precipitation conditions, hydride morphology, and hydride embrittlement in zirconium cladding material. The first part focuses on understanding which physics and mechanisms govern the formation of specific hydride microstructures. A quantitative phase field model has been developed to predict the hydride morphology observed experimentally and identify which mechanisms are responsible for circumferential and radial hydride precipitation. The model accurately predicts the elongated nanoscale hydride shape and the stacking of hydrides along the basal plane of the hexagonal zirconium matrix. When investigating the role of applied stress on hydride morphology, the model challenges some of the mechanisms proposed in previous studies to explain hydride reorientation. Although hydride reorientation has been hypothesized to be caused by a change in nanoscale hydride shape and orientation, the current model shows that these mechanisms are unlikely. This study focuses on the precipitation of nanoscale hydrides in polycrystalline zirconium to understand the physics and mechanisms responsible for the change in hydride microstructure from circumferential to radial under applied stress. It proposes a new mechanism where the presence of an applied stress promotes hydride precipitation in grains with circumferentially aligned basal poles. Nanoscale hydrides, even though they still grow along the basal plane of the hexagonal matrix, now grow and stack radially, thus leading to radial mesoscale hydrides. This mechanism is consistent with experimental observations performed in other studies. The second part of this dissertation focuses on the link between hydride morphology and hydride embrittlement. Although hydride microstructure can significantly influence Zr alloy nuclear fuel cladding's ductility, quantifying hydride microstructure is challenging and several of the metrics currently being used have significant shortcomings. A new metric has been developed to quantify hydride microstructure in 2D micrographs and relate it to crack propagation. As cladding failure usually results from a hoop stress, this new metric, called the Radial Hydride Continuous Path (RHCP), is based on quantifying the continuity of brittle hydride particles along the radial direction of the cladding tube. Compared to previous metrics, this approach more closely relates to the propensity of a crack to propagate radially through the cladding tube thickness. The RHCP takes into account hydride length, orientation, and connectivity to choose the optimal path for crack propagation through the cladding thickness. The RHCP can therefore be more closely linked to hydride embrittlement of the Zr alloy material, thus creating a relationship between material structure, properties, and performance. The new definition, along with previously proposed metrics such as the Radial Hydride Fraction (RHF), the Hydride Continuity Coefficient (HCC), and the Radial Hydride Continuity Factor (RHCF), have been implemented and automated in MATLAB. These metrics were verified by comparing their predictions of hydride morphology against expected values in simple cases, and the implementation of the new metric was validated by comparing its predictions with manual measurements of hydride microstructure performed on ImageJ. The RHCP was also validated against experimental measurements of fracture behavior and it was shown to correlate with cladding failure better than previous metrics. The information provided by these metrics will help accurately assess cladding integrity during operation, transportation, and storage.

Download or read book Mechanisms of hydride precipitation and dissolution in zirconium and titanium written by G. J. C. Carpenter and published by . This book was released on 1978 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydride Nucleation Growth Dissolution HNGD Model written by Florian Passelaigue and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In nuclear reactors, waterside corrosion of the Zircaloy nuclear fuel cladding tube causes hydrogen pick-up into the material. This hydrogen can cause zirconium hydrides to precipitate within the cladding. Since these hydrides are usually more brittle than the alloy, they can decrease the ductility of the cladding. Previous efforts made to describe hydrogen behavior and hydride precipitation resulted in the Hydride Nucleation-Growth-Dissolution (HNGD) model. This model can predict the distribution of hydrogen and the partition between solid solution and hydrides in Zircaloy samples that are subjected to a thermal treatment. However, in some cases the HNGD model gives unphysical results. Notably, if the system is close to steady-state, or if the initial hydrogen distribution is significantly heterogeneous the model calculations diverge from experimental results, predicting either no hydride precipitation, or hydride precipitation in a single node of the simulation mesh. The study presented in this dissertation describes how the HNGD model was improved upon to address these shortcomings. This was done using two hypotheses described below. Chapter 1 introduces the issue of hydrogen in Zircaloy cladding, and the experimental data used to validate the HNGD model. In Chapter 2, we review the phenomena described by the HNGD model, the equations used, and associated parameters. We also expose the causes for the unphysical results previously mentioned. Chapter 3 focuses on the two hypotheses. The first hypothesis is based on the assumption that, given enough time, the hydrogen atoms will find the most favorable nucleation spots in the Zircaloy (matrix defects, dislocations, etc), resulting in a decrease of the nucleation barrier. This is translated with a decrease of $TSS_P$ during temperature holds. The second hypothesis postulates that the hydride particles deform the matrix in a way that impacts the hydrogen solubility. These two hypotheses together allow for hydride precipitation to be triggered more easily, and for the hydrides to stay stable. A complete analytical solution (i.e. for the hydrogen in solid solution and in hydrides) was derived for the steady state of the system. Using this tool and the large experimental data set from Kammenzind, the impact of the newly introduced parameters is studied. An extensive validation of the modified HNGD model is performed using Kammenzind's experiments, as well as the benchmark and validation cases used during the initial development of the HNGD model. We show that the modified HNGD is able to predict the thickness of the hydride peak at steady state, which is a significant improvement compared to the initial model. Finally, the implementation of the modified HNGD model into the nuclear fuel performance code Bison is described in Chapter 4. We describe how the quality of the code is ensured when implementing an update in Bison. This modified HNGD model yields physical results when modeling experiments that mimic reactor conditions in terms of hydrogen pick-up, and does not degrade the simulations of experiments that were accurately modeled using the initial HNGD model. This improved HNGD model represents an improvement of the capability to predict the hydrogen behavior in cladding tubes during operation and in spent nuclear fuel during storage and transport.

Download or read book The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components written by Manfred P. Puls and published by Springer Science & Business Media. This book was released on 2012-08-04 with total page 475 pages. Available in PDF, EPUB and Kindle. Book excerpt: By drawing together the current theoretical and experimental understanding of the phenomena of delayed hydride cracking (DHC) in zirconium alloys, The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Delayed Hydride Cracking provides a detailed explanation focusing on the properties of hydrogen and hydrides in these alloys. Whilst the emphasis lies on zirconium alloys, the combination of both the empirical and mechanistic approaches creates a solid understanding that can also be applied to other hydride forming metals. This up-to-date reference focuses on documented research surrounding DHC, including current methodologies for design and assessment of the results of periodic in-service inspections of pressure tubes in nuclear reactors. Emphasis is placed on showing how our understanding of DHC is supported by progress in general understanding of such broad fields as the study of hysteresis associated with first order phase transformations, phase relationships in coherent crystalline metallic solids, the physics of point and line defects, diffusion of substitutional and interstitial atoms in crystalline solids, and continuum fracture and solid mechanics. Furthermore, an account of current methodologies is given illustrating how such understanding of hydrogen, hydrides and DHC in zirconium alloys underpins these methodologies for assessments of real life cases in the Canadian nuclear industry. The all-encompassing approach makes The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Component: Delayed Hydride Cracking an ideal reference source for students, researchers and industry professionals alike.

Download or read book Mechanisms of Hydride Reorientation in Zircaloy 4 Studied in Situ written by Arthur Motta and published by . This book was released on 2014 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zirconium hydride platelet reorientation in fuel cladding during dry storage and transportation of spent nuclear fuel is an important technological issue. Using an in situ x-ray synchrotron diffraction technique, the detailed kinetics of hydride precipitation and reorientation can be directly determined while the specimen is under stress and at temperature. Hydrided Zircaloy-4 dogbone sheet samples were submitted to various thermo-mechanical schedules, while x-ray diffraction data was continuously recorded. Post-test metallography showed that nearly full hydride reorientation was achieved when the applied stress was above 210 MPa. In general, repeated thermal cycling above the terminal solid solubility temperature increased both the reoriented hydride fraction and the connectivity of the reoriented hydrides. The dissolution and precipitation temperatures were determined directly from the hydride diffraction signal. The diffraction signature of reoriented hydrides is different than that of in-plane hydrides. During cooling under stress, the precipitation of reoriented hydrides occurs at lower temperatures than the precipitation of in-plane hydrides, suggesting that applied stress suppresses the precipitation of in-plane hydrides. The analysis of the elastic strains determined by the shift in position of hydride and zirconium diffraction peaks allowed following of the early stages of hydride precipitation. Hydride particles were observed to start to nucleate with highly compressive strain. These compressive strains quickly relax to smaller compressive strains within 30°C of the onset of precipitation. After about half of the overall hydride volume fraction is precipitated, hydride strains follow the thermal contraction of the zirconium matrix. In the case of hydrides precipitating under stress, the strains in the hydrides are different in direction and trend. Analyses performed on the broadening of hydride diffraction peaks yielded information on the distribution of strains in hydride population during precipitation and cooldown. These results are discussed in light of existing models and experiments on hydride reorientation.

Download or read book Habit Plane for Hydride Precipitation in Zirconium and Uranium zirconium written by F. W. Kunz and published by . This book was released on 1959 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiphase Field Modeling of the Formation Path of Delta Hydrides in Zirconium written by Jacob Luke Bair and published by . This book was released on 2016 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Zirconium alloys are commonly used in nuclear fuel rod claddings due to their high ductility, good corrosion resistance, and low neutron absorption cross section. Among the most important weaknesses of zirconium alloys is their affinity for hydrogen, resulting in formation of hydrides in the cladding, and leading to embrittlement and mechanical failure. Despite numerous studies on hydride precipitation in zirconium alloys, the nucleation and formation path of stable [delta] hydrides in [alpha] zirconium matrix are not yet fully understood. In this Ph. D. research project, two novel quantitative phase-field models were developed and utilized to advance our understanding of mechanisms of formation and evolution of hydrides in zirconium alloys. First, a phase-field model for unstable [gamma] hydride precipitation was created to build on previous computational models by including the actual Gibbs free energy of formation of hydrides in the total free energy of the system. Results from isothermal simulations of seeded and random nucleation in single crystal [alpha]-zirconium matrix showed that the thickness of non-equilibrium hydrides varied with temperature during evolution, and the hydrides were more rod-like (thinner) at higher temperatures and thicker at lower temperatures. Quench simulations with random nucleation indicated that the majority of precipitation occurs at early stages of quenching, but the size and shape of hydrides change as the temperature decreases. The most detrimental phase of hydrides in claddings is the stable [delta] phase. A multiphase model including the two metastable phases ([zeta] and [gamma]) and the [delta] phase was created to determine the effects of the intermediate phases on the nucleation and morphology of [delta] hydrides. Results from simulations both with and without applied strains indicated that the intermediate phases are influential in the initial formation and evolution of [delta] hydrides"--Abstract, page iv.

Download or read book Chemical Thermodynamics of Zirconium written by and published by Elsevier. This book was released on 2005-12-06 with total page 545 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume is part of the series on "Chemical Thermodynamics", published under the aegis of the OECD Nuclear Energy Agency. It contains a critical review of the literature on thermodynamic data for inorganic compounds of zirconium. A review team, composed of five internationally recognized experts, has critically reviewed all the scientific literature containing chemical thermodynamic information for the above mentioned systems. The results of this critical review carried out following the Guidelines of the OECD NEA Thermochemical Database Project have been documented in the present volume, which contains tables of selected values for formation and reaction thermodynamical properties and an extensive bibliography. * Critical review of all literature on chemical thermodynamics for compounds and complexes of Zr.* Tables of recommended Selected Values for thermochemical properties* Documented review procedure* Exhaustive bibliography* Intended to meet requirements of radioactive waste management community* Valuable reference source for the physical, analytical and environmental chemist.

Download or read book Hydride Precipitation Crack Propagation in Zircaloy Cladding During a Decreasing Temperature History written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. If such assessment analyses are to be done rigorously, they will be necessarily complex because the precipitation response of zirconium hydride platelets is a stochastic functional of hydrogen concentration, temperature, stress, fabrication defect/texture structures, and flaw sizes of the cladding. Thus, there are, and probably always will be, zirhydride questions to analytically and experimentally resolve concerning the consistency, the completeness, and the certainty of models, data, the initial and the time-dependent boundary conditions. Some resolution of these questions will be required in order to have a defensible preference and tradeoffs decision analysis for assessing risks and consequences of the potential zirhydride induced cladding failures during dry storage time intervals. In the following brief discussion, one of these questions is posed as a consequence of an anomaly described in data reproducibility that was reported in the results of tests for hydrogen induced delayed cracking. The testing anomaly consisted of observing a significant differential in the measurable crack velocities (quasi-steady state at a prescribed load and temperature values) that depended on the approach direction, from above or from below, to the test temperature value. The testing method used was restricted to approaching a prescribed test temperature value from above. This anomaly illustrates the known thermodynamic non-equilibrium processes in the precipitation kinetics of zirhydride platelets that are dependent on temperature and stress histories. Detailed solubility limits of hydrogen in Zircaloy as a function of temperature, in terms of zirhydride precipitation and zirhydride dissolution solubility curves, were reported recently. In addition, other tests to evaluate the influence of an applied stress state on zirhydride precipitation kinetics have also been recently reported.

Download or read book Hydride Platelet Reorientation in Zircaloy Studied with Synchrotron Radiation Diffraction written by Arthur T. Motta and published by . This book was released on 2011 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrogen ingress into zirconium alloy fuel cladding in light water reactors can degrade cladding performance as a result of the formation of brittle hydrides. In service, hydrides normally precipitate in the circumferential direction and are homogeneously distributed through the cladding thickness in ideal cases. However, temperature and stress gradients in the cladding can promote hydrogen redistribution. This hydrogen redistribution is responsible for the formation of hydride rims, dissolution, and reorientation of hydride precipitates and for the formation of brittle hydrides at stress concentration locations, all of which can reduce cladding resistance to failure. Thus, it is crucial to understand the kinetics of hydride dissolution and precipitation under load and at temperature. Studies of hydrogen behavior in zirconium alloys are normally performed post facto, which causes them to suffer both from a scarcity of data points and from the confounding effects of studying hydrides at room temperature that might be dissolved at higher temperature. In the current study, we have used synchrotron radiation diffraction to study the kinetics of hydride precipitation and dissolution in situ (under load and at temperature). Samples of hydrided Zircaloy-4 were examined in transmission by using 80 keV synchrotron radiation while undergoing heating and cooling in a furnace. Temperatures ranged from 20 to 550°C, and loads from 75 to 100 MPa were applied. The hydrides dissolved and reprecipitated in a different orientation when sufficiently high loads were applied. Through careful study of the intensities and full-width half maxima of the diffraction peaks as a function of time, load, and temperature, it was possible to identify the characteristic diffraction patterns for the reoriented hydrides so that the kinetics of dissolution, reprecipitation, and orientation of the hydrides could be followed. The analysis of the diffraction patterns allowed a detailed understanding of the kinetics of hydride evolution under temperature and stress, as presented in this work.

Download or read book Advanced Techniques for the Characterization of Hydrided Zirconium Alloy written by Gregory B. Allen and published by . This book was released on 2011 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zirconium alloy pressure tubes are an important component in CANDU nuclear reactors. During operation these tubes can pick up hydrogen as a result of a corrosion reaction, which can eventually lead to the precipitation of a secondary, brittle zirconium hydride phase. Hydrides tend to first form at flaws (stress concentrations), and when they fracture can initiate a time-controlled crack growth mechanism known as delayed hydride cracking (DHC). Since DHC is a known failure mechanism for pressure tubes, and an ongoing concern in the nuclear industry, more fundamental knowledge is required about the behaviour of hydrides precipitated at flaws. Several approaches were employed in this thesis to better characterize the effects and behaviour of hydrides at such stress concentrations. High energy X-ray diffraction, as well as in-situ SEM testing coupled with digital image correlation, were used to map the strains around stress concentrations where hydrides were present. These studies highlighted important differences in the behaviour of the hydride phase and the surrounding zirconium. To gain greater insight into hydride morphology, neutron tomography was used in an attempt to measure the through-thickness hydride distribution at flaws. A finite element model was also developed and verified against the X-ray strain mapping results. This model provided greater insight into details that could not be obtained directly from the experimental approaches, as well as providing a framework for future modeling to predict the effects of hydride precipitation under different conditions. Taken as a whole, these studies provide important information for improving service guidelines and avoiding conditions that favour embrittlement due to hydride precipitation.

Download or read book Zirconium in the Nuclear Industry written by George P. Sabol and published by ASTM International. This book was released on 1996 with total page 907 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement and Modeling of Second Phase Precipitation Kinetics in Zirconium Niobium Alloys written by Joseph Robson and published by . This book was released on 2010 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Commercial zirconium alloys contain second phase particles (SPPs) that are precipitated during processing. These particles not only influence mechanical properties but more crucially also have a profound influence on the corrosion performance. To understand how to control evolution and size distribution of SPPs, it is necessary to know how alloy composition and process variables influence the precipitation kinetics. In this work, a detailed study has been performed of the precipitation kinetics in binary Zr-1 wt % Nb, Zr-2.6 wt % Nb, and ternary variants with added iron and tin. A numerical model has also been developed to predict the precipitation kinetics of ?-Nb in niobium containing zirconium alloys. Precipitation has been tracked by synchrotron X-ray diffraction measurement of lattice parameter change in the zirconium matrix as solute is removed into SPPs. The X-ray data has been complemented by thermoelectric power measurements. The combination of these two approaches is shown to be effective in quantifying the overall precipitation kinetics of SPPs. The results confirm previous observations that without prior deformation, precipitation kinetics is very sluggish in the binary Zr-Nb system. Deformation accelerates precipitation, and this effect is much stronger for the 1 wt % Nb alloy than for 2.6 wt % Nb, because the supersatu-ration is least. Ternary additions also have a profound effect on the overall precipitation kinetics. Iron accelerates the rate of niobium loss from solution, whereas tin additions appear to increase the incubation time for the onset of precipitation of niobium.

Download or read book Theory of Plasticity written by Jagabanduhu Chakrabarty and published by Elsevier. This book was released on 2012-12-02 with total page 895 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasticity is concerned with the mechanics of materials deformed beyond their elastic limit. A strong knowledge of plasticity is essential for engineers dealing with a wide range of engineering problems, such as those encountered in the forming of metals, the design of pressure vessels, the mechanics of impact, civil and structural engineering, as well as the understanding of fatigue and the economical design of structures. Theory of Plasticity is the most comprehensive reference on the subject as well as the most up to date -- no other significant Plasticity reference has been published recently, making this of great interest to academics and professionals. This new edition presents extensive new material on the use of computational methods, plus coverage of important developments in cyclic plasticity and soil plasticity. A complete plasticity reference for graduate students, researchers and practicing engineers; no other book offers such an up to date or comprehensive reference on this key continuum mechanics subject Updates with new material on computational analysis and applications, new end of chapter exercises Plasticity is a key subject in all mechanical engineering disciplines, as well as in manufacturing engineering and civil engineering. Chakrabarty is one of the subject's leading figures.