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In Situ Scanning Electron Microscope Observation And Finite Element Method Analysis Of Delayed Hydride Cracking Propagation In Zircaloy 2 Fuel Cladding Tubes
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Book Synopsis In Situ Scanning Electron Microscope Observation and Finite Element Method Analysis of Delayed Hydride Cracking Propagation in Zircaloy-2 Fuel Cladding Tubes by : Toshio Kubo
Download or read book In Situ Scanning Electron Microscope Observation and Finite Element Method Analysis of Delayed Hydride Cracking Propagation in Zircaloy-2 Fuel Cladding Tubes written by Toshio Kubo and published by . This book was released on 2011 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the present research is to build a modeling method for delayed hydride cracking (DHC) of zirconium alloys. DHC tests were carried out on Zircaloy-2 cladding tubes in the chamber of a scanning electron microscope to directly observe the crack propagation and measure the crack velocity in the radial direction. These in situ observations showed that a sharply tipped crack propagated at a relatively high rate, while the velocity decreased when the crack tip was blunted, supporting the occurrence of intermittent crack propagation that could be expected from the DHC mechanism. V-KI curves or diagrams of crack velocity, V, versus stress intensity factor at a crack tip, KI, were obtained as a function of 0.2 % offset yield stress, hydride orientation, and pre-crack depth. The steady state crack velocity and the threshold stress intensity factor for the onset of the crack propagation tended to increase or decrease, respectively, with an increase in the 0.2 % offset yield stress. Analyses of stress distribution and hydrogen diffusion around a crack tip were made using a finite element computer code. The analyses showed that a strong hydrostatic pressure field was generated concentrically around the crack tip and hydrogen diffused towards the crack tip according to the hydrostatic pressure gradient. The crack velocity was estimated from the calculated hydrogen flux rate assuming the critical hydrogen quantity for the crack propagation. There was good agreement between the experiments and the calculations regarding the crack velocity and its dependency on KI. Calculations showed that the increase in the 0.2 % offset yield stress would accelerate the crack propagation by increasing the hydrostatic pressure at the crack tip.
Book Synopsis The Influence of Temperature and Yield Strength on Delayed Hydride Cracking in Hydrided Zircaloy-2 by : P. Efsing
Download or read book The Influence of Temperature and Yield Strength on Delayed Hydride Cracking in Hydrided Zircaloy-2 written by P. Efsing and published by . This book was released on 1996 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: To determine if delayed hydride cracking (DHC) can be the cause of the long axial cracks occasionally found in BWR fuel cladding, a systematic study of DHC in Zircaloy cladding has begun. In the initial stage of the project, a test technique was developed and applied to unirradiated samples of Zircaloy. The present study includes an investigation of the influence of the yield strength and temperature on the crack growth rate and the threshold stress intensity that must be exceeded before cracking begins.
Book Synopsis Delayed Hydride Cracking in Irradiated Zircaloy Cladding by : K. Pettersson
Download or read book Delayed Hydride Cracking in Irradiated Zircaloy Cladding written by K. Pettersson and published by . This book was released on 2000 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: Slow stable crack growth by a mechanism identified as a form of delayed hydride cracking has been studied on irradiated Zircaloy cladding. The background to the investigation was the formation of long axial cracks in defected fuel rods. Post-irradiation examination of such fuel rods has indicated that precipitation and subsequent cracking of hydrides at the tips of the long cracks has played an important role in the crack growth process. The present investigation conducted on irradiated cladding with hydrogen concentrations above about 500 ppm has demonstrated that a hydrogen-induced crack growth process can occur in such material. In the laboratory it was necessary to subject the samples to an overtemperature cycle in order to initiate crack growth after fatigue precracking. It was also observed that an incubation time on the order of 20 h was necessary before crack growth started. The crack growth rates were strongly dependent on the applied stress intensity factor K in a narrow range above a threshold value KIH, which was about 10 MPa?m, Stage I. The growth rate then reached a plateau value when it was independent of K, Stage II. This plateau value was about 10-6 m/s at 300°C and about 2 x 10-7 m/s at 200°C. This temperature dependence is consistent with a mechanism based on stress-induced diffusion of hydrogen at the stress concentration of the crack tip. Metallographic and fractographic observations suggest that the details of the mechanism can be best described as a localized reduction of fracture toughness due to reorientation of hydrides so that they become perpendicular to the applied stress in the region of the crack tip. This is somewhat in contrast to previous DHC mechanisms in which longer-range diffusion of hydrogen to one large hydride at the crack tip is usually modeled. The difference is that in the present case the hydride content is higher and therefore more hydrides are present.
Book Synopsis Hydride Precipitation Crack Propagation in Zircaloy Cladding During a Decreasing Temperature History by :
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.
Book Synopsis The Effect of Microstructure on Delayed Hydride Cracking Behavior of Zircaloy-4 Fuel Cladding--An International Atomic Energy Agency Coordinated Research Program by : C. Coleman
Download or read book The Effect of Microstructure on Delayed Hydride Cracking Behavior of Zircaloy-4 Fuel Cladding--An International Atomic Energy Agency Coordinated Research Program written by C. Coleman and published by . This book was released on 2010 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: The rate of delayed hydride cracking (DHC) has been measured in Zircaloy-4 fuel cladding in several metallurgical conditions using the pin-loading tension technique. In light water reactor (LWR) cladding in the cold-worked and cold-worked and stress-relieved conditions, the cracking rate followed Arrhenius behavior up to about 280 °C, but at higher temperatures the rate declined with no cracking above 300°C. Non-LWR cladding appeared to behave in the same manner. In LWR cladding in the recrystallized condition, the cracking rate was highly variable because it depended on KI within the test range up to 25 MPa√m, whereas in the other LWR claddings, cracking rate was independent of KI, indicating that KIH was below 11 MPa√m. The main role of microstructure was to control the material strength; the cracking rate increased as the strength increased. Although all the claddings had a radial texture, it did not protect the cladding from DHC. The DHC fracture surface consisted of flat broken hydrides, often in arcs, but no striations were observed, except in one specimen subjected to thermal cycles.
Book Synopsis Delayed Hydride Cracking of Zirconium Alloy Fuel Cladding by : International Atomic Energy Agency
Download or read book Delayed Hydride Cracking of Zirconium Alloy Fuel Cladding written by International Atomic Energy Agency and published by . This book was released on 2010 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: This publication examines the phenomena of delayed hydride cracking (DHC) in Zircaloy-4 claddings and presents the results of a coordinated research project on this subject. It discusses the circumstances and the mechanisms that lead to DHC in Zircaloy-4 cladding materials and documents the knowledge gained through an inter-laboratory comparison where the physical conditions for DHC have been studied. An advanced DHC testing methodology developed in Studsvik, Sweden, and consistent experimental data of international round-robin DHC velocity measurements in CANDU/PHWR and LWR cladding Zircaloy-4 materials are also attached.
Book Synopsis Fracture Behavior and Microstructural Characteristics of Irradiated Zircaloy Cladding by : HM. Chung
Download or read book Fracture Behavior and Microstructural Characteristics of Irradiated Zircaloy Cladding written by HM. Chung and published by . This book was released on 1987 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zircaloy cladding tube specimens from commercial power reactor fuel assemblies (burnup >22 MWd/kgU) have been deformed to fracture at 325°C by either the internal gas-pressurization or the expanding-mandrel technique in a helium or argon environment containing no fission product species (e.g., I, Cs, or Cd). The fracture surfaces of ten irradiated specimens fractured by internal gas pressurization were examined by scanning electron microscopy; six specimens were found to contain various degrees of the pseudocleavage feature that is characteristic of pellet-cladding interaction failures. Out of ten test specimens fractured by expanding-mandrel loading, five were found to contain regions of pseudocleavage on the fracture surfaces. The specimens exhibited "X-marks" on the outer surface and brittle incipient cracks distributed on the inner surface, which are also characteristic of pellet-cladding interaction failures. Transmission/high-voltage electron microscope examinations of the thin-foil specimens obtained from regions adjacent to the failure sites showed that the ductile-failure specimens were characterized by a high density of dislocations which showed normal ->?-type Burgers vectors. In contrast, the brittle-type specimens were characterized by comparatively few dislocations which formed substructures. The dislocations in the brittle specimens were decorated by Zr3O precipitates 2 to 6 nm in size, and cubic-ZrO2 precipitates ? 10 nm in size were also observed in high density. These observations indicate a general immobilization of the dislocations. The low-ductility brittle-type failures appear to have been produced primarily as a result of the Zr3O and cubic-ZrO2 precipitates, augmented by precipitates of bulk hydride 35 to 100 nm in size. The bulk nature of these precipitates, which contrasts with the surficial nature of monoclinic ZrO2 and ?-hydride precipitates, was indicated from stereomicroscopy of weak-beam dark-field images. In situ irradiation of the spent-fuel cladding specimens by 1-MeV electrons at 325°C indicates that the Zr3O and cubic-ZrO2 precipitation is irradiation-induced, whereas the bulk hydride is not.
Book Synopsis Research on Mechanisms of Stress Corrosion Cracking in Zircaloy by :
Download or read book Research on Mechanisms of Stress Corrosion Cracking in Zircaloy written by and published by . This book was released on 1981 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of internal gas pressurization tests, primarily at 320°C, on cladding tubes from two suppliers, Supplier A and Supplier B, are presented. The two lots show a substantial difference in iodine SCC susceptibility so a test matrix is used to resolve the relative contributions of surface condition, residual stress, and texture. Additional tests with constant deflection split-ring specimens and with unstressed cladding segments are used to understand crack initiation and the early crack growth stages of SCC. The difference in SCC susceptibility is due to crystallographic texture. Other variables such as surface finish, stress relief temperature, and residual stress have little or no effect. Mechanical properties, crack initiation, and crack propagation all depend on texture. Both initiation and propagation features are analyzed by scanning electron microscopy. A mechanism for crack initiation consistent with most observations in this study and with the work of other investigators is proposed. At 320°C, lifetime is crack initiation limited while several tests at 390°C indicate that lifetime is less initiation limited at higher temperature. 31 figures, 9 tables.
Book Synopsis Deformation and Fracture Characteristics of Spent Zircaloy Fuel Cladding by :
Download or read book Deformation and Fracture Characteristics of Spent Zircaloy Fuel Cladding written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: For a better understanding of Zircaloy fuel-rod failure by the pellet-cladding interaction (PCI) phenomenon, a mechanistic study of deformation and fracture behavior of spent power reactor fuel cladding under simulated PCI conditions was conducted. Zircaloy-2 cladding specimens, obtained from fuel assemblies of operating power reactors, were deformed to fracture at 325°C by internal gas pressurization in the absence of fission product simulants. Fracture characteristics and microstructures were examined via SEM, TEM, and HVEM. Numerous dislocation tangles and cell structures, observed in TEM specimens of cladding tubes that failed in a ductile manner, were consistent with SEM observations of a limited number of dimples characteristic of microvoid coalescence. A number of brittle-type failures were produced without the influence of fission product simulants. The brittle cracks occurred near the areas compressed by the Swagelok fittings of the internally pressurized tube and propagated from the outer to the inner surface. Since the outer surface was isolated and maintained under a flowing stream of pure helium, it is unlikely that the brittle-type failure was influenced by any fission product traces. SEM fractography of the brittle-type failure revealed a large area of transgranular pseudocleavage with limited areas of ductile fluting, which were similar in appearance to the surfaces produced by in-reactor PCI-type failures. A TEM evaluation of the cladding in the vicinity of the through-wall crack revealed numerous locations that contained an extensive amount of second-phase precipitate (Zr3O). We believe that the brittle-type failures of the irradiated spent fuel cladding in the stress rupture experiments are associated with segregation of oxygen, which leads to the formation of the order structure, an immobilization of dislocations, and minimal plastic deformation in the material.
Book Synopsis Characterization of Axial Fracture and Delayed Hydride Cracking Behaviour of Zircaloy Cladding Tubes by : G. Sanyal
Download or read book Characterization of Axial Fracture and Delayed Hydride Cracking Behaviour of Zircaloy Cladding Tubes written by G. Sanyal and published by . This book was released on 2011 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Is Spent Nuclear Fuel Immune from Delayed Hydride Cracking During Dry Storage? An IAEA Coordinated Research Project by : Christopher E. Coleman
Download or read book Is Spent Nuclear Fuel Immune from Delayed Hydride Cracking During Dry Storage? An IAEA Coordinated Research Project written by Christopher E. Coleman and published by . This book was released on 2018 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: Delayed hydride cracking (DHC) has been responsible for cracking in zirconium alloy pressure tubes and fuel cladding and is a concern for spent fuel storage. For cracking to start, sufficient hydrogen must be present for hydride to form at a flaw tip and the local tensile stress must be sufficiently large to crack the hydride (a crack will not extend if the threshold in the stress intensity factor, KIH, is not exceeded. A high-temperature limit exists when the yield stress of the cladding alloy becomes too low to crack the hydride. In this paper we describe measurements of KIH and the crack growth rate, V, in unirradiated Zircaloy-4 fuel cladding containing approximately 130 ppm hydrogen in the cold-worked stress-relieved condition representing pressurized water reactors (PWRs) and pressurized heavy-water (PHWR) reactors. Four methods are used to evaluate KIH. The test specimen and fixture used in these methods was the pin-loading tension configuration. The test temperature ranged from 227 to 315°C. The mean value of KIH below 280°C had little temperature dependence; it was about 5.5 MPa?m in the PWR cladding and slightly higher at 7 MPa?m in the PHWR material. At higher test temperatures, KIH increased dramatically to more than 12 MPa?m, whereas the crack growth rate declined toward zero. This behavior suggests that unirradiated Zircaloy-4 fuel cladding is immune from DHC above about 320°C; this temperature may be increased to 360°C by irradiation. The implications for spent fuel storage are that during early storage when the temperatures are high, any flaw will not extend by DHC, whereas at low temperatures, after many years of storage, flaws would have to be very large, approaching through wall, before being extended by DHC. To date, spent nuclear fuel is not known to have failed by DHC during storage, confirming the inference.
Book Synopsis Delayed Hydride Cracking of Zirconium Alloy Fuel Cladding by :
Download or read book Delayed Hydride Cracking of Zirconium Alloy Fuel Cladding written by and published by . This book was released on 2010 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This publication examines the phenomena of delayed hydride cracking (DHC) in Zircaloy-4 claddings and presents the results of a coordinated research project on this subject. It discusses the circumstances and the mechanisms that lead to DHC in Zircaloy-4 cladding materials and documents the knowledge gained through an inter-laboratory comparison where the physical conditions for DHC have been studied. An advanced DHC testing methodology developed in Studsvik, Sweden, and consistent experimental data of international round-robin DHC velocity measurements in CANDU/PHWR and LWR cladding Zircaloy-4 materials are also attached ... Subject Classification : 0800 - Nuclear fuel cycle and waste management. Responsible Officer : Mr. Victor Inozemtsev, NEFW."--Résumé de l'éditeur.
Book Synopsis Characterization of Axial Fracture and Delayed Hydride Cracking Behavior of Zircaloy Cladding Tubes by : G. Sanyal
Download or read book Characterization of Axial Fracture and Delayed Hydride Cracking Behavior of Zircaloy Cladding Tubes written by G. Sanyal and published by . This book was released on 2011 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Statistical Analysis of Hydride Reorientation Properties in Irradiated Zircaloy-2 by : S. Valance
Download or read book Statistical Analysis of Hydride Reorientation Properties in Irradiated Zircaloy-2 written by S. Valance and published by . This book was released on 2011 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The orientation of hydrides in fuel cladding determines the anisotropic fracture behavior of Zircaloy and the failure modes of cladding tubes. Approach coupling experiments using the cladding tube deformation test and finite element analysis have successfully led to the quantification of the stress influencing reorientation of hydrides in unirradiated samples. An improved version of this procedure was applied to six samples of irradiated Zircaloy-2 from two different rods with three classes of thermo-mechanical loading. It was found that at medium maximum temperature, when no more than half of the hydrides were dissolved, the mechanical loading showed no measurable effect. When most of the hydrides were dissolved, the orientation and location of the hydrides depended strongly on the mechanical loading: The hydrides spatial location followed the hoop tensile stress. When the number of loading cycles was raised, the fraction of radial hydrides increased even for very low hoop tensile stress. The inner side of the cladding showed a marked depletion of hydrides whatever the size of the hoop stress. Since our test setup involved a tri-axial stress state, the possible influence of the other components of the stress tensor was evaluated. Through the use of a classical nucleation law, it was shown that for our test setup, the hoop stress was the important mechanical quantity. Therefore, the inner side depletion of hydrides may be attributed to three other factors: Residual stress, a memory effect, and a pumping effect by the inner liner.
Book Synopsis Potential for delayed hydride cracking in welds of zircaloy-2 by : C. E. Coleman
Download or read book Potential for delayed hydride cracking in welds of zircaloy-2 written by C. E. Coleman and published by . This book was released on 1993 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Experimental and Analytical Investigation of the Mechanical Behavior of High-Burnup Zircaloy-4 Fuel Cladding by : Robert S. Daum
Download or read book Experimental and Analytical Investigation of the Mechanical Behavior of High-Burnup Zircaloy-4 Fuel Cladding written by Robert S. Daum and published by . This book was released on 2008 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sufficient mechanical ductility of high-burnup Zircaloy-4 fuel cladding is important to prevent large-opening ruptures and significant fuel dispersal during postulated in-reactor and spent-fuel processing accidents. The effect of irradiation, oxidation, and hydriding at high fuel burnup may degrade cladding ductility to the extent that such large ruptures are possible under severe loadings. To understand this susceptibility to failure, this study focused on mechanical testing coupled with detailed finite-element modeling and analyses. Under ring-compression-type loading at room temperature, tensile cracks form within the corrosion-induced oxide layer under elastic loading. The oxide crack then propagates into the cladding wall under additional loading with little to no measurable plastic strain, as confirmed by both experiment and analyses of plastic hoop strain in the ring. For cladding with the oxide removed prior to testing at ≤1 %/s, cracking of the underlying hydride rim comprised of circumferentially oriented hydrides occurs at low plastic hoop strain (≤3 %), whereas the finite-element analysis suggests that the base alloy with a relatively small amount of hydrides appears to fail at higher strain (>8 %). At even higher strain rates (≈400 %/s), cracking within the hydride rim occurs at near-zero ductility, but the base alloy continues to remain highly ductile. These room-temperature results indicate that the hydride rim is sensitive to strain rate, whereas the base alloy is relatively not. With the precipitation of ≈100 % radially oriented hydrides, the cladding exhibits near-zero ductility at room temperature and ≈0.1 %/s. This study suggests that the ring-compression test coupled with finite-element modeling and analysis may be used to estimate crack-initiation strains in irradiated cladding materials with susceptible microstructures and under various deformation rates.
Book Synopsis Temperature and Hydrogen Concentration Limits for Delayed Hydride Cracking in Irradiated Zircaloy by : JS. Schofield
Download or read book Temperature and Hydrogen Concentration Limits for Delayed Hydride Cracking in Irradiated Zircaloy written by JS. Schofield and published by . This book was released on 2002 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Critical temperatures for delayed hydride cracking (DHC) initiation during cooling (TRIT) and crack arrest during heating (TDAT) have been measured in experiments on specimens from a Zircaloy-2 electron beam weld irradiated to a fluence of 3 to 5 > 1025 n • m-2 (E > 1 MeV) and then hydrided to concentrations of 35 and 55 ppm. The experimental observations are shown to be consistent with a simple model based on previously determined hydrogen terminal solid solubility data for dissolution and precipitation, which describes conditions for sustained hydride precipitation at the crack tip. When plotted against bulk hydrogen concentration in solution, both TRIT and TDAT fall below the dissolution solvus temperature and above the precipitation solvus temperature. A key assumption in the model is that, while the local crack tip stress concentration causes local enhancement of the hydrogen concentration in solution, the hydride precipitation solvus is unaffected by stress. The good agreement obtained between measured and predicted critical temperatures provides strong support for this assumption.
