bluuebunny/crossref_metadata_2025_split huggingface dataset:
Behavior and Properties of Zircaloys in Power Reactors: A Short Review of Pertinent Aspects in LWR Fuel
Authors: Garzarolli F , Stehle H , Steinberg E 
Published: March 2009

Zircaloy-2 and -4, developed mainly in the United States, have been used in Germany for fuel rod claddings and in-core structural components from the beginning of reactor technology. Extensive studies of the material properties of the Zircaloys have been performed in Siemens laboratories since 1957. Irradiation testing was done in several test reactors. However, the combined effects of irradiation and real environmental conditions were determined through many experimental irradiations in existing power reactors. Elaborate examinations in the reactor pools of such experimental materials and of many standard fuel rods and assemblies after intermediate, full, and intentionally extended exposures were the main source of information and hard data. These programs were supported by several utilities and in certain areas carried out in cooperation with others.
Zircaloy-2 and -4 turned out to be very reliable materials that fulfilled all requirements for normal operation and likewise the requirements for postulated accidental conditions and for intermediate storage for many years. Optimization of Zircaloy-2 and -4 during recent years includes both optimization of microstructure and of chemical composition. BWRs and PWRs need differently optimized materials. Today's more demanding operation conditions and discharge burnups required a further optimization of the Zircaloys and for “hot” PWRs even the development of more corrosion-resistant Zr alloys. A significant improvement of PWR corrosion behavior can be achieved with Zr alloys using the alloying elements of Zircaloy with somewhat modified concentrations. Sn should be below or at least in the lower range of the ASTM specification range for Zircaloy-4, Fe and Cr should be somewhat higher, and Si should be specified as an alloying element rather than as an impurity.
Correlation Between Electrochemical Properties and Corrosion Resistance of Zirconium Alloys
Authors: Ito Y , Furuya T 
Published: March 2009

The electrochemical behavior of some zirconium alloys including Zry-2 with various ΣAi from 2.5 × 10-20 to 1.2 × 10-17 (h), modified Zry-2 with iron contents of 0.15, 0.25, and 0.5%, and standard Zry-4 was studied by measuring anodic polarization curves in sulfuric acid solution. The results of these electrochemical tests were compared with those of steam autoclave tests.
In Zry-2, the current peak was observed at 1250 mV (versus SCE) on the anodic polarization curve, and this peak area increased with ΣAi and with the size of secondary precipitates. Also, this peak was closely correlated with nodular corrosion resistance as expected from the above results. As iron contents in modified Zry-2 increased, the current peak at 1250 mV decreased and a new peak at 1900 mV appeared. The former peak disappeared and the latter peak increased further at 0.5% iron. In Zry-4, the current peak was observed at 1900 mV, but not at 1250 mV, and this behavior was the same as that of modified Zry-2 of 0.5% iron.
AEM observation of secondary precipitates in these zirconium alloys indicated that the peak at 1250 mV appeared when the Fe/Cr ratio of Zr(Fe,Cr)2 was below 1.0 and the peak at 1900 mV appeared when the ratio was above 1.5. In order to clarify the mechanism of these peak behaviors, the anodic polarization properties of intermetallic compounds that precipitated in zirconium alloys were studied. The results suggest that the peak at 1250 mV is related to the reaction Cr3+ → Cr6+ (soluble in solution) and the peak at 1900 mV is related to the reaction Fe3+ → Fe6+ (soluble in solution) and oxygen generation on iron-rich precipitates.
Long-Term In Situ Corrosion Investigation of Zr Alloys in Simulated PWR Environment by Electrochemical Measurements
Authors: Göhr H , Schaller J , Ruhmann H , Garzarolli F 
Published: March 2009

The corrosion behavior of Zircaloy-type alloys with different tin contents of 1.55, 0.70, and 0.55 wt% was studied at 350°C and 17 MPa in an environment similar to PWR primary water. For this non-interrupted test, a special autoclave system was used that was equipped with electrical feed that allowed followup on the growth of oxide layers by impedance spectroscopy and corrosion potential measurement at high temperature and pressure. As a reference electrode, a platinum wire was used that works as a hydrogen electrode according to the hydrogenated environment established during the start-up procedure. The test ran without interruption for 471 days.
Impedance spectra were taken at time intervals and evaluated for thickness and morphology of the oxide layer as well as for its electrical resistance. The tests without any temperature and pressure cycling showed similar oxidation behavior with repeated transitions as in discontinuously performed standard autoclave tests. Early in the pre-transition range, a dense oxide layer is formed, and fast changes of corrosion potential and electrical resistance are observed. The dense layer increases in thickness and homogeneity up to the transition, where a sudden breakdown occurs. Abrupt changes of the corrosion potential and electrical resistance were observed also at those points. After transition, a new dense layer is built up.
The corrosion potential changes are caused by a decrease of the electrical corrosion current with increasing oxide layer thickness, by the formation of a potential drop over the high-resistance dense oxide layer, and by structural changes at the transition points.
In general, alloys with different tin contents show similar behavior. However, they show differences in the times to transition, the kinetic constants deduced from their impedance spectra, and in the ionic and electronic resistance of the dense inner layer controlling corrosion.
Anodic Protection Provided by Precipitates in Aqueous Corrosion of Zircaloy
Authors: Isobe T , Murai T , Mae Y 
Published: March 2009

Alloying elements such as Fe and Cr are generally considered to be effective even in small quantities for corrosion resistance of Zircaloy-4. The maximum total solubility of Fe + Cr in a Zr-Sn matrix has been reported to be very low [1]. Therefore, most of these elements are observed in the form of ternary Zr-Fe-Cr-type precipitates.
To clarify the effects of precipitates on corrosion property, Zr-1.3 Sn-(Fe,Cr) alloys containing Fe + Cr from 45 up to 180 ppm (the Fe to Cr ratio is about 2) were melted from pure zirconium (X-bar Zr and EB-Zr) and pure alloying elements. They were subjected to corrosion testing in 633 K water and microstructural analysis. It was found that precipitate-free materials showed much larger weight gains than precipitate-containing materials even at the same alloy compositions.
Subsequently, a corrosion test on the precipitate-free material galvanically coupled with a noble intermetallic compound of Zr(Fe0.66Cr0.33)2 was performed. It was found that the precipitate-free material, having very poor corrosion resistance in itself, was covered with thin and adherent black film under galvanically coupled conditions. In addition, its oxide grain structure was almost the same as that of the precipitate-containing material Zircaloy. From these results, it was concluded that the good corrosion resistance of Zircaloy-4 is attributed to the anodic protection provided by precipitates in the alloy.
Detrimental Role of Hydrogen on the Corrosion Rate of Zirconium Alloys
Authors: Blat M , Noel D 
Published: March 2009

Recent studies have suggested that hydride precipitation at the metal/oxide interface could play a detrimental role on the waterside corrosion rate. Nevertheless, the mechanism of that detrimental role is not completely understood, and two hypotheses were investigated to understand the mechanism that controls the role of the hydrides. The first hypothesis is based on a mechanical effect: the hydrides precipitate at the metal/oxide interface and destroy the physical integrity of the “barrier” oxide layer. The second hypothesis is a modification of the transport properties of the oxide grown on the hydrided metal.
The detrimental role of hydrides on the corrosion rate was studied by charging unirradiated Zircaloy-4 cladding material with hydrogen to a level higher than the limit of solubility at 400°C. Both gaseous and cathodic charging techniques were used. Static corrosion tests were carried out in autoclave with steam at 400°C on an as-received and hydrided sample. The detrimental role of hydrides is confirmed for the post-transition corrosion rate, and that effect is more significant for high cathodic charging.
The results of the metallurgical examinations are discussed to provide an understanding of the mechanism. No relationship between hydrides, physical defects in the oxide, and local corrosion rate enhancement was found. Therefore, our results do not support the hypothesis of a mechanical effect at the scale of the performed examinations, but more detailed work is required to confirm this.
A Unified Model to Describe the Anisotropic Viscoplastic Behavior of Zircaloy-4 Cladding Tubes
Authors: Delobelle P , Robinet P , Bouffioux P , Geyer P , Le Pichon I 
Published: March 2009

This paper presents the constitutive equations of a unified viscoplastic model and its validation with experimental data. The mechanical tests were carried out in a temperature range of 20 to 400°C on both cold-worked stress-relieved and fully annealed Zircaloy-4 tubes. Although their geometry (14.3 by 1.2 mm) is different, the crystallographic texture was close to that expected in the cladding tubes. To characterize the anisotropy, mechanical tests were performed under both monotonic and cyclic uni- and bi-directional loadings, i.e., tension-compression, tension-torsion, and tension-internal pressure tests. The results obtained at ambient temperatures and the independence of the ratio Rp = εp θθ/εp zz. with respect to temperature would seem to indicate that the set of anisotropy coefficients does not depend on temperature. Zircaloy-4 material also has a slight supplementary hardening during out-of-phase cyclic loading.
We propose to extend the formulation of a unified viscoplastic model, developed and identified elsewhere for other initially isotropic materials, to the case of Zircaloy-4. Generally speaking, anisotropy is introduced through fourth order tensors affecting the flow directions, the linear kinematical hardening components, as well as the dynamic and static recoveries of the forementioned hardening variables. The ability of the model to describe all the mechanical properties of the material is shown. The application of the model to simulate mechanical tests (tension, creep, and relaxation) performed on true CWSR Zircaloy-4 cladding tubes with low tin content is also presented.
Effects of Hydride Precipitate Localization and Neutron Fluence on the Ductility of Irradiated Zircaloy-4
Authors: Garde AM , Smith GP , Pirek RC 
Published: March 2009

The ductility of highly irradiated Zircaloy-4 material was evaluated by conducting tube burst, tube tensile, and ring tensile tests on fuel cladding and guide tubes irradiated in two PWRs. The specimen fluence ranged between 9 and 12.3 × 1021 n/cm2 (E &gt; 1 MeV), and test temperatures ranged from 313 to 673 K. The average thickness of the waterside oxide layer on the specimens ranged from 12 to 114 μm. Specimens with an oxide thickness greater than about 100μm contained regions of spalling oxide and local areas of oxide significantly thicker than the specimen average. The corresponding average hydrogen contents ranged from 40 to 674 ppm for specimens without spalling oxide and estimated to be greater than 950 ppm with spalling. Non-uniform hydride distributions were observed in the specimens due to temperature gradients during operation.
The residual ductility for these high-fluence specimens is on the order of 1% uniform plastic strain for all the specimens except for two specimens with average concentration of hydrogen greater than 700 ppm and spalled oxide. The reduction in the material ductility due to radiation damage appears to be synergistically affected by localized hydride distributions and the orientation of hydride precipitates relative to the loading direction. The extent of ductility reduction due to hydride precipitates appears to be the most for the burst tests among the three tests investigated. The tensile specimens showed different fracture modes depending on deformation temperature, hydrogen concentration, local hydride volume fraction, and hydride orientation.
Neckdown and spiral fractures were observed. Examination of fracture surfaces indicated ductile failure in the metallic ligaments separating the hydride precipitates that appeared to have failed in a brittle fashion. The ductility data are analyzed by treating the material as a composite of relatively ductile metal phase separated by more brittle hydride platelets. Localization of hydride phase with a reduced presence of metallic ligaments in the composite results in reduction of ductility. A local hydride volume fraction greater than a critical value is needed to initiate and propagate fracture across the specimen cross section to thereby reduce the ductility below a set value. A model is proposed to suggest a possible ductility minima at intermediate fluences and the effect of hydride precipitates on ductility.
Fracture Toughness of Zircaloy Cladding Tubes
Authors: Grigoriev V , Josefsson B , Rosborg B 
Published: March 2009

The fracture toughness of Zircaloy-2 cladding has been estimated by means of the recently developed pin-loading (PL) tension test. Axially notched ring specimens, cut directly from different cladding (annealed, cold-worked, hydrided, and irradiated), have been tested in a way similar to that used for compact tension specimens.
The results of the PL tension tests, performed at temperatures of 293 and 573 K, revealed for actual cladding all main phenomena observed earlier for Zircaloy materials. A threshold hydrogen content of 600 to 700 wtppm, above which only brittle fracture occurred at ambient temperature, was observed for unirradiated cladding. Existence of a continuous hydride network in the cladding facilitated brittle fracture. There was no obvious influence of the hydrogen content of about 900 wtppm on the fracture toughness at 573 K. The irradiation changed the fracture toughness in accordance with its known influence on the ductility and strength of the cladding. Intensive load serrations occurred for both irradiated and unirradiated cladding during plastic deformation of the notched ring specimens at 573 K.
A maximum-load fracture toughness of about Jmax ≈ 100 kN/m, obtained for irradiated cladding at 573 K, is comparable with fracture toughness of the cold-worked unirradiated cladding and reasonably agrees with published results for pressure tube materials.
The PL tension test was shown to be an effective method for evaluating the fracture toughness of actual cladding after hydriding or irradiation.
Effects of Thermomechanical Processing on In-Reactor Corrosion and Post-Irradiation Mechanical Properties of Zircaloy-2
Authors: Huang PY , Mahmood ST , Adamson RB 
Published: March 2009

Interest continues to be high in the effects of irradiation on the microstructure and microchemistry of Zircaloy and on the resultant effects on performance of Zircaloy components in-reactor. In this study, we have investigated the behavior of material prepared to have excellent resistance to nodular corrosion in a BWR. Coupon specimens of Zircaloy-2 were prepared having a range of critical microstructural parameters (precipitate size and distribution) by varying the thermomechanical processing history (quench rate and cumulative annealing parameter). Irradiation was conducted in a BWR at 561 K to fluences between 1.3 and 8.5 × 1025 n/m2 (E &gt; 1 MeV).
As expected, nodular corrosion was absent in these materials, and, at low fluence, corrosion and hydriding of all materials was very low. At the highest fluences, patch-type uniform corrosion developed, with oxide thickness increasing with decreasing initial precipitate size. Detailed STEM investigation revealed that precipitates dissolved and decreased in size continuously until at the highest fluence no precipitates remained for material having the smallest initial precipitate size. Post-irradiation mechanical property tests showed strength somewhat higher than expected.
The results indicate that corrosion resistance and mechanical properties change as the microstructure evolves during irradiation. However, at the highest fluence tested, strength, ductility, and corrosion resistance ensure excellent performance of BWR components.
Experimental Determination of Yield and Flow Surfaces Under Axial-Torsional Loading
Authors: Lissenden CJ , Lerch BA , Ellis JR , Robinson DN 
Published: March 2009

The concept of a yield surface is central to the mathematical formulation of classical plasticity theories. However, at elevated temperatures, material response can be highly rate-dependent, which is beyond the realm of classical plasticity. Viscoplastic theories have been developed for just these conditions. In viscoplastic theories, the flow law is given in terms of inelastic strain rate rather than the inelastic strain increment used in rate-independent plasticity and in unified viscoplastic theories no yield criterion is used. Thus, surfaces of constant inelastic strain rate or flow surfaces, which describe hardening behavior, are considered to be more useful than yield surfaces.
Experimental procedures to determine yield surfaces in axial-torsional stress space are well established. The use of small-offset definitions of yield minimizes the change of material state and allows multiple loadings to be applied to a single specimen. Flow surfaces are determined using the same procedures with the exception that inelastic strain rates are used rather than total inelastic strains. The key to these experiments is precise, decoupled measurement of axial and torsional strain. With this requirement in mind, the performance of a high-temperature multiaxial extensometer was evaluated through comparison with strain gage results at room temperature. Yield surfaces (both initial and subsequent) were found to be nearly identical when determined for Type 316 stainless steel using the extensometer and strain gages. The extensometer was then used successfully to determine flow surfaces for Type 316 stainless steel at 650°C.
Fretting Fatigue Strength of Specimens Subjected to Combined Axial and Transversal Loading
Authors: Switek W 
Published: March 2009

The theoretical and experimental considerations presented in this paper refer to flat specimens, with a special bridge clamped to their surfaces, subjected to axial cyclic loading, transversal clamping load, and a friction force appearing on contacting surfaces. The theoretical analysis shows that the highest tensile stress exists at the edge of the bridge along with the maximum level of an elastic strain energy.
The fatigue experiments and the metallographic examinations of the specimens proved the theoretical assumption that the fatigue crack propagates in such a direction, that the total strain energy decrease, caused by the crack growth, is maximum. The main crack, which is responsible for the final fracture of the specimen, originates from the edge of the bridge, propagates initially at a 45° angle to the surface and, while growing, gradually becomes perpendicular to the surface.
The paper also presents a theoretical approach to the conditions of development of short fatigue cracks remaining in the area of residual stresses appearing as the result of clamping pressure. The linear theory of fracture mechanics has been applied to calculate the range of the stress intensity factor in the specimen and the fretting fatigue limit of the junction. The result of the experiments conducted with carbon steel are generally in good agreement with the calculations.
The Analysis of Underclad Cracks in Large-Scale Tests Using the Local Approach to Cleavage Fracture
Authors: Moinereau D , Rousselier G 
Published: March 2009

Electricité de France has conducted a large program including experiments on large-size cladded specimens and their interpretations to evaluate different methods of fracture analysis used in French safety studies regarding the risk of fast fracture in reactor pressure vessels. Four specimens made of ferritic steel A508 C13 with stainless steel cladding, containing small artificial underclad defects, have been tested in four-point bending. Experiments have been conducted at very low temperature, and crack instability by cleavage fracture without crack arrest was obtained in base metal.
The tests have been interpreted using the local approach to cleavage fracture (Weibull model) by two-dimensional finite element computations. The Weibull model parameters have been determined using axisymmetrical notched specimens. The probability of failure has been evaluated in each test using finite element analyses with varying mesh sizes. The results show an important effect of the size of the elements at the crack tip on the calculated probability of failure. Those effects are confirmed using the model of a CT specimen. Also discussed is the shallow flaw effect with the Weibull model.
Standardization Activities for Testing of Fire Resistant Fluids
Authors: Reichel J 
Published: March 2009

The use of mineral oil as a hydraulic fluid in industrial plants, installations and equipment may create a problem, if exposure of the fluid to sources of iginition are possible. Many industrial processes require the use of hydraulic fluids that afford better fire safety than achievable with mineral oils. In proposals to the governments of the member states of the European Union (EU) fire-resistant fluids intended for use in underground mines must conform the “Requirements and Tests Applicable to Fire Resistant Hydraulic Fluids used for Power Transmission” (7th Luxembourg Report, adopted by the Safety and Health Commission, March 3rd 1994). The immediate stimulus for this work, which spans a period of 35 years, was the disastrous fire which occurred in 1956 at the Bois du Cazier mine at Marcinelle in Belgium, resulting in 267 fatalities.
The general classifications of hydraulic fluids are given in ISO 6743/4 (Lubricants, Industrial Oils and Related Products — Class L — Classification, Part 4: Family H, Hydraulic Systems), guidelines for use have been developed in ISO 7745 (Hydraulic Fluid Power — Fire Resistant (FR) Fluid — Guidlines for Use), but no formal standards are available to interrelate fluid classification with the relative fire risk. Two fundamental parameters are considered when selecting tests for standardisation: 1. spray ignition tests and 2. flame propagation or wick tests. This paper discusses the use of testing methods to characterize the performance of conventional fire resistant hydraulic fluids.