bluuebunny/crossref_metadata_2025 huggingface dataset:
Enumeration of Scientific Populations by Immunofluorescence
Authors: Stanley PM , Gage MA , Schmidt EL
Published: March 2009

The fluorescent antibody (FA) staining technique is a powerful tool in microbial ecology since it makes possible the direct identification of microbial populations in mixed communities. A number of quantitative and qualitative immunofluorescence studies have great advanced our knowledge of the autecology of many microorganisms in diverse habitats. To illustrate the quantitative application of the technique in an aquatic habitat, the distribution of Nitrobacter, a chemoautotrophic nitrite-oxidizing bacterium, was determined in a Minnesota lake. Population densities of 2 to 10 × 102 cells/ml were relatively uniform in the upper 7 m of the water column but decreased to 0.1 to 1 × 102 in the bottom 3 m, which suggested that conditions in the upper layers were more favorable for nitrification. The distribution with depth on three consecutive days was quite similar, as were duplicate subsamples from the same sample. These results indicate that the method accurately measured the nitrobacter population density. Interference from debris and other cells was presumably the reason for nonproportionality between the sample volume assayed and the population density calculated from larger sample volumes. This interference determines the minimum population density which can be measured accurately by FA staining
Important Factors in Adenosine Triphosphate Determinations Using Firefly Luciferase: Applicability of the Assay to Studies of Native Aquatic Bacteria
Authors: Deming JW , Picciolo GL , Chappelle EW
Published: March 2009

Accurate determinations of intracellular adenosine triphosphate (ATP) content in natural aquatic samples, using the firefly luciferase ATP assay, require attention to several important procedural factors. A rationale for peak height measurements is presented, along with a comparison of commercially available photometers. Purified luciferase, stabilized with dithiothreitol, is recommended for low-level ATP measurements. Inorganic acids were found to be the most efficient extracting agents for bacterial ATP. Limitations of the assay as a bacterial biomass measurement or enumeration technique are discussed, with the conclusion that the assay is most valuable in conjunction with other measures of total microbial deviations from a baseline.
Measurement of Hydrocarbon Biodegradation Potentials and Enumeration of Hydrocarbon-Utilizing Microorganisms Using Carbon-14 Hydrocarbon-Spiked Crude Oil
Authors: Atlas RM
Published: March 2009

A most-probable-number (MPN) method is described for enumerating hydrocarbon-degrading microorganisms. Also, methods are described for measuring natural and nonnutrient-limited hydrocarbon biodegradation potentials. Both the enumeration and the activity measurements use carbon-14 hydrocarbon-spiked oil. The advantages and limitations of these methods for enumerating hydrocarbon utilizers and measuring hydrocarbon biodegradation are considered. Also, examples of the types of data generated by these methods and their interpretation are discussed.
Ultrasonic Techniques for Inspecting Flat and Cylindrical Composite Specimens
Authors: Liber T , Daniel IM , Schramm SW
Published: March 2009

Ultrasonic techniques are discussed for inspection and evaluation of flat and cylindrical composite specimens. Immersion ultrasonic techniques are described using a 5-MHz broad-band focused transducer in the pulse-echo mode. Two types of recording methods are employed, conventional pen-lift C-scanning and analog scanning, augmented with photographs of oscilloscope traces of the pulse at selected locations. The complete scanning system is described, including a fixture for scanning tubular specimens. The techniques discussed are applied to monitoring flaw growth in graphite/epoxy coupons of [(0/±45/90)s]2 and [02/±45])2s layups with four types of initial flaws subjected to fully reversed spectrum fatigue loading. The flaws investigated are (1) circular hole, (2) embedded film patch, (3) internal ply gap, and (4) surface scratches. It was found that, in general, flaw growth is greater in specimens of [(0/±45/90)s]2 layup than in those of [(022/±45)2s layup. The residual tensile strengths for the preceding specimens, determined after four lifetimes of fatigue testing, are not significantly lower than the initial strengths.
Detection of Damage in Composite Materials by Vibrothermography
Authors: Henneke EG , Jones TS
Published: March 2009

A new nondestructive inspection method, vibrothermography, has been studied here to determine its degree of application to the investigation of damage in composite materials. Subsurface damaged regions containing delaminations, relatively large matrix cracks, or matrix crazing are easily located by the method. A three-dimensional, anisotropic heat-conduction model, solved by a finite-difference method, has shown that the surface heat patterns monitored by thermography represent accurately the geometry and extent of the subsurface heat source.
Impact Damage Effects on the Strength of Advanced Composites
Authors: Labor JD
Published: March 2009

This paper discusses the effect of flaws created by impact damage on the strength of graphite/epoxy panels that were tested as sandwich beams and as skin panels on box beams. A majority of the panels were exposed to random spectrum fatigue loads prior to failing them under static loading conditions. The maximum loads in the fatigue spectrum were scaled to provide a strain equal to the B-basis matrix failure strain for the resin system used. Box beam skin panels were designed to fail by compressive panel buckling in order to evaluate the effect of the impact damage on the buckling strength of the panels. All testing was conducted at room temperature on panels with no moisture conditioning.

Marginally visible damage was found to cause a strength loss up to 35 percent in compression but less in tension. Acoustic C-scan inspections showed that none of the impact damage sizes grew during spectrum loading. Panel stability was unaffected by localized impact damage. The most severe impact damage caused strength losses comparable to drilled fastener holes.
Moisture-Induced Surface Damage in T300/5208 Graphite/Epoxy Laminates
Authors: Shirrell CD , Leisler WH , Sandow FA
Published: March 2009

A microscopic examination of hygrothermally expsoed T300/5208 cross-ply laminates is described. Moisture-induced surface and edge microcracks were observed in specimens exposed at 82° and 9, 20, 37, 74, and 91 percent relative humidity or water immersion. Specimens exposed at similar relative humidities but at lower temperatures (21, 43, and 63°C) generally did not form microcracks.

The severity and frequency of the microcracking at 82°C increased with relative humidity. The majority of the microcracks were observed to be oriented parallel to the graphite fibers in the surface laminae. Specimens with extensive microcracks were also observed to exhibit non-Fickian diffusion phenomena during their hygrothermal exposure.
A Ball-Rod Rolling Contact Fatigue Tester
Authors: Glover D
Published: March 2009

This paper describes the development of an accelerated rolling contact fatigue tester that minimizes the testing variables through the use of simple, expendable components. The important design features of the tester and the specimen and rolling element finishing technique are described. Test results comparing two similar testers are presented for both steel and ceramic.
Evaluation of Powder-Processed Metals for Turbine Engine Ball Bearings
Authors: Brown PF , Bogardus GA , Dayton RD , Schulze DR
Published: March 2009

Two different types of rolling element fatigue testers and a full-scale bearing tester were used in a program aimed at developing a highly fatigue-resistant powder-processed material (P/M) for use in turbine engine bearings. The testers were the single-ball machine evaluating 0.0238-m (15/16-in.)-diameter balls, a rolling contact fatigue machine evaluating 0.00953-m (⅜ in.) rods, and a full-scale bearing rig evaluating 140-mm-bore, 0.0238-m (15/16 in.)-diameter ball, angular contact thrust bearings.

The two-element testers, used to screen three different P/M alloys and the baseline vacuum induction melted-vacuum arc remelted (VIMVAR) M-50 alloy, each produced essentially the same ranking for these materials. The best results, about twice the life of the baseline VIMVAR M-50, were achieved with P/M CRB-7, a 14 percent chrome corrosion-resistant alloy. P/M M-50 produced lives equivalent to VIMVAR M-50. P/M T-15, a 4 percent chrome alloy, exhibited lives ranging from that realized with the baseline material down to one third of that level. Based on these tests, CRB-7 was selected as the material out of which the balls and races for 20 full-scale 140-mm bearings were subsequently fabricated and tested. The tests were conducted at a thrust load of 34 872 N (7 840 lb) and at a speed of 12 500 rpm. A wear problem encountered in these tests was circumvented by nickel plating the cage guiding surfaces of the inner ring lands. The B10 rolling contact fatigue life realized with these bearings was equivalent to that expected for these same bearings had they been made of conventional VIMVAR M-50 material. These results were quite encouraging considering the fact that this was the first attempt at applying powder processing to the manufacture of aircraft-quality rolling element bearings.
Microstructural Control in Microalloyed Steels
Authors: Cohen M , Hansen SS
Published: March 2009

High-strength low-alloy (HSLA) steels constitute a classic metallurgical development in which alloying additions and thermomechanical processing have been brought together effectively to attain desired combinations of engineering properties through microstructural control. Moreover, the microstructural control is relatively inexpensive because the alloying elements are used only in small concentrations as carbide-formers, and the associated thermomechanical processing is introduced merely as a modification of the final hot-rolling operation. A key feature of the resulting microstructure is the small ferritic grain size that provides a favorable balance of strength and toughness in the as-rolled steel.

Here, we examine the interactions in columbium-treated HSLA steels among austenite chemistry, plastic deformation, strain-induced carbonitride precipitation, recrystallization characteristics, and the subsequent transformation of the thermomechanically-processed or conditioned austenite to the final ferrite-based structures. The latter transformations are studied in order to relate the ferrite nucleation and growth as well as its ultimate morphology to the state of the prior austenite.
An Evaluation of Double-Torsion Testing—Analysis
Authors: Fuller ER
Published: March 2009

The double-torsion test configuration has many advantages over conventional fracture mechanics configurations for the evaluation of subcritical crack growth parameters and fracture toughness. These advantages—such as crack-length independence, four-point loading, simple specimen geometry, and ease of precracking—have been responsible for the increased use of the double-torsion configuration in recent years. However, before double-torsion testing can be adopted as a standard configuration, a number of unresolved questions need to be answered about the double-torsion specimen and about the experimental techniques involved in its use.

The purpose of this paper is to address some of these questions and to indicate where further effort is needed to establish the validity of double-torsion testing. Assumptions of a compliance analysis for the double-torsion configuration are examined with particular attention given to the influence on experimental results that the violation of any of these assumptions may have. An analytical expression is derived for the compliance of a finite-thickness beam in torsion and is compared to the empirical compliance. Again the emphasis is on the assumptions of the derivation and how some of these restrictions might be relaxed.
Fracture Surface Energy Measurements by the Notch-Beam Technique
Authors: Bansal GK , Duckworth WH
Published: March 2009

The notch-beam technique (NBT) for determining fracture surface energies (γi) of ceramic materials is discussed. Basic principles involved in the technique are reviewed, and effects of different test variables on measured γi values are examined. In addition, merits and limitations of the technique are discussed, and measured values are compared with those obtained by other techniques.
Fracture Toughness: The Role of Indentation Techniques
Authors: Evans AG
Published: March 2009

The quantitative measurement of the radial fractures that occur around hardness indentations in brittle materials has long been advocated as a measure of the fracture toughness. The evolution of the technique and the fundamental basis for toughness determination by indentation are described. The latest experimental results on a range of brittle materials are used to demonstrate the utility of the technique. Finally, the role of the technique, within the toughness testing repertoire, is discussed.
Effect of Material and Environmental Variables on Localized Corrosion of Zirconium Alloys
Authors: Lunde L , Videm K
Published: March 2009

The nodular attack of α-annealed Zircaloy-2 and Zircaloy-4 in steam at 500°C is dependent upon the presence of hydrogen in the environment, the important function being the hydrogen to steam ratio rather than partial pressures. The uniform corrosion between the nodules was unaffected by the hydrogen in the steam. β-quenched Zircaloy-2 showed the opposite behavior, suffering nodular corrosion in hydrogen-free steam and corroding uniformly in steam with hydrogen additions. Nodules did initiate on Ozhenite-0.5, but did not develop into serious localized attack for α-annealed material. Alloys with higher niobium content and Valoy were independent of hydrogen in the steam and they never suffered localized corrosion. The chromium-rich particles in Valoy did not influence the oxidation of the matrix adjacent to the particles under hydrogenated conditions. The iron-rich particles in the Zircaloys and in Ozhenite-0.5 decreased the oxidation of matrix in a region around each particle. Nodules initiated by oxide cracking over grain boundaries in areas with few intermetallic particles. The observed influence of hydrogen in the steam on nodular corrosion is attributed to its effect on the electron conductance of the oxidized iron-rich precipitates.
Ductility of Zircaloy Canning Tubes in Relation to Stress Ratio in Biaxial Testing
Authors: Andersson T , Wilson A
Published: March 2009

A biaxial-burst testing machine has been designed in which biaxial plane stress tests can be carried out on tubular material with any stress ratio in the range σθ:σz 4:5 to 2:1, where 2:1 implies the closed-end burst test. Unirradiated Zircaloy tubes cold worked 80 percent, recrystallized at 575°C, and characterized by a texture having a basal pole tilt angle of 33 deg were tested at room temperature with various stress ratios, namely, 4:5, 1:1, 5:4, 3:2, and 2:1. In addition, tension and open-end burst tests were carried out in conventional machines.

The uniform ductility measured as uniform effective strain displays a minimum at the stress ratio 3:2. It has been found experimentally that the stress ratio for minimum uniform ductility corresponds to deformation under a plane strain loading condition, that is, the stress ratio which gives no change in the tube length. The fracture ductility defined as the effective strain at fracture exhibits a minimum at the stress ratio 5:4. When bulging begins, the applied stress ratio cannot be kept constant, but the stress ratio decreases due to an increased axial stress. This behavior probably explains the observed shift in minimum ductility from the uniform value 3:2 to the fracture value 5:4.
Performance of Irradiated Copper and Zirconium Barrier-Modified Zircaloy Cladding Under Simulated Pellet-Cladding Interaction Conditions
Authors: Tomalin DS , Adamson RB , Gangloff> RP
Published: March 2009

Expanding mandrel laboratory simulations of the pellet-clad interaction (PCI) mechanism (including argon, iodine, and cadmium environments) were employed to evaluate copper barriers and zirconium-lined tubing performance. Zircaloy-2 and copper-plated and zirconium-lined barrier tube specimens were tested in the unirradiated (cold-worked) and in the irradiated (recrystallized) conditions at about 600 K. Tubing was irradiated at 620 K to a fast (E > 1 MeV) fluence near 2 × 1025 n/m2.

Brittle PCI-type failures were produced in unirradiated Zircaloy-2 tubing by expanding mandrel loading with iodine and cadmium. Failure strains were further reduced for irradiated Zircaloy-2 tested in each embrittling environment. Fractographic analyses revealed brittle fracture surface features similar to those reported for failed fuel rods. In contrast, high-strain ductile ruptures were produced in both unirradiated and irradiated tube samples tested in argon. These findings support the PCI description for fuel rod fractures. Zirconium-lined Zircaloy was not embrittled by cadmium even after neutron irradiation. High average failure strains and ductile fracture surface features were observed for the zirconium-lined tubing tested with cadmium, analogous to Zircaloy-2 tested in an inert environment. Similar experiments with low-pressure (4 to 40 Pa) gaseous iodine produced brittle cracking in the zirconium liner and in the underlying Zircaloy, both before and after irradiation, but at average strains well in excess of those required for brittle failure of Zircaloy tubing. Copper-electroplated Zircaloy tubing also exhibited excellent resistance to simulated PCI failure for both irradiated and unirradiated conditions when exposed to iodine or cadmium. Average failure strains and fractographic features were similar to results obtained for Zircaloy-2 tested in an inert environment. Mechanisms for the performance of copper zirconium barrier tubing were discussed. It was concluded that, based on laboratory testing, both copper plated and zirconium-lined cladding systems offer significant potential for improved PCI resistance. Reactor evaluations are required to confirm this conclusion.
Analysis of Irradiation Growth and Multiaxial Deformation Behavior of Nuclear Fuel Cladding
Authors: Clevinger GS , Adams BL , Murty KL
Published: March 2009

Postirradiation analysis of the multiaxial strain behavior of nuclear fuel cladding requires a comprehensive evaluation of the various mechanisms contributing to the total observed principal strains. Measurements are usually taken for diametral change, which accrues as a result of irradiation-enhanced multiaxial creep, and of changes in axial length, which is predominantly caused by irradiation-induced growth. In this context, it is important to note that under multiaxial loading, the generalized strain vector produced by creep deformation is not coincident with the hoop direction of the cladding except under special conditions and, similarly, that the expected direction of the irradiation growth component derived from texture considerations is not coincident with the axial direction of the tubing. Rather, both mechanisms usually produce component strains in each of the principal directions of the cladding. It is generally observed, in fact, that the total strain vector determined from postirradiation measurements is well displayed from that which would be predicted for either creep deformation or the irradiation growth mechanism and is obviously the resultant strain produced by the combined effects of irradiation growth and multiaxial creep deformation.

Thus, it becomes important in efforts to model and predict this behavior from baseline laboratory test results and material anisotropy constants to appropriately separate the strain components that result from irradiation growth from those produced by multiaxial creep behavior. This paper describes a procedure that leads to an expected direction of the creep vector based on multiaxial flow equations for an anisotropic material and a predicted irradiation growth vector based on crystallographic texture analyses and stress-free irradiation growth data. The observations discussed here support the hypothesis that irradiation growth is essentially stress independent in Zircaloy and suggest that anisotropic multiaxial strain ratios due to creep or plastic deformation are unaffected by the presence of a neutron flux.

The mechanistic aspects of irradiation growth are discussed, particularly as they relate to cold-worked material, and the ideas of Northwood are extended to hypothetically account for observed variations in irradiation damage rate and loss of ductility in materials having varying degrees of cold work and recrystallization.
Predicting High-Temperature Transient Deformation from Microstructural Models
Authors: Sills HE , Holt RA
Published: March 2009

We have developed a multicomponent model to describe the transient plastic deformation of Zircaloy fuel sheathing during postulated loss-of-coolant accidents (LOCA). From deformation maps, we identify three creep mechanisms, which in principle, occur in all three phase fields of Zircaloy-4 (α, α + β, β): diffusional creep, dislocation creep and athermal strain. Diffusional creep (phase boundary or grain boundary sliding) is modeled in the α and α + β phase fields. Dislocation creep is modeled in all three phase fields and controlled by a work-hardening/recovery expression. Athermal strain has practical significance only at lower temperatures (< 900 K). The sum of the strain rates of the three deformation mechanisms is the total plastic strain rate. At a particular point in the stress-temperature field, one mechanism usually dominates.

Microstructural changes that affect deformation are also taken into account; these are changes in grain structure, recrystallization, and the α ⇌ (α + β ) ⇌ β phase transformation. When two components are present (α + β or recrystallized and unrecrystallized), they are assumed to deform with equal rates according to the appropriate single-phase model.

The individual components of the model give excellent agreement with the isothermal data on which they are based, and the entire model gives very good agreement with transient data over a range of temperatures from 700 to 1600 K, a range of heating rates from 0 to 100 K/s, and a range of strain rates from 10-5 to 10-1 s-1. Several applications of the model in evaluating the history dependence of deformation are given.
Advances in Understanding and Predicting Inelastic Deformation in Zircaloy
Authors: Oldberg S , Miller AK , Lucas GE
Published: March 2009

The mathematical model MATMOD-Z has been built to permit computer simulation of in-reactor Zircaloy deformation behavior. The 250 to 450°C temperature range is covered together with a wide range of possible strain rates, accrued strains, and as-fabricated material conditions. MATMOD-Z is comprised of coupled time-rate equations in stress, strain, temperature, fast neutron flux, and certain material state variables. These latter quantities are: Fdef, representing the friction stress due to isotropic deformation-induced obstacles; Fsol, representing the friction stress due to solute drag; R, the “rest stress,” or back stress due to directional obstacles; and f2, the Kearns texture number in the direction bisecting the basal pole intensity peaks. Comparison of MATMOD-Z predictions to independent test data indicate a distribution of errors in predicted stress given complex strain-time-temperature history with standard deviation of the order of 17 percent. The most important source of error is thought to lie in an effect not treated in the current model, namely, increased solute drag with increasing dislocation density.
Influence of Iodine on the Strain and Rupture Behavior of Zircaloy-4 Cladding Tubes at High Temperatures
Authors: Hofmann P
Published: March 2009

The stress corrosion cracking (SCC) behavior of short tubular Zircaloy-4 specimens by the action of iodine (initial iodine concentration: 0.1 to 10 mg/cm3) was investigated out-of-pile between 600 and 1100°C under inert gas conditions. The Zircaloy cladding tube was used as-received and with an inner preliminary oxidation. Moreover, the influence of the uranium oxide (UO2) oxygen potential on the SCC behavior was studied.

The burst and creep-rupture tests (time-to-rupture ≤ 15 min) clearly show that the deformation behavior of Zircaloy cladding tubes below 850°C is heavily influenced by the presence of iodine. A failure of Zircaloy tubes takes place that is characterized by little deformation as compared to reference specimens without iodine. With decreasing temperature, the burst strain is greatly reduced. Moreover, in the isothermal, isobaric experiments, the time-to-failure of the iodine containing specimens is markedly shorter as compared to the iodine-free reference specimens. Internal preoxidation of the cladding tube or UO2 in the specimens exert an additional influence on the mechanical properties of Zircaloy.

Scanning electron microscope examinations of the rupture surfaces of the cladding tubes show that in the presence of iodine and at burst temperatures below 850°C the cracks in the cladding material are mainly intergranular followed by ductile residual rupture. By contrast, iodine-free specimens are exclusively subject to ductile failure.
Studies on Zircaloy Fuel Clad Ballooning in a Loss-of-Coolant Accident—Results of Burst Tests with Indirectly Heated Fuel Rod Simulators
Authors: Erbacher F , Neitzel HJ , Wiehr K
Published: March 2009

Burst tests with indirectly heated fuel rod simulators were performed under cooling and temperature conditions postulated for a loss-of-coolant accident (LOCA) of a pressurized water reactor (PWR). The tests were designed to investigate the ballooning behavior of Zircaloy fuel rod claddings and to determine the resulting coolant channel blockage in a rod bundle.

The deformation behavior of the Zircaloy cladding tubes was found to be influenced mainly by local effects due to nonuniform temperature distributions. Single rod and bundle tests exhibited large azimuthal and axial temperature differences. This resulted in relatively small and axially limited strains of the Zircaloy cladding tubes and a tolerable coolant channel blockage in the rod bundle.
Tube-Burst Response of Irradiated Zircaloy Spent-Fuel Cladding
Authors: Bauer AA , Lowry LM , Gallagher WJ
Published: March 2009

Transient-heating tube-burst tests were conducted on a 50.8-cm length of Zircaloy cladding obtained from spent-fuel rods irradiated in the H. B. Robinson power reactor to a peak burn-up of 30 MWD/kg. Internal electrical resistance heaters were used to achieve nominal heating rates of 28°C/s for the tests. The tests were conducted in steam and the independent experimental variable was the initial level of helium pressurization.

Tube burst pressures varied from 0.965 to 12.514 MPa. Corresponding burst stresses and temperatures varied from 7.5 MPa and 1135°C to 99.1 MPa and 734°C, respectively. Failure strains ranged up to 46 percent when burst occurred at upper (α + β) and β-phase temperatures and up to 30 percent for failures occurring at lower temperatures.

No significant difference in burst behavior between unirradiated and spent nuclear fuel Zircaloy cladding was observed experimentally. No influence of axial restraint on burst strains was noted.
Effect of Oxygen on the Deformation of Zircaloy-2 at Elevated Temperatures
Authors: Rizkalla AS , Holt RA , Jonas JJ
Published: March 2009

During some hypothetical loss-of-coolant accidents (LOCA), Zircaloy fuel sheathing is expected to reach temperatures in excess of 1273 K and to oxidize rapidly. The objective of the current work was to determine the effect of oxygen on the mechanical behavior of Zircaloy-2 at temperatures above 1273 K.

Zircaloy-2 containing 1 200, 4 000, 8 000, and 12 000 ppm oxygen was deformed in compression at 1275, 1375, and 1475 K at constant true strain rates of 10-4 to 10-1 s-1. The flow stress of Zircaloy-2 increases by a factor of 3 to 4 as the oxygen concentration is increased from 1200 to 12 000 ppm. Approximately half of this increase is due to solid solution strengthening by oxygen and approximately half to the effect of oxygen on the volume fraction of the much stronger α-zirconium. The stress exponent of the strain rate of both phases appears to be unaffected by oxygen, being 3.5 to 4.0 for β-zirconium and 5 to 6 for α-zirconium. In the (α + β)-phase field, the stress sensitivity at low strain rates is low, suggesting that some form of boundary sliding mechanism contributes to flow.

The stress-strain curves are either “normal” flow curves, with work hardening and saturation of the flow stress, or “abnormal” flow curves, in which a maximum or peak stress is reached at low strains, followed by flow softening. The flow stress peaks are attributed to an aging or clustering effect that occurs when the α phase is enriched in iron and chromium, and the flow softening is attributed to strain-enhanced declustering or coarsening of the precipitates.
Interaction of Oxidation and Creep in Zircaloy-2
Authors: Burton B , Donaldson AT , Reynolds GL
Published: March 2009

In the event of a loss-of-coolant accident in water-cooled reactors, the Zircaloy-2 cladding is subjected to a rapid increase in temperature and stress in an oxidizing environment. Accurate numerical values of creep parameters are thus required for use in tube deformation models that predict fuel cladding behavior during such an accident. Also, it is necessary to know quantitatively the effect of oxidation on creep behavior.

Creep tests have been performed in the temperature range 1000 to 1925 K on Zircaloy-2. In this temperature range, the material undergoes a phase transformation from α to β phase at ∼1100 K. Tensile creep results on these two phases have been performed in vacuum. The α-phase material was tested in strip form in a conventional creep machine, although to obtain data at high temperatures in the β phase, resistance-heated wire specimens were used. The creep of both the α and β phases of Zircaloy in the unoxidized condition can be satisfactorily represented by the Dorn equation for dislocation creep controlled by lattice diffusion:ε˙i=AiGibikT(σGi)niDiwhere i = α, β and the creep parameters Ai and ni take the values:Aα=1.67×1011Aβ=0.6nα=5.36nβ=3.7

Further experiments are reported on the influence of oxygen on creep. The first series of experiments on material with oxygen in uniform solid solution indicate that oxygen has no effect on the creep of β-phase material until the solubility limit of oxygen is reached. However, the creep of α-phase material is significantly modified by the presence of dissolved oxygen. Creep rate is shown to decrease according to the expressionε˙=ε˙0exp⁡(−βC)where ε˙0 is the creep rate of Zircaloy-2 containing no dissolved oxygen, β is a constant at a given stress and temperature, and C is the oxygen concentration. Numerical values of β are discussed in the text.

Creep of duplex α + β phase is also investigated using techniques both of equilibrating the structure at test temperature before testing and also admitting measured quantities of oxygen during test. Using these techniques combined with experiments at different temperatures permits a wide range of structures to be obtained and transient effects to be observed. The relationships between the different morphologies of the duplex material, the relative proportions of the two phases, and creep behavior are discussed.

Grain boundary sliding in β-phase Zircaloy-2 is also investigated. The rate of sliding is shown to vary, with stress raised to a power slightly greater than unity with an activation energy close to that for lattice diffusion, and results are interpreted in terms of sliding controlled by diffusion between undulations in the boundary geometry. The geometry required to satisfy the observed rates of sliding is estimated. It is shown that oxygen has no effect on sliding, although nitriding inhibits sliding.
Research Needs in Aquatic Toxicology and Hazard Assessment: A Sojourner's Perspective
Authors: Dickson KL
Published: March 2009

To establish itself as a legitimate discipline, aquatic toxicology must not become static—content with resolving old problems—but must always be willing to move into new and different areas. There are a number of research needs in aquatic toxicology which deserve the attention of investigators. We need research programs in aquatic toxicology which ask the question of how chemicals affect aquatic organisms. Generally, in the past we have only been concerned if a chemical kills an organism or if it prevents reproduction, but not with how it does these things. More research is needed to illucidate the chemical mechanisms and modes of action. Perhaps from this we can develop better chemical structure-activity relationships. Basic research into anatomy, physiology, nutritional requirements, pathology, and life histories of our test organisms is needed. We need a major research program to determine if the chronic effects we observe in our laboratories, such as depressed reproduction and growth, have ecological significances. Through better knowledge of life histories and the use of population modeling, perhaps it will be possible to meet this need. It is essential that we develop test methods and a data base which identify how chemicals affect an ecosystem's functional processes. Ecologists recognize the value of protecting ecosystem functions but have only primitive tools with which to assess the potential impacts of chemicals on these functional processes. Studies must be conducted to identify when a chemical is biologically available. Are sorbed materials biologically available? Finally, researchers in aquatic toxicology should explore the efficacy of aquatic test organisms as surrogates for humans. Screening chemicals for potential health effects by using fish or other aquatic organisms has many advantages over currently used mammalian toxicology test species, low cost being a prime example. However, knowledge of the metabolism and physiology of aquatic test species must be established.
Increasing the Usefulness of Acute Toxicity Tests
Authors: Stephan CE
Published: March 2009

The conceptually and practically simple acute toxicity test provides information that is useful in the protection of aquatic life from pollution. Standardization increases the usefulness of routine acute tests by increasing their quality and comparability and allowing the study of various aspects of acute toxicity. For example, available data show that for certain materials some species of aquatic animals are at least 5000 times more acutely sensitive than other species, whereas for other materials the range of acute sensitivity is less than a factor of 50. Various theoretical interpretations of the relationship of toxicity to time within a test have been proposed to improve the usefulness of the acute test, but such theories have not been supported by adequate pertinent data. The usefulness of routine acute toxicity tests can be increased, however, by basing the results not on one effect or another but on a combination of all severe adverse effects, such as death, immobilization, and loss of equilibrium.
Effects of Kelthane and Pydrin on Early Life Stages of Fathead Minnows (Pimephales promelas) and Amphipods (Hyalella azteca)
Authors: Spehar RL , Tanner DK , Gibson JH
Published: March 2009

Embryonic, Larval, and early juvenile stages of fathead minnows (Pimephales promelas) and juvenile amphipods (Hyalella azteca) were exposed to Kelthane, and fathead minnows were exposed to Pydrin in a small self-contained continuous-flow diluter system for approximately 30 days. Survival of the newly hatched larvae was found to be the most sensitive measure of the effect on fathead minnows of both pesticides. Pydrin was approximately 90 times more toxic to fathead minnows than Kelthane. The lowest effect concentrations of Kelthane and Pydrin were 13 times lower than the 96-h median lethal concentration (LC50) values for fathead minnows exposed in Lake Superior water. The upper and lower chronic limits for Kelthane were 39 and 19 µg/litre for fathead minnows and 33 and 19 µg/litre for amphipods. The chronic limits for Pydrin and fathead minnows were 0.43 and 0.33 µg/litre. The mean bioconcentration factors (BCFs) for Kelthane were 3 700 with fathead minnows and 10 000 with amphipods. The mean BCF for Pydrin with fathead minnows was 3 200. Residue concentrations and BCFs for both pesticides increased with increased water concentrations.
Availability of a Hexachlorobiphenyl Isomer to Benthic Amphipods from Experimentally Contaminated Natural Sediments
Authors: Lynch TR , Johnson HE
Published: March 2009

The present study was designed to determine the availability of radiolabeled 2,4,5,2′,4′,5′-hexachlorobiphenyl (HCBP) to benthic amphipods from experimentally contaminated natural sediments. Amphipods accumulated HCBP primarily by direct uptake from water as a function of exposure time. However, organisms that were directly exposed to the sediments had consistently higher (2.3 to 10.8×) HCBP concentrations than did organisms exposed only to the sediment-desorbed residues in the water. Experimental results demonstrated that the substrate organic matter content and particle size affected the concentrations of HCBP in the water and, in turn, in the organisms. The removal of sediment organic matter enhanced HCBP accumulation by both substrate-exposed and water-exposed organisms. Amphipods accumulated the least HCBP when exposed to silt-clay particle size fractions which contained organic matter. The substrate particle size was less important than the organic content in determining HCBP availability to the amphipods.
Field Validation of Water Quality Criteria for Hydrophobic Pollutants
Authors: Schnoor JL
Published: March 2009

A comparison of laboratory and field bioconcentration factors (BCFs) is made for a variety of hydrophobic pollutants, including dieldrin, dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE), chlordane, polychlorinated biphenyl (PCB), and heptachlor epoxide. The bioconcentration factors calculated from field data in Iowa rivers, the Coralville Reservoir in Iowa, Lake Ontario, and Lake Superior are within a factor of 1 to 4 of laboratory-derived bioconcentration factors in the fat of fish. The U.S. Environmental Protection Agency's water quality criteria are also within a factor of 1 to 4 of estimated field concentrations which would result in a maximum permissible tissue concentration (MPTC). Field bioconcentration factors normalized on a fat or oil basis correlate with the octanol-water partition coefficient of 13 hydrophobic pollutants.

Bioconcentration data were utilized in a mathematical model to calculate the fate and transport of dieldrin in the Coralville Reservoir. The author demonstrates that laboratory-derived BCFs can be used in fate and effects modeling with order-of-magnitude results or better.
Aquatic Insects as Measures of Trace Element Presence in Water: Cadmium and Molybdenum
Authors: Colborn T
Published: March 2009

Metal concentrations in rivers and streams vary continually. An indicator of toxic trace metals is needed to establish recent maximum levels. An initial study was conducted during the summer of 1979 on Coal Creek and Slate River, Gunnison County, Colo., to test whether aquatic insects could be used to assay for low-level element presence. Aquatic insects were taken from Coal Creek above a mine tailing break. Both live and air-dried insects were transplanted to the Slate River below the discharge from the mine and removed consecutively for 3 days. Water samples were taken simultaneously with each insect collection. The dissolved ions in a litre of stream water were concentrated to 25 ml with the use of an ion-exchange resin column. The results demonstrate that the ratio of the concentration of the element in the insect to the concentration of the element in the water, the field concentration factor (FCF), for each genus of aquatic insect is more sensitive than a water sample for measuring the level of cadmium in water. The insect cadmium accumulation and water cadmium levels exhibited a repeated relationship in the Slate River. The similarity between the sorption of cadmium by the live and dead insects indicates that cadmium uptake is more than a physiological process. Mayflies concentrate cadmium and molybdenum more than caddis flies, and of the mayflies tested the Drunella grandis sorbs the most. Equilibration between water and insect concentration of cadmium appears to take place after 72 h.
A Seasonal Analysis of Stress in a Stream Ecosystem Using a Nontaxonomic Approach
Authors: Matthews RA , Kondratieff PF , Buikema AL
Published: March 2009

A nontaxonomic method for monitoring stream community response to sewage stress was tested for 1 year on two small streams in southwest Virginia. The method represents an improvement in field testing approaches through increased replicability, decreased sampling time, and year-round applicability. Adenosine triphosphate (ATP) levels from microbial communities in organically stressed portions of Cedar Run were significantly higher than the unstressed portions of Cedar Run and Wilson Creek, whereas chlorophyll a levels were significantly lower. Microbial autotrophy indexes (AIs) calculated from the ATP and chlorophyll measurements increased significantly below the outfall. The AIs were inversely related to macroinvertebrate diversity and the number of taxa. Macroinvertebrate functional groups showed a balance between scrapers, collector-gatherers, and collector-filterers at all unstressed stations and a predominance of collector-gatherers or collector-gatherers and collector-filterers at the stressed stations. A significant inverse correlation was found between the AIs and the proportion of macroinvertebrate scrapers.
Use of the Hazard Assessment Approach for Evaluating the Impact of Chlorine and Ammonia in Pueblo, Colorado, Domestic Wastewaters on Water Quality in the Arkansas River
Authors: Lee GF , Jones RA , Newbry BW , Heinemann TJ
Published: March 2009

A short-term, intensive study has been conducted on the potential impact of the chlorine, and to a lesser extent the ammonia and nitrite, associated with the domestic wastewater discharge from the city of Pueblo, Colo. on the water quality (beneficial uses) of the Arkansas River downstream from the discharge. The hazard assessment approach was used in the planning of the study and in data interpretation.

The wastewater treatment plant (WWTP) effluent mixed slowly with the river, forming a narrow effluent plume extending downstream for about 1000 m; in this “zone of mixing” contaminant concentrations were sufficient to kill caged fathead minnows in 4 days or less. A continuous “zone of passage” existed past the discharge in which no visually apparent adverse effects on caged fish were found in 4 days' exposure.

Chlorine concentration decreased with the distance downstream of the discharge, but, based on the concentrations found, there is a potential for chlorine impact on aquatic life for a distance of about 15 km. Outside the zone of physical mixing of the effluent and the river, nitrite and un-ionized ammonia concentrations were below the corresponding Colorado water quality guidelines; however, questions regarding their impact on the water quality within this zone were raised and need to be addressed in future studies.
Evaluation of Steels for Arctic Line Pipe
Authors: Abrams H , Roe GJ
Published: March 2009

Line pipe for transporting gas from Arctic fields is subjected to the conditions of an extremely hostile environment. Bethlehem Steel has been conducting an extensive program to evaluate the materials and processes that can produce the property requirements for Arctic-grade line pipe. In the course of the program, several alloy combinations were evaluated. The paper describes each of these, but concentrates on the vanadium-columbium (V-Cb) alloy grade, which we feel is the most practical and economical to produce. The critical aspects, from steelmaking to plate rolling and testing, are described. A regression analysis correlation of chemistry and processing to microstructure and properties is presented. This correlation permits the prediction of plate and pipe properties on the basis of the chemistry and processing. The dependence of properties on a number of specific microstructural features is illustrated by metallographic studies.
Possibilities for Microstructural Control During Hot Working of Austenitic Stainless Steels
Authors: Ahlblom B , Roberts W
Published: March 2009

The development of fine-grained microstructures by hot working to strains sufficient to effect at least partial dynamic recrystallization has been investigated by hot compression experiments on two austenitic stainless steels. After deformation, specimens were either held at the working temperature or cooled at a constant rate. As expected, fine structures are produced after working at low temperatures but, unfortunately, these tend to be mixed, the smaller grains originating from dynamic recrystallization and the coarser from static (metadynamic) recrystallization during holding/cooling. This heterogeneity is less pronounced after working at higher temperatures and, for given deformation conditions, tends to be eliminated as the cooling rate is reduced.
Microstructures Versus Properties of 29-4 Ferritic Stainless Steel
Authors: Aggen G , Deverell HE , Nichol TJ
Published: March 2009

The subject of this investigation is a low interstitial 29Cr-4Mo ferritic stainless steel developed and patented by E.I. duPont de Nemours and Co., Inc. The alloy, commonly known as 29-4, is characterized by exceptionally high resistance to chloride pitting and stress corrosion cracking and by comparatively good room temperature toughness and ductility.

Sheet specimens from a commercial heat were exposed for times up to 100 h at temperatures from 371 to 982°C (700 to 1800°F). Metallographic changes that were observed were correlated to changes in impact and tensile properties, crevice corrosion in ferric chloride, and intergranular corrosion resistance in ferric sulfate-sulfuric acid. Excess phase identifications and studies of failure modes were conducted on selected samples.

Two embrittlement regions were found centered at about 482°C (900°F) and 760°C (1400°F). The lower temperature embrittlement region is quite narrow and was ascribed to 475°C (885°F) embrittlement. No deterioration in corrosion resistance was detected in this embrittlement region. Embrittlement occurred much more rapidly in the higher temperature region and existed over a wide temperature range. Crevice corrosion resistance and corrosion resistance to ferric sulfate- sulfuric acid deteriorated rapidly in this embrittlement region. Changes in mechanical properties and corrosion resistance upon heat treating in the region were ascribed primarily to the precipitation of sigma and chi phases.
Super Waspaloy Microstructure and Properties
Authors: Deye DJ , Couts WH
Published: March 2009

Waspaloy is currently one of the more widely used alloys for turbine disk applications in the aerospace industry. However, higher engine performance demands by aircraft engine manufacturers have resulted in a number of approaches by material suppliers to upgrade the alloy. These approaches range from simple compositional modifications to a combination of chemistry modifications coupled with thermal mechanical processing. One such approach resulted in what is now commonly referred to as Super Waspaloy.

Tension, low-cycle fatigue, and creep rupture tests of Waspaloy and Super Waspaloy forgings were conducted from room temperature to 1089 K (1500°F), after which material properties were reviewed and correlated with the disk microstructure.