bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue-Crack Propagation in Electroslag Weldments
Authors: Kapadia BM , Imhof EJ
Published: March 2009

The paper discusses the results of an investigation of fatigue-crack propagation behavior of as-deposited electroslag weldments in two hot-rolled structural steels, ASTM A36 and ASTM A588 Grade A. Fatigue-crack growth tests were conducted on 1T wedge-opening-loading (WOL) specimens machined from six 1-in.-thick and four 4-in.-thick weldments that were representative of electroslag welds for bridges. The testing was done in air at room temperature under tension-to-tension sinusoidal loading. Various orientations and locations of the fatigue crack in relation to the weld geometry were investigated.

The fatigue-crack growth rates (da/dN) in the weldments were similar to, or up to five times slower than, the rate in the base steels. The retardation in crack-growth rate was most pronounced at low values of the stress-intensity factor range (ΔK) and was substantially greater for crack propagation in the coarse-grained heat-affected zone (HAZ) and bond-line regions than in the weld metal. Marked variations in the microstructure of the weld metal and HAZ had no signficant influence on crack-propagation behavior, which appeared to be influenced primarily by the residual stresses in the weldments as discussed in a separate paper.

The results of this study show that the upper bound of the crack-growth behavior for low-strength structural steels may be used as a conservative estimate of the crack-propagation behavior of as-deposited electroslag weldments in such steels. On this basis, the prediction of the service life of electroslag-welded structures subjected to cyclic loads, and the determination of safe inspection intervals, may be made by the same approach as that presently used for standard structural-steel weldments made by other processes.
Fatigue Growth of Surface Cracks
Authors: Cruse TA , Meyers GJ , Wilson RB
Published: March 2009

Fatigue-crack growth in gas-turbine engines generally involves surface initiated cracks of semielliptical shape (surface crack) or quarter-elliptical shape (corner crack). Such cracks initiate in regions of locally high stresses and stress gradients. A major aspect of the design system prediction of cyclic growth of these cracks is the development of efficient yet accurate fatigue-crack growth analytical models.

A major advance in modeling accuracy and efficiency has been achieved through the combined use of boundary-integral equation models of three-dimensional crack problems and a weight function representation of elliptical crack growth. Surface and corner crack-fatigue growth data have been compared to the results predicted by the design system analytical model. In general, excellent agreement has been obtained. Some questions concerning the important features of surface and corner-crack growth as well as the weight function method are addressed.
Dependence of JIc on the Mechanical Properties of Ductile Materials
Authors: Lanteigne J , Bassim MN , Hay DR
Published: March 2009

Application of the relation JIc = KIc2/E yields values of JIc which are different from those measured directly. This difference is attributed to the plasticity of the crack tip. A more accurate relation for evaluation of JIc which takes into consideration the mechanical properties of the material such as the yield stress and Young's modulus, and based on compliance tests, is formulated. Experimental tests which demonstrate the validity of this equation are presented.
Determination of R-Curves for Structural Materials Using Nonlinear Mechanics Methods
Authors: McCabe DE
Published: March 2009

The crack line wedge loaded method of test, originally intended for R-curve determination of ultrahigh strength sheet materials is now being used to evaluate the toughness of low-strength, high-toughness steels. The testing technique and equipment used is described in detail. Use is made of an elastic return slope concept on specimens under dominant plastic conditions to determine the extent of slowstable crack extension. A crack-tip opening displacement (CTOD) approach, incorporating plastic hinge modeling, is used to determine KR values. Also, a JR approximation technique is introduced for comparison to KR determined by the CTOD approach. R-curves typical of structural grades of steel are presented and examples of instability condition predictions are cited.
Corrosion Fatigue Properties of Ti-6Al-6V-2Sn (STOA)
Authors: Krupp WE , Ryder JT , Pettit DE , Hoeppner DW
Published: March 2009

The corrosion fatigue crack properties of Ti-6Al-6V-2Sn (STOA) were studied in room-temperature laboratory air, dry air, high-humidity air, and 3.5 percent sodium-chloride solution environments. The alloy was characterized by chemical, microstructural, tensile, and fracture-toughness properties. Corrosion fatigue tests were conducted using wedge-open load (WOL), center-cracked-through (CCT) and part-through-cracked (PTC) specimens. Frequency and environmental interactions were studied as well as the effects of orientation and stress ratio. The effect of frequency was to increase the fatigue crack growth rate as the frequency was decreased. A severe effect of frequency was noted in salt water where at 0.1 Hz, crack-growth rates increased to such a high level that failure occurred at Kmax levels significantly below the stress-corrosion cracking threshold. Fractographic studies showed no apparent cause of this unexpected phenomenon.
Fatigue-Crack Propagation Through a Measured Residual Stress Field in Alloy Steel
Authors: Underwood JH , Pook LP , Sharples JK
Published: March 2009

Fatigue crack-propagation tests were performed using 5 by 30 mm cross-section bend specimens of a nickel-chromium-molybdenum steel. The fatigue crack-propagation rate was determined from a group of stress-free specimens by measuring crack length on the specimen surfaces at intervals during cycling. Residual stress was produced in a second group of specimens by using a localized plastic deformation process. Resistance strain gages were first applied near one edge of each specimen along the line of intended crack growth. A series of 1-mm-deep plastic indentations was then made along the opposite edge of the specimen using a 25-mm-diameter pin. The strain gages provided a direct, accurate measure of the elastic, residual stress produced on one side of the specimen due to the local plastic deformation on the opposite side.

Measured crack-propagation rates in the specimens with residual stress are compared with rates in residual stress-free specimens. Crack-propagation rates are lower, as expected, near the edge of the specimen where the initial residual stress is compressive. Propagation rates remain lower even as the crack grows deeper into the specimen where the initial residual stress is tensile, which is not what would be expected from a simple superposition of stresses. However, an analysis involving the combination of the applied stress-intensity factor with that estimated from a redistribution of the residual stress in the specimens can account for the lower crack-propagation rates.
Automated Design of Stiffened Panels Against Crack Growth and Fracture Among Other Design Constraints
Authors: Davis CS
Published: March 2009

A Fortran IV computer program has been developed to design integrally stiffened two-panel boxes subject to fatigue-crack growth and fracture as well as side constraints, displacements, yielding, and local and general buckling. For crack growth and fracture, stress-intensity factors are compounded from available solutions, and final crack sizes are estimated using R-curve methods for the fracture constraints. An average and integrate strategy is employed for life prediction. Mathematical programming is used for design optimization, and approximation concepts reduce the constraint calculation effort. In the design procedure, multilayered constraint deletion and replacement of original constraint analyses by approximate substitutes define a sequence of approximate subproblems for design solution. For each subproblem, an extended Fiacco-McCormick penalty function is used with a modified Davidon-Fletcher-Powell deflected gradient algorithm for the unconstrained minimizations. The effective slope of crack growth with respect to stress-intensity factor is central to the success of procedures developed. This slope provides a normalizing exponent for the design constraints and a weighting exponent for efficient interpolation and quadrature to predict crack-growth lives. Probabilistic treatment of identified uncertainties in the crack growth ahd fracture analysis, in place of across the board safety factors, has improved design efficiency.
Evaluation of Current Procedures for Dynamic Fracture-Toughness Testing
Authors: Server WL , Wullaert RA , Sheckherd JW
Published: March 2009

Instrumented impact test requirements for impact velocity, inertial loading, time to fracture, and frequency response were developed as a part of a large testing program sponsored by the Electric Power Research Institute (EPRI). These test procedures relied heavily on current ASTM standards plus the composite experience of investigators throughout the world. This paper provides experimental verification of the EPRI developed procedures and clarifies some of the empirical relationships used in the procedures. The material investigated was a 4340 steel (Rc52) which was relatively insensitive to loading rate. Load-time information obtained simultaneously from an instrumented tup and strain-gaged specimen was analyzed for tests performed at various impact velocities. The results indicate that the EPRI developed procedures are conservative and allow reliable fracture-toughness measurements to be made.
Dynamic Fracture Toughness of SA533 Grade A Class 2 Base Plate and Weldments
Authors: Logsdon WA , Begley JA
Published: March 2009

Dynamic fracture toughness tests were performed on four base plate heats and six weldments of SA533 Gr A Cl 2 pressure vessel steel. Linear elastic KId results were obtained at low temperatures while J-integral techniques were utilized to evaluate dynamic toughness over the transition and upper shelf temperature ranges. Loading rates in terms of ˙K were on the order of 2 to 4 × 104 ksi in∕s(2.2to4.4×104MPam∕s). Charpy and drop weight nil-ductility transition (NDT) tests were performed to permit a comparison of toughness results with the American Society of Mechanical Engineers (ASME) code reference toughness KIR curve. Dynamic instrumented precracked Charpy tests on base plate material were included for a comparison with compact toughness (CT) specimen results. All dynamic fracture-toughness values of SA533 Gr A Cl 2 base, weld, and heat affected zone (HAZ) material exceeded the ASME code reference toughness KIR curve. Fracture-toughness values obtained via small specimen dynamic JId tests (1.0 in. (2.5 cm) thick CT specimens) compared well with previously developed large specimen KId values. Dynamic instrumented precracked Charpy toughness values were also comparable at low temperatures but failed to meet minimum J specimen size limitations midway into the transition-temperature range. At this point, Charpy toughness values increased dramatically compared to JId results meeting a 25 JId/σf size criterion and, thus, should not be considered a valid representation of fracture toughness. True upper shelf dynamic fracture-toughness results are also presented. The point of crack initiation (which provides the minimum measured value of JId) was identified rather than the typical maximum load point.
Prediction of Fracture Toughness KIc of 2¼Cr-1Mo Pressure Steels from Charpy V-Notch Test Results
Authors: Iwadate T , Karaushi T , Watanabe J
Published: March 2009

The validity of the Barsom, Rolfe, and Novak correlation between Charpy energy, yield strength, and KIc in the upper-shelf region has been confirmed for 2¼Cr-1Mo pressure vessel steels. The relationship between the excess temperature and KIc/KIc-upper shelf has also been developed. Based on these relationships, KIc transition curves may be predicted from Charpy V-notch test results of 2¼Cr-1Mo pressure vessel steels.
Zircaloy—Three Years after the Hearings
Authors: Johnston WV
Published: March 2009

The U.S. Atomic Energy Commission (AEC) Acceptance Criteria for Emergency Core Cooling Systems stipulated conservative positions with respect to the transient temperature limits of Zircaloy because of the scatter or nonstatistical nature of existing data. In the United States and in a number of other countries, programs were initiated to obtain the desired information. The results of U.S. Nuclear Regulatory Commission (NRC) sponsored new research on Zircaloy oxidation kinetics, expansion and rupture, transient radiation damage annealing, and oxygen diffusion in β-Zircaloy are presented which serve to quantify the conservative positions taken. Additional short-term data needs are presented. Expected trends of future research are indicated to be in the direction of improved understanding of cladding failure from pellet-cladding interaction during power ramps or anticipated transients without scram (ATWS) and in understanding (experimentally and analytically) the multiaxial yielding of anisotropic materials such as Zircaloy.
High Temperature Strain Behavior of Zircaloy-4 and Zr-2.5Nb Fuel Sheaths
Authors: Hunt CEL , Foote DE
Published: March 2009

The ballooning behavior of Zircaloy-4 fuel sheaths at high temperatures has been reported previously by Hardy. Similar tests have been done on Zr-2.5Nb tubes. In both materials, the importance of the phase transformation from hexagonal close-packed to body-centered-cubic structure is evident. Towards the upper boundary of the two-phase (α + β) region where β-phase material would dominate, there is a marked discontinuity in the strain versus temperature results. They indicate that the solid solution strengthening in the β-phase is more effective than the second phase particle strengthening in the α-phase.

At normal operating temperatures, Zr-2.5Nb is stronger than Zircaloy-4. However, above 600°C it enters the two-phase temperature region and becomes weaker than Zircaloy-4 which is still within the α-phase. In the β-phase, where Zr-2.5Nb contains about twice as many atoms in solid solution as Zircaloy-4, the former again becomes stronger. At 1000°C, the strain rate of Zr-2.5Nb is about two orders of magnitude less than that of Zircaloy-4 at the same stress.
Diffusion of Oxygen in Beta-Zircaloy and the High Temperature Zircaloy-Steam Reaction
Authors: Pawel RE , Perkins RA , McKee RA , Cathcart JV , Yurek GJ , Druschel RE
Published: March 2009

As a part of a broader program designed to consider oxidation-related phenomena important during the high temperature reaction of Zircaloy in steam under conditions anticipated for a hypothetical loss-of-coolant accident in a light water reactor, the diffusivity of oxygen in beta-Zircaloy-4 and the isothermal oxidation rates of Zircaloy-4 in steam were determined. Both sets of measurements were made in the temperature range 900 to 1500°C (1652 to 2732°F), and considerable care was exercised to ensure the accuracy of temperature determinations.

Diffusivity determinations were made using an 18O radioactivation technique; supplemental measurements were made by Auger electron spectroscopy and by observations of the movement of (α + β)/β boundaries during diffusion anneals. We observed no differences between tracer and chemical diffusivity values or among oxygen diffusivities determined in zirconium, Zircaloy-2, and Zircaloy-4. Between 1000 and 1500°C (1832-and 2732°F) the combined data set for the diffusion of 16O (corrected for mass effects from the 18O data) was represented by Dβ=0.0263 exp(−28200/RT) cm2/s

Oxidation rate curves were determined at 50°C (90°F) intervals, ten specimens being used to define the curve at each temperature. Above 1000°C (1832°F) parabolic oxidation behavior was observed; below that temperature, the curves for the rate of growth of the oxide layer were not parabolic. For this reason, statistical evaluation of the data based on parabolic kinetics was limited to temperatures above 1000°C except for alpha-layer growth, which followed parabolic kinetics over the entire temperature range. The rate constants were well represented between 1000 and 1500°C by Arrhenius relationships given by δ2φ2=0.01126 exp(−35890/RT) cm2/s δ2φ2=0.7615 exp(−48140/RT) cm2/s δ2ξ2=0.3412 exp(−41700/RT)cm2/sδ2τ2=0.1811 exp(−39940/RT) (g/cm2)2/s where δ2/2 are the rate constants (defined by dK/dt=1/Kδ2/2 K) for oxide layer growth, ϕ alpha layer growth, αXI layer growth (oxide + alpha), ξ; and total oxygen consumption, τ.
Zircaloy-4 Oxidation in Steam Under Transient Oxidizing Conditions
Authors: Dobson WG , Biederman RR , Ballinger RG
Published: March 2009

Oxidation of Zircaloy-4 in unlimited steam has been studied under conditions simulating a loss of coolant accident (LOCA) using a specimen heating system (“Gleeble”). Simple linear ramp transients have been analyzed as well as a few postulated LOCA transients for currently operating light water nuclear power plants. Comparison is made between computer code prediction using isothermal oxidation kinetics and experimental observation with regard to the extent of oxidation.

Simulation of Zircaloy oxidation assuming a stepwise isothermal model using isothermal kinetics developed by the authors is compared to experimental measurements of the extent of oxidation. This computer code, designated TRANS 1, accounts for prior oxidation present and results in agreement with experimental measurements of oxide and oxygen stabilized α-thicknesses for high heating and slow cooling rate transient profiles. However, as heating rate decreases and cooling rate increases, this model becomes increasingly conservative. Modeling, using either a series-expansion or a slope-based isothermal kinetics model, results in essentially the same prediction as TRANS 1.

A one-dimensional finite-difference moving-boundary diffusion model has been developed and found to predict accurately isothermal oxidation behavior of Zircaloy-4 in steam. This model also can be used to predict transient behavior. In addition to predicting oxide and stabilized a thicknesses, this code is capable of predicting oxygen concentration gradients in all phases present, total oxygen as the summation of oxygen present in each phase, and formation of oxygen stabilized α-incursions in the β-phase if accurate diffusion coefficients and appropriate phase equilibrium information are known.
Nodular Corrosion of Zircaloy-2 and Some Other Zirconium Alloys in Steam Generating Heavy Water Reactors and Related Environments
Authors: Trowse FW , Sumerling R , Garlick A
Published: March 2009

In steam generating heavy water reactors (SGHWR), nodular or “patch-type” corrosion is the dominant form of attack on Zircaloy, as it is in other boiling or oxygenated reactor environments. The most severe oxidation occurs close to the stainless steel spacer grids, although nodules are seen elsewhere on cladding and on non-fueled components, a maximum thickness of 160 μm at 20 MWd/kg uranium local burn-up having been recorded to date. The extensive data from post-irradiation examination of SGHWR fuel elements are reviewed and discussed from the points of view of determination of rate laws for oxide growth and the establishment of corrosion mechanisms.

A rate law for oxide growth on Zircaloy-2 at grid positions is determined empirically by seeking correlations between oxidation and irradiation exposure. It is concluded that a linear relationship between oxide thickness and local fast fluence or burn-up represents the data reasonably well, the dependence upon channel flow and exit quality being less significant. Zr-2.5Nb alloy, in the recrystallized condition, was more resistant to nodular oxidation than was Zircaloy-2.

The mechanism of nodular corrosion cannot be expressed in quantitative terms yet, but a qualitative approach is valuable in suggesting wider ranging correlations and possible ameliorative measures. The suggested mechanism requires: (a) an enhancement of the general corrosion rate, controlled in-reactor by coolant chemistry and radiolysis but dependent also upon galvanic coupling or flow effects, or both; and (b) factors specifically responsible for nodule initiation and growth, for example, local cathodic depolarization at intermetallic inclusions and stress-induced recrystallization of the oxide.

The effect of metallurgical factors in the metal substrate and of surface treatment of the alloy also are discussed and current experimental work, intended to check some of the postulated features of the oxidation mechanism, is describe.
Nodular Corrosion of the Zircaloys
Authors: Johnson AB , Horton RM
Published: March 2009

Oxide nodules form on Zircaloy nuclear components under irradiation. Similar nodules were observed on Zircaloy coupons in cold-rolled or extruded conditions after autoclave treatments at 475 and 500 °C in steam at 1500 to 1700 psi. The stages of nodular corrosion in the autoclave were: nodule nucleation, growth, coalescence, propagation to accelerated uniform corrosion, and complete specimen oxidation. Observations on boiling water reactor (BWR) fuel rods suggest that a similar progressive attack has occurred; however, in no case has the in-reactor attack appeared to progress to the stage of complete component failure.

Recent autoclave tests confirmed the nodular character of the attack on cold-worked materials. Alpha anneals (up to 790 °C) did not suppress the nodular attack consistently. However, alpha + beta (840 °C) and beta (1010 and 1040 °C) anneals did suppress the attack if they were followed by a fast cool. The efficacy of the anneals applied similarly to Zircaloy-2 and Zircaloy-4. Stresses associated with U-bend specimens and heavy (86 percent) cold work did not enhance the nodular attack before stress relief occurred.

Additional work is required to confirm preliminary evidence that materials in the reactor and autoclave environments respond similarly to factors such as metallurgical conditions. Availability of an accurate ont-of-reactor prediction of in-reactor performance would be valuable for materials screening, though not necessarily for mechanism definition.

The nodular attack on reactor components appears to depend on nuclear flux, and develops in oxygenated reactor coolants, principally in the vicinity of fuel rod spacers. Experience with irradiated specimens in reactor loops suggests that uniform concentrations of dissolved oxygen alone do not cause the large nodules which frequently develop on BWR fuel rods.

Localized water chemistry associated with flow disturbances or, in some cases, dissimilar metals in fuel spacers, may be factors in the nodular attack in-reactor.
Use of State Variables in the Description of Irradiation Creep and Deformation of Metals
Authors: Hart EW , Li CY
Published: March 2009

Our understanding and mode of description of the effects of irradiation on metal creep and deformation are not satisfactory as yet. This is due in part to the limitations on experimentation in radiation environment. Because of such limitations, theoretical considerations must play a strong role in the interpretation and representation of the phenomena. Reliable representations are necessary if we are to extrapolate the measured behavior beyond the experimental ranges of stress, temperature, flux, and time duration. Virtually all of the theoretical considerations currently employed are based on micromechanical models for the deformation behavior. While the fundamental mechanisms proposed, in fact, may be identified correctly, it is not at all clear that the quantitative conclusions from them are accurate. After all, the detailed micro-mechanical description of deformation even in the absence of irradiation is still moot.

The recent theoretical and experimental development of a plastic equation of state for metal deformation has led to the identification of some of the principal micro-mechanisms in phenomenological terms. The role of the individual mechanisms can be related to the state variables of the description, and those variables are directly accessible measurable quantities.

In this paper we will explore how irradiation might affect this description. It will be shown that the radiation flux and the radiation fluence are expected to affect different components of the equation of state. The resultant description makes considerable use of the information developed in radiation-free environment.
Irradiation Growth of Zircaloy
Authors: Adamson RB
Published: March 2009

Data on irradiation growth of Zircaloy is presented. Irradiation growth is defined as irradiation-induced changes in dimensions in the absence of an applied stress. It is shown that the primary variables are fluence, irradiation temperature, amount of prior cold work, heat treatment, and texture. For recrystallized Zircaloy: growth (a) increases as f, the fraction of basal poles in measurement direction, decreases; shrinkage is possible for large f-factors, (b) increases with increasing temperature up to about 300°C, above which it decreases, (c) tends towards saturation for fluences greater than about 1 × 1021 neutrons (n)/cm2(E> 1 MeV). For cold worked/ stress relieved material: growth (a) increases linearly with fluence up to at least 3 × 1021 n/cm2, and (b) increases linearly with increase in the amount of cold work. For recrystallized material, all irradiation growth is recovered during suitable thermal anneals, while for cold worked material only a portion of the growth is recoverable. Rapid recovery occurs above 350°C (644°F) with an activation energy of 1.67 eV. Mechanistic implications of the gathered data are discussed.
Zircaloy-2 Pressure Tube Elongation at the Hanford N Reactor
Authors: Alexander WK , Fidleris V , Holt RA
Published: March 2009

The Hanford N Reactor contains 1004 cold-worked Zircaloy-2 pressure tubes made by four different fabrication routes. They operate at 395 to 560°F (475 to 566 K) with a hoop stress of 8400 psi (58 MPa) and a peak neutron flux of 2.2 × 1013 neutrons (n)/cm2/s (>1 MeV). Length measurements on all the tubes after 50 000 h of operation show elongation up to 0.4 percent in proportion to channel power.

The highest average elongation (0.35 percent) is observed in tubes fabricated with a high extrusion ratio (29:1) and a high amount of cold work (30 percent). The lowest elongation (0.19 percent) is observed in tubes fabricated with a lower extrusion ratio (13:1) and a lower amount of cold work (17.5 percent). Intermediate elongations (0.26 percent) are observed in tubes fabricated with a high extrusion ratio (29:1) and low cold work (17.5 percent) or a low extrusion ratio (8:1) and high cold work (30 to 35 percent).

The elongations and diameter changes are analyzed in terms of two separate components: a stress independent component, irradiation growth, and a stress dependent component, irradiation creep. The magnitudes and signs of the two components depend on texture, dislocation density (cold work), and neutron flux. The analysis correctly predicts the dimensional changes of the four types of tubes from structural data and uniaxial in-reactor creep and growth data obtained from the literature.
In-Reactor Creep of Zr-2.5Nb Fuel Cladding
Authors: Kohn E
Published: March 2009

Commercially produced Zr-2.5Nb fuel cladding was biaxially creep tested in and out-reactor to generate data for fuel modeling studies. A creep equation was developed describing the steady-state hoop-creep rate at temperatures between 300 and 500°C. The equation assumes that two mechanisms of creep operate at low and high stresses and that the rates of these are additive. The results show little effect of a fast neutron flux of 5 × 1017 neutrons (n)/m2/s on creep rate at 400°C and above but an enhancement of about two in the creep rate at 320°C. The biaxial creep of Zr-2.5Nb fuel cladding is about ten times more rapid than that of pressure-tube materials of the same composition. Texture and second-phase distribution are considered to be the causes of the differences in behavior.

Some measurements also have been made on irradiation growth of fuel cladding in the longitudinal direction. These are discussed.
Effect of Stress on Radiation Damage in Neutron Irradiated Zirconium Alloys
Authors: Northwood DO , Gilbert RW , Coleman CE
Published: March 2009

Structures developed in zirconium alloys during irradiation creep have been characterized by transmission electron microscopy (TEM). Alloys investigated were annealed Zircaloy-2, cold-worked Zircaloy-2 and cold-worked Zr-2.5Nb pressure tube material. Thin films were taken from material deformed in the NRU, NRX and Pickering-3 reactors at temperatures of 530 to 600 K under stresses of 117 to 552 MPa giving strains in the range 0.14 to 8.8 percent. Stress-induced orientation of dislocation loops makes a negligible contribution to irradiation creep at all stresses. At the lower stresses (and hence strains), the size and distribution of the damage is unaffected by stress, being the same in the head and gage sections of creep specimens. At higher stresses (strains), there is much clearing of the damage by plastic deformation. The deformation however is very uneven, producing structures in different grains of the same specimen that can show no deformation, swaths cleared of irradiation damage, or dislocation tangles or cell formation. The relevance of these TEM observations to irradiation creep mechanisms is discussed.
Fabrication of Zirconium Alloys into Components for Nuclear Reactors
Authors: Cheadle BA
Published: March 2009

Over 80 percent of the world's annual output of zirconium is fabricated into components for nuclear reactors. In 1976 the CANadian Deuterium Uranium (CANDU) power reactor program will require nearly 500 Mg of zirconium and by 1986 the requirement will have risen to nearly 800 Mg. Most of this is fabricated into tubes which can cost as much as $80/kg.

Small thin walled tubes for fuel cladding are fabricated by heavily cold working extruded tubes. The most important fabrication parameter in producing the desired crystallographic texture, hydride orientation, and mechanical properties is the cold reduction route. The deformation also must be controlled carefully to ensure that these properties are uniform, both through the wall thickness and around the circumference of the tube.

Large-diameter thin-walled tubes are used to guide coolant flow, guide control rods, or for calandria tubes. These tubes can be made by seam welding annealed sheet and they can be made to very close dimensional tolerances. The weld and heat-affected zones must be recrystallized by cold work and heat treatment so that they have adequate ductility after irradiation.

Pressure containment tubes usually are fabricated by hot extrusion and cold worked a limited amount to size. The most important fabrication parameters are the forging and extrusion processes because they determine the crystallographic texture and the microstructure of the tubes. The advantages of different fabrication techniques and the properties of the tubes are discussed.
Mechanical Properties, Anisotropy, and Microstructure of Zircaloy Canning Tubes
Authors: Stehle H , Steinberg E , Tenckhoff E
Published: March 2009

Tensile, burst, and creep tests have been conducted at 320 to 400°C on Zircaloy tubing. The main emphasis was placed on moderately stress-relieved tubing although tubing ranging from cold worked to fully recrystallized conditions also was investigated.

Refined test techniques have been utilized to determine creep and burst loci. The anisotropy, which is not pronounced for standard tubing at elevated temperatures, is compared with texture measurements. The results are fitted with the Hill equation for anisotropic generalized stress. Creep rates are smaller under compressive stresses than under tensile stresses.

Primary creep decreases steadily as the final annealing temperature is increased. The steady state creep rate, however, shows a minimum for moderately stress-relieved material.

Burst elongation increases and yield strength decreases just at the onset of primary recrystallization while the uniform burst elongation increases at slightly higher annealing temperatures.
Progress in Modeling of Zircaloy Nonelastic Deformation Using a Unified Phenomenological Model
Authors: Miller AK
Published: March 2009

Substantial progress has been made towards developing a constitutive equation for Zircaloy which is both accurate and applicable to a wide variety of situations and a broad range in temperature. Starting with a previously presented phenomenological model (MATMOD) for nonelastic deformation under complex stress and temperature histories, the equations have been improved so that they now can in-elude important solute effects such as negative strain-rate sensitivity and a plateau in the curve of yield strength versus temperature. Material constants for Zircaloy-2 have been calculated from standard test data (creep and tension tests). Using these constants, simulations of a number of complex situations (all out of pile) have been generated and are compared with the experimental observations. These comparisons include transient-temperature tube-burst results, strain-rate sensitivity versus temperature, effect of cold work on creep rate, unusual drops in creep rate under constant stress but increasing temperature, and peaks in the apparent activation energy. The results indicate that this relatively simple set of equations is capable of a fairly realistic representation of Zircaloy deformation over a wide range of temperature.
Acoustic Emission during Room Temperature Fatigue Crack Growth and Fracture of Zr-2.5Cb Alloy Specimens
Authors: Schwenk EB , Hutton PH , Igarashi M
Published: March 2009

The objective of this investigation was to determine acoustic emission (AE) properties of unhydrided and hydrided Zr-2.5Cb during room temperature fatigue crack growth and fracture. Determination of AE behavior is important as a basis for continuous on-line monitoring in nuclear reactor pressure tubes fabricated from Zr-2.5Cb.

AE was monitored during mechanical loading of notched sheet specimens and during fatigue crack growth of simulated pressure-loaded axially notched tubular specimens. The tubular specimens involved mechanical loading within the tube which produced stress conditions similar to a free-end-cap, fluid-pressurized specimen. The sheet specimens showed AE characteristics related to the stress intensity factor, K, through the notch edge opening displacement and were unaffected by hydrogen level. The simulated pressure tubular specimen AE data were related by a power law to the fatigue crack: growth rate and may be affected by hydrogen level.

Pooling of water around an AE sensor did not alter the AE detected during fatigue loading. Addition of water and penetrating oil to a crack tip both produced significant increases in the indicated AE per load cycle.

The results of this investigation provided encouraging evidence of the feasibility of on-line monitoring of Zr-2.5Cb pressure tubing.
Factors Controlling Hydrogen Assisted Subcritical Crack Growth in Zr-2.5Nb Alloys
Authors: Simpson LA , Nuttall K
Published: March 2009

The delayed failure of cold-worked Zr-2.5Nb pressure tube. material has been studied using static load tests on compact-tension specimens containing hydrogen within the range ∼ 10 to 400 μg/g. The experimental approach was to measure crack velocity (V) as a function of crack tip stress intensity factor (K), temperature and hydrogen content, relate these data to fractographic and metallographic observations, and compare the results with recent models of hydrogen embrittlement. Slow crack growth was observed at all temperatures between 25 and 325 °C and at K values between ∼ 10 and 50 MPam. Below 250°C, the V-K relationships exhibited two-stage behavior; at K > 15 to 20 MPam, the crack velocity was only weekly dependent on stress intensity, whereas at smaller K values, the crack velocity decreased rapidly with K, an indication of a threshold value of K ∼ 5 to 10 MPam. The crack velocity increased with increase in temperature, although because of scatter in the data, this could not be expressed quantitatively. At 250°C and above, slow crack growth was not reproducible except after a thermal cycle. The thermal cycle produced a region of reoriented hydrides concentrated at the crack tip which significantly reduced the incubation period for crack growth and confirmed the important role of the hydride phase in the fracture process. Fractography showed that the features of the slow growth fracture were similar at all temperatures studied. The main observations were of ductile striations, or stretch zones, parallel to the crack front, with brittle, plate-like regions, some of which contained cleavage features, between the striations. A fracture mechanism is suggested which involves the repeated precipitation of hydride at the crack tip, followed by crack advance through this embrittled region, and crack arrest in the more ductile matrix, leading to discontinuous crack growth. This general mode of crack growth has been considered in a recent model for embrittlement in hydride-forming materials, the predictions of which show good agreement with the results from this study.
Hydride Reorientation and Fracture in Zirconium Alloys
Authors: Simpson CJ , Kupcis OA , Leemans DV
Published: March 2009

Under conditions of high tensile stress, the Zr-2.5Nb alloy has been shown to he susceptible to a very slow crack propagation failure mechanism. This failure mechanism, hydride cracking, has been studied extensively since leaks developed in the pressure tubes of Reactor Units 3 and 4 at Ontario Hydro's Pickering Nuclear Generating Station in Aug. 1974. The failures have been attributed to reorientation and preferential redistribution of hydrides under high tensile stresses, followed by progressive fracture of these hydrides. Mechanical tests, acoustic emission data, and metallographic studies relevant to this mechanism will be presented and related to the occurrence of cracks in the Zr-2.5Nb reactor pressure tubes.
Standardization Works on Testing Procedures for Zircaloy Cladding Tubes in Japan
Authors: Mishima Y
Published: March 2009

In past few years interlaboratory tests were performed among three working groups in Japan. The groups consisted of representatives from various organizations including national laboratories, fuel manufacturers, and cladding tube manufacturers.

Test methods for longitudinal and circumferential strength of Zircaloy cladding tube were discussed. In the tension test, the shape of the plug or mandrel was found to be highly effective for the longitudinal elongation value obtained, as it restrains the deformation of the tube toward decreasing diameter. Tapered plug, therefore, will give larger elongation, and the degree of taper has a notable effect on the elongation value. The improvement in the present manual, therefore, is to be recommended.

In the internal-pressure burst test, the closed-end method showed a larger burst pressure and smaller circumferential elongation than the open-end method. The restraint of the longitudinal deformation of the tube is an important factor in this burst test as the reduction in thickness is quite difficult in such a featured tube. A testing method, therefore, should be chosen as to what sort of information is necessary, corresponding to the actual condition in the reactor concerned.

Measurements of grain size and hydride orientation factor also were discussed, and the results obtained were compared.
Optimal Impact Study Design and Analysis
Authors: Green RH
Published: March 2009

An optimal impact study design is possible if (1) the impact has not yet happened, (2) the type of impact and when and where it will happen are known, (3) measurements on both biological and environmental variables can be obtained from the samples, and (4) an area which will not receive the impact, but is otherwise similar to the impact area, is available to serve as a control. The example presented here is based on simulated data consisting of sample estimates of species abundances and environmental variables. A total of 36 samples are distributed among locations in the impact and control areas and between “before” and “after” impact times. A multivariate analysis of variance approach permits a test of the null hypothesis that any change in the biotic community of the impact area does not differ from that in the control area. A procedure which permits impact-related biotic change to be related to environmental change is illustrated, and the results are displayed visually. Use for subsequent biological monitoring to detect a future impact of the same type is illustrated. A cluster analysis approach, which both effectively displays the impact effects and corroborates the analysis of variance results, is illustrated. Design and analysis options are discussed extensively.
Use of Ranking Methods to Assess Environmental Data
Authors: Gertz SM
Published: March 2009

Nonparametric or distribution-free statistics are a method to quantitatively assess environmental data and environmental impact. This statistical methodology is advantageous in many cases because of the computational ease and the fact that few if any assumptions are needed about the sampled populations. This is particularly important in ecological studies, since organisms are distributed typically in a clumped or patchy fashion, and the use of parametric or normal statistics is ill advised, even if data transformations are made.

Specifically ranking methods are discussed. Tests examined include the rank sum test, signed rank test, one-way analysis of variance, and two-way analysis of variance. It is shown that these statistical techniques are oftentimes the method of choice for evaluating ecological data. Examples of their use to assess ecological data and water chemistry data are given.
Use of Indices of Diversity and Hierarchical Diversity in Stream Surveys
Authors: Kaesler RL , Herricks EE , Crossman JS
Published: March 2009

Brillouin's equation (H) for species diversity is preferred to other measures from information theory because it is not biased and does not require unrealistic assumptions about the populations being sampled. Diversities of small replicated samples give a better indication of environmental differences between stations than single large samples. Species diversity may be partitioned hierarchically either according to the categories of the taxonomic hierarchy or any other hierarchy. Taxonomic hierarchical diversity reveals components of diversity at each taxonomic level. For several examples, generic diversity revealed nearly as much about community structure as species diversity, suggesting that discriminating higher taxa rather than identifying species can be often used in aquatic ecology, with savings of time and money. Hierarchial diversities of classifications based on functional morphology and trophic group analysis appear to be promising for applied work and worthy of further investigation.
Statistical Analysis of the Presence-Absence Component of Species Composition Data
Authors: Hendrickson JR
Published: March 2009

Species lists make up much of the historical and present-day information presented in conjunction with environmental impact assessments. Most such lists have not been analyzed to determine whether the patterns of occurrence of species are indicative of differences in water quality. Statistical procedures are proposed to determine whether patterns of species occurrence are found in the data and, if so, which samples and species appear to contribute most strongly to the observed patterns. The application of these procedures is discussed with examples.
Maximum Weekly Average Temperature for 316(a) Demonstrations
Authors: Ferraro FA , Gaulke AE , Loeffelman CM
Published: March 2009

In determining the effects of thermal discharges on certain species of fish, the concept of Maximum Weekly Average Temperature has received much attention in 316(a) studies. Based on laboratory data, the Maximum Weekly Average Temperatures for growth, reproduction, and winter survival have been determined for eggs, larvae, and adults for a number of fish species. How these criteria should be applied to be receiving stream temperatures to best represent the thermal conditions to which fish are subjected has not been fully considered.

Several approaches to calculating the Maximum Weekly Average Temperatures for receiving water bodies are discussed. Examples include a more simplistic approach of using averages of daily mean temperatures of consecutive 7-day increments for each year of the data set; 7-day running averages of daily mean temperatures for the entire data set; or averages based on cumulative distributions of daily average temperatures.

These methods and results are compared to determine which of these methods may be the more reasonable and representative approaches. The running average and the weekly average methods (Methods A and C) both yield acceptable and preferred values of Receiving Water Body Maximum Weekly Average Temperatures.
Sampling Design for Some Trace Elemental Distributions in New York Bight Sediments
Authors: Saila SB , Anderson EL , Walker HA
Published: March 2009

The paper outlines a model to describe the spatial distribution of selected trace elements (chromium, copper, nickel, lead, and zinc) in New York Bight sediments. Empirical tests of the fit of existing data by means of cumulative probability plots on log-normal probability paper and goodness-of-fit tests demonstrate conformity to the log-normal distribution predicted by the model. An adaptive sampling strategy for describing the spatial distribution of the trace elements is developed, based on a knowledge of the sampling distributions of the elements. The spatial distribution of the sampling stations conforms to the expected nonuniformity of the trace metal concentrations of interest, providing for a more efficient allocation of sampling effort.
An Analysis of NGI Simple Shear Apparatus for Cyclic Soil Testing
Authors: Shen CK , Sadigh K , Herrmann LR
Published: March 2009

A numerical analysis parametric study was conducted to determine the stress and strain states within an idealized soil specimen enclosed by a wire-reinforced rubber membrane and tested in the Norwegian Geotechnical Institute (NGI) simple shear apparatus. The computations were performed utilizing a finite-element program applicable to three-dimensional elastic analysis of nonaxisymmetrically loaded axisymmetric solids. Orthotropic membrane elements were incorporated in the program to simulate the action of the wire-reinforced rubber membrane. A total of 14 cases was analyzed using different combinations of material properties, membrane stiffness, specimen geometry, and boundary displacements. In general, for the values of the parameters studied, the uniformity of shear strain distribution improves as (1) the specimen height-to-diameter ratio is decreased, (2) the percent of wire-reinforcement is increased, (3) the elastic modulus of the soil decreases, (4) the Poisson's ratio of the soil decreases, and (5) the applied horizontal displacement is increased.