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An evaluation of alternative cleaning methods for removing an organic contaminant from a stainless steel part

Description: As of December 1995, the manufacture of Freon, along with many other chlorofluorocarbons (CFCs), was prohibited by the Clean Air Act of 1990 (CAA). The ban of CFC solvents has forced manufacturers across the country to search for alternative metal cleaning techniques. The objective of this study was to develop a thorough, scientific based approach for resolving one specific manufacturer`s problem of removing organic contamination from a stainless steel part. This objective was accomplished with an approach that involved: (1) defining the problem, (2) identifying the process constraints, (3) researching alternate cleaning methods, (4) researching applicable government regulations, (5) performing a scientific evaluation and (6) drawing conclusions.
Date: August 1, 1996
Creator: Boyd, J.L.
Partner: UNT Libraries Government Documents Department

Growth and properties of InGaAs/FeAl/InAlAs/InP heterostructures for buried reflector/interconnect applications in InGaAs thermophotovoltaic devices

Description: Thermophotovoltaic cells consisting of InGaAs active layers are of extreme promise for high efficiency, low bandgap TPV conversion. In the monolithic interconnected module configuration, the presence of the InGaAs lateral conduction layer (LCL) necessary for the series connection between TPV cells results in undesirable free carrier absorption, causing a tradeoff between series resistance and optical absorption losses in the infrared. A potential alternative is to replace the LCL with an epitaxial metal layer that would provide a low-resistance interconnect while not suffering from free carrier absorption. The internal metal layer would also serve as an efficient, panchromatic back surface reflector, providing the additional advantage of increased effective optical thickness of the InGaAs cell. In this paper, the authors present the first results on the growth and development of buried epitaxial metal layers for TPV applications. High quality, single crystal, epitaxial Fe{sub x}Al{sub 1{minus}x} layers were grown on InAlAs/InP substrates, having compositions in the range x = 0.40--0.80. Epitaxial metal layers up to 1,000 {angstrom} in thickness were achieved, with excellent uniformity over large areas and atomically smooth surfaces. X-ray diffraction studies indicate that all FeAl layers are strained with respect to the substrate, for the entire composition range studied and for all thicknesses. The FeAl layers exhibit excellent resistance characteristics, with resistivities from 60 {micro}ohm-cm to 100 {micro}ohm-cm, indicating that interface scattering has a negligible effect on lateral conductivity. Reflectance measurements show that the FeAl thickness must be at least 1,000 {angstrom} to achieve > 90% reflection in the infrared.
Date: November 1, 1998
Creator: Ringel, S.A.; Sacks, R.N.; Qin, L.; Clevenger, M.B. & Murray, C.S.
Partner: UNT Libraries Government Documents Department

Dynamic and static error analyses of neutron radiography testing

Description: Neutron radiography systems are being used for real-time visualization of the dynamic behavior as well as time-averaged measurements of spatial vapor fraction distributions for two phase fluids. The data in the form of video images are typically recorded on videotape at 30 frames per second. Image analysis of he video pictures is used to extract time-dependent or time-averaged data. The determination of the average vapor fraction requires averaging of the logarithm of time-dependent intensity measurements of the neutron beam (gray scale distribution of the image) that passes through the fluid. This could be significantly different than averaging the intensity of the transmitted beam and then taking the logarithm of that term. This difference is termed the dynamic error (error in the time-averaged vapor fractions due to the inherent time-dependence of the measured data) and is separate from the static error (statistical sampling uncertainty). Detailed analyses of both sources of errors are discussed.
Date: March 1, 1999
Creator: Joo, H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

1997 environmental monitoring report for the Bettis Atomic Power Laboratory, Pittsburgh Site

Description: The 1997 results for the Bettis-Pittsburgh radiological and nonradiological environmental monitoring programs are presented. The results demonstrate that the existing procedures ensured that releases to the environment during 1997 were in accordance with applicable Federal, State, County, and local regulations. Evaluation of the environmental data indicates tat current operations at the Site continue to have no adverse effect on human health and the quality of the environment. A conservative assessment of radiation exposure to the general public as a result of Site operations demonstrates that the dose received by any member of the public was well below the most restrictive dose limits established by the Environmental Protection Agency, the Nuclear Regulatory Commission, and the US Department of Energy. A risk assessment of potentially exposed populations to chemical residues in the environment at the Site demonstrates that these residues do not pose any significant risk to human health or the environment.
Date: December 31, 1997
Partner: UNT Libraries Government Documents Department

The effect of pressure on annular flow pressure drop in a small pipe

Description: New experimental data was obtained for pressure drop and entrainment for annular up-flow in a vertical pipe. The 9.5 mm. pipe has an L/D ratio of 440 to insure fully developed annular flow. The pressure ranged from 140 kPa to 660 kPa. Therefore the density ratio was varied by a factor of four approximately. This allows the investigation of the effect of pressure on the interfacial shear models. Gas superficial velocities between 25 and 126 m/s were tested. This extends the range of previous data to higher gas velocities. The data were compared with well known models for interfacial shear that represent the state of the art. Good results were obtained when the model by Asali, Hanratty and Andreussi was modified for the effect of pressure. Furthermore an equivalent model was obtained based on the mixing length theory for rough pipes. It correlates the equivalent roughness to the film thickness.
Date: September 1, 1996
Creator: de Bertodano, M.A.L.; Beus, S.G. & Shi, Jian-Feng
Partner: UNT Libraries Government Documents Department

Review of computational thermal-hydraulic modeling

Description: Corrosion of heat transfer tubing in nuclear steam generators has been a persistent problem in the power generation industry, assuming many different forms over the years depending on chemistry and operating conditions. Whatever the corrosion mechanism, a fundamental understanding of the process is essential to establish effective management strategies. To gain this fundamental understanding requires an integrated investigative approach that merges technology from many diverse scientific disciplines. An important aspect of an integrated approach is characterization of the corrosive environment at high temperature. This begins with a thorough understanding of local thermal-hydraulic conditions, since they affect deposit formation, chemical concentration, and ultimately corrosion. Computational Fluid Dynamics (CFD) can and should play an important role in characterizing the thermal-hydraulic environment and in predicting the consequences of that environment,. The evolution of CFD technology now allows accurate calculation of steam generator thermal-hydraulic conditions and the resulting sludge deposit profiles. Similar calculations are also possible for model boilers, so that tests can be designed to be prototypic of the heat exchanger environment they are supposed to simulate. This paper illustrates the utility of CFD technology by way of examples in each of these two areas. This technology can be further extended to produce more detailed local calculations of the chemical environment in support plate crevices, beneath thick deposits on tubes, and deep in tubesheet sludge piles. Knowledge of this local chemical environment will provide the foundation for development of mechanistic corrosion models, which can be used to optimize inspection and cleaning schedules and focus the search for a viable fix.
Date: December 31, 1995
Creator: Keefer, R.H. & Keeton, L.W.
Partner: UNT Libraries Government Documents Department

Interfacial Friction in Gas-Liquid Annular Flow: Analogies to Full and Transition Roughness

Description: New film thickness and pressure gradient data were obtained in a 5.08 by 101.6 mm duct for nitrogen and water in annular flow. Pressures of 3.4 and 17 atm and temperatures of 38 and 93 C were used to vary the gas density and liquid viscosity. These data are used to compute interfacial shear stresses and interfacial friction factors for comparison with several accepted literature correlations. These comparisons are reasonable for small values of the relative film thickness. However, the new data cover conditions not approached by the data used to construct those correlations. By combining the current data with the results of two other comprehensive modern experimental studies, a new correlation for the interfacial friction factor has been developed. This correlation adds elements of transition roughness to Wallis' fully-rough analogy to better predict interfacial friction factors over a wide range of gas Reynolds numbers and liquid film thicknesses.
Date: March 1, 1999
Creator: Bauer, R.C.; Beus, S.G. & Fore, L.B.
Partner: UNT Libraries Government Documents Department

Fatigue Crack Propagation from Notched Specimens of 304 SS in elevated Temperature Aqueous Environment

Description: Fatigue crack propagation (FCP) rates for 304 stainless steel (304SS) were determined in 24 degree C and 288 degree C air and 288 degree C water using double-edged notch (DEN) specimens of 304 stainless steel (304 SS). Test performed at matched loading conditions in air and water at 288 degree C with 20-6- cc h[sub]2/kg h[sub]2O provided a direct comparison of the relative crack growth rates in air and water over a wide range of crack growth rates. The DEN crack extension ranged from short cracks (0.03-0.25 mm) to long cracks up to 4.06 mm, which are consistent with conventional deep crack tests. Crack growth rates of 304 SS in water were about 12 times the air rate. This 12X environmental enhancement persisted to crack extensions up to 4.06 mm, far outside the range associated with short crack effects. The large environmental degradation for 304 SS crack growth is consistent with the strong reduction of fatigue life in high hydrogen water. Further, very similar environmental effects w ere reported in fatigue crack growth tests in hydrogen water chemistry (HWC). Most literature data in high hydrogen water show only a mild environmental effect for 304 SS, of order 2.5 times air or less, but the tests were predominantly performed at high cyclic stress intensity or equivalently, high air rates. The environmental effect in low oxygen environments at low stress intensity depends strongly on both the stress ratio, R, and the load rise time, T[sub]r, as recently reported for austenitic stainless steel in BWR water. Fractography was performed for both tests in air and water. At 288 degree C in water, the fracture surfaces were crisply faceted with a crystallographic appearance, and showed striations under high magnification. The cleavage-like facets on the fracture surfaces suggest that hydrogen embrittlement is the primary cause ...
Date: August 1, 2002
Creator: Wire, G. L. & Mills, W. J.
Partner: UNT Libraries Government Documents Department

Mean Stress and Environmental Effects on Fatigue in Type 304 Stainless Steel

Description: Fatigue life tests were performed in air on Type 304 stainless steel (304 SS) to establish the effect of mean stress under both load control and strain control. An apparent reduction of up to 26% in strain-amplitude occurred in the low and intermediate cycle regime (< 10{sup 8} cycles) for a mean stress of 138 Mpa. A quantitative description of mean stress effects using the Smith-Watson-Topper equivalent strain parameter was developed, which incorporates mean stress through the maximum stress. This description provided a tighter fit to the data, and allowed separation of mean stress and cold work effects. With this separation, the effect of mean stress was reduced to 12% decrease in strain amplitude at 138 Mpa. The stress-life curve apparently increased with increasing mean stress, due to the significant work hardening that occurred in tests with high mean stresses, especially under load control. Tests were performed on double-edge notched specimens of 304 SS in air and low oxygen water at 288 C. The elastically calculated increase in the notch tip stress accounted within 10% for the fatigue life reductions for a K{sub t} = 4.8 notch, but was 38% conservative for a K{sub t} = 8.8 notch. Fatigue crack initiation lives (defined as an 0.127 mm crack) in low oxygen water at 288 C were reduced by a factor of four to eight on cycles over those in air. Crack growth occurred throughout most of the fatigue ''initiation'' life. The increase in crack growth rate of 304 SS in water appears to be large enough to explain the reduced ''initiation'' life in this environment.
Date: April 1, 1999
Creator: Kandra, J.T.; Leax, T.R. & Wire, G.L.
Partner: UNT Libraries Government Documents Department

Qualification of a Method to Calculate the Irrecoverable Pressure Loss in High Reynolds Number Piping Systems

Description: High Reynolds number test data has recently been reported for both single and multiple piping elbow design configurations at earlier ASME Fluid Engineering Division conferences. The data of these studies ranged up to a Reynolds number of 42 x 10[sup]6 which is significantly greater than that used to establish design correlations before the data was available. Many of the accepted design correlations, based on the lower Reynolds number data, date back as much as fifty years. The new data shows that these earlier correlations are extremely conservative for high Reynolds number applications. Based on the recent high Reynolds number information a new recommended method has been developed for calculating irrecoverable pressure loses in piping systems for design considerations such as establishing pump sizing requirements. This paper describes the recommended design approach and additional testing that has been performed as part of the qualification of the method. This qualification testing determined the irrecoverable pressure loss of a piping configuration that would typify a limiting piping section in a complicated piping network, i.e., multiple, tightly coupled, out-of-plane elbows in series under high Reynolds number flow conditions. The overall pressure loss measurements were then compared to predictions, which used the new methodology to assure that conservative estimates for the pressure loss (of the type used for pump sizing) were obtained. The recommended design methodology, the qualification testing and the comparison between the predictions and the test data are presented. A major conclusion of this study is that the recommended method for calculating irrecoverable pressure loss in piping systems is conservative yet significantly lower than predicted by early design correlations that were based on the extrapolation of low Reynolds number test data.
Date: September 1, 2002
Creator: Sigg, K. C. & Coffield, R. D.
Partner: UNT Libraries Government Documents Department

Initiation of environmentally-assisted cracking in low-alloy steels

Description: Environmentally-Assisted Cracking (EAC) in low alloy steels is activated by a critical level of sulfide ions at the crack tip, which is produced from dissolution of sulfide inclusions (MnS, FeS, etc.) in the steel following exposure by a growing crack. EAC of concern herein is the increase of fatigue crack growth rate of up to 40 to 100 times the rate in air that occurs at 240--300 C in high temperature LWR or boiler water environments. The initiation of EAC is the onset of the higher fatigue crack growth rates in fully developed cracks already presumed to be present due to fatigue, stress corrosion cracking, or induced by fabrication. Initiation of EAC is induced by a change in loading parameters causing the fatigue crack growth rate to increase from a small multiple (2--4) to 40--100 times the air rate. A steady state theory developed by Combrade, suggests that EAC will initiate only above a critical crack velocity and cease below this same velocity. However, more recent tests show that EAC can persist down to much lower velocities (100 times lower) in low oxygen water at slightly lower temperatures. A special set of experiments on high sulfur plate material demonstrate that EAC will not initiate from surface cracks with low sulfide inventories at low crack tip velocities. Transient diffusion calculations show that a finite crack extension at a high crack tip velocity is necessary to initiate EAC, providing a possible explanation for the lack of high crack growth observations reported in low alloy steels in structural applications involving low oxygen environments.
Date: June 1996
Creator: Wire, G. L. & Li, Y. Y.
Partner: UNT Libraries Government Documents Department

Strain energy density-distance criterion for the initiation of stress corrosion cracking of alloy X-750

Description: A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.
Date: May 1, 1996
Creator: Hall, M.M. Jr. & Symons, D.M.
Partner: UNT Libraries Government Documents Department

Development of a scattering probability method for accurate vapor fraction measurements by neutron radiography. Revision 1

Description: Recent test results indicated drawbacks associated with the simple exponential attenuation method (SEAM) as currently applied to neutron radiography measurements to determine vapor fractions in a hydrogenous two-phase flow in a metallic conduit. The scattering component of the neutron beam intensity exiting the flow system is not adequately accounted for by SEAM, and this leads to inaccurate results. To properly account for the scattering effect, a neutron scattering probability method (SPM) is developed. The method applies a neutron-hydrogen scattering kernel to scattered thermal neutrons that leave the incident beam in narrow conduits but eventually show up elsewhere in the measurements. The SPM has been tested with known vapor (void) distributions within an acrylic disk and a water/vapor channel. The vapor (void) fractions deduced by SPM are in good agreement with the known exact values. Details of the scattering correction method and the test results are discussed.
Date: November 1, 1998
Creator: Joo, H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Design and modeling considerations relative to the phenomena associated with flow recirculation in branched piping systems

Description: Design and analytical modeling considerations associated with recirculating flow in piping systems with tee and Y connections are presented. Flow recirculation, in many process piping networks, can produce nonsteady flow and associated thermal conditions. In the flow recirculation discussion, experimental data is presented for a 90 degree branch piping (tee connection) using four different branch pipe sizes over a wide velocity range [Coffield and Kolar (1990)]. The discussion also includes recent test data for a 45 degree, Y connected, branch piping design. Designers can use this information by directly applying the limiting conditions that are presented at the design stage, or in evaluating the performance of existing systems. For example, although flow recirculation may result in complicated flow patterns, it often can have the beneficial effect of mixing low velocity branch line fluid with the primary system fluid as it approaches the intersection. In branch pipe systems where flows are at different temperatures this recirculation helps attenuate the potential for large thermal stresses. The recirculation flow patterns are strongly affected by the branch angle and thus they are presented as a function of the branch angle.
Date: December 31, 1996
Creator: Coffield, R.D.; Chauvet, D.M. & Ogle, G.G.
Partner: UNT Libraries Government Documents Department

The long range migration of hydrogen through Zircaloy in response to tensile and compressive stress gradients

Description: Zircaloy-4, which is used widely as a core structural material in pressurized water reactors (PWRs), picks up hydrogen during service. Hydrogen solubility in Zircaloy-4 is low and zirconium hydride phases precipitate after the Zircaloy-4 lattice becomes supersaturated with hydrogen. These hydrides embrittle the Zircaloy-4, degrading its mechanical performance as a structural material. Because hydrogen can move rapidly through the Zircaloy-4 lattice, the potential exists for large concentrations of hydride to accumulate in local regions of a Zircaloy component remote from its point of entry into the component. Much has been reported in the literature regarding the long range migration of hydrogen through Zircaloy under concentration gradients and temperature gradients. Relatively little has been reported, however, regarding the long range migration of hydrogen under stress gradients. This paper presents experimental results regarding the long range migration of hydrogen through Zircaloy in response to both tensile and compressive stress gradients. The importance of this driving force for hydrogen migration relative to concentration and thermal gradients is discussed.
Date: November 1, 1998
Creator: Kammenzind, B.F.; Berquist, B.M.; Bajaj, R.; Kreyns, P.H. & Franklin, D.G.
Partner: UNT Libraries Government Documents Department

The effect of potential upon the high-temperature fatigue crack growth response of low-alloy steels. Part 1: Crack growth results

Description: Corrosion-fatigue crack propagation experiments were conducted on several low-alloy steels in elevated temperature aqueous environments, and experimental parameters included temperature, sulfur content of the steel, applied potential level, and dissolved hydrogen (and in one case, dissolved oxygen) concentration in the water. Specimen potentials were controlled potentiostatically, and the observation (or non-observation) of accelerated fatigue crack growth rates was a complex function of the above parameters. Electrochemical results and the postulated explanation for the complex behavior are given in Part II.
Date: April 1, 1997
Creator: James, L.A. & Moshier, W.C.
Partner: UNT Libraries Government Documents Department

InGaAs monolithic interconnected modules (MIM)

Description: A monolithic interconnected module (MIM) structure has been developed for thermophotovoltaic (TPV) applications. The MIM device consists of many individual InGaAs cells series-connected on a single semi-insulating (S.I.) InP substrate. An infrared (IR) back surface reflector (BSR), placed on the rear surface of the substrate, returns the unused portion of the TPV radiator output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Also, the use of a BSR obviates the need to use a separate filtering element. As a result, MIMs are exposed to the entire emitter output, thereby maximizing output power density. MIMs with an active area of 1 x 1-cm were comprised of 15 cells monolithically connected in series. Both lattice-matched and lattice-mismatched InGaAs/InP devices were produced, with bandgaps of 0.74 and 0.55 eV, respectively. The 0.74-eV modules demonstrated an open-circuit voltage (Voc) of 6.158 V and a fill factor of 74.2% at a short-circuit current (Jsc) of 842 mA/cm{sup 2}, under flashlamp testing. The 0.55-eV modules demonstrated a Voc of 4.849 V and a fill factor of 57.8% at a Jsc of 3.87 A/cm{sup 2}. IR reflectance measurements (i.e., {lambda} > 2 {micro}m) of these devices indicated a reflectivity of {ge} 83%. Latest electrical and optical performance results for the MIMs will be presented.
Date: December 31, 1997
Creator: Fatemi, N.S.; Jenkins, P.P.; Weizer, V.G.; Hoffman, R.W. Jr.; Wilt, D.M.; Scheiman, D. et al.
Partner: UNT Libraries Government Documents Department

Stress intensity magnification factors for fully circumferential cracks in valve bodies (thick cylinders)

Description: The stress intensity solutions presented herein were obtained using an energy method in conjunction with a two-dimensional finite element program in order to explicitly account for curvature effect for fully circumferential cracks. The magnification factors for a specific crack depth were calculated by successively loading the crack surface by a uniform, linear, quadratic, and a cubic loading distribution. The magnification factors can be used to calculate the stress intensity factors by superposition method. The functions for each load condition in terms of radius to thickness ratio (R/t) and a fractional distance in terms of crack depth to thickness ratio (a/t) were developed. The validity of these functions is R/t = 1.5 to 10.0 and for 0.0125 {le} a/t {le} 0.8125. The functions agree to within 1% of the finite elements solutions for most magnification factors.
Date: November 1, 1998
Creator: Toor, P.M.
Partner: UNT Libraries Government Documents Department

The hydrogen embrittlement of Ni-Cr-Fe alloys

Description: It has been proposed that the stress corrosion cracking (SCC) of nickel-based alloys in low-temperature hydrogenated water is due to hydrogen embrittlement. The purpose of this work was to investigate the role of chromium on hydrogen embrittlement of Ni-Cr-Fe alloys and thus develop a better understanding of the low-temperature SCC phenomenon. The effect of chromium on the hydrogen embrittlement was examined using tensile tests followed by material evaluation via scanning electron microscopy and light optical microscopy. Four alloys were prepared with chromium contents ranging from 6 wt. percent to 35 wt. percent. In the noncharged condition, ductility, as measured by the percent elongation or reduction in area, increased as the alloy chromium content increased. Hydrogen appeared to have only minor effects on the mechanical properties of the low chromium alloys. The addition of hydrogen had a marked effect on the ductility of the higher chromium alloys. In the 26% chromium alloy, the elongation to failure was reduced from 53% to 14% with a change in fracture mode from ductile dimple to intergranular failure. A maximum in embrittlement was observed in the 26% Cr alloy. The maximum in embrittlement coincided with the minimum in stacking-fault energy. It is proposed that the increased hydrogen embrittlement in the high-chromium alloys is due to increased slip planarity caused by the low stacking-fault energy. Slip planarity did not appear to affect the fracture of the noncharged specimens.
Date: December 31, 1996
Creator: Symons, D.M.
Partner: UNT Libraries Government Documents Department

The effect of potential on the high-temperature fatigue crack growth response of low alloy steels: Part II, electrochemical results

Description: Environmentally assisted cracking (EAC) in low alloy steels was found to be dependent on externally applied potential in low sulfur steels in high temperature water. EAC could be turned on when the specimen was polarized anodically above a critical potential. However, hydrogen (H) additions inhibited the ability of potential to affect EAC. The behavior was related to formation of H ions during H oxidation at the crack mouth. A mechanism based on formation of H sulfide at the crack tip and H ions at the crack mouth is presented to describe the process by which sulfides and H ions affect the critical sulfide concentration at the crack tip.
Date: April 1, 1997
Creator: Moshier, W.C. & James, L.A.
Partner: UNT Libraries Government Documents Department

Evaluation of Oxide Dispersion Strengthened (ODS) molybdenum alloys

Description: A series of fourteen (14) novel high-strength molybdenum alloy compositions containing a dispersion of very fine (< 1 {mu}m diameter) oxide particles were consolidated using two proprietary powder metallurgy techniques. The developmental compositions were evaluated to determine the microstructural stability and mechanical properties from cryogenic (-148{degrees}F) to elevated temperatures (4000{degrees}F) for material in the as-swaged (>98% cold work) condition and for as-swaged material in the heat treated condition. Extremely fine oxide particle sizes (<1000 {Angstrom}) were observed by Transmission Electron Microscopy (TEM) for a number of the experimental compositions in the as-swaged condition. A one hour recrystallization temperature as high as 3990{degrees}F was measured and a ductile-to-brittle transition temperature as low as {approximately}58{degrees}F for material in the recrystallized condition was determined. The preliminary results support the alloy design concept feasibility.
Date: December 31, 1995
Creator: Bianco, R. & Buckman, R.W. Jr.
Partner: UNT Libraries Government Documents Department

1996 environmental monitoring report for the Bettis Atomic Power Laboratory, Pittsburgh Site

Description: The 1996 results for the Bettis-Pittsburgh radiological and non-radiological environmental monitoring programs are presented. The primary mission of the Bettis Laboratory has been directed toward the design, development, testing, and operation of nuclear reactor propulsion plants for naval surface and submarine vessels. The results obtained from the monitoring programs demonstrate that the existing procedures ensured that releases to the environment during 1996 were in accordance with applicable federal, state, county, and local regulations. Evaluation of the environmental data indicated that the current operations at the Site continue to have no adverse effect on the quality of the environment. A conservative assessment of radiation exposure to the general public as a result of Site operations demonstrated that the dose received by any member of the public was well below the most restrictive dose limits established by the Environmental Protection Agency, the Nuclear Regulatory Commission and the US Department of Energy. A risk assessment of potentially exposed populations to chemical residues in the environment at the Site demonstrated that these residues do not pose any significant health risk.
Date: 1996
Partner: UNT Libraries Government Documents Department

Materials and process development for the monolithic interconnected module (MIM) InGaAs/InP TPV cells

Description: Four major components of a thermophotovoltaic (TPV) energy conversion system are a heat source, a graybody or a selective emitter, spectrum shaping elements such as filters, and photovoltaic (PV) cells. One approach to achieving a high voltage/low current configuration is to fabricate a device, where small area PV cells are monolithically series connected. The authors have termed this device a monolithic interconnected module (MIM). A MIM device has other advantages over conventional one-junction cells, such as simplified array interconnections and heat-sinking, and radiation recycling capability via a back surface reflector (BSR). The authors confine the contents of this article to the MIM materials, process development, and some optical results. The successful fabrication of InGaAs/InP MIM devices entails the development and optimization of several key components and processes. These include: isolation trench via geometry, selective chemical etching, contact and interconnect metallization, dielectric isolation barrier, back surface reflector (BSR), and anti-reflection (AR) coating. The selection, development, and testing of the materials and processes described above for MIM fabrication will be described.
Date: June 1, 1997
Creator: Fatemi, N.S.; Jenkins, P.P.; Hoffman, R.W. Jr.; Weizer, V.G.; Wilt, D.M.; Murray, C.S. et al.
Partner: UNT Libraries Government Documents Department

Optical properties of thin semiconductor device structures with reflective back-surface layers

Description: Ultrathin semiconductor device structures incorporating reflective internal or back surface layers have been investigated recently as a means of improving photon recuperation, eliminating losses associated with free carrier absorption in conductive substrates and increasing the above bandgap optical thickness of thermophotovoltaic device structures. However, optical losses in the form of resonance absorptions in these ultrathin devices have been observed. This behavior in cells incorporating epitaxially grown FeAl layers and in devices that lack a substrate but have a back-surface reflector (BSR) at the rear of the active layers has been studied experimentally and modeled effectively. For thermophotovoltaic devices, these resonances represent a significant loss mechanism since the wavelengths at which they occur are defined by the active TPV cell thickness of {approximately} 2--5 microns and are in a spectral range of significant energy content for thermal radiators. This study demonstrates that ultrathin semiconductor structures that are clad by such highly reflective layers or by films with largely different indices of refraction display resonance absorptions that can only be overcome through the implementation of some external spectral control strategy. Effective broadband, below-bandgap spectral control using a back-surface reflector is only achievable using a large separation between the TPV active layers and the back-surface reflector.
Date: November 1, 1998
Creator: Clevenger, M.B.; Murray, C.S.; Ringel, S.A.; Sachs, R.N.; Qin, L.; Charache, G.W. et al.
Partner: UNT Libraries Government Documents Department