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Improved size uniformity of sol-gel spheres by imposing a vibration on the sol in dispersion nozzles

Description: A major part of the Th-- /sup 233/U fuel cycle program at ORNL has been concerned with the development of sol-gel processes to prepare ThO/sub 2/ and ThO/ sub 2/--/sup 233/UO/sub 2/ spheres. The formation of sol drops having a uniform and controlled diameter is important to any sol-gel process for preparing oxide kernels for High Temperature Gas-Cooled Reactor fuels. A recently developed technique that incorporates use of a sol disperser with vibration has met the dispersion requirements for ORNL sol-gel processes better than any of the previous techniques employing dispersers alone. With this new technique, the breakup of sol streams from orifices or capillaries is made more uniform and regular by imposing a vibration, at the natural frequency of drop formation, on the sol at the entrance to the orifices or capillaries. This techn-que has been applied to two-fluid nozzles to form 1,000 to 88,000 sol drops per minute. Batches consisting of 1 to 13 kg of fired ThO/sub 2/ spheres 370 to 500 mu in diameter had average diameters within 1% of the predicted values and standard deviations of 2.5 to 5.0 mu . Yields after both size and shape separation were greater than 95% and were usually greater than 98% in a 30- mu range. The same technique was applied to shear nozzles at rates up to 192,000 drops per minute. Nozzles of this type use multiple orifices and are more dependable for larger capacities than multiple two-fluid nozzles. (auth)
Date: May 1, 1973
Creator: Haas, P. A. & Lackey, W. J.
Partner: UNT Libraries Government Documents Department

Effect of deposition conditions on the properties of pyrolytic silicon carbide coatings for high-temperature gas-cooled reactor fuel particles

Description: Silicon carbide coatings on HTGR microsphere fuel act as the barrier to contain metallic fission products. Silicon carbide coatings were applied by the decomposition of CH/sub 3/SiCl/sub 3/ in a 13-cm-diam (5-in.) fluidized-bed coating furnace. The effects of temperature, CH/sub 3/SiCl/sub 3/ supply rate and the H/sub 2/:CH/sub 3/SiCl/sub 3/ ratio on coating properties were studied. Deposition temperature was found to control coating density, whole particle crushing strength, coating efficiency, and microstructure. Coating density and microstructure were also partially determined by the H/sub 2/:CH/sub 3/SiCl/sub 3/ ratio. From this work, it appears that the rate at which high quality SiC can be deposited can be increased from 0.2 to 0.5 ..mu..m/min.
Date: October 1, 1977
Creator: Stinton, D. P. & Lackey, W. J.
Partner: UNT Libraries Government Documents Department

Improved gas distributor for coating HTGR fuel particles

Description: A new and improved gas distributor was developed for use in coating fuel particles for the HTGR. The coating gas enters the coating furnace through multiple thin regions of a porous plate. This more uniformly disperses the gas and leads to improved coating properties. High-quality carbon and SiC coatings have been deposited with the new distributor in both 13- and 24-cm-diam coating furnaces.
Date: January 1, 1977
Creator: Lackey, W. J.; Stinton, D. P. & Sease, J. D.
Partner: UNT Libraries Government Documents Department

Improved gas distributor for coating HTGR fuel particles

Description: The important criteria to be considered in design of the gas distributor are: (1) The distributor should ideally spread or disperse the gas over the full area of the coating chamber to maximize the particle gas contact area and thereby increase both particle circulation and the percentage of the input gas that ends up as coating. (2) The gas should not heat up during its passage through the distributor. Otherwise the gas would partially decompose prematurely, causing excessive coating deposition within or on the distributor. (3) The distributor should be designed to minimize accidental drainage of particles from the furnace and blowover of particles into the effluent system. (4) The distributor should be capable of depositing both carbon and SiC coatings of high quality as regards to density, preferred orientation, permeability, defective fraction, and other product attributes. (5) The distributor should be amenable to use with large particle charges and short turnaround times and be simple, inexpensive, and reliable. We have devised a simple distributor that incorporates the five criteria listed above. The new design is termed a blind-hole frit. All the gas passes through the thinned blind-hole regions, and thus the gas velocity is considerably higher than for a flat frit of uniform thickness. Because of its high velocity, the gas does not have time to reach a high enough temperature to cause deposition within the frit. Also most of the resistance to gas flow is provided by the porous distributor and not by the particle bed; therefore, localized variations of the quantity of particles above any particular gas inlet do not significantly alter the flow rate through that inlet.
Date: January 1, 1977
Creator: Lackey, W. J.; Stinton, D. P. & Sease, J. D.
Partner: UNT Libraries Government Documents Department

Coating crystalline nuclear waste forms to improve inertness

Description: Crystalline waste forms of high simulated waste loading were successfully coated with layers of pyrolytic carbon and silicon carbide. Sol-gel technology was used to produce microspheres that contained simulated waste. A separate process for cesium immobilization was developed, which loads 5 wt % Cs onto zeolite particles for subsequent coating. The chemical vapor deposition process was developed for depositing thin layers of carbon and silicon carbide onto particles in a fluidized-bed coater. Pyrolytic carbon-coated particles were extremely inert in numerous leach tests. Aqueous leach test results of coated waste forms were below detection limits of such sensitive analytical techniques as atomic absorption and inductively coupled plasma atomic emission.
Date: January 1, 1981
Creator: Stinton, D.P.; Angelini, P.; Caputo, A.J. & Lackey, W.J.
Partner: UNT Libraries Government Documents Department

Influence of process variables on permeability and anisotropy of Biso-coated HTGR fuel particles

Description: The effect of several important process variables on the fraction of defective particles and anisotropy of the low-temperature isotropic (LTI) coating layer was determined for Biso-coated HTGR fuel particles. Process variables considered are deposition temperature, hydrocarbon type, diluent type, and percent diluent. The effect of several other variables such as coating rate and density that depend on the process variables were also considered in this analysis. The fraction of defective particles was controlled by the dependent variables coating rate and LTI density. Coating rate was also the variable controlling the anisotropy of the LTI layer. Diluent type and diluent concentration had only a small influence on the deposition rate of the LTI layer. High-quality particles in terms of anisotropy and permeability can be produced by use of a porous plate gas distributor if the coating rate is between 3 and 5 ..mu..m/min and the coating density is between about 1.75 and 1.95 g/cm/sup 3/.
Date: November 1, 1977
Creator: Stinton, D. P.; Lackey, W. J. & Thiele, B. A.
Partner: UNT Libraries Government Documents Department

Inspection of high-temperature gas-cooled reactor recycle fuel

Description: Inspection of recycle fuel for High Temperature Gas-Cooled Reactors (HTGRs) involves many operations which, because of the high radiation level associated with the presence of /sup 232/U, must be performed in shielded (5 cm of lead) glove boxes containing automated sample handling and analysis equipment. Equipment for obtaining representative fuel particle samples and for pneumatically transferring particles and fuel rods through long tubes has been developed. Schemes for cross checking inspection data were devised to determine the accuracy and precision of several analytical techniques as well as to detect occasional errors in analytical data. The density of the particle buffer coating layer was shown to increase significantly during deposition of the overlying pyrocarbon coating layer. A method was developed for measuring the final buffer density to an accuracy of about 0.05 g/cm/sup 3/ while not requiring sampling at the buffer stage of the coating operation. Methods using high pressure mercury pycnometry were developed to measure both the amount of open porosity and the geometric density of low temperature isotropic (LTI) coatings. With this technique the LTI density can be measured with a precision of about 0.01 g/cm/sup 3/. A 1500/sup 0/C gaseous chlorine leaching technique was shown to be useful for measuring defective Biso-coated particle fractions for both loose particles and particles bonded into fuel rods. An automated particle size analyzer suitable for glove box operation was developed with the capability for measuring particles at the rate of 1500 per min. Successful techniques for measuring particle shape and strength were also developed. 16 figures, 5 tables.
Date: June 1, 1977
Creator: Pechin, W. H.; Lackey, W. J.; Sease, J. D. & Eatherly, W. P.
Partner: UNT Libraries Government Documents Department

Determination of defective particle fraction in HTGR fuels

Description: The fuel for the High-Temperature Gas-Cooled Reactor (HTGR) consists of uranium and thorium species in the form of microspheres individually encapsulated in layers of pyrolytic carbon and silicon carbide. In the characterization of these particles, an important consideration is the fraction in a particular sample that may have defective coatings which would allow the release of gaseous and metallic fission products. A method for this determination, which has been in use for almost a decade, is the chlorine leach in which the gas is passed over the particles at 1000/sup 0/C, and the fuel that is exposed by coating defects is volatilized and collected as the heavy metal chlorides. However, when the particles have been bonded into a fuel rod, the removal of exposed fuel from particles in the intact rod requires long exposure times (16-50 hours). A much more rapid procedure (2-3 hours) is described in which the chlorination of fuel rods is done at 1500/sup 0/C. The method is also applicable to loose particles. Also described is an adaptation of the chlorine leach at 1000/sup 0/C for the treatment of irradiated fuel rods in a hot cell.
Date: November 1, 1976
Creator: LaValle, D. E.; Costanzo, D. A.; Lackey, W. J. & Caputo, A. J.
Partner: UNT Libraries Government Documents Department

Device for sampling HTGR recycle fuel particles

Description: Devices for sampling High-Temperature Gas-Cooled Reactor fuel microspheres were evaluated. Analysis of samples obtained with each of two specially designed passive samplers were compared with data generated by more common techniques. A ten-stage two-way sampler was found to produce a representative sample with a constant batch-to-sample ratio.
Date: March 1, 1977
Creator: Suchomel, R. R. & Lackey, W. J.
Partner: UNT Libraries Government Documents Department

Development of silicon nitride composites with continuous fiber reinforcement

Description: The composites were fabricated using ultrafine Si powders prepared by attritor milling; the powders exhibits full conversion to Si nitride in < 3 h at {le} 1200 C (these conditions reduce degradation of the fibers compared to conventional). Effects of processing conditions on fiber properties and the use of fiber coatings to improve stability during processing as well as change the fiber-matrix interfacial properties were investigated. A duplex carbon-silicon carbide coating, deposited by CVD, reduced fiber degradation in processing, and it modified the fiber-matrix adhesion. Si nitride matrix composites were fabricated using reaction sintering, forming laminates, filament-wound plates, and tubes. In each case, an attritor milled Si powder slurry is infiltrated into ceramic fiber preforms or tows, which are then assembled to form a 3-D structure for reaction sintering. The resulting composites have properties comparable to chemical vapor infiltration densified composites, with reasonable strengths and graceful composite fracture behavior.
Date: October 1, 1993
Creator: Starr, T. L.; Mohr, D. L.; Lackey, W. J. & Hanigofsky, J. A.
Partner: UNT Libraries Government Documents Department

Sol-gel technology applied to crystalline ceramic nuclear waste forms

Description: The sol-gel process is being developed for the solidification and isolation of high-level nuclear fuel waste. Three gelation methods are being developed for producing alternative waste forms. These include internal gelation for producing spheres of up to 1 mm diam suitable for coating, external gelation, and water extraction methods for producing material suitable for alternate ceramic processing. In this study internal gelation has been used to produce ceramic spheres of various alternative nuclear waste compositions. A gelation system capable of producing 100-g batches has been assembled and used for development. Waste forms containing up to 70 wt % simulated Savannah River Plant waste have been produced. Dopants such as Cs, Sr, Nd, Ru, and Mo were used in some experiments to observe side waste streams and sintering effects. Synroc microspheres were coated with both low-density carbon, high-density impermeable carbon, high-temperature dense SiC, and SiC deposited at temperatures near 900/sup 0/C. Other gelation methods and other alternative waste forms are being developed.
Date: January 1, 1980
Creator: Angelini, P.; Bond, W.D.; Caputo, A.J.; Mack, J.E.; Lackey, W.J.; Lee, D.A. et al.
Partner: UNT Libraries Government Documents Department

Grain structure and growth of dispersed phase BN-AlN coatings grown via chemical vapor deposition

Description: This paper discusses the variation in microstructures encountered during the separate depositions of boron nitride (BN) and aluminium nitride (AlN) as well as during the codeposition of BN-AlN dispersed phase ceramic coatings. This combination was chosen in order to take advantage of the self lubricating properties of hexagonal BN along with the hard, erosion resistance of AlN. Films were characterized using scanning and transmission electron microscopy (SEM and TEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). A range of coating microstructures are possible depending on the conditions of deposition. The best films produced, in terms of hardness, density, and tenacity, were a fine mixture of turbostratic BN and preferentially oriented A1N whiskers aligned with the whisker axis perpendicular to the substrate surface as seen by both electron microscopy and x-ray diffraction. 4 refs., 9 figs., 1 tab.
Date: January 1, 1990
Creator: Freeman, G.B.; Lackey, W.J.; Hanigofsky, J.A. (Georgia Inst. of Tech., Atlanta, GA (USA). Georgia Technology Research Inst.); Lee, Woo Y. (United Technologies Research Center, East Hartford, CT (USA)) & More, K.L. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department