DOCSLIB.ORG

Dissolution and Clarification of Rertr Silicide Fuels*

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Dissolution and Clarification of Rertr Silicide Fuels* DISSOLUTION AND CLARIFICATION OF RERTR SILICIDE FUELS* George C. Rodrigues E. 1. du Pont de Nemours Co. Savannah River Laboratory Aiken, SC 29808 XA04C1501 Abstract SRP may reprocess spent REM fuel as early as FY-85. Candidate RERTR fuels include uranium oxides, aluminides, and sicides. Much less is known about the behavior of uranium sicides during Purex reprocessing than either uranium oxides or aluminides. Studies were performed at SRL with RERTR silicide fuels to ensure their reprocessability. The results of dis- solution and head-end clarification studies with both unirradiated and irradiated fuel are presented. Introduction Highly enriched uranium fuels from a number of foreign and domestic research and test reactors are currently reprocessed at the Department of Energy's (DOE) Savannah River Plant (SRP). The objective of the Reduced Enrichment Research and Test Reactor (RERTR) program is to demonstrate on- version of these reactors to low enriched uranium (LEU) fuels to reduce the potential for diversion of highly enriched uranium. Ideally, this conver- sion should be accomplished without changing the fuel configuration or de- grading reactor performance. Conversion to LEU under these constraints requires that the new fuel elements contain up to 41/2 times as much total uranium. Advanced powder metallurgy fabrication techniques utilizing high density oxides, aluminides, and sicides should produce reliable fuels with uranium loadings in the desired range. Candidate silicide intermetallic compounds are U3Si, U3Si2, and U3SiAl. While a good deal is known about reprocessing oxides and aluminidesl,2, information on reprocessing sicides is limited and dissolution of some uranium sicides has proven difficult. In addition, dissolved silicon can disrupt solvent extraction2j3. Therefore, reprocessing studies on silicide fuels were required to demonstrate compati- bility with current SRP operations. Aluminum clad fuels are reprocessed at SRP using a modified PUREX process. The irradiated fuel and cladding is first codissolved in mercury catalyzed nitric acid Trace fluoride is sometimes required for high burnup fuels. Fluoride catalytically attacks silicon which grows into the aluminum cladding by neutron capture during irradiation. Dissolved silicon above 100 ppm can severely disrupt solvent Sxtraction by stabilizing emulsions of the organic and aqueous phases Dissolved fuel is treated with gelatin (referred to as a gelatin strike), which polymerizes the dis- solved silicon to a solid which can be separated by centrifugation. The dissolved fuel is also treated with a reverse permagnianate strike. This step lowers the gamma radiation level by scavaging Zr-95Nb in the MnO2 The information contained in this article was developed during the course of work under Contract No. DE-AC09-76SROOOOI with the U.S. Department of Energy. 134 precipitate formed. Uranium and plutonium are then separated from the dis- solved fission products and cladding by solvent extraction into a tributyl phosphate-normal paraffin mixture.1 Studies at Savannah River Laboratory (SRQ examined dissolution rate, silicon removal,-and nuclear safety aspects of dissolving and clarifying REM silicide fuels. Summary REM silicide fuels were successfully dissolved in mercury catalyzed nitric acid in bench-scale tests. Trace fluoride was necessary for a con- sistent and reasonable dissolution rate of irradiated silicide fuel. The dispersed fuel phase dissolved at least as fast as the aluminum matrix and cladding. Solids remaining after dissolution were amorphous silica contain- ing negligible uranium. Average composition of the dissolved fuel solution was 24 gm/l U, 3.OM H, 1.3M A1+3, and 6.9M NO3_. A reverse permanganate strike gave satisfactory results. A gelatin strike reduced dissolved sili- con to less than 70 ppm, which is acceptable to solvent extraction. Irradi- ated fuel was dissolved and clarified as feed for bench-scale solvent ex- traction studies. Discussion Headend dissolution and clarification studies were conducted at SRL with both unirradiated and irradiated RERTR miniplates provided by Argonne National Laboratories (ANL). These developmental fuel elements were pre- pared for fabrication and irradiation studies. Depleted miniplates were produced during fabrication and uranium loading studies at ANL. Enriched miniplates were produced at ANL and irradiated to about 30% 235U burnup in the Oak Ridge Reactor (ORR) for post-irradiation examination at ANL. Dissolution Studies Bench-scale studies demonstrated that RERTR silicide fuels show no significant difference in dissolution from aluminum clad fuels now reproc- essed at SRP. Dissolution procedures for REM silicide fuels are based on current SRP practices and previous SRL studies on dissolution of aluminum clad fuels. REM dissolution studies were conducted in bench-scale glassware. The dissolver apparatus consisted of an electrically heated flask fitted with a water cooled reflux condenser. The flask was also fitted with a burette for metering in reagents during dissolution. Studies with the intensely radio- active irradiated fuel were conducted in SRL's heavily shielded High Level Cells (HLC) facility. Boiling 3M HN03 - 0.002M Hg+2 completely dissolved sections 4 gms each) of unirradiated miniplates of all three silicide compositions. Initial dissolution was vigorous, but with controllable foaming. Boiling 8M HN03 0.002M Hg+2 exhibited initial dissolution rates so high that foaming was barely controlled in the oversized condenser used. Dissolution in IM HN03 0.002M Hg+2 was slow and inconsistent. One dissolution was made wit-h- re- duce(i-Hg+2 (0.0002M). This run reduced the dissolution rate by almost 12 135 and showed that Hg+2 is necessary to the dissolution. The dispersed fuel particles dissolved as fast as the aluminum matrix and cladding in all tests. The range of total dissolution times of 7 to 15 hours for all tests compares favorably with times for fuels now processed at SRP. The acid consumed during the course of a dissolution was replenished periodically with makeup HN03- 16M HN03 makeup acid constantly sustained a higher dissolution rate than 8M for the same total makeup H added. A two hour boiling digestion period issolved any fuel particles remaining after all large cladding fragments were dissolved. This digestion also precipi- tated most of the dissolved silicon as fluffy, white amorphous silica. The dissolution rate of unirradiated fuel was unaffected by .01M KF. Trace fluoride (0.01M KF) was necessary to provide vigorous and con- sistent dissolution of 307. burnup miniplates. With no fluoride present, the irradiated fuel dissolved slowly and inconsistently. The dissolution rate of irradiated fuel was 36% higher with fluoride. Analysis by neutron activation and plasma source emission spectroscopy showed that solid residues remaining after dissolution contained negligible uranium (see Table 1). The solid residues from unirradiated fuel appeared to be amorphous silica. The solids from irradiated fuel were darker and more granular in appearance, but again appeared to be precipitated silica. Table I Uranium Loss to Dissolution Residues Composition % Total U Lost Unirradiated U3Si2 0.07% U3Si 0.12% U3SiAl 0.30% Irradiated U3Si 0.01% Clarification Studies Current SRP clarification steps were successfully tested on dissolved unirradiated and irradiated RERTR silicide fuels. The dissolved fuel was first treated with a reverse permanganate strike. Digested dissolver solution was brought to 75% and 0.014M Mn(NO3)2 was added. This was followed by sufficient KMnO4 to react wiTh 90% of the Mn+2 present. This reaction is shown below: 3Mn(NO3)2 + 2KMnO4 + 2H20 --- 0- 5MnO2 + 2KNO3 4 HN03 The precipitated MnO2 cake centrifuged easily from the solution in less than five minutes at 1100 G's in a bottle centrifuge. A gelatin strike successfully removed dissolved silicon to less than 70 ppm. 50 mg/l of gelatin was added to the dissolver solution and held at 75% for 30 minutes. Dissolved fuels initially contained as much as 180 ppm 136 dissolved silicon. A visible quantity of gelatin precipitated silica was observed only three times during these studies. This solid easily centri- fuged from the solution in less than 10 minutes at 1100 G's in a bottle centrifuge. Feed Preparation Demonstrations Integrated dissolution and clarification was demonstrated with whole REM miniplates. The resulting solutions provided feed for bench-scale solvent extraction studies. An unirradiated miniplate of each silicide composition was dissolved and clarified by the procedures tested above with no problems observed. Two each U3Si and U3SiAl irradiated miniplates were processed in the same way with good results. Conclusions These studies demonstrate that spent RERTR silicide fuels can be suc- cessfully dissolved and clarified for reprocessing at SRP. Trace fluoride will probably be necessary for dissolution. A gelatin strike will be neces- sary to ensure satisfactory solvent extraction performance. All dissolving and feed preparation procedures dveloped and tested are within the present technical standards for SRP reprocessing. References 1. M. L. Hyder, W. C. Perkins, M. C. Thompson, G. A. Burney, E. R. Russell, H. P. Holcomb, and L, F. Landon, Processing of Irradiated, Enriched Uranium Fuels at the Savannah River Plant, USDOE Report DP-1500, E. du Pont de Nemours and Co., Inc., Savannah River Laboratory, Aiken, SC (April 1979). 2. B. E. Paige, G. W. Gibson, and K. L. Rohde, The Effect of Silicon on Fabrication and Reprocessing of Aluminum Alloy Reactor Fuels, USDOE Report IN-1194, Idaho Nuclear Corporation, National Reactor Testing Station, Idaho Falls, ID (November 1968). 3. H. J. Groh, Removal of Silica from Solutions of Nuclear Fuels, USAEC Report DP-293, E. I. du Pont de Nemours Co., Inc., Savannah River Laboratory, Aiken, SC (June 1958). 137.
Load more

Recommended publications
  • Structural and Dynamical Trends in Alkali-Metal
    Article pubs.acs.org/JPCC Structural and Dynamical Trends in Alkali-Metal Silanides Characterized by Neutron-Scattering Methods † ‡ † § ∥ † ∥ Wan Si Tang,*, , Mirjana Dimitrievska,*, , Jean-Noel̈ Chotard, Wei Zhou, Raphael̈ Janot, ⊥ † Alexander V. Skripov, and Terrence J. Udovic † NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, United States ‡ Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, United States § National Renewable Energy Laboratory, Golden, Colorado 80401, United States ∥ Laboratoire de Reactivité ́et Chimie des Solides (LRCS), UMR 7314 CNRS, Universitéde Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France ⊥ Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia *S Supporting Information ABSTRACT: Structural, vibrational, and dynamical properties of the mono- and mixed-alkali silanides (MSiH3, where M = K, Rb, Cs, K0.5Rb0.5,K0.5Cs0.5, and Rb0.5Cs0.5) were investigated by various neutron experiments, including neutron powder diffraction (NPD), neutron vibrational spectroscopy (NVS), neutron- scattering fixed-window scans (FWSs), and quasielastic neutron scattering (QENS) measurements. Structural characterization showed that the mixed compounds exhibit disordered (α) and ordered (β) phases for temperatures above and below about 200− 250 K, respectively, in agreement with their monoalkali correspondents. Vibrational and dynamical properties are strongly influenced by the cation environment; in particular, there is a red shift in the band energies of the librational and bending modes with increasing lattice size as a result of changes in the bond lengths and force constants. Additionally, slightly broader spectral features are observed in the case of the mixed compounds, indicating the presence of structural disorder caused by the random distribution of the alkali-metal cations within the lattice.
    [Show full text]
  • Doping Effects on Transition-Metal Silicides: Crystal Structures and Physical Properties of Aluminium Doped Rhenium Silicide
    BearWorks MSU Graduate Theses Summer 2020 Doping Effects on Transition-Metal Silicides: Crystal Structures and Physical Properties of Aluminium Doped Rhenium Silicide Victoria DeCocq Missouri State University, [email protected] As with any intellectual project, the content and views expressed in this thesis may be considered objectionable by some readers. However, this student-scholar’s work has been judged to have academic value by the student’s thesis committee members trained in the discipline. The content and views expressed in this thesis are those of the student-scholar and are not endorsed by Missouri State University, its Graduate College, or its employees. Follow this and additional works at: https://bearworks.missouristate.edu/theses Part of the Inorganic Chemistry Commons, and the Materials Chemistry Commons Recommended Citation DeCocq, Victoria, "Doping Effects on Transition-Metal Silicides: Crystal Structures and Physical Properties of Aluminium Doped Rhenium Silicide" (2020). MSU Graduate Theses. 3563. https://bearworks.missouristate.edu/theses/3563 This article or document was made available through BearWorks, the institutional repository of Missouri State University. The work contained in it may be protected by copyright and require permission of the copyright holder for reuse or redistribution. For more information, please contact [email protected]. DOPING EFFECTS ON TRANSITION-METAL SILICIDES: CRYSTAL STRUCTURES AND PHYSICAL PROPERTIES OF ALUMINIUM DOPED RHENIUM SILICIDE A Master’s Thesis
    [Show full text]
  • Appendix a of Final Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-Lev
    Appendix A Inventory and Characteristics of Spent Nuclear Fuel, High-Level Radioactive Waste, and Other Materials Inventory and Characteristics of Spent Nuclear Fuel, High-Level Radioactive Waste, and Other Materials TABLE OF CONTENTS Section Page A. Inventory and Characteristics of Spent Nuclear Fuel, High-Level Radioactive Waste, and Other Materials ................................................................................................................................. A-1 A.1 Introduction .............................................................................................................................. A-1 A.1.1 Inventory Data Summary .................................................................................................... A-2 A.1.1.1 Sources ......................................................................................................................... A-2 A.1.1.2 Present Storage and Generation Status ........................................................................ A-4 A.1.1.3 Final Waste Form ......................................................................................................... A-6 A.1.1.4 Waste Characteristics ................................................................................................... A-6 A.1.1.4.1 Mass and Volume ................................................................................................. A-6 A.1.1.4.2 Radionuclide Inventories ...................................................................................... A-8 A.1.1.4.3
    [Show full text]
  • Low Temperature Chemical Vapor Deposition and Method for Depositing a Tungsten Silicide Film with Improved Uniformity and Reduced Fluorine Concentration
    Europaisches Patentamt 19 European Patent Office Office europeen des brevets © Publication number : 0 591 086 A2 12 EUROPEAN PATENT APPLICATION © Application number : 93480132.5 © int. ci.5: H01L 21/3205, C23C 16/44, C23C 16/42, H01L 21/285 @ Date of filing : 10.09.93 The application is published incomplete as filed @ Inventor : Gow, Thomas Richard (Article 93 (2) EPC). The points in the 4 Lyman Drive description at which the omission obviously Williston, VT 05495 (US) occurs have been left blank. Inventor : Lebel, Richard John Box 2255A RD1 © Priority : 30.09.92 US 954783 Sheldon, VT 05483 (US) @ Date of publication of application : @ Representative : Klein, Daniel Jacques Henri 06.04.94 Bulletin 94/14 Compagnie IBM France Departement de Propriete Intellectuelle @ Designated Contracting States : F-06610 La Gaude (FR) DE FR GB © Applicant : International Business Machines Corporation Old Orchard Road Armonk, N.Y. 10504 (US) © Low temperature chemical vapor deposition and method for depositing a tungsten silicide film with improved uniformity and reduced fluorine concentration. © A tungsten silicide (WSix) film is formed by GROWTH RATE ( mg/m i n ) chemical vapor deposition using the reduction of tungsten hexafluoride (WF6) with dichlorosi- O — ro lane (SiH2CI2) referred to as DCS and a reduc- ing agent comprising silane (SiH4), hydrogen, or a mixture thereof. According to the method of the present invention, the WSix film is formed in a CVD reactor operating at a low pressure and at a wafer temperature between about 300 and 550°C. In the preferred embodiment, a thin nucleation layer is deposited before the WSix film.
    [Show full text]
  • Tailoring of Transition Metal Silicides As Protective Thin Films On
    THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Tailoring of Transition Metal Silicides as Protective Thin Films on Austenitic Stainless Steel PUI LAM TAM Department of Materials and Manufacturing Technology CHALMERS UNIVERSITY OF TECHNOLOGY Gothenburg, Sweden 2011 Tailoring of Transition Metal Silicides as Protective Thin Films on Austenitic Stainless Steel PUI LAM TAM ISBN 978-91-7385-560-0 © PUI LAM TAM 2011 Doktorsavhandlingar vid Chalmers tekniska högskola Ny series nr 3241 ISSN 0346-718X Department of Materials and Manufacturing Technology Chalmers University of Technology SE-412 96 Gothenburg Sweden Tel: +46 (0)31-772 1000 Fax: +46 (0)31-772 1310 www.chalmers.se Printed by Chalmers Reproservice Göteborg, Sweden 2011 Abstract Transition metal silicide is an important material used in microelectronic devices and a possible candidate for high temperature application. The objective of this study is trying to make use of this material in a new way as protective thin films on engineering materials. The brittle nature of the silicides can thus be compensated by the ductile bulk material and the surface corrosion resistance can be improved. The choices of thin film constituents are targeted at the transition metal elements including titanium (Ti, Z = 22), chromium (Cr, Z = 24), iron (Fe, Z = 26) and nickel (Ni, Z = 28) in combination with silicon (Si, Z = 14) to form the binary-component intermetallic compounds by means of ion-beam sputter deposition, which was carried out in an ultrahigh vacuum (UHV) chamber at 10 -6 Pa. The chosen substrate material is AISI 304 stainless steel. Thin film characterisations were conducted by means of surface analysing instruments: X-ray photoelectron spectrometer (XPS) and grazing incidence X-ray diffractometer (GIXRD).
    [Show full text]
  • The Mechanism Behind the Calcium Aluminum Silicide Ternary Structural Preference and the Origin of Its Semimetal Behavior
    THE MECHANISM BEHIND THE CALCIUM ALUMINUM SILICIDE TERNARY STRUCTURAL PREFERENCE AND THE ORIGIN OF ITS SEMIMETAL BEHAVIOR by Torey Elizabeth Semi A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Applied Physics). Golden, Colorado Date Signed: Torey Elizabeth Semi Signed: D.M. Wood Thesis Advisor Golden, Colorado Date Signed: Dr. Thomas Furtak Professor and Head Department of Engineering ii ABSTRACT CaAl2Si2 is the prototype of the CaAl2Si2 class of Zintl structures established to be useful as thermoelectrics. We propose that CaAl2Si2 be interpreted as an ordinary covalently bonded, tetrahedrally coordinated quasi-semiconductor consisting of a large distortion of the wurtzite structure with the almost fully ionized Ca inserted at an interstitial site. We support this interpretation via a structural mapping and calculations for both a charged binary primitive cell and a Si4 primitive cell. Our intent is to explain the unusual structure of the CaAl2Si2 class of semiconductors, the origin of its semimetallic behavior, the basis for its stability and the effect of substituting other column II atoms for Ca on these properties. To be clear, this work does not examine the nature of the true band gap, or the transport coefficients of CaAl2Si2. GW corrections are not discussed, in view of the focus on the origins of stability of this peculiar structure. iii TABLE OF CONTENTS ABSTRACT . iii LIST OF FIGURES . vi LIST OF TABLES . xi ACKNOWLEDGMENTS . xii CHAPTER 1 INTRODUCTION . 1 1.1 Thermoelectric Materials . 2 1.2 Thermoelectric Efficiency .
    [Show full text]
  • Critical Issues in the Heteroepitaxial Growth of Alkaline-Earth Oxides on Silicon J
    Critical issues in the heteroepitaxial growth of alkaline-earth oxides on silicon J. Lettieri, J. H. Haeni, and D. G. Schlom Citation: Journal of Vacuum Science & Technology A 20, 1332 (2002); doi: 10.1116/1.1482710 View online: http://dx.doi.org/10.1116/1.1482710 View Table of Contents: http://scitation.aip.org/content/avs/journal/jvsta/20/4?ver=pdfcov Published by the AVS: Science & Technology of Materials, Interfaces, and Processing Articles you may be interested in Theoretical investigation of the alkaline-earth dihydrides from relativistic all-electron, pseudopotential, and density-functional study J. Chem. Phys. 126, 104307 (2007); 10.1063/1.2437213 Interface formation during molecular beam epitaxial growth of neodymium oxide on silicon J. Appl. Phys. 99, 074105 (2006); 10.1063/1.2188051 Hetero-epitaxy of perovskite oxides on GaAs ( 001 ) by molecular beam epitaxy Appl. Phys. Lett. 85, 1217 (2004); 10.1063/1.1783016 In situ observation of epitaxial growth of [Au/Co/Cu] and [Cu/Co/Au] superlattices and their magnetic interface anisotropies J. Appl. Phys. 90, 5104 (2001); 10.1063/1.1413230 Stranski-Krastanov growth of Al on Cr layers during molecular-beam epitaxial growth and its influence on the structure of epitaxial (001) Al/Cr superlattices J. Appl. Phys. 87, 159 (2000); 10.1063/1.371838 Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions. Download to IP: 128.84.143.26 On: Tue, 16 Jun 2015 17:57:48 Critical issues in the heteroepitaxial growth of alkaline-earth oxides on silicon J. Lettieri, J. H. Haeni, and D.
    [Show full text]
  • Formation of Gems and Precious Stones from Cheap and Plentiful Materials, and Other Somewhat Sensational Operations Which Had A
    A4 PaAer firesenteed at lie 162d Meeti g of the Amzerican Institute of Electrical E-ngineers at Nez York, February 2&ti 1Q902. THE ELECTRIC FURNACE IN INDUSTRIAL CHEMISTRY. BY CHARLES B. JACOBS. In its early days the electric furnace labored under the burden of the prophecies of its wonderful possibilities and products, and seems to have been more or less associated in the popular mind with the production of diamonds from amorphous carbon, the formation of gems and precious stones from cheap and plentiful materials, and other somewhat sensational operations which had a tendency to obscure, for a time, the knowledge of its useful- ness in the field of industrial chemistry. Notwithstanding the fact that DeChalmot, the Cowles brothers and others, had been operating the electric furnace for some years in the production of alloys from very refractory ores, it was not until Acheson produced carbide of silicon, Willson obtained carbide of calcium in commercial quantities, and Moissan pub- lishbd his scientific investigations in Le Four Electrique, that the value of the electric furnace for the production of substances use- ful in the arts began to be generally recognized. Since that time, however, its field of usefulness has been steadily increasing until it is now obtaining recognition as an im- portant factor in industrial chemistry. Reference to the patent lists of the various countries will show an immense variety of electric furnaces, but they may all be classified under three general types which have been modified in numerous ways to meet the special requirements of the var- ious processes for which they are intended.
    [Show full text]
  • BLABER- a Review of the Optical Properties of Alloys and Intermetallics for Plasmonics
    A review of the optical properties of alloys and intermetallics for plasmonics M G Blaber, M D Arnold and M J Ford* Institute for Nanoscale Technology, Department of Physics and Advanced Materials, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia *[email protected] Abstract. Alternative materials are required to enhance the efficacy of plasmonic devices. We discuss the optical properties of a number of alloys, doped metals, intermetallics, silicides, metallic glasses and high pressure materials. We conclude that due to the probability of low frequency interband transitions, materials with partially occupied d-states perform poorly as plasmonic materials, ruling out many alloys, intermetallics and silicides as viable. The increased probability of electron-electron and electron-phonon scattering rules out many doped and glassy metals. Contents 1. Introduction 2. Plasmonic Materials: Definition and review of metals 2.1 Quality factors and the ideal plasmonic material 2.2 A review of the optical properties of metals 3. Alloys 3.1 Noble metal alloys 3.2 Transition metal alloys 4. Intermetallics 4.1 Alkali metal binary intermetallics 4.2 Noble metal binary intermetallics 4.3 Group 13 binary intermetallics 4.4 Other binary intermetallics 4.5 Ternary Intermetallics 5. Silicides 6. High pressure materials 7. Liquid metals and glassy/amorphous materials 7.1 Liquid Metals 7.2 Metallic Glasses and amorphous alloys 1. Introduction As nanofabrication techniques become increasingly fast and accurate, the performance of plasmonic systems relies less and less on structure fabrication and more on the fundamental limitations of the underlying materials. Plasmonics has seen an exponential growth, due mainly to the sheer diversity of applications, from optical cloaking [1] to superlensing [melville2005, pendry2000] as well as single molecule surface enhanced raman spectroscopy [2], parasite therapy [3] and optical circuits[4] with high speed optical switching[5, 6].
    [Show full text]
  • UNITED STATES PATENT OFFICE Augustus F
    Patented Jan. 27, 1931 1790,552 UNITED STATES PATENT OFFICE AUGUSTUs F. MEEHAN, OF CHATTANOOGA, TENNESSEE, ASSIGNOR TO MEEHANITE METAL CORPORATION, OF CHATTANOOGA, TENNESSEE, A CORPORATION OF TEN NESSEE ATLOY FOR MANUEFACTURE OF CAST IRON NoDrawing. Application filed August 39, 1928. Serial No. 303,889. The present invention relates to the treat produce a casting containing approximately ment of metals, and, more particularly, to 3% of combined carbon, and even in iron the treatment of molten metal in the manu containing less than 1% of combined carbon. facture of castings. By the statement that the silicide is sub 5 An object of the invention is to provide a stantially free from iron, is meant that the 55 process for the manufacture of castings of iron content of the treating agent or alloy special strength and uniformity, such as will is relatively inconsiderable. insure the quality sought in the finished cast I have also found that in the production of S. castings, the silicide agent may be accom O fretofore, when deemed essential, it has panied to advantage by a second alkaline 60 been the practice in the manufacture of grey earth metal, such as magnesium, strontium, iron castings to add to the molten metalia barium, etc. For example, an alloy agent of suitable agent in order to obtain the carbon in calcium, silicon and an inconsiderable the desired forms. amount of iron may also include to advan 5 In the breaking down of the iron carbide tage either magnesium or strontium or bari 65 in the metal during solidification, ferro-sili um, etc.
    [Show full text]
  • Overview of Properties and Performance of Uranium-Silicide Compounds for Light Water Reactor Applications
    Appendix 11: Oxidation Tests on U3Si2, UN and UO2 Pellets in Synthetic Air LWR Accident Tolerant Fuels—II 987 Overview of Properties and Performance of Uranium-Silicide Compounds for Light Water Reactor Applications A.T. Nelson, J.T. White, D.D. Byler, J.T. Dunwoody, J.A. Valdez and K.J. McClellan Los Alamos National Laboratory P.O. Box 1667 Los Alamos, NM, 87545 [email protected] INTRODUCTION focused on a more critical evaluation of their thermophysical properties to temperatures near their The uranium-silicon binary system possesses a range melting points. These compounds have seen limited of compounds that have been historically investigated and characterization at temperatures low relative to those utilized to a limited extent as nuclear reactor fuels. Of the anticipated of an LWR fuel, but even here appreciable multiple compounds, U3Si and U3Si2 are most familiar; scatter is present [2]. Lesser-studied compounds such as their high uranium densities have made them an intriguing USi and U3Si5 have received virtually no attention from choice for incorporation into composite plate fuels in previous researchers regarding their thermal conductivity, research reactors and other low power core redesigns heat capacity, and thermal expansion as a function of where retained neutronic performance was desired at temperature. Accurate knowledge of these properties is lower enrichments [1]. This increased uranium density essential to modeling of heat transport in reactor systems. compared with uranium dioxide (UO2) has made them The renewed focus on accident tolerance has also attractive to a new generation of nuclear fuels research emphasized consideration of the off-normal performance driven by the renewed push for accident-tolerant light of materials in nuclear reactor systems.
    [Show full text]
  • Chemical Vapor Deposition of Tungsten Silicide (Wsi ) for High Aspect Ratio Applications
    Thin Solid Films 443 (2003) 97–107 ( ) Chemical vapor deposition of tungsten silicide WSix for high aspect ratio applications B.Sella *,, A.Sanger¨ ,abac G.Schulze-Icking , K.Pomplun , W.Krautschneider aInfineon Technologies, Konigsbrucker¨¨ Strasse 180, 01099 Dresden, Germany bInfineon Technologies AG, Balanstrasse 73, 81541 Munich, Germany cTU Hamburg-Harburg, Techn. Electronics, Eissendorfer Strasse 38, 21071 Hamburg, Germany Received 15 January 2003; received in revised form 24 May 2003; accepted 13 June 2003 Abstract Chemical vapor deposition of tungsten silicide into high aspect ratio trenches has been investigated using a commercial 8-inch Applied Materials Centura single wafer deposition tool.For an in-depth study of both step coverage and stoichiometry, a ( ) combined chemistryytopography simulator has been developed.Dichlorosilane reduction of tungsten hexafluoride WF6 has been ( ) identified as a suitable chemistry to fill deep trenches with tungsten disilicide, while for WF64 reduction with silane SiH or ( ) disilane Si26 H fundamental drawbacks have been identified for extreme aspect ratios.In the process range under study, good agreement is observed between the simulated step coverages and those obtained from scanning electron microscope images.The simulations predict a deposition regime in which both good step coverage and a suitable stoichiometry are achieved inside deep trenches. ᮊ 2003 Elsevier B.V. All rights reserved. Keywords: Chemical vapor deposition; Deposition process; Nanostructures; Tungsten 1. Introduction decreases, while at the same time their length increases. To still maintain sufficient current into and out of With continuously decreasing groundrules in modern DRAM capacitors, low resistivity plugsyvias are indis- ULSI manufacturing, there exists a strong demand for pensable for future DRAM generations.
    [Show full text]