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Investigations on Cesium Uranates and Related Compounds

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Investigations on Cesium Uranates and Related Compounds INVESTIGATIONS ON CESIUM URANATES AND RELATED COMPOUNDS ACADEMISCH PROEFSCHRIFT TER VERKRIJGING VAN DE GRAAD VAN DOCTOR Λ t' IN OE WISKUNDE EN NATUURWETENSCHAPPEN AAN DE UNIVERSITEIT VAN AMSTERDAM OP GEZAG VAN DE RECTOR MAGNIFICUS DR. G. OEN BOEF, HOOG- LERAAR IN DE FACULTEIT OER WISKUNDE EN NATUURWETENSCHAPPEN. IN HET OPENBAAR TE VERDEDIGEN IN DE AULA DER UNIVERSITEIT (TIJDELIJK IN DE LUTHERSE KERK, INGANG SINGEL 411, HOEK SPUI) OP WOENSDAG 16 JUNI 1976 OM 0 15.00 UUR PRECIES DOOR ANDRÊ BERNARD van EGMOND GEBOREN TE HENGELO (O) Ιί.'Λίά? Μ ^;,**,,χ —ir- Υ' promotor : prof.dr. B.O. Loopstra co-promotor: prof.dr.ir. E.H.P. Cordfunke co-referent: prof.dr. J.A. Goedkoop pit llf I il IpJ I•f va** > , ",. ---.υ V ~'\ '"·*'\ί· aan mijn ouders voor Ietje -4- Aan allen, die in enige vorm hebben meegewerkt aan het totstandkomen van dit proefschrift, betuig ik mijn hartelijke dank. In het bijzonder dank ik Gernna van Voorst en Anneraieke Berentsen voor de syntheses van de uranaatpreparaten en Piet van Vlaanderen voor de hulp bij het Rontgenwerk. De vakgroep Chemische Fysica van de Technische Hogeschool Twente zeg ik dank voor het beschikbaarstellen van de PW1100 éénkristaldiffrac- tometer en de afdeling Fysica van het Reactor Centrum Nederland voor het gebruik van de PW1150 poederdiffTactometer. Veel dank ben ik verschuldigd aan mevr.drs. E.M.M. Rutten-Keulemans die enkele computerprogramma's voor mij toegankelijk maakte» Veel waardering heb ik voor het typewerk dat verzorgd werd door mevr. A. Schuyt-.-Fasen en voor de zorg van de reprografische dienst van het Reactor Centrum Nederland, besteed aan het drukken van dit proef- '. -Λ " " . schrift. De direktie van het Reactor Centrum Nederland ben ik erkentelijk voor de mogelijkheid de tekst van dit proefschrift ook als extern rapport (RCN-246) te laten verschijnen. ••;ii ν; "Α -5- CONTENTS page CHAPTER I INTRODUCTION 9 1.1. Nuclear technology and cesium uranates 9 1.2. X-ray diffraction SO 1.2.1. Single-crystal X-ray diffraction 10 1.2.2. Powder X-ray diffraction 12 1.3. Crystallographic computing 13 References 15 CHAPTER II CHARACTERIZATION OF THE PHASES IN THE Cd-U-0 SYSTEM 17 2.1. Introduction 17 2.2. Experimental 17 2.3. Hexavalent cesium uranates 18 2.A. The Cs-U-0 system in air 21 2.4.1. Compositions with Cs/U > 0.5 and < 0.5 21 2.4.2. The equilibrium Cs^O^**Cs^O^ + ^ 22 2.5. The Cs-U-0 system at low oxygen pressures 24 References 24 CHAPTER III THE CRYSTAL STRUCTURES OF Cs2U4O|2 26 '-•.•'•f- 3.1. Introduction 26 im-.'-v. 3.2. Experimental 26 3.3. The crystal structure of ct-Cs U 0 26 ""- ' ί- -" '< 3.3.1. Crystal data and intensity measurement 26 3.3.2. Structure determination of β-0ε2ϋ,0 28 3.4. The crystal structures of £J- and y-Cs-U.O.- 29 3.4. ]. Crystal data 29 3.4.2., The crystal structures of β- and Y-CS2U4OJ2 30 3.5. Discussion 31 References 33 CHAPTER IV THE CRYSTAL STRUCTURES OF Cs^O^ AND Cs^O^ 35 4.1. Introduction 35 4.2. Experimental 35 4.3. Crystal data and crystal structure of Cs.U.O.. 36 • }::.;• ν ζ^Μ 4.4. Crystal data and crystal structure of Cs.U,.O,, 38 i J ID 39 4.5. Discussion 42 Refe.. Alic Or*. Pi·: HMM -6- ^M CHAPTER V THE CRYSTAL STRUCTURES OF Cs2U15°46 Cs2UO4 5.1. Introduction 5.2. Experimental ï,3. The crystal structure of Cs.U 0 ? 5.4. The crystal structure of Cs2U?022 5.5. The crystal structure of Cs U.-O,, 5.6. The crystal structure of CSjUO, 5.7. Discussion References CHAPTER VI THE CRYSTAL STRUCTURES OF Cs^Oj 6.1. Introduction 6.2. Experimental 6.3. The X-ray analysis of a-CsXO. 6.4. The X-ray analysis of β-CsJ5J37 6.5. The X-ray analysis of γ-Cs U20_ 6.6. The neutron analysis of a-Cs.U„O_ 6.7. Discussion References CHAPTER VII POTASSIUM AND RUBIDIUM URANATES 65 7.1. Introduction 65 7.2. Experimental 65 7.3. Hexavalent uranates 65 7.3.1. The potassium uranate system 65 7.3.2. The rubidium uranate system 67 7.3.3. The crystal structures of M-U.O-, and M2U2O7 (M - K,Rb) 67 7.4. Pentavalent uranates 69 7.5. Discussion 69 References 71 CHAPTER VIII CRYSTAL CHEMISTRY OF THE ALKALI URANATES 73 8.1. Introduction 73 8.2. Structural characteristics of uranates(VI) 73 if 8.3. Uranium(-oxygen) motifs in alkali uranates(VI) 78 8.3.1. The mono- and diuranate region 80 8-3.2. The high M/U-ratio region 81 ' " '" ül \irn it'! -7- : \A t • , ''.-^ page 3&J: 8.3.3. The 3D-structure region 8! 8.3.4. Cs2UI5O46 and the M^O^ (M - K,Rb,Cs) 82 8.3.5. The tetraurar.ate region 83 8.4. Uranium-uranium distances and uranium-oxygen bonding 84 8.5. The composition of the uranium layers 86 8.6. Uranium layer in Cs2U,O._ and Cs-U5O.6 90 8.7. Influence of the metal radius on the interplanar ,.•·>..<· , , distances in layer structures of uranates(VI) 91 8.8. Uranates(V) with the perovskite structure 94 References 95 APPENDICES 98 SAMENVATTING 122 CURRICULUM VITAE 124 '7 ' -9- CHAPTER I. INTRODUCTION 1.1. Nuclear technology and cesium uranates Uranium has been successfully applied in nuclear technology as a source Η. •'-'' of energy since the Second World W;ir. In most of the nuclear reactors 235 the isotope U - which occurs for only 0.7% in natural uranium - is used. Therefore nuclear technologists have looked for a method to harness the greater part of the available uranium, the U isotope, for the production of energy. This can be achieved in a fast-breeder reactor, in 238, which the U isotope is converted into the fissile plutonium isotope 239 Pu. The construction of a prototype reactor is a joint project of the governments of Western-Germany, Luxemburg, Belgium and The Netherlands. The work described in this thesis has been partly performed within the scope of this fast-breeder reactor project. During fission of the nuclear fuel many elements are formed such as iodine, molybdenum, rubidium, cesium [I], Some of these elements will diffuse from the hot centre of the (U,Pu)-oxide pellets (2500°-2900°C) to the cooler parts of the fuel pins (50O°-700°C) [2,3,4]. In the re- sulting medley of elements three types of chemical reactions can occur: 1. reactions between fission products mutually, mainly producing ir.olyb- dates [5,63; 2. corrosion of the stainless steel pin cladding by fission products, forming chromates [7,8]; 3. reactions between fission products and the nuclear fuel (U,Pu)- oxide, resulting in the formation of uranates [8,9] and piutonates. Since cesium is found in substantial quantities among the fission products [1] cesium uranates will also be formed during irradiation I 10}. The formation of cesium uranates appears to be strongly dependent on the (partial) oxygen potential in the fuel rod [2,3,10], and may rlfly a sifc~ nificant role in the swelling of the fuel and even cause fuel pin failure 19], Therefore a study of the Cs-U-0 system is clearly called for. In addition, uranates are of great interest to structural chemistry, As early as 1935 Frankuchen demonstrated I In·· existence of the linear con- 2+ figuration (O-U-0) in the crystal structm >I solium uranyl acetate [J 11. Since that time many uranium compound.·- e 'ujen shown to contain this uranyl group. In I960 Kovba investigatec o regularities in uranate structures [121, while Keller consider*d some uranates in an ex- -10- tensive structural study on actinide compounds some years later [13]. However, both authors had no detailed structural information on cesium uranates available. In addition many investigations concerning the other alkali uranates, frequently contradicting earlier statements and even mutually conflicting, have been published since the last decade. In this thesis the crystal structures of the cesium uranates are described, whereas the rubidium and potassium uranate systems are re- investigated. Finally the structural information on the alkali uranates is classed in a way similar as Kovba and Keller did for earth alkaline uranates mainly. 1.2. X-ray diffraction One of the commonly adopted techniques to obtain structural information from solid compounds is X-ray diffraction. Since numerous authors have described both theory and practice of X-ray diffraction, only some sum- ι -C - , --' marizing remarks will be made here, chiefly for a clear apprehension of the description of the computer programs used in this study. ii^^^Single-crjrs tal_X-ray_dif fraction When a rotating single crystal is exposed to an X-ray beam a pattern of diffracted beams is obtained. The direction of the weak diffracted beams is fixed by the orientation of the crystal, the size of the unit cell from which the crystal can be thought to be built, and the wavelength of the applied X-rays. The angle 2Θ between the diffracted beam and the beam passing through the crystal is given by 2 d sin θ = λ (1.2.1) where λ is the wavelength of the X-rays, and d is the interpianar spacing "?/• "--• • of the reflection planes. The value d can be calculated from the unit f cell constants by 2A' + k2B' + 12C' + 2klD' 21hE' 2hkF' (1.2.2) /..·;.ƒ,·';•• .-ir" •; - in which A', B', C', D', E' and F'.are related to the unit cell para- meters a, b, c, a, 0 and γ, and h, k, 1, the so-called Laue-indices, can •mm -•< • m -11- Η Λ forra any combination of three integers.
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