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Interesting Developments in UO{sub 2} Technology; Progres interessants dans la technologie du bioxyde d'uranium; Interesnye usovershenstvovaniya tekhnologii UO{sub 2}; Recientes progresos en la tecnologia del UO{sub 2}

Conference:

Abstract

Now that several UO{sub 2}-fuelled reactors are operating routinely, good irradiation performance of UO{sub 2} is taken for granted. It is therefore stimulating to find that significant developments are still occurring. Most exciting was the recent discovery by Battelle Memorial Institute workers that a particular single crystal of UO{sub 2} had a very high thermal conductivity at elevated temperatures. Following controversy over the matter, an irradiation at Chalk River demonstrated that the large grains formed in operating fuel elements do not necessarily exhibit this enhanced conductivity. Our laboratory experiments have shown that the enhancement is only present in hypostoichiometric compositions and depends little, if any, on the absence of grain boundaries. Indeed, the high conductivity can be obtained in polycrystalline sinters by controlling the stoichiometry. It has long been known that sheath elongation could be reduced by fabricating the UO{sub 2} pellets with depressions in their end faces. Later it was shown that movement of the fuel into a void at the end of the pellet stack was impeded by diametral expansion of the fuel and its mechanical interaction with the sheath. The biggest advance in minimizing sheath distensions has been the realization that longitudinal and diametral expansions are interrelated  More>>
Authors:
Robertson, J. A.L. [1] 
  1. Atomic Energy of Canada Ltd., Chalk River, Ontario (Canada)
Publication Date:
Nov 15, 1963
Product Type:
Conference
Resource Relation:
Conference: Conference on New Nuclear Materials Technology, Including Non Metallic Fuel Elements, Prague (Czech Republic), 1-5 Jul 1963; Other Information: 4 figs., 47 refs.; Related Information: In: New Nuclear Materials Including Non Metallic Fuel Elements. Vol. II. Proceedings of the Conference on New Nuclear Materials Technology, Including Non Metallic Fuel Elements| 586 p.
Subject:
36 MATERIALS SCIENCE; CHALK RIVER; FUEL ELEMENTS; FUELS; GRAIN BOUNDARIES; IRRADIATION; PLASTICS; POLYCRYSTALS; SINTERS; THERMAL CONDUCTIVITY; URANIUM DIOXIDE; XENON
OSTI ID:
22116360
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA13R0467073015
Submitting Site:
INIS
Size:
page(s) 57-75
Announcement Date:
Jul 29, 2013

Conference:

Citation Formats

Robertson, J. A.L. Interesting Developments in UO{sub 2} Technology; Progres interessants dans la technologie du bioxyde d'uranium; Interesnye usovershenstvovaniya tekhnologii UO{sub 2}; Recientes progresos en la tecnologia del UO{sub 2}. IAEA: N. p., 1963. Web.
Robertson, J. A.L. Interesting Developments in UO{sub 2} Technology; Progres interessants dans la technologie du bioxyde d'uranium; Interesnye usovershenstvovaniya tekhnologii UO{sub 2}; Recientes progresos en la tecnologia del UO{sub 2}. IAEA.
Robertson, J. A.L. 1963. "Interesting Developments in UO{sub 2} Technology; Progres interessants dans la technologie du bioxyde d'uranium; Interesnye usovershenstvovaniya tekhnologii UO{sub 2}; Recientes progresos en la tecnologia del UO{sub 2}." IAEA.
@misc{etde_22116360,
title = {Interesting Developments in UO{sub 2} Technology; Progres interessants dans la technologie du bioxyde d'uranium; Interesnye usovershenstvovaniya tekhnologii UO{sub 2}; Recientes progresos en la tecnologia del UO{sub 2}}
author = {Robertson, J. A.L.}
abstractNote = {Now that several UO{sub 2}-fuelled reactors are operating routinely, good irradiation performance of UO{sub 2} is taken for granted. It is therefore stimulating to find that significant developments are still occurring. Most exciting was the recent discovery by Battelle Memorial Institute workers that a particular single crystal of UO{sub 2} had a very high thermal conductivity at elevated temperatures. Following controversy over the matter, an irradiation at Chalk River demonstrated that the large grains formed in operating fuel elements do not necessarily exhibit this enhanced conductivity. Our laboratory experiments have shown that the enhancement is only present in hypostoichiometric compositions and depends little, if any, on the absence of grain boundaries. Indeed, the high conductivity can be obtained in polycrystalline sinters by controlling the stoichiometry. It has long been known that sheath elongation could be reduced by fabricating the UO{sub 2} pellets with depressions in their end faces. Later it was shown that movement of the fuel into a void at the end of the pellet stack was impeded by diametral expansion of the fuel and its mechanical interaction with the sheath. The biggest advance in minimizing sheath distensions has been the realization that longitudinal and diametral expansions are interrelated through the volume expansion of the fuel whose hot core is appreciably plastic. Our empirical knowledge of the factors determining the release of fission-product gases from UO{sub 2} has improved. In particular, increasing the irradiation exposure from 10{sup 15} to 10{sup 18} fissions/cm{sup 3} can reduce the apparent diffusion rates for xenon in UO{sub 2} during subsequent anneals by a factor of 10{sup 3}. The gas is probably immobilized in minute traps, some existing in the original material and some generated by irradiation damage. Detailed analysis indicated slow escape from the traps, presumably from the finite solubility of the xenon in UO{sub 2}. With the ability to perform in-reactor measurements a new phase of more meaningful experiments is just starting. These will determine whether any potential economic advantage lies in novel forms of fuel. Meanwhile, continuing development of sintered UO{sub 2} in the simple rod geometry will provide stiff competition. (author) [French] Maintenant que plusieurs reacteurs alimentes au bioxyde d'uranium sont en exploitation normale, on peut considerer que les performances nucleaires de cette matiere sont satisfaisantes et il faut se rejouir de voir se realiser encore de nouveaux progres dans cette branche de la technologie. L'evenement le plus remarquable dans ce domaine est assurement la decouverte des chercheurs de Battelle qui ont observe recemment qu'a haute temperature un monocristal de UO{sub 2} etait doue d'une tres forte conductivite thermique. A la suite d'une controverse sur ce point, une experience d' irradiation faite a Chalk River a montre que les grains de grande dimension formes dans des elements combustibles en fonctionnement ne presentent pas necessairement cette conductivite accrue. Les experiences de laboratoire ont revele que cette augmentation de la conductivite ne se presente que dans les compositions hypostoechiometriques et ne depend guere de l'absence de joint de grain. En fait, la forte conductivite peut etre obtenue dans des frittes polycristallins, si l'on maintient la composition stoechiometrique optimum. On sait depuis longtemps qu' il est possible de reduire rallongement des gaines en menageant des depressions sur chacune des bases des pastilles de UO{sub 2}; on a montre par la suite que si on laissait un vide aux extremites de l'empilement des pastilles, la tendance du combustible a remplir ce vide etait entravee par la dilatation diametrale des pastilles et leur interaction mecanique avec la gaine. On a realise un tres grand progres en vue de reduire los distensions de la gaine lorsqu'on s'est rendu compte que les dilatations longitudinales et diametrales etaient liees entre elles et etaient l'expression de la dilatation cubique du combustible dont le noyau chaud a une plasticite sensiblement elevee. Les connaissances empiriques sur les facteurs qui conditionnent le degagement de produits de fission gazeux liberes par UO{sub 2} ce sont ameliorees. On a constate notamment qu'en portant de 10{sup 15} a 10{sup 18} le nombre de fissions par cm{sup 3}, on peut abaisser d' un facteur de 10{sup 3} les vitesses apparentes de diffusion du xenon dans UO{sub 2}, au cours de recuits subsequents. Le gaz est probablement immobilise dans des pieges minuscules, les uns preexistant dans le materiau original, les autres resultant des dommages dus a l'irradiation. Une analyse minutieuse montre que le gaz s'echappe lentement des pieges, peut-etre en raison de la valeur finie de la solubilite du xenon dans UO{sub 2}. La possibilite que l'on a maintenant de faire des mesures en pile marque le debut d'une nouvelle serie d'experiences plus interessantes, qui permettront dorenavant de se rendre compte directement si la mise au point de nouveaux types de combustible offre des avantages economiques. En attendant, les efforts se poursuivront, suscitant une competition serree, pour ameliorer les elements en bioxyde d'uranium fritte, composes de barreaux en geometrie simple. (author) [Spanish] Ahora que funcionan regularmente varios reactores alimentados con UO{sub 2}, el buen rendimiento de este material frente a la irradiacion se da por supuesto. Por ello, es estimulante observar que todavia se producen novedades significativas en este terreno. Una de las mas interesantes fue el descubrimiento, recientemente realizado por los investigadores del Instituto Battelle, de que determinados monocristales de UO{sub 2} poseen gran conductibilidad termica a temperaturas elevadas. A raiz de la controversia habida sobre la materia, un experimento de irradiacion efectuado en Chalk River demostro que los granos de gran tamafio que se forman en el curso de la irradiacion de los elementos combustibles no presentan necesariamente ese aumento de conductibilidad. Los experimentos realizados en el laboratorio del autor han demostrado que dicho aumento se produce solamente en las composiciones hipoestequiometricas y es independiente, o depende escasamente, de la inexistencia de bordes de los granos. En efecto, esa conductibilidad elevada puede obtenerse en cuerpos poiicristalinos sinterizados por modincacion de sus proporciones estequiometricas. Se sabe desde hace tiempo que el alargamiento de las vainas podia aminorarse elaborando pastillas de UO{sub 2} con depresiones en las caras de los extremos. Mas tarde se demostro que la dilatacion diametral del combustible y su interaccion mecanica con la vaina impedia el desplazamiento del combustible hacia el hueco existente en e l extremo del paquete de pastillas. El progreso mas decisivo para reducir al minimo las distensiones de las vainas ha sido advertir que las dilataciones longitudinales y diametrales estan mutuamente relacionadas por la dilatacion volumetrica del combustible, cuyo nucleo caliente es sensiblemente plastico. Ha mejorado nuestro conocimiento empirico de los factores que determinan el escape de productos de fision gaseosos del UO{sub 2}. En particular, si el grado de irradiacion aumenta de 10{sup 15} a 10{sup 18} fisiones/cm{sup 3}, los indices de difusion aparente del xenon en el UO{sub 2} pueden presentar un valor mil veces inferior en el curso de recocidos subsiguientes. El gas queda probablemente inmovilizado en diminutas trampas de las cuales algunas existen ya en el material original, mientras que otras se deben a loe danos provocados por las radiaciones. Un analisis minucioso permite apreciar pequeflos escapes de las trampas, debidos probablemente a la solubilidad finita del xenon en el UO{sub 2}. Ahora que se da la posibilidad de realizar mediciones en el reactor, se esta iniciando una nueva fase de.experimentos mas significativos, que permitiran determinar si las nuevas formas de combustible pueden ofrecer alguna ventaja economica. Mientras tanto, el continuo perfeccionamiento de las barras combustibles de UO{sub 2} sinterizado en geometrias simples dara lugar a una renida competencia. (author) [Russian] Sejchas, kogda neskol'ko reaktorov, v kotorykh toplivom sluzhit UO{sub 2}, nakhodyatsya v postoyannoj ehkspluatatsii, khoroshie radiatsionnye -svojstva UO{sub 2} ne nuzhdayutsya v dokazatel'stve. Priyatno uznavat' o tom, chto vazhnye usovershenstvovaniya eshche poyavlyayutsya. Naibolee znachitel'nom za poslednee vremya yavilos' otkrytie sotrudnikami istituta Behttely ochen' vysokoj teploprovodnosti otdel'nogo odinochnogo kristalla UO{sub 2} pri povyshennykh temperaturakh. Provedennoe v svyazi s raskhozhdeniem mnenij po ehtomu voprosu obluchenie v Chok-Rivere pokazalo, chto bol'shie zerna, obrazuyushchiesya v rabotavshikh toplivnykh ehlementakh, ne obyazatel'no obladayut ehtoj povyshennoj provodimost'yu. Ehksperimenty nashej laboratorii pokazali, chto povyshenie imeet mesto tol'ko v podstekhiometricheskikh soedineniyakh i malo zavisit, esli voobshche zavisit, ot otsutstviya granits zeren. Bezuslovno, vysokaya provodimost' mozhet byt' poluchena v polikristallicheskikh spekshikhsya materialakh putem regulirovaniya stekhiometrii. Davno izvestno, chto udlinenie obolochki mozhno umen'shit', esli izgotovit' tabletki ieh UO{sub 2} s uglubleniyami na tortsovykh poverkhnostyakh. Pozzhe bylo pokazano, chto smeshcheniyu topliva v pustoe prostranstvo v kontse trubki s tabletkami meshaet diametral'noe rasshirenie topliva i ego mekhanicheskoe vzaimodejstvie s obolochkoj. Samym bol'shim dostizheniem v otnoshenii svedeniya k minimumu rasshireniya obolochki yavilos' uyasnenie togo, chto prodol'noe, i diametral'noe rasshireniya vzaimosvyazany cherez posredstvo ob{sup e}mnogo rasshireniya topliva, goryachaya serdtsevina kotorogo dovol'no plastichna. Rasshirilis' nashi prakticheskie znaniya faktorov, opredelyayushchikh vydelenie iz UO{sub 2} gazov, yavlyayushchikhsya produktami deleniya. V chastnosti, uvelichenie oblucheniya s 10{sup 15} do 10{sup 18} delenij/cm{sup 2} mozhet snizit' ochevidnye skorosti diffuzii dlya ksenona v UO{sub 2} pri posleduyushchikh obzhigakh na koehffitsient 10{sup 3}. Gaz, po-vidimomu, uderzhivaetsya v mel'chajshikh lovushkakh, chast' iz kotorykh sushchestvuet v iskhodnom materiale, a chast' obrazuetsya v rezul'tate radiatsionnogo povrezhdeniya. Tshchatel'nyj analiz pokazal sushchestvovanie medlennoj utechki iz lovushek, chto, veroyatno, ob''yasnyaetsya ogranichennoj rastvorimost'yu ksenona v UO{sub 2}. Vozmozhnost' osushchestvleniya izmerenij v reaktore otkryvaet novuyu fazu eshche bolee vazhnykh ehksperimentov. Oni pokazhut, imeyutsya li kakie-libo potentsial'nye ehkonomicheskie preimushchestva v novykh formakh topliva. V to zhe vremya budut prodolzhat'sya nastojchivye razrabotki spechenoj UO{sub 2} v prostoj geometrii sterzhnya. (author)}
place = {IAEA}
year = {1963}
month = {Nov}
}