This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour. Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present. Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly. To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation. <b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM

For many decades zirconium alloys have been commonly used in the nuclear power industry as fuel cladding material. Besides their good corrosion resistance and acceptable mechanical properties the main reason for using these alloys is the low neutron absorption. Zirconium alloys are exposed to a very severe environment during the nuclear fission process and there is a demand for better design of this material. To meet this requirement a thermodynamic database is useful to support material designers. In this thesis some aspects of the development of a thermodynamic database for zirconium alloys are presented. A thermodynamic database represents an important facility in applying thermodynamic equilibrium calculations for a given material providing: 1) relevant information about the thermodynamic properties of the alloys e.g. amount and composition of phases, oxygen activity, heat capacity etc, and 2) significant information for the manufacturing process e.g. heat treatment temperature. The basic information in the database is first the unary data, i.e. pure elements; those are taken from the compilation of the Scientific Group Thermodata Europe (SGTE) and then the binary and ternary systems. All phases present in those binary and ternary systems are described by means of the Gibbs energy as a function of composition and temperature. Many of those binary systems have been taken from published or unpublished works and others have been assessed in the present work. The elements included in the databse are: C, Fe, Cr, Nb, Ni, Mo, O, Si, Sn, and Zr + H, and the assessment performed under this thesis are: Cr-Sn, Mo-Zr, Sn-Zr, Fe-Nb-Zr and Nb-O-Zr. All the calculations have been made using Thermo-Calc software and the representation of the Gibbs energy obtained by applying Calphad technique with some use of ab initio calculations. / QC 20100902

<p>This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour.</p><p>Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present.</p><p>Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly.</p><p>To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation.</p><p><b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM</p>

La durabilité et l’intégrité des matériaux employés au sein des installations du parc électronucléaire est une préoccupation permanente des exploitants de centrales. Lors de l’irradiation du combustible dans des réacteurs à eau pressurisée (REP), l’ensemble combustible-gaine est sujet à de nombreuses modifications induites par l’irradiation. En particulier, la dilatation des éléments combustibles, concomitante au fluage en compression du gainage, conduit à la mise en contact de ces matériaux, permettant l’oxydation de la surface interne de la gaine, d’abord de manière ponctuelle, affectant à terme la quasi-totalité de la surface interne avec le temps. A fort taux de combustion, on constate une liaison de la périphérie du combustible avec le gainage métallique, constituant le phénomène d’accrochage combustible-gaine et conditionnant les transferts thermiques ainsi que le comportement mécanique des crayons combustibles. L’objectif principal de ce travail de thèse est d’approfondir les connaissances sur l’interaction physico-chimique combustible-gaine, en déterminant notamment l’origine de leur adhésion ainsi que son évolution en fonction du taux de combustion. A cet effet, des études d’inter-diffusion sur des matériaux modèles hors et sous irradiation ionique ont été réalisées, en complément de caractérisations détaillées d’interfaces combustible|gaine d’échantillons irradiés en REP. La comparaison des résultats obtenus sur matériaux modèles avec ceux obtenus sur échantillons irradiés en REP, permettent de formuler de solides hypothèses sur la nature, l’origine et l’évolution de l’accrochage combustible-gaine en REP. / Durability and integrity of materials used in nuclear power plants is a continuous concern of the nuclear power plant owners and developers. During the fuel irradiation in pressurised water reactors (PWR), the whole fuel-clad assembly is subjected to several irradiation-induced modifications. In particular, the fuel element expansion concomitant to the cladding creeping, leads to the contacting of both materials, allowing the oxidation of the inner side of the clad, locally at first, then tending to affect the overall cladding inner surface. At high burnup, a bonding of the fuel periphery with the metallic cladding can be observed, forming the fuel-clad bonding phenomenon, which conditions the thermal transfers and the mechanical behaviour of the fuel rods. The main objective of this PhD, is to further the knowledges of the physic-chemical interaction between fuel and clad, by identifying especially the origin of their bonding and its evolution with burnup. For that purpose, studies on inter-diffusion couples were performed on model materials both under ionic irradiation and not, completing detailed characterisations of the fuel|clad interface of samples irradiated in PWR. Comparison of the results obtained on model materials with those obtained on samples irradiated in PWR, allows making reliable assumptions on the nature, the origin and the evolution of the fuel-clad bonding in PWR.

Dans les Réacteurs à Eau Pressurisée (REP), en conditions hypothétiques accidentelles d'Accident de Perte de Réfrigérant Primaire, les gaines de combustible en alliage de zirconium subissent une oxydation importante à haute température. Pour ralentir ce phénomène, le CEA développe et étudie des gaines innovantes revêtues de chrome. Cependant, l'intégrité du revêtement doit être maintenue en service et notamment sous irradiation aux neutrons. L'objectif principal de la thèse est d'étudier le comportement sous irradiation de ce concept de gainage. On s'intéresse en particulier à la microstructure de l'interface Zr/Cr avant et après irradiation puisque cette dernière régit l'adhérence du dépôt au substrat. Des irradiations aux ions ont été effectuées afin de simuler le dommage causé par les neutrons dans un REP. Une approche multi-échelle est utilisée pour caractériser les échantillons avant et après irradiation. En particulier, la Microscopie Electronique en Transmission (MET) a permis de caractériser finement la microstructure de l'interface Zr/Cr. Un premier type d'interface Zr/Cr est observé et montre la présence de phases nanométriques de types Zr(Fe,Cr)2 C14 et ZrCr2 C15. Après irradiation, la phase C14 serait stabilisée, au détriment de la phase C15, par ségrégation du fer à l'interface. Pour une seconde interface, obtenue dans des conditions de dépôt différentes, seule la phase C15 est observée. Sous irradiation in-situ au MET, une dissolution de cette phase est constatée. Dans tous les cas, la conservation des continuités de plans cristallographiques à travers l'interface avant et après irradiation permet de conclure à une bonne adhérence du revêtement au substrat. / In Light Water Reactors (LWR) under hypothetical accidental conditions such as LOss of Coolant Accident (LOCA), zirconium alloy fuel claddings undergo significant oxidation at high temperatures. To limit this phenomenon, innovative chromium coated nuclear fuel claddings are studied at CEA. However, the integrity under neutron irradiation of such coating for in-service conditions must be preserved..The main objective of this PhD work is to study the behavior under ion irradiation of this new cladding concept. We especially focus on Zr/Cr interface microstructure evolution under irradiation, since the latter controls the adhesion of the coating to the substrate. Ion irradiations were performed to simulate the damage caused by neutrons in LWR. A multi-scale approach is used to characterize the samples before and after irradiation. In particular, Transmission Electron Microscopy (TEM) was used to characterize, at an atomic scale, the microstructure of the Zr/Cr interface. A first type of Zr/Cr interface is observed and shows the presence of nanometric phases of Zr(Fe,Cr)2 C14 and ZrCr2 C15 types. After irradiation, the C14 phase seems to be stabilized over the C15 phase, by segregation of iron at the interface. For a second interface, obtained using different deposition conditions, only C15 phase is observed. Under in-situ TEM irradiation, dissolution of the C15 phase is observed. Whatever the Zr/Cr interface type, preservation of the continuity of crystallographic planes before and after irradiation throughout the interface is demonstrated and thus induces a good adhesion of the coating to the substrate.

Made available in DSpace on 2014-10-09T12:42:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:07Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Made available in DSpace on 2014-10-09T12:42:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:07Z (GMT). No. of bitstreams: 0 / Biomateriais para uso em implantes devem exibir propriedades como biocompatibilidade, biofuncionalidade e resistência à corrosão. O uso do titânio e suas ligas em aplicações biomédicas vem continuamente aumentando devido à sua maior taxa resistência-peso, superior biocompatibilidade e resistência à corrosão, boas propriedades mecânicas e baixo módulo de elasticidade quando comparado a outros materiais biomateriais metálicos como aço inox e ligas Co-Cr. Um importante aspecto para o sucesso de um implante é a utilização de materiais com módulo de elasticidade baixo, próximo ao do osso, pois estudos indicam que a transferência insuficiente de carga entre implante e osso pode resultar em reabsorção óssea e afrouxamento do implante, que é chamado efeito de blindagem de tensão (stress shielding effect). A liga ternária Ti13Nb13Zr apresenta em sua composição somente elementos considerados biocompatíveis, possui menor módulo de elasticidade que ligas Co-Cr, aço inox e Ti6Al4V, e superior resistência à corrosão. Neste trabalho foi estudado o efeito do teor de nióbio e zircônio nas propriedades mecânicas da liga ternária TiNbZr numa faixa de composições com quantidade de titânio constante em 74 %peso e teor de Nb e Zr variando entre 6 e 20 %peso, produzida por metalurgia do pó a partir de pós hidrogenados e método de mistura elementar, após diferentes condições de processamento e tratamentos térmicos. Os resultados de caracterização microestrutural obtidos por MEV e difração de raios X mostraram que o aumento do teor de Nb não produziu alterações significativas na fração volumétrica das fases e e, o aumento do teor de Zr proporcionou o aumento da fração de fase , favorecendo a formação da estrutura de Widmanstätten. O aumento dos teores de Nb e Zr produziram alterações nas microestruturas dos materiais que levaram ao aumento dos valores de módulo de elasticidade e dureza, e com aumento do teor de Zr houve aumento da susceptibilidade à corrosão. Nas condições de processamento utilizadas, a liga Ti13Nb13Zr apresentou as propriedades mecânicas e microestruturais mais indicadas para utilização como biomateriais. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-08-25T17:43:02Z No. of bitstreams: 0 / Made available in DSpace on 2016-08-25T17:43:02Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nesse trabalho foi proposto investigar a estabilidade de fases do sistema zircônia-escândia (ScSZ) por meio do estudo termodinâmico de nanopartículas, na faixa de 0 a 20% em mol de Sc2O3, e a partir da introdução de um segundo aditivo (Dy2O3 e Nb2O5) ao ZrO2 contendo 10% em mol de Sc2O3 (10ScSZ). A estabilidade de fases do ScSZ foi avaliada com base em dados termodinâmicos determinados pelas técnicas de microcalorimetria de adsorção de água e calorimetria de dissolução à alta temperatura. As soluções sólidas foram sintetizadas pelo método de coprecipitação de hidróxidos. Dados termodinâmicos foram determinados para as formas polimórficas encontradas (monoclínica, tetragonal, cúbica, romboédrica &beta; e &gamma;) por difração de raios X no ScSZ. Esse trabalho resultou no diagrama de fases em nanoescala de tamanho de partícula-composição. Os efeitos produzidos pela introdução de aditivos na matriz de 10ScSZ foram investigados visando obter a possível estabilização da estrutura cúbica (c) e a supressão da transformação de fase c-&beta;, característica do sistema binário. As composições foram sintetizadas por coprecipitação de hidróxidos e por reações em estado sólido para fins comparativos. Os materiais foram sinterizados convencionalmente e por sinterização assistida por campo elétrico. A estabilização completa da fase cúbica ocorreu a partir de teores molares de 1% de Dy2O3 e 0,5% de Nb2O5. O menor teor de Nb2O5 necessário para a estabilização da fase foi atribuído à provável formação da fase líquida durante a sinterização e ao menor tamanho do íon Nb5+. Os resultados de difratometria de raios X em alta temperatura e análise térmica mostraram que houve supressão da transição c-&beta;. As amostras contendo 0,5% mol de Nb2O5 apresentaram valores de condutividade iônica similares aos do 10ScSZ sem aditivos em uma ampla faixa de temperatura com elevada estabilidade em um período de 170 h a 600 °C. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP: 12/03319-5