The generation of electricity in light water nuclear power plants uses zirconium alloys as the primary containment and cladding of the nuclear fuel. The environmental impacts of the production of zirconium alloys have been analyzed form a lifecycle perspective. From the mining of the zirconium-bearing mineral zircon to the finished zirconium alloy tube. A qualitative study indentifying the production processes and their potential environmental impacts have been performed. A quantitative study to perform a lifecycle analysis of the zircon mining and mineral separation was carried out. The life cycle analysis for the zircon mining was compared to the current lifecycle analysis (LCA) in Vattenfall's Forsmark nuclear power plant environmental product declaration (EPD). The results showed that the additional impact on Forsmark's EPD, when including the mining of zircon, is below 0.1% of the current levels for all parameters analyzed. A lifecycle analysis for the production of zirconium metal and zirconium alloy tube could not be performed due to lack of data from the zirconium metal industry. The major direct emissions from the zircon mining industry are related to the use of fossile fuels in machinery. The major direct emissions from the zirconium metal manufactoring industry are related to the use of acids.

Lors d’un scénario hypothétique d’Accident par Perte de Réfrigérant Primaire (APRP), les gainages combustibles en alliage de zirconium subissent des sollicitations thermomécaniques sévères dans des environnements chimiques très oxydants. L’évolution des conditions de pression et de température ainsi que la présence du fluide réfrigérant peuvent entraîner dans un premier temps le ballonnement-éclatement puis l’oxydation sous vapeur et la prise d’hydrogène à haute température ainsi que des chargements mécaniques axiaux lors du renoyage final.L’objectif de la thèse est d’identifier les mécanismes et les paramètres clés qui gouvernent la rupture lors de la phase de renoyage sous traction. Des essais semi-intégraux, visant à reproduire un scénario APRP sur des tronçons de gaines de Zircaloy−4, ont été réalisés afin d’étudier le comportement de ce matériau dans de telles conditions.Un seuil fonction de la durée d’oxydation à haute température, à partir duquel la gaine rompt lors du renoyage, est mis en évidence. Deux lieux de rupture sont identifiés : la zone ballonnée où l’oxydation est maximale et la prise d’hydrogène nulle, ainsi que la zone dite « d’hydruration secondaire », sous la zone ballonnée, où la prise d’hydrogène est conséquente et l’oxydation moindre. Par ailleurs, un scénario de la rupture par rapport à la chronologie du renoyage a été établi.Cependant, le traitement macroscopique de ces essais ne permet pas de discriminer ces deux lieux de rupture, car la rupture intervient indépendamment dans le ballon et hors zone ballonnée en fonction du transitoire appliqué et de la morphologie du ballonnement-éclatement. Une approche locale a été mise en place, à partir de la caractérisation microstructurale et fractographique systématique des éprouvettes d’essai, afin d’établir un critère de rupture dépendant de l’état du matériau.La distribution complexe des éléments chimiques et des phases dans l’épaisseur de la gaine a été déterminée. Les changements de phase dans le ballon fortement oxydé, menant à une microstructure globalement fragile, ont été explicités. Une loi de seuil à rupture, en zone d’hydruration secondaire, a été identifiée à l’aide des mesures d’épaisseurs de phases et du profil de teneur en hydrogène. / During hypothetical Loss-Of-Coolant-Accident (LOCA) scenarios, zirconium alloy fuel cladding tubes are subjected to severe thermo- mechanical loading conditions in highly oxidising chemical environments. Pressure and temperature evolution together with cooling water can lead to ballooning and burst followed by steam oxidation and hydrogen uptake at high temperature, and then axial loading during the final reflooding stage.This study focuses on the identification of mechanisms and key parameters which drive cladding fracture during the reflooding stage under axial tensile load.Laboratory-scale semi-integral tests simulating LOCA transients on Zircaloy−4 test rods have been realised. A fracture/no-fracture threshold of oxidation duration at high temperature has been determined. Two fracture locations have been identified: i) the burst zone with maximal oxidation and no hydrogen uptake, and ii) the “secondary hydriding” zone below the burst zone, with substantial hydrogen absorption and lower oxidation levels. Moreover, a scenario of fracture as a function of the reflooding chronology has been identified. Nevertheless, the macroscopic treatment of these tests has not permitted to discriminate these two fracture locations because fracture independently occurs in and out of the burst zone, whatever the applied transient and the balloon and burst morphologies.From systematic microstructural and fractographic characterisation of test specimens, a local approach aiming at identifying a fracture threshold as a function of the microstructural state of the material has been applied. The complex distribution of chemical elements and phases across the cladding thickness has been determined. Phase transformations in the highly-oxidised balloon, leading to a globally brittle microstructure have been explicated. In the secondary hydriding zone, a fracture threshold criterion has been identified by means of layer thickness measurements and hydrogen uptake profile.

Effect of electrochemical absorption of hydrogen has been studied on the Zr-based amorphous alloys. The influence of hydrogen absorption on the stability of the amorphous phase and its crystallisation was investigated. Additionally, the cathodic hydrogen reaction mechanism on the surface of the alloy, the reversibility of the absorbed hydrogen and the hydrogen diffusion in the alloy were studied. These alloys are able to absorb large amounts of hydrogen (>1:1 hydrogen to metal ratio) but a rearrangement of the amorphous matrix takes place so that Cu rich areas are detected on the surface and Zr-hydride may precipitate. The thermal stability and crystallisation behaviour depends on the hydrogen concentration in the alloy. At low hydrogen concentration, the thermal stability deteriorates and primary crystallisation of Cu and/or Cu-rich phases is observed. At high hydrogen concentration, primary crystallisation of Zr-hydride takes place. The cathodic polarisation behaviour of amorphous Zr-based alloys as derived from Tafel plots reveals three characteristic potential regions reflecting the different mechanisms of hydrogen on the surface. In the Tafel region, hydrogen discharge and adsorption takes place on the alloy surface as fast steps reactions followed by the rate determining electrodic desorption reaction step in competition with hydrogen absorption as a fast step. In the further negative potential region, the current density is independent on the potential as both the Volmer and the Heyrowsky reactions take place at the same rate and the hydrogen mass transfer from the solution to the electrode surface is the rate-determining step. In the high polarisation region, all the partial hydrogen reactions take place intensively. The reversibility of the absorbed hydrogen tests reflects the possibility of hydrogen desorption from different energy sites in the amorphous alloy. The diffusion of hydrogen in the Zr-based alloys is comparable with that in the crystalline Pd and it is reduced in the pre-hydrogenated samples.

Le procédé VAR (Vacuum Arc Remelting ou refusion à l'arc sous vide en français) est employé dans la production d'alliages à haute performance pour les industries aéronautique (aciers spéciaux, superalliages et alliages de titane) et nucléaire (alliage de zirconium). Comme pour tous les procédés de fonderie, la maîtrise de l'homogénéité chimique et de la structure métallurgique des lingots coulés par le procédé VAR constitue un enjeu industriel important. Les travaux présentés dans ce mémoire visent à identifier, pour les alliages de zirconium en particulier, les effets de la convection naturelle et de la convection forcée due au brassage électromagnétique sur la macroségrégation. Dans ce but, un modèle numérique a été développé. Il est basé sur la résolution couplée des équations de conservation d'énergie, de quantité de mouvement et de solutés, dans des conditions d'écoulement laminaire ou turbulent. La modélisation de la solidification tient compte du couplage fort entre le transport d'énergie et de solutés dans la zone pâteuse. Afin de décrire la microségrégation, la diffusion restreinte des solutés dans les phases liquides et solides peut être prise en compte. Parallèlement, deux électrodes chimiquement homogènes d'alliages Zircaloy-4 et M5® ont été spécialement refondues dans un four VAR industriel sur le site de CEZUS à Ugine (Savoie, France). La macroségrégation des lingots obtenus a été caractérisée.La comparaison entre les mesures expérimentales et les résultats de simulation a montré que pour un alliage dont l'intervalle de solidification est important (comme l'alliage Zircaloy-4), la convection solutale dans la zone pâteuse peut avoir une influence essentielle sur la macroségrégation de la région centrale du lingot. Par ailleurs, le mouvement de grains équiaxes lors de l'application d'un brassage électromagnétique de forte intensité semble accentuer significativement la macroségrégation dans la région externe du lingot. Pour un alliage dont l'intervalle de solidification est faible (comme l'alliage M5®), nous avons montré que la macroségrégation dépend plus spécifiquement de la convection forcée due au mode de brassage électromagnétique appliqué au cours de la refusion / Vacuum Arc Remelting (VAR) is used to produce high performance alloys for the aeronautic (special steels, superalloys, titanium alloys) and nuclear (zirconium alloys) industries. As for all casting processes, the control of the chemical homogeneity and the metallurgical structure in VAR ingots is an important industrial issue. The goal of this thesis is to identify, for zirconium alloys in particular, the effects of the natural convection and the forced convection due to the electromagnetic stirring on macrosegregation. To this purpose, a numerical model has been developed. It is based on the solution of the coupled transient energy, momentum and solute transport equations, under laminar or turbulent flow conditions. The solidification modeling accounts for a full coupling between energy and solute transport in the mushy zone. The finite diffusion of solutes in both solid and liquid phases can be taken into account to describe microsegregation. In addition, chemically homogeneous Zircaloy-4 and M5® electrodes have been specially remelted in an industrial VAR furnace at the CEZUS plant in Ugine (Savoie, France). The macrosegregation of the ingots has been measured. The comparison between the experimental measurements and the simulation results showed that for an alloy with a large solidification interval (like Zircaloy-4), the solutal convection in the mushy zone could have an essential influence on the macrosegregation in the inner part of the ingot. Furthermore, the motion of equiaxed grains caused by a strong stirring seems to seriously intensify macrosegregation in the outer part of the ingot. For an alloy with a small solidification interval (like M5®), we have shown that the macrosegregation depends more specifically on the forced convection due to the type of stirring applied during the remelting

Effect of electrochemical absorption of hydrogen has been studied on the Zr-based amorphous alloys. The influence of hydrogen absorption on the stability of the amorphous phase and its crystallisation was investigated. Additionally, the cathodic hydrogen reaction mechanism on the surface of the alloy, the reversibility of the absorbed hydrogen and the hydrogen diffusion in the alloy were studied. These alloys are able to absorb large amounts of hydrogen (>1:1 hydrogen to metal ratio) but a rearrangement of the amorphous matrix takes place so that Cu rich areas are detected on the surface and Zr-hydride may precipitate. The thermal stability and crystallisation behaviour depends on the hydrogen concentration in the alloy. At low hydrogen concentration, the thermal stability deteriorates and primary crystallisation of Cu and/or Cu-rich phases is observed. At high hydrogen concentration, primary crystallisation of Zr-hydride takes place. The cathodic polarisation behaviour of amorphous Zr-based alloys as derived from Tafel plots reveals three characteristic potential regions reflecting the different mechanisms of hydrogen on the surface. In the Tafel region, hydrogen discharge and adsorption takes place on the alloy surface as fast steps reactions followed by the rate determining electrodic desorption reaction step in competition with hydrogen absorption as a fast step. In the further negative potential region, the current density is independent on the potential as both the Volmer and the Heyrowsky reactions take place at the same rate and the hydrogen mass transfer from the solution to the electrode surface is the rate-determining step. In the high polarisation region, all the partial hydrogen reactions take place intensively. The reversibility of the absorbed hydrogen tests reflects the possibility of hydrogen desorption from different energy sites in the amorphous alloy. The diffusion of hydrogen in the Zr-based alloys is comparable with that in the crystalline Pd and it is reduced in the pre-hydrogenated samples.

In this work a manufacturing method for UN, ZrN and (U,Zr)N pellets was established at the nuclear fuel laboratory at KTH Stockholm/Sweden, which consists of the production of nitride powders and their sintering into pellets by spark plasma sintering. The nitride powders were produced by the hydriding-nitriding route using pure metal as starting material. This synthesis was performed in a stream of the particular reaction gas. A synthesis control and monitoring system was developed, which can follow the reactions in real time by measuring the gas flow difference before and after the reaction chamber. With the help of this system the hydriding and nitriding reactions of uranium and zirconium were studied in detail. Fine nitride powders were obtained; however, the production of zirconium nitride involved one milling step of the brittle zirconium hydride. Additionally uranium and zirconium alloys with different zirconium contents were produced and synthesized to nitride powders. It was found that also the alloys could be reduced to fine powder, but only by cyclic hydriding-dehydriding. Pellets were sintered out of uranium nitrides, zirconium nitrides, mixed nitrides and alloy nitrides. These experiments showed that relative densities of more than 90% can easily be achieved for all those powders. Pellets sintered from mechanically mixed nitride powders were found to still consist of two separate nitride phases, while nitride produced from alloy was demonstrated to be a monophasic solid solution both as powder and as sintered pellets.