Abstract
Generally, the atomization of UMo particles is done under vacuum or argon atmosphere, and the surface modification of these UMo particles is, usually, carried on through a further process. The techniques for surface modification of atomized UMo particles, aimed to control the Fuel/Matrix interaction, involve, in some cases, complex methodologies and often with minor effect due to the limited solubility of third elements in solid UMo alloy. The atomization and surface conditioning, applied in separate stages, may affect the efficiency of powder production process. Then, the main goal of this study is to explore the surface modification of UMo particles in liquid state or during the solidification that follows the centrifugal atomization process. Through the change of atomization atmosphere, could be possible to promote liquid/gas reactions, with a higher solubility of the modifier element in micro drops of UMo alloy, before they become solid particles. This paper presents comparative results of centrifugal atomization of UMo particles, carried out under inert argon and reactive nitrogen atmospheres. Dissolved nitrogen contents, measured by SEM-EDS analyses, reached up to 7.57 wt% at the center of under nitrogen atomized particles, very higher than 0.84 wt% of nitrogen measured at the center of UMo particle atomized under argon. The presence of uranium nitride was partially verified by conventional XRD analysis. Nevertheless, Out-of-Pile interaction test result, reveals decreasing of aluminium contents into UMo particles atomized under nitrogen atmosphere; Just 3.77 wt% of Al was the maximum content detected in the center of these particles, very lower than 29.11 wt% of Al measured inside UMo particles atomized under argon. Finally, it is possible to conclude that the atomization under reactive atmosphere may modify the surface composition and the behavior of UMo fuel particles dispersed in aluminium, for dispersion type nuclear fuel application.
Highlights
The qualification of high density nuclear fuel based on UMo alloy requires, necessarily, solve the fuel/matrix interaction issues
According to the available literature, several methodologies have been developed for surface coating of UMo particles, some of them based on solid-solid reactions, as the pack cementation technique to form silicon-rich surface layers [3], others based on solid-gas reactions, such as thermal treatments under nitrogen atmosphere to form uranium nitride layers [4], and solid-plasma reactions, such as PVD or CVD applied to the formation of Zr or ZrN layer [5]
The most generalized method and, apparently, the most proper for UMo alloy particles production, the goal of this study is to propose the modification of the surface of UMo particles, during the atomization process, in which the alloy is, by short time, in liquid state
Summary
The qualification of high density nuclear fuel based on UMo alloy requires, necessarily, solve the fuel/matrix interaction issues. According to the available literature, several methodologies have been developed for surface coating of UMo particles, some of them based on solid-solid reactions, as the pack cementation technique to form silicon-rich surface layers [3], others based on solid-gas reactions, such as thermal treatments under nitrogen atmosphere to form uranium nitride layers [4], and solid-plasma reactions, such as PVD or CVD applied to the formation of Zr or ZrN layer [5] All these methodologies are carried out with UMo fuel particles in solid state, which limits the solubility of the element added to modify the surface. According to the analysis of Bugl J. et al [6], the uranium would form a eutectic with the UN, so that the solubility could be even lower at the annealing temperatures applied for particles surface coating
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