Síntese e caracterização de ligas de urânio U-Zr-Nb

Abstract

The main objective of this investigation was to provide subsidies to establish a long lasting strategy in the fabrication of metallic nuclear fuels based on alloys of the γ-(U, M', M") type - with M' and M" = transition metals - for nuclear power reactors of the compact PWR kind. In this sense, U-X(83Zr-17Nb) metallic alloys - with X = 38 - 60 wt.% - were arc melted and, in sequence, heat treated at different atmospheres and temperatures. At the end of the heat treatment, the annealed samples were quenched in water to room temperature. After each preparation step, the samples were characterized by X-ray diffraction - to identify the present crystalline phases - and by scanning electron microscopy or dispersive energy spectroscopy, to determine the resulting microstructure. The results showed that the as-melted samples crystallized mostly with the γ-(U, Zr, Nb) phase, presenting a considerably homogeneous microstructure. The exception was on account of the zirconium richest sample which revealed, besides the γ-(U, Zr, Nb) phase, a macro segregation of the ß-Zr phase. It was further observed that the quenching procedures originated a martensite phase (α") and induced the partial decomposition of the γ phase in the δ e α phases, in relative amounts that depended on X. In addition, the quenching produced a better-shaped grain boundary, with irregular precipitates along the boundaries and inside the grains.