Gamma decomposition and powder formation of 'gamma'-U8Mo nuclear fuel alloys

Abstract

Gamma uranium-molybdenum alloys have been considered as the fuel phase in plate type fuel elements for MTR reactors, mainly due to their acceptable performance under irradiation and metallurgical processing. To their use as a dispersion phase in aluminum matrix, a necessary step is the conversion of the as cast structure into powder, and the technique considered at IPEN / CNEN - Brazil is HDH (hydrationdehydration). This paper describes the first results of hydrogen absorption and its relation to powder formation of the γ-U8Mo alloy. After their production by induction melting, samples were thermally treated under constant flow of hydrogen for temperatures varying from 500oC to 600oC and times from 2 to 4 hours. Curves relating mass incorporation and time for the above temperatures were obtained, and the results were related to its fragmentation. It was observed that even after the dehydration, samples can be fragmented under specific conditions of isothermal treatments, and that there is a strong correlation between absorption and the rate of gamma decomposition. A value of 568,39oC was obtained for the maximum in the rate of gamma decomposition, which is related to the eutectoid transformation temperature of this alloy.