Papers by Author: Elita F. Urano de Carvalho

Abstract: New nuclear fuel material with high density in uranium is envisaged for intense irradiation research reactors. The alloy U-Mo has been researched as a feasible candidate to be used in such reactors. This nuclear fuel is conceived to be used encapsulated in aluminum matrix. Nevertheless, there are interaction products of U-Mo/Al which form porosity during irradiation, leading to routine operation harms in research reactors. This interaction is due to solid solution interdiffusion of species, mainly of Al towards U-Mo region forming reaction products. This interaction could be studied by on-pile method, observing the occurrence of formed products during irradiation, but this method is costly and used only for long term experiments in very few reactors in the world. For this, several out-of-pile studies using heat treatments of diffusion pairs are carried out at adequate temperatures and times, just below the -phase eutectoid temperature to simulating the interdiffusion and formation U-Mo-Al phases. In the present study, it was employed a new developed assembling method to prepare interdiffusion pairs by immersing sliced U-10Mo sticks inside molten Al. These samples are made by induction furnace, in temperature range ~660-670 °C, under controlled argon atmosphere, in order to entrap molten Al around U-Mo sticks and so keeping this entangled structure after solidification. The interdiffusion pairs are then cut and prepared for treatments. This novel sample preparation guarantees full contact between the U-Mo and Al without oxidation contact, creating so, the ideal conditions for interdiffusion investigation of the interfaces of Al/U-Mo. Preliminary results to study interaction products where achieved by heat treatments during 5h at 550°C. Observations and calculations from SEM/EDS microstructures and XRD diffractograms revealed few microns interaction layer between the matrix and the fuel material, resembling phases reported in the literature for the interaction products between U-Mo-Al. This layer is mainly composed by Al and U, Mo phases, probably (U, Mo)Al3 and phases containing Si, as U3Si5 and a proposed one Al2Si3U3 that fits better to XRD spectrum of experimented diffusion pairs.

Abstract: Powdered uranium silicide (U3Si2) 20% U235 enriched is an intermetallic compound used as nuclear fuel material dispersed in aluminum to be the meat of fuel elements. U3Si2 powder is the state-of-the-art as nuclear fuel material mostly used in modern research reactors. Its recent established fabrication in IPEN replaced the previous ceramic powder U3O8 used in the fuel of IEAR1 (IPEN/CNEN, São Paulo, Brazil). The U3Si2 is a compound with 92.3%wtU and 7.7%wtSi. Its production is made by induction furnace melting using metallic uranium, produced by magnesiothermic reaction, and pure silicon. The induction furnace melts under argon controlled environment using zirconia crucible. Homogenization of liquid bath at 1800°C is a compromise between crucible resistance and homogenized melting, avoiding hazardous happenings. IPEN produced its first lot of enriched U3Si2 in September 2004, with a continuous fabrication ever since. This research work represents the ability of having fully Brazilian supply of this strategic and high cost nuclear material. The fuel quality meets the world quality standards required by International Atomic Energy Agency (IAEA) and RERTR standards. Brazilian production of U3Si2 powder not only closed the fuel cycle, from uranium mineral to fuel element, but also allowed higher productivity of nuclear medicine radioisotopes by IEA-R1.