Manufacturing low enriched uranium metal by magnesiothermic reduction of UF4

摘要

This work presents an experimental description of thermal and physical studies to attain a practical manufacturing process of uranium metal enriched to 20% U-235 (LEU - Low Enriched Uranium) by metallothermic reduction of UF4, with nuclear purity, for reduced amounts (1000 g of uranium) and with radioactive safety. Uranium metal is needed to produce nuclear fuel elements based on uranium silicide (intermetallic U3Si2) and irradiation targets to produce Mo-99. This process is a part of Brazilian efforts to fabricate the fuel elements for its research reactors, primarily aiming at the production of radioisotopes for nuclear medicine. The magnesiothermic reduction is influenced by variables which are related to the starting material UF4 and the thermal conditions for its reduction. These variables are investigated. The physical arrangement of the crucible/reduction reactor/furnace system and the management of the furnace thermal input in the reduction reactor during the heating were studied. Thermal simulation experiments provided delineation for the reactants' thermal progress before the ignition of the metalothermic reaction. The heat input to the reduction system has proved to be the main variable that influenced the efficiency of the process. The levels of metallic yield and reproducibility have been improved, making the production process reproductive and economically viable. The typical yield in the production of uranium metal was above 80%. Unrecovered uranium metal is present in the MgF2 slag and can be recovered at the level of 96% yield. The process of recovering the uranium from the slag is also discussed. (C) 2017 Elsevier Ltd. All rights reserved.