Study of the elaboration of U3O8 by the Modified Direct Denitration process (MDD)
Abstract
In the nuclear industry, uranium trioxide (UO3) is considered an intermediate in the preparation of uranium metal or uranium dioxide (UO2), which are the two most widely used nuclear fuels. Several processes have been described for transforming solutions of uranyl nitrate UO2(NO3)2 into uranium trioxide. Among these processes, Modified Direct Denitration (MDD) has been implemented to prepare Uranium trioxide with high reactivity. This process consists of adding ammonium nitrate to a pure uranyl nitrate solution to form the double salt (NH4)2UO2(NO3)4.2H2O which decomposes by calcination to produce a UO3 powder. The objective of this work is to study, first, the thermal decomposition of double salt (NH4)2UO2(NO3)4.2H2O in nitrogen atmosphere by thermogravimetry in order to determine the formation temperatures of the different phases and second, the determination of the optimal parameters (time and temperature) to prepare stable triuranium octoxide (U3O8) using muffle furnace. As results, the MDD product obtained is an orange colored and free flowing UO3 powder, having a surface area in the target range [5-12 m2/g]. In addition, by calcination of UO3 powder at 650°C for one hour, U3O8 oxide is obtained. The identification of the latter by the O/U ratio gave a value of 2.65, which is in the range [2.6-2.66]. This suggests that the oxide produced under these conditions is β-U3O8.
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