Thermal studies on the interaction behavior of ternary nitrate mixtures of UO2(NO3)2⋅6H2O–NaNO3–Sr(NO3)2 at elevated temperatures

Abstract

Thermal and X-ray diffraction measurements have been used to study the formation of various nitrato-complexes as intermediates and mixed oxides as end products using different mol ratios of the ternary mixtures of UO2(NO3)2⋅6H2O, NaNO3 and Sr(NO3)2 at high temperatures. These results indicate the interaction of UO2(NO3)2⋅6H2O and NaNO3 in equimolar ratio to form sodium uranyl nitrate monohydrate (Na[UO2(NO3)3]⋅H2O), dimerized sodium uranyl oxynitrate (Na2[(UO2NO3)2(O)2]) and sodium diuranate (Na2U2O7). The decomposition temperature of Sr(NO3)2 decreased by 60°C in the presence of in-situ formed Na2U2O7. The uranium of Na2U2O7 intermediate reacts with Sr(NO3)2 to form various strontium uranium mixed oxides depending on Sr to U ratio in the initial mixtures. During the interaction of Sr(NO3)2 with Na2U2O7, sodium separates out as amorphous Na2O in the mixtures, containing Sr to U ratio ⩾1. Na2O phase is not formed in the uranium rich ternary mixture.