Thermal studies on the interaction behavior of ternary nitrate mixtures of UO 2 (NO 3 ) 2 ⋅6H 2 O–NaNO 3 –Sr(NO 3 ) 2 at elevated temperatures

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 UO 2 (NO 3 ) 2 ⋅6H 2 O, NaNO 3 and Sr(NO 3 ) 2 at high temperatures. These results indicate the interaction of UO 2 (NO 3 ) 2 ⋅6H 2 O and NaNO 3 in equimolar ratio to form sodium uranyl nitrate monohydrate (Na[UO 2 (NO 3 ) 3 ]⋅H 2 O), dimerized sodium uranyl oxynitrate (Na 2 [(UO 2 NO 3 ) 2 (O) 2 ]) and sodium diuranate (Na 2 U 2 O 7 ). The decomposition temperature of Sr(NO 3 ) 2 decreased by 60 °C in the presence of in-situ formed Na 2 U 2 O 7 . The uranium of Na 2 U 2 O 7 intermediate reacts with Sr(NO 3 ) 2 to form various strontium uranium mixed oxides depending on Sr to U ratio in the initial mixtures. During the interaction of Sr(NO 3 ) 2 with Na 2 U 2 O 7 , sodium separates out as amorphous Na 2 O in the mixtures, containing Sr to U ratio ⩾1. Na 2 O phase is not formed in the uranium rich ternary mixture.