Reaction mechanisms of the thermal conversion of Pu(IV) oxalate into plutonium oxide

Preparation, sintering and leaching of optimized uranium thorium dioxides

“…The samples were then found to be fully dehydrated after heating between 533 and 593 K. Anhydrous U 1Àx Th x (C 2 O 4 ) 2 solid solutions were found to be stable up to 633-663 K: in this range of temperature, the oxalate group decomposition yields CO and CO 2 and the corresponding actinide dioxide. Contrarily to what has been observed during the thermal decomposition study of Pu(C 2 O 4 ) 2 Á 6H 2 O [15], the existence of carbonated or oxo-carbonated intermediates was not found in this study. This could be explained by the different redox behaviour of U(IV) compared to Pu(IV) since the formation of Pu(C 2 O 4 )(CO 3 ) 0.5 and Pu(C 2 O 4 ) 0.5 (CO 3 ) was associated to the reduction of Pu(IV) in Pu(III) which redox reaction is unlikely for uranium in our operating conditions.…”

Direct carbothermic reduction of actinide oxalates: Example of Nd(III) oxalate–carbon mixtures conversion

“…The lanthanide oxalato-carbonate, Ln 2 (C 2 O 4 ) 2 (CO 3 ) formation, as an intermediate compounds was supported with past works on ytterbium [17], and plutonium [18]. The evolution of the X-ray pattern of neodymium oxalate during heating in argon showed the transformation of the decahydrate into an amorphous phase at 80°C and the crystallization of the neodymium oxide at about 800°C.…”

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

“…Also, the nature of the carbon species inside the oxide phase and their localisation could be widely different. On the one hand, several authors reported the presence of carbonated or oxocarbonated species when converting actinide oxalates under inert or reducing atmospheres [20]. Such compounds could still exist in some of the samples fired at the lowest temperatures (typically below 600 • C), and are expected to delay and/or hinder the sintering processes [39].…”

“…They particularly provide quick, quantitative and homogenous precipitation of cations from aqueous mixtures, and offer the possibility to incorporate simultaneously actinides presenting different oxidation states [17,18]. Moreover, the corresponding oxides are easily obtained through a heating conversion step [19,20]. New parameters coming from the thermal history of the oxide powder have then emerged and required to be studied.…”