XAS study of U(1-y)PuyO2 solid solutions
Résumé
A new procedure for (U,Pu)O2 nuclear fuel manufacturing based on the oxalic co-precipitation of U(IV) and Pu(III) followed by the thermal conversion of the co-precipitate into oxide is under development. In order to fully investigate the ideality of solid solution with Pu content equal to 50, 30, 15 and 7 at.percent, XRD and XAS characterizations at uranium and plutonium LIII edges have been undertaken. Using XRD, a face centred cubic structure was observed in each case, and the cell parameter deduced obeys satisfactorily the Vegard-s law. However, EXAFS measurements moderate these results, only the (U0.5Pu0.5)O2 sample leads to the same conclusion as XRD. For the lower plutonium concentration, a disordered hyperstoichiometric structure (U1-yPuy)O2+x have been evidenced. In those compounds, cuboctahedral oxygen defects are only located around uranium atoms and not in the Pu environment. Thus, a much complex structure than suggested by the XRD is observed with certainly a non-random distribution of plutonium atoms into the uranium sites of the UO2+x structure