Synthesis of new mixed actinides oxalates as precursors of actinides oxide solid solutions

In an integrated fuel cycle such as considered for generation IV nuclear systems, actinides co-conversion processes play an important role by producing mixed actinides compounds used as starting materials for fuel re-fabrication. Among the different co-conversion routes considered, oxalic co-precipitation is one of the investigated ways to synthesised actinides mixed oxides. Oxalic co-conversion of a solution containing a tetravalent actinide An(IV) and a trivalent actinide An(III) under controlled conditions leads to the precipitation of two original series of mixed An(IV)–An(III) oxalate compounds (An(IV) = Th, Np, U or Pu and An(III) = Pu or Am) characterized by an unexpected An(IV)–An(III) crystallographic mixed site which induces a local homogeneity of the composition at a molecular scale. These families of mixed oxalates correspond to two solid solutions of type M2+xAnIV2−xAnIIIx(C2O4)5·nH2O and M1−x[AnIII1−xAnIVx(C2O4)2·H2O]·nH2O (M = single charged cation), with hexagonal or tetragonal symmetry, respectively.