INVESTIGATION OF THE U-O-NA AND (U,PU)-O-NA PHASE-DIAGRAMS - STUDY OFNA3UO4 AND NA-3(U,PU)O-4 PHASES

The detailed study of U-O-Na and (U,Pu)-O-Na phase diagrams, correspon ding to Na(3)MO(4) (M=U or U,Pu) composition, by high temperature neut ron diffraction, room temperature X-ray diffraction and microcalorimet ry, has revealed the existence of metastable compounds and the formati on of a solid solution by dissolution of MO(2) in Na(3)MO(4). The exis tence of these new phases, with a disordered crystal structure, allows improved correlation with the previous results on the phase in equili brium with MO(2) and Na.