Phase separation behaviour of (U_0.7 Pu_0.3) O_2−x (1.92<x<2.00) based fuels containing actinides and/or lanthanides

Phase separation behaviour was investigated to better understand the phase diagram in the U-Pu-O system. The effects of adding minor actinides and lanthanides on the phase separation behaviour were evaluated by using thermal analysis, X-ray diffraction analysis and microstructure observation. The maximum phase separation temperature of (U_0.7Pu_0.3)O_2−x was 633K. The amount of phase separation increased with decreasing O/M ratio from 2.00 to 1.92. The phase separation region expanded with Pu content and lower limit of Pu content was estimated to be about 20%. The effects of minor actinide and lanthanide addition on the phase separation temperature were also evaluated. It is concluded that the phase separation would not significantly affect the irradiation behaviour or pellet production.