The phase state at high temperatures in the MOX-SiO2 system

Influence of impurity Si on microstructure in a plutonium and uranium mixed oxide (MOX), which is used for fast breeder reactor fuel, was investigated, and phase state in 25% SiO2 - (U0.7Pu0.3)O2 was observed as a function of oxygen chemical potential. Compounds composed of Pu and Si with other elements were observed at grain boundaries of the MOX parent phase in the specimens after annealing. These compounds were not observed in the grain interior and the MOX phase was not affected significantly by impurity Si. It was found that the compounds tended to form more observably with decreasing O/M ratio and with increasing annealing temperatures.