Evidence of a new crystalline phase in U-Gd-O phase diagram

The U-Gd-O phase diagram was investigated in its high Gd content part. Several samples with the general (U1−y, Gdy)O2±x composition were prepared by sintering under Ar H2 5% atmosphere. The samples were characterized by SEM-EDS and X-ray diffraction. A new cubic crystalline phase was evidenced at high a Gd content that was not expected from previous literature. Rietveld refinements showed that its crystalline structure is related to C-Gd2O3 phase. The existence of this compound has to be taken into account in the sintering of (U,Gd)O2 nuclear fuel.