SOLID-STATE REACTIONS OF URANIUM OXIDE AND ALKALI-METAL CHROMATES - CHARACTERIZATION OF NEW URANATES

New uranate phases, Rb2U4O11 and Rb2U3O8.5 in the Rb-U-O system and Na 2U3O9 and Na(y)U1-yO2-x (y = 0-0.2) in the Na-U-O system were prepared and characterised by X-ray, thermal and chemical methods. Na(y)U1-yO2 -x was found to be a solid solution of Na2O in UO2 with fluorite struc ture with a limited solid solubility of 10 mole% Na2O. These new phase s reported could lead, in addition to the modification of the phase di agrams, to a better understanding of the fuel-fission product-coolant- clad chemical interactions. The new phases were identified during stud ies on solid state reactions of chromates of caesium, rubidium, potass ium and sodium with uranium oxides upto 1200-degrees-C in inert atmosp here. These reactions have shown that different uranates are obtained depending upon the O/U of the starting uranium oxide, with chromium se parating as chromium oxide (Cr2O3).