A thermogravimetric study of the decomposition of UO3 to U3O8 in relation to the conditions of pretreatment of ammonium uranate

The fabrication of nuclear fuel generally involves the preparation of intermediate uranium oxides (UO3 and U3O8) which can be processed either to ceramic or to metallic nuclear fuel. Ammonium uranate (AU) was precipitated from uranyl nitrate with ammonia gas and dried without washing, or washed with water, methanol, and/or methanol-acetone, and dried. Four DTG stages of decomposition appeared. Dissociation of UO3 to U3O8 at 600 deg - 700 deg C was associated with an Ediss of 355-492 kJ x mol-1, dependent on the mode of washing the AU. For the production of U3O8, washing of AU with water and drying at 50 deg C , and/or precalcination at and beyond 350 deg C, is recommended. (author) 22 refs.; 1 fig.; 4 tabs