U3O8 and UO2 obtained from ADU (ammonium diuranate) ultrasonically treated

At present, obtention of U3O8 used in the manufacturing of MTR plates nuclear fuels, is performed by hydrolysis of UF6 to obtain uranyl fluoride. Uranyl fluoride is precipitated with ammonium hydroxide to get ammonium polyuranate (ADU). Afterwards ADU is calcinated to U3O8 and mechanical and thermally treated in order to obtain a powder in a determined specification. In the present work, ultrasound has been applied in the stage of precipitation of ADU and for different times in the stage of digestion in order to fasten the stages of ADU filtering and eliminate the U3O8 milling and sieving. Experiences on UO2 have also been performed. The aspect of ADU changes considerably when they have been ultrasonically treated, its filtering rate is faster and it is easier to dry as it contains less humidity. U3O8 obtained after 800degreeC calcination of treated ADU results in an easy to desagregate powder. Only a soft mechanical treatment is needed to be performed on it before starting thermal treatment at 1400degreeC. After thermal treatment at 1400degreeC treated U3O8 has shown adequate characteristics of size, shape and density (8.2 g/cm3). Regarding UO2, the shape of the agglomerates is almost spherical, leading to a free-flowing powder, whose apparent and TAP density showed to be adequate. The characteristics of the different compounds were followed by electron scanning micrographies, X-Rays, specific area measurements and differential thermal analysis. The great advantage of ultrasound appliance is that hard mechanical treatment is avoided in the obtention of U3O8, saving time and effort. Furthermore, UO2 proves to be adequate to make pellets, the same precursor could be used in the obtention of both uranium oxides. (author). 5 refs., 6 figs