Abstract

The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for UO_2 kernel preparation. In this study, ADU compound particles were calcined to UO_3 particles in air and Ar atmospheres, and these UO_3 particles were reduced and sintered in 4%-H_2/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to UO_3 phases at 500°C. At 600°C, the U_3O_8 phase appeared together with UO_3. After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric UO_2. As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of U_3O_7 and U_4O_9.

• Keywords: UO_2 kernel;UO_3 microsphere;Uranium compounds;