KINETIC-STUDIES ON DISSOLUTION OF UO2 POWDERS IN ACID-SOLUTIONS BY USING CERIUM(IV) OR CHLORINE DIOXIDE AS OXIDANTS

The UO2 powders of 100-150, 150-212, 212-250, and 250-300 mu m were di ssolved in HNO3 or HCl solutions containing strong oxidants to examine their effect on the dissolution rates. Cerium(IV) species and ClO2 we re used as oxidants in HNO3 and HCl solutions, respectively The Ce(IV) species were prepared by bubbling O-3 gas into HNO3 solutions contain ing Ce(NO3)(3). All dissolution experiments were carried out under rap id stirring conditions which make it possible to neglect the diffusion effect. Dissolution reactions were analyzed on the assumptions that t he UO2 powders are spherical particles and homogeneously dissolved fro m their external surface. Dissolution rate constants (Phi) in mol . cm (-2). min(-1) were measured at various concentrations of oxidants and temperatures. Furthermore, the effect of acid concentrations on the di ssolution rate was also examined. As a result, the dissolution rate co nstants Phi were found to be expressed as Phi=k(N)[Ce(IV)][H+](0.6) fo r HNO3 solution([HNO3]=1-5 M, Temp. less than or equal to 30 degrees C ) and Phi=k(H) [ClO2][H+](-0.3) for HCl solution([HCl]=1-5 M, Temp. le ss than or equal to 30 degrees C), respectively. Activation energies(k J . mol(-1)) for the apparent dissolution rate constants are 44.1+/-1. 9 for the HNO3 solution system and 33.5+/-2.8 far the HCl solution sys tem. respectively.