Kinetic Studies on Dissolution of UO_2 Powders in Acid Solutions by Using Cerium(IV) or Chlorine Dioxide as Oxidants
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The UO<SUB>2</SUB> powders of 100-150, 150-212, 212-250, and 250-300μm were dissolved in HNO<SUB>3</SUB> or HCl solutions containing strong oxidants to examine their effect on the dissolution rates. Cerium(IV) species and ClO<SUB>2</SUB> were used as oxidants in HNO<SUB>3</SUB> and HCl solutions, respectively. The Ce(IV) species were prepared by bubbling O<SUB>3</SUB> gas into HNO<SUB>3</SUB> solutions containing Ce(NO<SUB>3</SUB>)<SUB>3</SUB>. All dissolution experiments were carried out under rapid stirring conditions which make it possible to neglect the diffusion effect. Dissolution reactions were analyzed on the assumptions that the UO<SUB>2</SUB> powders are spherical particles and homogeneously dissolved from their external surface. Dissolution rate constants (O) in mol•cm<SUP>-2</SUP>•min<SUP>-1</SUP> were measured at various concentrations of oxidants and temperatures. Furthermore, the effect of acid concentrations on the dissolution rate was also examined. As a result, the dissolution rate constants Φ were found to be expressed as Φ=kN[Ce(IV)][H<SUP>+</SUP>]<SUP>0.6</SUP> for HNO<SUB>3</SUB> solution([HNO<SUB>3</SUB>]=1-5M, Temp. ?? 30°C) and Φ=kH [ClO<SUB>2</SUB>][H<SUP>+</SUP>]<SUP>-0.3</SUP> for HCl solution([HCl]=1-5M, Temp. ?? 530°C), respectively. Activation energies(kJ•mol-1) for the apparent dissolution rate constants are 44.1+1.9 for the HNO<SUB>3</SUB> solution system and 33.5+2.8 for the HCl solution system, respectively.
- Journal of Nuclear Science and Technology
Journal of Nuclear Science and Technology 33(2), p.152-156, 1996-02-25
Atomic Energy Society of Japan