Influence of a microwave radiation on dissolution kinetics of UO₂, CeO₂, and Co₃O₄ in nitric environment

This research thesis addresses the issue of dissolution oxides present in spent nuclear fuels. As previous studies outlined important increases of oxide dissolution rate when submitted to microwaves, the issue is then to apply such a technique to PuO₂ which is the most difficult oxide to dissolve. As plutonium may be handled only in certified laboratories and under strict safety conditions, the author studied the influence of a microwave radiation on the dissolution kinetics of other and various metallic oxides in a nitric environment. The choice of this nitric environment is imposed by conditions met in the nuclear industry. Oxides are chosen according to two criteria: dissolution times ranging from few minutes to few days, various responses to electromagnetic radiation (different values for the real and imaginary parts of their dielectric permittivity). Three oxides are retained: UO₂ and CeO₂ (to model PuO₂) and Co₃O₄. After a recall of some theoretical aspects of the response of a dielectric material to an electromagnetic field, a comparison between conventional and microwave heating, the author presents the main results obtained by using microwaves in chemistry (organic synthesis, ceramic sintering, acid dissolution). He reports the experimental study of nitric dissolution of oxides by conventional heating, and the dielectric characterisation of the studied oxides. He presents the experimental microwave set-up, and reports and discusses experimental results obtained for the dissolution of UO₂, CeO₂ and Co₃O₄ in HNO₃