Ultrasound effects on the dissolution of refractory oxides (CeO2 and PuO2) in nitric acid

Refractory oxides such as CeO2 and PuO2 are very difficult to be dissolved. They often involve the use of powerful reagents which further management is difficult (especially for nuclear waste). Conceming PuO2 used in nuclear fuels manufacturing, new dissolution techniques has been studied using ultrasound effects (20, 500 and 700 kHz) on powder oxides dipped into the nitric acid solutions. The experiment was tested to produce free radicals generated by cavitation (bubble implosion) to obtain either the oxidative or reducing conditions required for PuO2 dissolution. The formation of submicronic particles easier to solubilize was investigated. To enhance the dissolution mechanism and the production of free radicals, various scavengers (organic acids or alcohols) and solubilized gases were tested. The mechanical and chemical effects on oxide dissolution behavior were analyzed.