OXIDATIVE DISSOLUTION OF PLUTONIUM DIOXIDE IN NITRIC-ACID IN THE PRESENCE OF OZONE .2. OVERALL PROCESS OF DISSOLUTION - SULFURIC-ACID CONTAINING SYSTEMS

A kinetic study is made of the oxidative dissolution of plutonium diox ide calcined at 600-800 and 1600 degrees C in nitric acid in the prese nce of ozone. Interphase reaction PuO2 + Ce(IV) is the limiting stage of the dissolution of low-calcined PuO2 at {PuO2}(0) less than or equa l to 5 x 10(-3) mol l(-1) solvent. In the case of systems containing s ulfuric acid, the same is true for {PuO2}(0) less than or equal to 1 x 10(-4) mol l(-1) solvent. With {PuO2}(0) = 0.08-0.85 mol l(-1) standa rd solvent [4 M HNO3 + (1-3)x 10(-2) M Ce + 1.5 x 10(-2) M H2SO4] and at t = 70-92 degrees C, the limiting stage of the process is interphas e oxidation of cerium(III) with ozone and/or ozone transfer through th e gas-solution interface. For high-calcined PuO2, linear dependences o n plutonium dioxide weight per liter of the solvent in the system are established for both the apparent rate constant of the process and cer ium(IV) concentration: k = (1.19 +/- 0.09) x 10(-2)-(8.2 +/- 1.4) x 10 (-2){PuO2}(0), mol(-1) l(-1) s(-1); [Ce(IV)] = (1.4 +/- 0.1) x 10(-2)- (9.1 +/- 1.4) x 10(-2)(PuO2), M.