Self-reduction of dioxoplutonium VI: Characterization and modeling of radiolytic and disproportionation pathways

Kinetic modeling shows that self-reduction of dioxoplutonium VI is consistent with disproportionation of Pu(VI) and reaction of the Pu(VII) product with water, as well as with alpha-particle radiolysis of water and reaction of products with Pu(VI). Comparison of predicted and observed [Pu(VI)]-time data confirms that self-reduction of 238Pu(VI) at pH 0 is induced by radiolysis, but that self-reduction reactions of 239Pu(VI) at pH 1.5 and 242Pu(VI) at pH 6 are driven by disproportionation. Modeling of [Pu(VI)]-time behavior of solutions containing 210Po as an alpha source shows that control of the reduction path changes from disproportionation to radiolytic over time at pH 0.7. Self-reduction of Pu(VI) consistently follows the most rapid path as determined by pH, Pu(VI) concentration, and the isotopic state of Pu. Chemistry and kinetics of the processes by which Pu(VI) self-reduction drives the decrease in average oxidation number of plutonium-containing solutions over time are discussed.