Reaction of plutonium dioxide with water: Formation and properties of PuO2+x

Results show that PuO2-x, a high-composition (x less than or equal to 0.27) phase containing Pu(VI), is the stable binary oxide in air, This nonstoich iometric oxide forms by reaction of dioxide with water and by water-catalyz ed reaction of dioxide with oxygen. The PuO2 + H2O reaction rate is 0.27 na nomoles per meter squared per hour at 25 degrees C; the activation energy a t 25 degrees to 350 degrees C is 39 kilojoules per mole. Slow kinetics and a Low Lattice parameter-composition dependence for fluorite-related PuO2+x are consistent with a failure to observe the phase in earlier studies. Perp lexing aspects of plutonium oxide chemistry can now be explained.