Reaction chemistry of plutonium with vanadium pentoxide in molten salts

Vanadium pentoxide, V2O5, has been proposed as an oxidant for the stabiliza tion of reduced forms of plutonium within pyrochemical salt residues from p lutonium pyrochemical processes at the Rocky Flats Environmental Technology Site because of its large reduction potential and its ability to react via normal solid-state reactions. However, when V2O5 was used to oxidize actua l process residues results were highly variable. This paper discusses the r eaction chemistry of PuCl3, Pu degrees and PuOCl with V2O5 under a variety of conditions, including in the presence and absence of a NaCl/KCl salt mat rix. This work is the first systematic study of the solid-state oxidation o f plutonium species by vanadium pentoxide. For PuCl3 a greater than or equa l to 1:1 V2O5:PuCl3 ratio is needed for complete oxidation. Increasing the amount of V2O5 from 1 to 2 equivalents increases the contribution of side r eactions, including reactions of V2O5 with the process equipment and/or sal t matrix, and produces undesirable non-volatile ternary and quaternary vana dium compounds. The oxidation of PuOCl is similar to that of PuCl3. Greater than a 1:1 V2O5:PuOCl ratio is required to achieve adequate conversion of PuOCI to PuO2. Oxidation of Pu degrees by V2O5 is more complex than the PuC l3, or PuOCl oxidations. Complete oxidation of Pu degrees to Pu(IV) in the presence of the salt matrix does not occur with up to 6 equivalents of V2O5 . However, conversion of Pu degrees to Pu(IV) occurs rapidly in the absence of the salt matrix. (C) 2001 Elsevier Science B.V. All rights reserved.