Plutonium Oxidation State Geochemistry in the SRS Subsurface Environment

The environmental mobility of plutonium (Pu) is profoundly influenced by its oxidation state. Pu(IV) is 2 to 3 orders of magnitude slower moving than Pu(V) or Pu(VI). For performance and risk assessment calculations, Pu waste has been assumed to exist in the less mobile reduced form, Pu(IV). Resent work on the chemistry of Pu02 by Haschke and others (2000) has shown that Pu02 surface is oxidized in the presence of water, forming as much as 27 percent Pu(VI). This has significant implications to existing SRS programs (including the Pu Immobilization, LLW disposal and Remediation of the Old Burial Ground) and future SRS programs (including MOX and pit disassembly). The hypothesis of this Strategic Research and Development study was that even if Pu(VI) is produced in the waste form as suggested by Haschke and others (2000), it will be quickly reduced to Pu(IV) in the SRS subsurface environment. The overall objective of the research was to test this hypothesis through laboratory and computational studies conducted by Savannah River Technology Center and Clemson University scientist