Pu(V) transport through Savannah River Site soils - an evaluation of a conceptual model of surface- mediated reduction to Pu (IV).

Over the last fifteen years the Savannah River Site (SRS) in South Carolina, USA, was selected as the site of three new plutonium facilities: the Mixed Oxide Fuel Fabrication Facility, Pit Disassembly and Conversion Facility, and the Pu Immobilization Plant. In order to assess the potential human and environmental risk associated with these recent initiatives, improved understanding of the fate and transport of Pu in the SRS subsurface environment is necessary. The hypothesis of this study was that the more mobile forms of Pu, Pu(V) and Pu(VI), would be reduced to the less mobile Pu(III/IV) oxidation states under ambient SRS subsurface conditions.

Uptake, distribution, and velocity of organically complexed plutonium in corn (Zea mays).

Lysimeter experiments and associated simulations suggested that Pu moved into and through plants that invaded field lysimeters during an 11-year study at the Savannah River Site. However, probable plant uptake and transport mechanisms were not well defined, so more detailed study is needed. Therefore, experiments were performed to examine movement, distribution, and velocity of soluble, complexed Pu in corn.

Distributions of radionuclide sorption coefficients (Kd) in sub-surface sediments and the implications for transport calculations.

The effect of the spatial variability of K(d) on calculations of contaminant travel time in the vadose zone was determined. Depth discrete measurements of K(d) were made for a suite of radionuclides ((109)Cd, (57)Co, (60)Co, (85)Sr, (137)Cs, and (88)Y) utilizing a sediment core from the E-Area at the Savannah River Site. The K(d)'s were ordered as (85)Sr(2+) < (137)Cs(+) < (109)Cd(2+) < (57)Co(2+) = (60)Co(2+) << (88)Y(3+) and the values generally fell below or near the lowest quartile of values reported in the literature.

Influence of sources on plutonium mobility and oxidation state transformations in vadose zone sediments.

Well-defined solid sources of Pu(III) (PuCl3), Pu(IV) (Pu (NO3)4 and Pu (C2O4)2), and Pu(VI) (Pu02(NO3)2) were placed in lysimeters containing vadose zone sediments and exposed to natural weather conditions for 2 or 11 years. The objective of this study was to measure the release rate of Pu and the changes in the Pu oxidation states from these Pu sources with the intent to develop a reactive transport model source-term. Pu(III) and Pu(IV) sources had identical Pu concentration depth profiles and similar Pu release rates.

Influence of pH on plutonium desorption/solubilization from sediment.

Aqueous Pu concentrations and oxidation state transformations as a function of pH were quantified and compared between sorption/desorption studies and literature solubility values. When Pu(V) was added to a red subsurface sandy-clay-loam sediment collected near Aiken, South Carolina, 99% of the Pu sorbed to the sediment within 48 h. Throughout the study, > or = 94% of the Puaq remained as Pu(V), whereas < or = 6% was Pu(VI) and < or = 1% was Pu(IV).