Enhance Plutonium Mobility During Long-Term Transport Through an Unsaturated Subsurface Environment: Iron and Manganese Oxide Characterization
EMSL Project ID
6491
Abstract
Plutonium mobility in the subsurface environment is significantly influenced by its oxidation state: Pu(V/VI) is 500 times more mobile than Pu(III/IV). Plutonium (IV) and Pu(VI) were placed in Savannah River Site (SRS) lysimeters that were exposed to natural weather conditions with the intent of measuring the influence of Pu oxidation state on Pu mobility through the SRS subsurface sediments. Sediment cores from these lysimeters were collected 11 years later and total Pu concentration as a function of depth were determined. Laboratory studies showed that Pu is quickly reduced from Pu(VI) to Pu(IV) by these sediments. These tests also showed that Pu(IV) oxidation may also be occurring. Reactive transport modeling of the system supported the hypothesis that oxidation of Pu(IV) was occurring in the lysimeter sediments at a very slow, yet potentially very important, rate (ko=10-8 hr-1). Without oxidation included in the model, Pu was expected to move only 4 cm below the source over the 11-year period. With oxidation, the model correctly predicted that Pu would travel 12 cm below the source. Equally important, the simulation results including Pu oxidation captured important features of the Pu-profile data.The objective of this research is to characterize the sediment minerals and to identify the minerals capable of reducing and oxidizing the Pu. Uncontaminated (no Pu added) sediments maintained under reducing and oxidizing conditions from the Control lysimeters will be used in this study. We request the support of Dr. Ravi K. Kukkadapu to help us conduct Mossbauer on the clay/silt fraction of untreated, ammonium oxalate treated, and dithionite citrate buffer treated sediment samples. We also request that SEM/EDX analyses also be conducted, as appropriate, on these samples. We anticipate using this data in a manuscript and then in the renewal of our EMSP proposal, which will include Dr. Kukkadapu as a collaborator.
Project Details
Project type
Exploratory Research
Start Date
2004-02-04
End Date
2007-06-03
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members