Speciation and structural characterization of plutonium and actinide- organic complexes in surface and ground waters. Annual progress report, September 1996--September 1997

摘要

The authors proposed research is designed to study the association of actinides with dissolved organic complexes in subsurface waters. Actinide-humic matter associations in natural waters have been investigated previously, but they have postulated that much of the actinide binding activity may be supported by colloidal biopolymers. To investigate this, they are developing techniques to sample and identify organic constituents in groundwater, and to measure the Pu associated with different fractions of organic matter. Year 1 activities have focused on: (1) sampling techniques to minimize contamination and artifact formation, and to establish mass balances, (2) separation of Pu isotopes by oxidation state, and (3) analytical development of techniques for separation and identification of organic constituents from natural waters. Their proposed research calls for field work at the Savannah River and Hanford Sites (SRS and HS, respectively). Towards this, they have been working on establishing protocols for ultra-clean (fg level) cross-flow filtration (CFF) techniques suitable for thermal ionization mass spectrometric (TIMS) analysis. A series of tests have been completed and the results have shown no Pu contamination from the CFF system was observable as long as the system is rigorously cleaned with acid, base and nano-pure water. They have also collected a water sample from a pond near the laboratory in Woods Hole, MA to test blank conditions in the field, and to determine system mass balances. Blank levels were found to be satisfactory, and the mass balance is 100--210% for both (sup 239)Pu and (sup 240)Pu, the only two isotopes measurable in the sample. This is one of the major assurances for the success of the project because CFF will be the major sampling tool the authors will use to study natural Pu-organic complexes. Another important result from the field test is that > 80 % of the dissolved Pu (based on the TIMS measurements) is in colloidal form.