Analysis of 'mixed' nuclear wastes: Chemodynamics and organic diagenesis

Analytical methods, using specialized 'hot cell' and radiation hood facilities, have been developed for the full spectrum characterization of a complex concentrate waste derived from defense waste reprocessing over 20 years ago. Its radionuclide (∼ 1 Ci/L) and inorganic (molar concentrations) contents are quite complex, as one might expect. The waste's organic content, originally composed of chelating and complexing agents like EDTA, HEDTA, NTA and citrate (the source-term organics), proved to be much more complex than anticipated. In addition to the source-term organics, many structurally-related organics were also identified in the waste, presumably derived from the transformation, or diagenesis, of the source-term compounds. In order to confirm this hypothesis and to study the process of organic diagenesis in a controlled laboratory setting, a synthetic complex concentrate waste was prepared based on the analyses of the actual waste. The source term organics (EDTA, HEDTA, NTA and citrate) were added to a synthetic waste matrix, composed of inorganics sans the radionuclides. Incubation of this synthetic mixed waste at ambient temperature in the dark yielded ∼ 50% degradation of the source-term organics into myriad progeny compounds, i.e., chelator and complexor fragments, very similar to those found in the actual waste. Incubation of the synthetic waste in a γ-source (60Co) yielded even more organic diagenesis, confirming that the 'organic chemistry' of mixed wastes is not static but very dynamic