Dynamic Effects of Tank Waste Aging on Radionuclide-Complexant Interactions - Final Report - 10/01/1997 - 10/01/2000

The long-range objective of this project is to provide a scientific basis for safely processing high-level nuclear tanks wastes for disposal. Our goals are to identify a means to prepare realistic simulant formulations for complexant-containing Hanford tank wastes, and then use those simulants to determine the relative importance of various organic complexants and their breakdown products on the partitioning of important radionuclides. The harsh chemical and radiolytic environment in high-level waste tanks alters both the organic complexants and the metal species, producing radionuclide-chelator complexes that resist standard separation methods. A detailed understanding of the complexation reactions of the key radionuclides in tank wastes would allow for reliable, science-based solutions for high-level waste processing, but a key problem is that tank waste samples are exceedingly difficult to obtain, transport and handle in the laboratory. In contrast, freshly-prepared simulated wastes are safe and readily obtained, but they do not reproduce the partitioning behavior of actual tank waste samples. For this project, we will first artificially age complexant-containing tank waste simulants using microwave, ultrasound, and photolysis techniques that can be applied in any standard laboratory. The aged samples will be compared to samples of actual Hanford tank wastes to determine the most realistic aging method, on the basis of the organic fragments present, and the oxidation states and partitioning behavior of important radionuclides such as 90Sr, 99Tc, and 239Pu. Our successful completion of this goal will make it possible for scientists in academic and industrial laboratories to address tank waste remediation problems without the enormous costs and hazards associated with handling actual tank waste samples. Later, we will use our simulant aging process to investigate the relative effects of chelator degradation products on the partitioning of important radionuclides from the waste. Using NMR-active labels in the chelators, we will use a combinatorial approach of generating multiple chelator fragments in a single experiment and then determining which, if any, of the fragments have a negative effect on the separations chemistry. Our successful completion of this goal will specifically identify the most problematic organic fragments in complexant-containing waste and provide the basis for developing successful treatment strategies for these wastes