The overall objective of this project is to provide a scientific basis for safely processing complexant-containing high-level tank wastes for disposal. Our key goals are to identify a means to prepare realistic complexant-containing tank waste simulants, and to use those simulants to determine the relative importance of organic complexants and their breakdown products on the partitioning of important radionuclides. These goals will be accomplished by artificially aging complexant-containing tank waste simulants using microwave, ultrasound, and photolysis techniques. The simulants will be compared to samples of actual Hanford tank wastes to determine the most realistic aging methods, on the basis of the organic fragmentation and the partitioning behavior of important radionuclides. Also, 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 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.