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Executive SummaryThe purpose of this report is to review recent progress made in determining the chemical mechanisms, kinetics, and stoichiometry of gas generation in Hanford waste tanks. Information has been gathered from the results of laboratory studies with simulated wastes, laboratory studies with actual waste core samples (Tanks SY-10 1 and SY-103), studies of thermal and radiolytic reactions in the gas phase, and gas solubility evaluations. In-tank gas composition data are also briefly reviewed.
Laboratory Studies Using Simulated WastesStudies at the Georgia Institute of Technology (GIT), which were aimed at developing a mechanistic understanding of the formation of flammable gases via the thermal decomposition of complexants, have been completed and a summary report issued . Conducted under subcontract to Pacific Northwest National Laboratory (PNNL)?) these studies also established thermal fragmentation pathways for chelators in simulated Hanford double-shell tank wastes. Barefield et al. (1995Barefield et al. ( , 1996 studied the long-term thermal decomposition of HEDTA under thermal conditions. They have determined changes in the concentration of HEDTA and decomposition fiagments as a function of time to approximately 7000 hours. Breakdown products of HEDTA include ethylenediaminetriacetic acid (ED3A), glycine, unsymmetric ethylenediaminediacetic acid (u-EDDA), symmetric ethylenediaminediacetic acid (s-EDDA), ethylenediaminemonoacetic acid (EDMA), imidodiacetic acid (IDA), formaldehyde, formate, and acetate, all of which have been identified in Hanford double-shell tank wastes.Hydrogen is one of the byproducts of chelator fragmentation by thermal processes Barefield et al. 1995Barefield et al. , 1996. The aluminate and nitrite ions are believed to play an important role in initiating the decomposition reaction, through the formation of a coordination complex involving those two ions. The coordinated nitrito ligand is expected to be much more electrophilic than the fiee nitrite ion and more reac...
