Studies related to chemical mechanisms of gas formation in Hanford high-level nuclear wastes. 1998 annual progress report

'The objective of this work is to develop a detailed mechanistic understanding of the thermal reactions that lead to gas production in certain high-level waste storage tanks at the Hanford, Washington site. Prediction of the combustion hazard for these wastes and engineering parameters for waste processing depend upon both a knowledge of the composition of stored wastes and the changes that they undergo as a result of thermal and radiolytic decomposition. Since 1980 when Delagard 1 first demonstrated that gas production (H{sub 2} and N{sub 2}O initially, later N{sub 2}{sup -} and NH{sub 3}{sup -}) in the affected tanks was related to oxidative degradation of metal complexants present in the waste, periodic attempts have been made to develop detailed mechanisms by which the gases were formed. These studies have resulted in the postulation of a series of reactions 2 that account for many of the observed products, but which involve several reactions for which there is limited, or no, precedent. For example, Al(OH){sub 4}{sup -} has been postulated to function as a Lewis acid to catalyze the reaction of nitrite ion with the metal complexants, NO{sup -} is proposed as an intermediate, and the ratios of gaseous products may bemore » a result of the partitioning of NO{sup -} between two or more reactions. These reactions and intermediates have been the focus of this project since its inception in 1996.'« less