Status and integration of studies of gas generation in Hanford wastes

Abstract

DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or impiied, or assumes any legal liability or rrsponsibility for the accuracy, completeness, or usefulness of any infonnation, apparatus, product, or procxss disdosed, or represents that its use w w l d not infringe privately owned rights. Refemtee herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DECLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. 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...

Overview of the Flammability of Gases Generated in Hanford Waste Tanks

“…These substances have been observed in many laboratory studies with simulants and in laboratory studies with actual waste samples (Ashby et al 1992(Ashby et al , 1993(Ashby et al , 1994Barefield et al 1995Barefield et al , 1996Bryan and Pederson 1993Camaioni et al 1997;Delegard 1980;Johnson 1997;King et al 1997;Meisel et al 1991aMeisel et al , 199lb, 1992Meisel et al , 1993Person 1996;Pederson and Bryan 1996). These same products are found in the headspaces of actual waste tanks and in gas samples obtained using the RGS (Johnson 1997;Mahoney et al 1999).…”

Data Observations on Double Shell Tank (DST) Flammable Gas Watch List Tank Behavior

“…An excellent summary and interpretation of the results obtained through 1996 is given by Pederson and Bryan (1996). Besides samples from a number of SSTs, DST wastes tested include AN-I05 core composites (Person 1998), convective layer samples from AW-IO1 (Bryan and King 1998) and SY-103 , and a core composite sample from SY-101 (Person 1996).…”

Flammable gas issues in double-contained receiver tanks. Revision 1

“…The thermal and radiolytic calculations summarized by Hu (1997) are based on the thermal and radiolytic models first outlined by Hopkins (1994) and Graves (1994), as modified by Pederson and Bryan (1996). The flammable gas mixtures in DCRTs reported by were calculated using the equations and models summarized by Hu (1997).…”

“…The safety assessment found no indication that mixer pump operation had caused any changes in "unreleasable" gas. Pederson and Bryan (1996) conducted laboratory tests with DST simulants to assess whether ammonia sorbed onto tank solids in significant quantities. (While the behavior of SST solids cannot be inferred directly from these studies, these are the only experimental data available.)…”